Weismann Differential [Archive]

Chris Weismann

06-06-2013, 11:21 AM

I tripped upon this forum this morning. I bit late I know. Anyway, I read the posts and because of the general secretiveness we have maintained about the unit, I can tell you all that it does not operate like you think. Furthermore, we have kept it secret so people don't try to copy it and steal it. I will say this though, it is not a sprag device and thus all the assumptions about the Weismann Locker are wrong. Even Carroll's statements are incorrect, or at least taken out of context and incorrectly explained, like going straight into the wall. Without going into a full discussion at this point, I will leave you with this simple explanation, quoting Sir Jack Brabham. "It acts like a spool under acceleration, and it opens on corner entry". I'll add that off gas it is fully locked in a straight line and still opens on corner entry. A key to it's function is that unlike every other differential that seeks the path of least resistance when a wheel loses traction for what ever reason, the Weismann Locker seeks the path of most resistance, so the instant a wheel loses torque, all the torque is transfered instantly to the wheel on the ground... the only device to do so. The unladen wheel does not slip. It is not a limited slip.

I call it the Unlocker now because fundamentally it is locked and it opens under certain conditions.

That ought to get you guys thinking.

When I have time, I will tackle each of the "statements" above and clarify them... like the parasitic losses involved, etc...

Chris Weismann

GSpeedR

06-06-2013, 12:15 PM

It sounds as though it operates like a Detroit Locker.

Marshall Grice

06-06-2013, 03:56 PM

spring loaded sprague, like this?
http://www.google.com/patents/...#v=onepage&q&f=false (http://www.google.com/patents/US3283611?printsec=drawing#v=onepage&q&f=false)

Warpspeed

06-06-2013, 05:37 PM

Originally posted by Chris Weismann: because of the general secretiveness we have maintained about the unit

Chris Weismann
And that is the whole problem Chris.

There is nothing really stopping anyone from buying one of your magic diffs and then pulling it apart to copy, or at least study and learn from.
In fact I am surprised that has not already happened if it is as good as claimed.

There are some pretty clever and determined people at the top of motor racing, and in the commercial auto industry, and if your diff is so vastly superior, why is it not more widely used and copied ?

But like many automotive "secrets", 200 miles per gallon carburettors, and special spark plugs that unlock 30% more horsepower, I tend to avoid secret mystery products supplied without engineering data or specifications.

We are all engineers here, and if you are going to convince us, we need something more tangible
more than the considered opinion of one famous driver on which to base an engineering design.

Pete Marsh

06-06-2013, 07:56 PM

It would be nice to see a totally unambiguous description of what it does, (without revealing anything to do with your method).
An equation or other description in terms of the torque and velocity (if relevant) at each shaft such that it's function can be calculated for any vehicle situation. It's the transition behaviour that is of interest, so "open in corners and locked under power" is of little use. How and when did it get between those two extremes?

Pete

Markus

06-07-2013, 04:37 AM

Note: this is my understanding of 60s Weismann differential, it's hard to tell what's different in the modern version.

Seems to be build around 2 preloaded and interconnected two-way sprag clutches and a damping mechanism.

Resistance of the output (or input) is used to engage the sprag clutches, both input and output driven, and rotational speed difference is used to open the sprag clutch of the faster spinning wheel (input driven) or slower spinning wheel (output driven). Interconnection makes sure one sprag clutch is always engaged. Friction plates are used as dampers to remove oscillation between input driven and output driven "unlocking" states.

During straight line (accelerating or declerating) the differential is 100% locked. During acceleration in corner and steady state cornering (preload) all engine torque is applied to inside wheel if it has traction. During decleration in corner the outer wheel does all the engine braking. Whenever there's a traction difference between the tires that overcomes the preload the tire with more traction gets 100% of the torque.

Without driving one it's hard to say how an FSAE car would handle but I'd imagine the car would be a challenge for the driver...
Example:
Coming down the straight: 100% locked.
Braking before corner: 100% locked.
Steering input to enter corner: 100% locked.
Starting to corner (off throttle): 100% outside wheel.
Cornering (on throttle): 100% inside wheel.
Lifting the inner wheel: 100% outside wheel.
Regain grip on corner exit: 100% inside wheel.

One interesting property to note is the requirement for the driven axle to be already cornering for the diff to unlock. This might not be a huge effect on wide tracks and good braking points but in FSAE that means no more trail braking into hairpins... You might want to be as close to constant velocity as possible when entering a turn.

Also the diff doesn't have any mechanical split torque states, it's either 50%-50% or 0%-100%. Only way to achieve a torque split is the rapid switching between states and it's hard to say what kind of effect that has on handling...

Final note, in the above 0% = 0% + damper preload and 100% = 100% - damper preload. And I take no responsibility if the above is correct in any way. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Charles Kaneb

06-07-2013, 10:57 AM

Originally posted by Warpspeed:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Weismann: because of the general secretiveness we have maintained about the unit

Chris Weismann
And that is the whole problem Chris.

There is nothing really stopping anyone from buying one of your magic diffs and then pulling it apart to copy, or at least study and learn from.
In fact I am surprised that has not already happened if it is as good as claimed.

There are some pretty clever and determined people at the top of motor racing, and in the commercial auto industry, and if your diff is so vastly superior, why is it not more widely used and copied ?

But like many automotive "secrets", 200 miles per gallon carburettors, and special spark plugs that unlock 30% more horsepower, I tend to avoid secret mystery products supplied without engineering data or specifications.

We are all engineers here, and if you are going to convince us, we need something more tangible
more than the considered opinion of one famous driver on which to base an engineering design. </div></BLOCKQUOTE>

The 100-mpg carburetor never won at least half a dozen F1 titles, damn near every Indycar road race from 1966-1985, and every CanAm race not won by a Porsche or Chaparral. U.S. Patent #3283611 was issued in 1966.

However it works, it does.

Unfortunately, I haven't heard of it being used since 1988. I was three years old then.

Chris, there are about 200 FSAE cars built in America every year. If you can build us a differential, able to transmit around 800 lbs*ft total drive torque, weighing in at 8 lbs or less, for around three grand, you'll sell out. If you need someone who can distribute it for you, Taylor Race Engineering might be interested.

Chris Weismann

06-07-2013, 11:30 AM

Gentleman,

With all due respect, I was quickly reminded why I don't chat on forums after reading some posts here. However since there is a lot of misconceptions about our "Magic Diff", I feel that I must at least eliminate some of them.

I quoted Jack Brabham because of all racer drivers I could have picked (alive or dead) he was technically one of the smartest ever. If you don't know that, research the man. The only other driver that comes close, and actually I can argue he was smarter in some ways, was Bruce McLaren. Bruce used the locker in both his can am cars and his F1 cars. Denny Hulme was probably the biggest fan of the locker because it suited his style of driving... flat out.

Jack had to have the Weismann Locker without knowing how it worked because he was getting his ass kicked by a rookie driving a Weismann equiped Brabham in '65... that rookie went on to win the usac indy championship that year. His name was Mario.

I made our website to set the record straight and rewrite history in some cases. Just for a sampling of the cars that were successful with the locker, check out www.weismann.net/innovations.html (http://www.weismann.net/innovations.html) and www.weismann.net/lockers.html (http://www.weismann.net/lockers.html)

Forgive me for not making a more professional looking site, most of these pages look like they do because I wrote them in html in '95-'97 and I haven't touched them since.

Again I don't want to insult anyone, but if there is one thing that I've learned growing up in racing, there are many great engineers out there, but very few are actually special. In my junior year I finally realized that my dad was one of the special ones, and the smartest man I have ever known. Not because he was my dad, but because he had more insight to solving engineering problems than anyone I have ever met. And his track record is proof of that.

Ask yourself, there are plenty of great chefs out there, but why hasn't anyone been able to reverse engineer KFC's secret receipe? no doubt some have come close, but none have actually succeeded without gaining some information that they were unaware of. I mean there is only 9 secret herbs and spices...

Same goes for the Weismann Locker. A company that my dad employed in the 60s to make some locker parts, tried to go around him and flog it on their own. Trouble is that they didn't understand all the aspects of it and they failed.

Ferrari in the 70s on the other hand succeeded, but only after they had the Locker in their hands. My dad let them test it. They said one driver liked it, one did not. So they rejected it. End of story. Until my dad and I were watching a grand prix and a certain great driver named Gilles ripped off a rear wheel. He drove around the track at speed to the pits and promptly waited for a new tire. The damage ended his race, but without the Locker, there was no way he could have driven around the track - and I stress, he drove around quickly. Only a spool could have worked, but you don't run a spool on a road race course. My dad was so pissed off, because Ferrari stole it. Did they have the right? No.

What right do any of you have to reverse engineer something that doesn't belong to you? Even if the patents have run out on some of the versions? BTW I still have a version patented, which we use extensively in the military vehicles we provide drivetrains for. www.weismann.net/military.html (http://www.weismann.net/military.html). There are other military vehicles, but I haven't shown them for obvious reasons.

We no longer patent ideas because a patent is only a license to litigate. Do you think we can beat Ferrari or Honda in court? And in Italian or Japanese court?? Besides, you show everybody your idea for free. But not all aspects of the locker are patented for a reason.

So Mr. Grice has posted one of my dad's versions of his dad's idea. There is more than enough info to get your minds thinking, provided you take the time to digest it's functions properly and remove all other diffs from your mind.

The Weismann Locker is not a spague!! But the WL is rotationally engaged or disengaged and that is where the similarity ends. And it is not a Detroit Locker, or it would be called as such. The DL mechanism is not even close.

Also it is torque sensing in the truest sense... ie, it proportions the torque according to the available tire patches ability to accept torque. It is not just 100% and !00% off. That is why it is Magic. Under traction limited cases, either because of excess horsepower or track conditions, the tires that have the traction will drive the car forward with no wheel slip. Yes you can exceed the traction on both tires and then yes both tires are slipping, but the WL is locked... by default.

Alright, I have to get to work now, but I'll be back.

GSpeedR

06-07-2013, 12:35 PM

Also it is torque sensing in the truest sense... ie, it proportions the torque according to the available tire patches ability to accept torque. It is not just 100% and !00% off. That is why it is Magic. Under traction limited cases, either because of excess horsepower or track conditions, the tires that have the traction will drive the car forward with no wheel slip. Yes you can exceed the traction on both tires and then yes both tires are slipping, but the WL is locked... by default.

Any locked differential is 'torque-sensing' such that torque is distributed depending upon the axle/tire reactions: the load paths are in parallel. So that's clearly not magic. I assume that the "magic" part is the mechanism that (continuously?) transitions between its truly locked state and open state as the reacted torque delta increases.

It sounds like a very interesting device.

Markus

06-07-2013, 01:22 PM

I will stand with my explanation until its properly shot down.

I don't know the proper word for the clutch type used but "2-way sprag clutch" should be explanatory to most while it's technically incorrect. I guess bi-directional roller clutch might be closer to correct term.

And because of those cluthes I still claim the differential has only 2 mechanical torque-split states: 50%-50% and 0%-100% (+- preload)**. And you need rotational speed difference to change to the latter state, so in engineering terms it doesn't sense torque but the instant reaction of losing it.

So here's where I see the "Magic": the differential locking-unlocking action can be achieved with very high frequency, essentially creating "virtual" torque-split states (think PWM) in the range of 0%/100% to 100%/0% (+- preload). During a manouver the differential changes between states fast enough so that the tires "see" it as a stepless change in torque-split.

This type of "virtual" control with 2 mechanical states is used in many branches of engineering but it's the first time I ran to it in differentials. And I have to admit that I like it. http://fsae.com/groupee_common/emoticons/icon_smile.gif

** There's actually 3 mechanical states:
Both outputs coupled to input.
"Left" output only coupled to input.
"Right" output only coupled to input.

Warpspeed

06-07-2013, 05:17 PM

Marcus, I had heard rumors that the Weismann diff worked something like a detroit locker with damping, but was not prepared to say so, because I did not know for sure and did not wish to cloud the issue further.

Carroll Smith gave a brief synopsis of the various available diff type, and his opinions of their various virtues and failings.

He called the detroit locker (in his own unminced words) "an abortion", and he rated the Weismann locker very highly.
And that has clouded the issue for me ever since.

Most of us realise that the differential will have a profound effect on vehicle dynamics and handling, and different differential types are each more suited to totally different applications, and sometimes driver preference.

Anyone that has driven a true locker will know the sudden violent change in vehicle response when it switches instantly from one condition to the other.

Which brings us back to the main problem.
Just because a Formula One driver, and maybe the most technically knowledgeable one ever, says a Weismann is in his opinion the best solution for Formula One, does not make it best, or even suitable for every other class of racing or even a road car.

I can understand a hot shot Ferrari test driver getting all excited about shaving .001 seconds off his lap times.
And I can also understand Ferrari marketing not liking sudden violent transitions between understeer or oversteer as the diff suddenly switches to the opposite mode for an inexperienced and startled driver.

Crashed Ferraris and dead drivers do not help sales figures, so older and wiser heads may have preferred a more benign engineering solution.
Nothing wrong a locker diff, just probably not the best solution for a Ferrari or the type of overconfident drivers that sometimes drive them.

Marshall Grice

06-07-2013, 05:23 PM

Originally posted by Markus:
And because of those cluthes I still claim the differential has only 2 mechanical torque-split states: 50%-50% and 0%-100% (+- preload)**. And you need rotational speed difference to change to the latter state, so in engineering terms it doesn't sense torque but the instant reaction of losing it.

So here's where I see the "Magic": the differential locking-unlocking action can be achieved with very high frequency, essentially creating "virtual" torque-split states (think PWM) in the range of 0%/100% to 100%/0% (+- preload). During a manouver the differential changes between states fast enough so that the tires "see" it as a stepless change in torque-split.

This type of "virtual" control with 2 mechanical states is used in many branches of engineering but it's the first time I ran to it in differentials. And I have to admit that I like it. http://fsae.com/groupee_common/emoticons/icon_smile.gif

** There's actually 3 mechanical states:
Both outputs coupled to input.
"Left" output only coupled to input.
"Right" output only coupled to input.
I disagree with it (at least the version shown in the patent) only having discreet locked and unlocked states. you have the rollers acting as wedges in between the driving and driven elements. as you apply more torque the friction between the rolling elements and the driving/driven elements increases in proportion to the input torque until they lock. Think of how a clutch type diff cross shaft applies increased clamp load to the pressure rings in proportion to the input torque. only in this case instead of the wedging force being in the the axial direction it is in a radial direction.

Marshall Grice

06-07-2013, 05:30 PM

also, i don't see this unit having a discreet 50/50 torque split state. there is no geared interconnection between any of the parts. if you lose the clamp load you lose the connection between the driving and driven elements.

key to notice it's called a "locker" not a differential. http://fsae.com/groupee_common/emoticons/icon_wink.gif

06-07-2013, 09:32 PM

At last, an interesting thread about mechanical stuff! (And not an Indian in sight, yahoo!!! http://fsae.com/groupee_common/emoticons/icon_smile.gif)

I agree with a lot of what Chris says about commercialising good ideas. My guess is that most of the "magic" in the WL is in the form of detailed dimensional tolerances, heat treatments and hardnesses, preload spring-rates, and even the type of oil used, or not used (ie. no moly?).

I also agree with Tony that just because it works great in F1, that doesn't necessarily mean it is good for FSAE.

In particular, is it really a good thing to send most of the power to the wheel with most of the traction?
Especially when the car has a very high rear-track-to-wheelbase ratio (~4/5 in FSAE, cf. ~1/2 in F1)?
And the car is driven by amateurs?

To explain, here is a brief summary of pros and cons of some "diffs", with more emphasis on the cons.

1. SPOOL.
Pro. - Both wheels always driven, so you can get home if you lose a rear wheel (which is why all Le Mans Porsches had spools).
Con. - When equally loaded, both wheels try to make the car go straight (= bad on corners, especially tight ones).
When unequally loaded, or when on "split-mu" surfaces, the wheels give different thrusts, and thus try to steer the car.

2. OPEN DIFF.
Pro. - Both wheels always give equal thrust, so any thrust vector is always down centreline of car. The diff never tries to steer the car.
Con. - Both wheels have thrust of weakest wheel, so if one wheel in air (or on oil/wet clay/ice), then NO thrust.

3. FULL TORQUE VECTORING (eg. 2 x IVTs, or 2 x electric motors).
Pro. - Complete control of torque AND speed at each wheel.
Con. - If control system is visited by glitch, then both wheels might receive full torque, but in opposite directions (= very entertaining, and this has happened)!

Of the above, the open-diff has the most benign disadvantages. It doesn't mess with the car's handling, and it "fails" very safely (= no thrust). Its main disadvantage of low thrust due to spinning inner-wheel in a corner (or on split-mu) can be largely fixed with more rear percentage. And while cost-wise the spool is best, the open-diff is a close second.

All the other diff types seem, IMO, to be expensive ways of compensating (and only partially so) for a lack of rear percentage.

Z

murpia

06-08-2013, 07:15 AM

Reading the patent, and generally thinking about the device, the 'magic' is clearly the means by which the rollers get their initial wedging motion. Once wedged, there is a positive feedback effect to keep them engaged.

Without the initial wedging, the half-shaft discs could just remain stationary with the outer housing rotating and the rollers spinning relative to the half shaft discs.

Differential action (relative motion of the two half shaft discs) such that it is, must come from a small amount of roller skidding on the half shaft discs. I do wonder how much actual true differential action ever comes from this skidding and how much from relative tyre slip (as per a spool). I doubt a Weismann equipped vehicle would work well in tight turns without the tyres operating at high slip ratios.

I'd be tempted to try and model this, if I had the time...

Regards, Ian

Chris Weismann

06-11-2013, 10:51 AM

The "magic" is in how it senses torque. It is in how it locks up, not how it disengages.

Markus, Sorry but you shot yourself down. You are still not "seeing" it virtually in your head. But don't take offense, you aren't the first and you won't be the last. You need to remain open minded. Seeing you are in huntington beach, I invite you to come to our shop in costa mesa to play with one on the bench. And if after some schooling you are still not convinced, I suggest you take up another profession.

Also as I stated before it is not on/off, ie not 100% on, and then "violently" off. If it was, it would be diablolical in the rain. Instead it is smooth and very drivable.. and it the rain it is at it's best.

Gilles Villeneuve was not a test driver. At Watkins Glenn in 1979, he was around 19 seconds a lap faster than the rest of the field in changing conditions. He was the only one running with our Locker. Those that were present were astounded at his performance. He had help.

Jack Brabham went on to win the 1966 World Championship in F1 the first year he ran it. His teammate Denny Hulme won it the next year. Those Brabham cars were down on power to the BRMs and the Ferraris. But they had help. Also my dad made a trick auto trans for those cars to give them the advantage on the standing starts, but that is another topic.

All Can Am championships between 1966 and 1983 were won with our Locker.

All 4 GT40 Le Mans wins were won with the Weismann Locker. Carroll Smith was the team manager for Ford in those days. My dad designed the MKII and got no credit to this day for doing that work. He also designed the manual and auto transmissions for those cars.

Anyway... if you are traction limited, the locker will out perform any other diff. So if your SAE cars are traction limited for whatever reason, then it can help.

With the advent of wings, ie ground effects, the wheel slip conditions began to go away, and therefore the distinct advantage of the Locker also went away... the cars were not so traction limited.

In !981 (I think) Danny Ongais crashed heavily between 3 and 4 at Indy. The car was completely destroyed and Danny is lucky to have both his legs today as he was hanging outside the front of the car as his car ground to a halt. A very successful, if not the most successful chief mechanic at Indy George Bignotti, was asked his opinion as to why the car crashed so suddenly. He said something like "Well since is has a Weismann transmission, it must have a Weismann Locker, and if it broke an axle, the Locker will put you in the wall."

The next day there was a picture of Danny laying in the car against the wall, the transmission was broken wide open and in it you can clearly see... a spool. But the damage was done.

My dad decided to stop making the Locker because he was tired of fighting close minded people. When Ken Miles was testing in 1967 at Riverside in turn 9 in a GT40 MKIII, the "j" car, and was killed, the locker was blamed for the crash. It was later found out to be because of a broken upright from a poor brake mount design.

Why was Locker so quickly blamed? Because it was the trick device that very few people understood properly.

Lesson here is don't assume... assumptions are the mother of all f*** ups.

Any diff can make you crash if an axle breaks... but depending on which axle breaks, you could spin into the infield or into a wall. Danny's crash was not because of a broken axle. For consideration of the man that designed that car, I will not expose the failure as he has chosen to hide it all these years. I know what happened because I helped him design his next car and we spent a lot of time on the area of failure to ensure it didn't happen again. But I digress...

Back to the Locker. It is not a spague device for Pete's sake. (pun intended, my dad's name was Pete!) It is a roller clutch that locks in both directions and freewheels in both directions.

Mechanically speaking, a sprague has two cylindrical races, no cams! The srague's cage takes a ton of load from the pawls, the Lockers cage manly keeps the rollers phased and straight in relationship to the cams, therefore it sees no load. The spague is 100% on or 100% off!

A roller clutch isn't.

It is only similar because the Locker locks when the relative movement of the inner and outer races engage it. Period. So eliminate the srague from your minds.

Ok, one thing that you are all missing... the rollers roll up the cam as more torque is applied... that is the key to understanding the torque sensing. The Locker is still fundamentally a differential.

So imagine this... on a road course in a high horsepower car with no wings, going flat out into say a 150 mph turn without lifting, and then continue though the turn still without lifting onto a straight. Then come back to me and explain how you think that the Weismann Locker can't be torque sensing.

And one last thing about our dear friend Carroll Smith. I suggest to all of you that you buy all his books and learn from them all you can, especially if you intend to get into racing. He wrote these books to teach you "how to win." His style of writing is funny and at the same time on point. If you assume you know it all and don't need to, then good luck when you have to compete against a student that has understood his teachings.

I remember Carroll coming by our shop after my dad's death in 1997 to see how my brother Patrick and I were holding up. I told him that I was so disappointed for not asking him some questions about things I was still unclear on. He put his arm around me and said, "Don't worry son, you asked enough questions". Made me feel better, but I still regret not asking more.

And that is my finally lesson for today, learn all you can from old people... they have the experience that you don't. I'm not that old, I'm 46, but I was 7 days old when I was in Jack Brabham's helmet bag on the starting grid at Riverside. I got a massive head start.

Chris Weismann

06-11-2013, 11:02 AM

Originally posted by Z:

2. OPEN DIFF.
The diff never tries to steer the car.

Z

Sorry Z.

My grandfather was driving in the snow in a Crosley (sp?)(similar to a bug I think) when his open diff caused him to lose control and crash when one of the driven wheels hit an ice patch.

While stuck in the snowbank, he pondered about how the open diff caused him to crash and came up with the locker concept. Then my dad got involved and they made a locker for the car. Then they set about pulling crashed cars out of snow backs.

My dad went to GM with the intention to put the locker into pickup trucks. Unlaidened pickups in the snow have the least amount of tractive effort.

GM wasn't interested because it wasn't race proven. My dad then met Roger Ward and the rest is racing history.

Warpspeed

06-11-2013, 06:09 PM

I have to agree with Z here.

The exactly equal torque fed to both rear wheels under any and all conditions that a fully open diff creates, cannot steer the car.

It is hardly surprising that hitting an ice patch caused a car to totally lose traction and then go completely out of control.
You cannot seriously blame having an open diff as being the cause of the resulting accident.

Jay Lawrence

06-11-2013, 10:44 PM

Chris,

It does not matter how much experience you or your dad had, you cannot convince people based on some stories from the past, and nor should you be able to. If you are interested in fostering drivetrain development in this series (which would be a start to wider acceptance of your diff) you need to talk to us like engineers (numbers, graphs, useful engineering information). Just because a gun driver went round a corner at 150mph doesn't mean your diff is torque sensing.

Tony, not so sure I agree with that. Well, I agree in principle, but in practice I find the open diff on my RWD road car to be quite unsettling when pushed. I can't quite match the equal torque theory with the practice. Perhaps when the speed differential between outside/inside is very high (due to an ice patch or whatever) and then you regain some inside traction, the inertia of the wheel/axle assembly causes some unbalance in the torque distribution. Maybe I'm talking rubbish too.

Markus

06-12-2013, 12:00 AM

Jay, that wraps it quite well.

Originally posted by Chris Weismann:
You are still not "seeing" it virtually in your head.

...

Seeing you are in huntington beach, I invite you to come to our shop in costa mesa to play with one on the bench.
I guess this is truly a blind trying to lead a blind then... http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

Chris Weismann

06-14-2013, 01:53 PM

Jay,

I understand your point from an engineering point of view. But data can be misread, especially by those with a predisposition.

And I fully understand that you cannot convince some people by stories from the past, or even the present since we are racing and winning with the locker still.

There are those, that need to be gifted a test to convince them... the true skeptics, that need to feel it to understand.

Quoting pheyden from an earlier post. "I have driven with all type of diffs before, open, locked, ZF, constant mesh and Weismann, and I would take the Weismann hands down."

Now I don't know who this man is, but are you going to suggest he is telling you a story, or do you think he must not be a gifted driver, or whatever else you can come up with to discount what he said?

If you can't take it from someone who has driven one, or what had been published, then you can only look at the stopwatch to see the difference - because frankly, who is going to turn over their data to you so you can be convinced.

We got into the transmission business because of the arrogance of some "engineers" out there. They would say, "Well you claim there is a locker in there, but how do we know for sure. We can't see inside it."

And smart racers who, sometimes aren't engineers, don't go out there an tell everyone they are racing it.

And one said "It is a Weismann transmission, and therefore it must have a Weismann Locker in it."

Why?
Not every racing situation requires a locker. A spool and tire stagger at Indy is a quicker alternative because of rotational inertia. But that is an engineering decision to make, once one has tested all the options.

Because of arrogant engineers, my dad chose not to deal with it any more and would only make the locker for special projects and friends.

Back to the open diff causing steering. Picture this scenerio. At Bonneville in the late '80s, a friend named Tony Piner who was trying to break 200 mph in a '29 street roaster and get into the 200 mph club.

The reactive torque from his engine twisted the chassis so much that the left rear wheel came off the ground. Because the open diff spins the wheel with no traction, it quickly exceeded the wheel speed of the ground. When the chassis sat the wheel back, the car would instantly spin. He spun it 3 times before my brother interveened. Pat welded up the open diff and it went 235 mph, breaking the world record.

There is not much traction on salt.

In normal operating conditions. the open diff is all you ever want. But in those extreme cases where you are traction limited... the inherent weakness in the concept of the open diff is exposed. And then some engineer said, "hey, if we put some belleville washers and drag washers in there we could eliminate the spinning... and the limited slip was born. Trouble is that it is "limited and it slips".

Computer controlled, hydraulically actuated pistons over an open diff is an even better band-aid, but the fundamental concept is flawed.

And that is why you have so many other types of diffs out there. But they all under extreme traction conditions follow "the path of least resistance", and they will slip. Your engine torque just gets pissed away.

The Weismann Locker doesn't slip. It does it all mechanically, instantly. It is "mechanically active". It senses when it has torque mechanically and instantly locks up. When the tire can no longer handle the torque, the tire slips and losses reactive torque and the locker senses the loss and equally then reduces the torque to that tire mechanically and transfers it to the other wheel mechanically if the tire can take it.

I don't need to take anymore of my time here trying to convince anyone. I came here to sort out the misconceptions about of Weismann Locker, to explain our unique position we finds ourselves after 50 years in racing with the Locker, and to help those that are truly interested in understanding how it works its magic. I like to teach, but you can't teach those who don't want to learn.

Our track record speaks for itself. Carroll Smith wrote about it in all his books, so did Paul Van Vaukenburg. It doesn't not have to be taken on faith.

And I have given you guys subtle clues to think about. But they have all fallen on "blind" eyes. It seems that nobody wants to really think anymore... pity. Anyway I'm here to tell you I'm not going to give you our concept. I will, however, work with "believers".

My brother thinks I'm wasting my time. Maybe. The way I look at it, if you really understand what the locker can do, then maybe one day when you get into a situation where the locker will solve your problems, you'll know where to come.

The JAMMA, a military vehicle that got licensed to Force Protection, came about that way. A clever engineer, that had never worked with us before, was hired to design this vehicle.

It has two Weismann Lockers, front and back. If you find pictures of it, note how the lower a arms are back to back. A feature possible because of our recent, patented concept of the locker.

We came up with the idea because a race engineer said, "we couldn't have our cv joints back to back and still have a diff. We built it to spite him. The idea is valid. The vehicle works.

Markus,
The offer still stands. No sweat of my back if you don't.

Mr Kaneb, thank you for your post.

Ian - murpia,
The situation was:
If you had full steering lock, going into a hairpin, and the car was pushing, the locker would continue to push you, and if you happen to be aimed at a wall, then to quote Carroll, "Hello wall!". The reason is that in a turn the locker drives predominately the inside wheel, thus creating a push.

Mr Pare,

I once spoke with Al Unser Sr. about driving the Weismann Locker at Indy. He said if you lifted too much at Indy, then the transition from driving the inside rear on gas, to the outside rear off gas tended to make the back end of the car fish around some and that was not too comfortable going thru turns 3 and 4 at Indy at 200 mph. So he preferred to run the spool and tire stagger. Purely a driver preference.

I appreciate all you guys taking the time to post.

Chris Weismann

Owen Thomas

06-14-2013, 03:23 PM

Chris,

I just wanted to post some clarifications to close up any gaps in understanding you may have about this community (FSAE), mostly because I hate to see people getting frustrated over simple miscommunications.

FSAE is a student-oriented competition with a 1-year design cycle (more information at http://students.sae.org/compet...mulaseries/about.htm (http://students.sae.org/competitions/formulaseries/about.htm), as well as on this forum). Because of the nature of the series, the vast majority of teams do not have the resources or desire to reverse engineer or "steal" your designs.

Looking at the few posts immediately following your own introductory post, you will notice that people were primarily asking about what the Weismann locker does, not how it does it. As interesting as it may be to us to learn how it all works, what is important is the outcome, or how it affects torque delivery in different situations. Perhaps I've missed it, but it seems as though you are hesitant to explain this. This appears to be the cause of Jay's and Markus' (who lives in Helsinki, Finland) posts, which are focused on figuring out the details which would aid in an engineering decision to use (or not use) the locker.

Chris, there are about 200 FSAE cars built in America every year. If you can build us a differential, able to transmit around 800 lbs*ft total drive torque, weighing in at 8 lbs or less, for around three grand, you'll sell out.
Charles said this, and I believe he is correct; but only if you provide quantitative specifications. As mentioned earlier, it is doubtful that one team would have the resources to work directly with you to develop an FSAE specific Weismann unit - although many of us would probably love to do so. What I'm saying is that there is literally no way that I am aware of in which we could implement and test one of your lockers, and without some kind of data on what the unit does, we don't have a reason to. Surely the F1 teams who ran the Wiesmann did not choose it based on loose opinions and previous results, they must have made the decision on a technical basis. So where's the information they had?

cal_len1

06-14-2013, 05:57 PM

The one thing about our competition that makes it special over say F1 or anything else is the design tent. We have to explain to the judges why we chose the differential and how it affects the handling of the car. And if we just tell the judge that it locks and uses magic to unlock and bias torque, they will not be happy. I'm not saying that the diff is not something good or bad, because none of us know as we have never used one.

Because of the nature of the series, the vast majority of teams do not have the resources or desire to reverse engineer or "steal" your designs.

This is pretty spot on, because face it, a lot of teams don't even have the time to finish their cars in time for comp, let alone reverse engineer a diff. We are all engineers, if we see some data all of this misunderstanding will go away and will have a lot more sympathy for your cause. You just can't keep telling us it operates by "magic" that doesn't exactly cut it.

Callen Schmalz
SDSM&T Formula Hardrocker Racing
Drivetrain Lead

Warpspeed

06-14-2013, 06:15 PM

Chris, people here are student engineers doing their best to design a vehicle that is going to not only have to race, but be judged on it's technical merits by some very serious design judges.

These students will probed in depth for the TECHNICAL reasons why they designed a Weismann diff into their car, and receive marks for the quality and depth of their knowledge.

An answer such as "a famous guy once said he liked it, but how it actually functions is a big secret" is just not going to cut it with the design judges.

billywight

06-14-2013, 08:20 PM

I don't need to take anymore of my time here trying to convince anyone. I came here to sort out the misconceptions about of Weismann Locker, to explain our unique position we finds ourselves after 50 years in racing with the Locker, and to help those that are truly interested in understanding how it works its magic. I like to teach, but you can't teach those who don't want to learn.

Is this a joke? If not, then the only joke here is you Chris... You haven't presented any information that could be convincing. You came to "sort out the misconceptions" by doing what, presenting no technical information? And to say your diff is magic is just laughable! Everyone here is here to learn, the problem is the "teacher" is not willing to teach... Until you present technical descriptions, drawings, pictures, etc, the only arrogant "engineer" here is you, and I use the term engineer loosely.

06-14-2013, 10:33 PM

Originally posted by Chris Weismann:
The reactive torque from his engine twisted the chassis so much that the left rear wheel came off the ground. Because the open diff spins the wheel with no traction, it quickly exceeded the wheel speed of the ground. When the chassis sat the wheel back, the car would instantly spin. He spun it 3 times before my brother interveened. Pat welded up the open diff and it went 235 mph, breaking the world record.

I agree that an open-diff can "steer" a car as described above. Even the small amount of friction in the gears can cause a small yawing force. Likewise, the sudden loss of thrust when a wheel spins can be a problem, and also the sudden loss of cornering grip when the wheel spins...

Nevertheless, a spool can be a bigger PITA, because it tries to make you go straight when you want to turn, and occassionally tries to make you turn when you want to go straight (eg. split-mu). This is why tractors (which live for traction!) normally have open-diffs, but allow you to lock the diff on those rare occassions when it helps.

My understanding of the WL (so far?) is that it is somewhere between these two extremes (open and spool). Probably closest in most "normal" racing conditions to a pair of one-way clutches (spragues) driving each wheel. At the very least, it seems that it does want to mess with the car's handling, as per Chris's quote;

"If you had full steering lock, going into a hairpin, and the car was pushing, the locker would continue to push you, and if you happen to be aimed at a wall, then to quote Carroll, "Hello wall!". The reason is that in a turn the locker drives predominately the inside wheel, thus creating a push."

Anyway, FSAE/Autocross is a lot different to other forms of circuit racing in that there are a lot more corners, and most of them are relatively tight (like above hairpin). So any "steering" effect from the diff can be a disadvantage. So given the choice of a $3k? Weismann Locker, a $3k+ Drexler, and a ~$0 open-diff (taken from some small car at the wreckers), I reckon the open-diff, with ~60% rear weight and lots of aero, has the least disadvantages. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

PS. By NOT serving you up all the answers on a plate here, Chris is encouraging you students to think for yourselves. You are not always going to get gold-stars for simply cutting-and-pasting some junk off the interweb... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Markus

06-15-2013, 01:13 AM

Chris, I appreciate your offer but I will not book flight tickets to US just to see the diff. If you can "see it in your head" that I live on the other side of the big lake, you'll understand.

I have an accurate enough vision of how the diff works (the version in the patents, it's beyond me if changes have been made). I don't have time nor interest in describing it here to make sure everybody understands, hence the quite vague descriptions I gave (to give us engineers something to think, and still more than you gave in your posts).

I don't know if you misread, or misunderstood my posts but for example you agree with the major points in my descriptions in your post. http://fsae.com/groupee_common/emoticons/icon_smile.gif

The diff has no skidding or slipping parts as you and the patent enforce (except the damper), which means the outputs can either be coupled or decoupled. That means the only possible mechanical torque split states of the device are 50/50, 0/100, no way over or around the fact. This doesn't mean the transitions between the states are violent, that was your deliberate misunderstanding, and I was actually claiming the exact opposite.

You're not the first one here bitter about not getting the respect you desire. I'm sorry but that's mainly because of the attitude you approach us with.

Also "magic" is fooling common people with distractions and tricks, "believers" can keep going to Justin Bieber concerts. Magic and beliefs shouldn't have a place in engineering, data and facts don't play games.

If it makes you feel any better I like the approach and design of the diff and think it might work wonders on wide open tracks or especially offroad (overcoming the biggest disadvantage of Torsen). Whether it works for FSAE or not, it's hard to say. The tracks are narrow and tight and the WL's tendency to straighten the car both accelerating and declerating won't really help.

06-15-2013, 05:16 AM

FWIW, back in 2005 I suggested that you FSAEers consider a pair of one-way clutches (= spragues, or even ratchets) for the final drive (= "diff"). These would allow the engine to drive each wheel forward, but would free-wheel backward (think of bicycle hub). So they would act like an open-diff on corner entry for good turn-in (no torque applied to wheels), and like a spool on corner exit (driving more the inner wheel, so straightening the car).

The one-way clutches would only work in FSAE because no reverse gear is required. The WL can drive in both forward and reverse directions, so you can use reverse gear (useful, I guess, for army trucks, and many other racing series). I was suggesting these one-way clutches because they could be bought or even made quite cheaply (again, think over-sized bicycle ratchets). Their behaviour is half-way between open-diff and spool, and is quite good, all things considered. I don't know if any teams have ever tried this???
~o0o~

Oh, yes, and regarding "magic", I recall Claude talking a lot about "magic numbers" and the like in his seminars. Quite common in motorsports... http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Z

Chris Weismann

01-13-2014, 02:46 PM

Gentleman,

I'm back to stir the pot.
I have been meaning to come back and write about something that happened last June, but I didn't feel comfortable writing about it then for reasons that will become obvious when you read about it below.

But Z's post caught my attention and the timing was right.

A few years back we came up with a new Weismann Locker for offroad racing trucks, and we debuted it with the late Rick Huseman. We used the Weismann Locker concept but made it only one-way drive for two main reasons. One to allow the front wheels to roll when landing on the front, thereby eliminating the back drive thru the ring gear and pinion and to the transfer case and gearbox, thus saving parts from breakage; and two, to allow the front end to disconnect and act like a Pro-2 truck and rotate quickly. It works great, you can drive the truck wherever you want to, i.e. high line in the fluff, or down low and tight around corners. We won the championship and it was one of the main reasons why that truck was the one to beat up until Rick died in a plane crash. We called it the Weismann Unlocker.

We then made another version of it, but this time we put it in the front wheels, and we did it for Ricky Johnson's Pro-4 truck. Ricky was a motocross legend before making the move to offroad race trucks. He won the 2011 and 2012 TORC Pro-4 Offroad championships with the Wheel Unlocker... the prototype is still being raced today in his truck.

This past Friday, Red Bull had a unique one-off offroad race on the ski slopes in Maine in an event called the Red Bull FrozenRush. Pretty cool event, no pun intended even thought it was just above zero. Ricky Johnson won the event. And since some people don't think quotes mean anything, I'm going to quote him anyway.

"Once again I can't thank Weismann enough for their great differential. It works just as good in the snow as it does in mud, sand or tacky dirt. Thank you for helping me win the first Red Bull FrozenRush."

We had the top 3 trucks running our Unlockers. Greg Adler gave us a good plug too from what he told me. NBC will air the event on Feb 2nd at 3:00 ET.

Back to Z's post...

One-way clutches, and more specifically sprague clutches, can and do work, but like anything, they have their baggage to engineer around as well.

Drivers that like to pedal the car mid corner for balance won't like the feel as there is no engine braking to settle the rear. But more crucial; Spagues don't like the sudden engagements, spike loads from landing under throttle or getting run into, and they don't like lots of torque.

Another offroad racer Carl Renezeder can attest to the woes of srague clutches since his Pro-4 team decided that they could use sprague clutches too. It worked, but was extremely fragile and it cost him many races. So they got their smart little heads together and redesigned it so that they can change out the sprags every round; but that can be very expensive and they have to pull their whole front end apart to do that as well... not very fun between rounds and if you have ever seen how much stuff there is built around the front differential that you have to remove before you can get the diff carrier out, you can understand why Carl has given up on that approach for this year.

Conversely, another offroad racer Adrian "Wildman" Cenni left our prototype "SideWinder Front Unlocker" in his truck for the last three rounds of this past season of TORC Pro-4 without checking it. To the racing offroad community, the fact that the prototype "Cenni-Proof" is testament enough. That they didn't check it for the last three rounds is unheard of reliability.

The RC offroad truck manufacturer Team Associated caught on and is using a crude ratchet up front. I say crude, because like a Detroit Locker, it is a discreet ratchet and therefore doesn't engage instantly with rotation direction change; and it is hard on the engagement. BUT because of the light torque and weight of a RC Truck, they can get away with it.

And lastly, and I have gone back and forth on whether or not to bring this up, but since I'm here and this was a topic of debate on this page...

In my opinion, the rear differential that was in the car that the late Allan Simonsen was racing in caused his fatal crash at Le Mans this past year in the opening laps of the race. To see what I'm about to describe, you need to be looking at the in car footage from the car behind him. As Allan was going thru the Tetre Rouge left hand turn about to head down a fast straight in the very slick, wet conditions, his car drifted out and up onto the curb. Because his car was so stiffly sprung, as the left wheel climbed the curb, the right rear wheel came off the ground as well. And because Allan was accelerating out of the turn for the run down the straight, the unloaded right wheel then sped ahead of the wheel on the ground very quickly as all limited slips take the path of least resistance. As the car ran down the curb and back down on the track, the right wheel then touched the ground and instantly shot the car off to the left. There was absolutely nothing Allan could do after that as it spun him into the grass and into the barrier practically head on. It gutted me to see it and I didn't watch the rest of the race. Crashes do happen, but not without a cause.

The crash was officially put down as a racing accident.

My condolences to Allan Simonsen's family, and I apologize for bringing this to light in a forum.

Magic is term that the less educated use to describe things they can't comprehend.

Chris W

Jay Lawrence

01-14-2014, 12:37 AM

Chris,

I've just had this wicked idea! I've invented a widget that will totally regrow your hair and make you 23.7% more intelligent! It uses vitamin R to boost your nanoparticulators and give you untold amounts of amazing! Testimony from my mate Jimmy Bob: "Of all the things, this is the best thing in the world!"

Are you convinced or do you just lack the education to comprehend the magic in my widget?

You haven't provided any information that would make any team likely to pursue this further. We have no price, no mass, no size, no explanation, no data. Are you now expecting us to buy your diff because it may or may not have used its 'magic' to save Allan Simonsen's life? That's insulting to us and him. You don't even need to explain HOW it works. You just need to provide some sort of data that shows WHAT it does, and give us some details like mass and suitable shaft/housing/mounting types.

Stop going on about off-road race cars. We are not building off-road race cars.

murpia

01-14-2014, 08:30 AM

Gentleman,
I'm back to stir the pot.
...

The RC offroad truck manufacturer Team Associated caught on and is using a crude ratchet up front. I say crude, because like a Detroit Locker, it is a discreet ratchet and therefore doesn't engage instantly with rotation direction change; and it is hard on the engagement. BUT because of the light torque and weight of a RC Truck, they can get away with it.

...
Chris W
One-way clutches have been used in RC racing, both on-road and off-road since at least 1984 as far as I know and probably earlier than that. Rather than 'getting away with it' with it's implication of negative understanding and / or implementation, they can be highly refined pieces of technology with well understood vehicle dynamics effects.

Yes there are implementations with discrete ratchets but you have to ask how important that is when 60 degrees of shaft rotation occurs in 0.003s (yes I can show that working out). Regardless, I have a set in my garage which date back to 1986 and make use of roller clutches on precision ground shafts much like (my best estimate of) your 'magic' diff uses.

Their genesis comes from the one-way hubs fitted to many early part-time 4WD vehicles (WW2 Jeep, Land Rover Series 1 & 2, etc.) instead of a centre differential. Driveline 'wind up' occurs because at slow speed and / or during tight cornering the average front wheel speed exceeds the average rear wheel speed. 4WD RC cars often do not have a centre differential so this wind-up can cause unwanted slow speed understeer.

Various implementations exist across the various RC on and off road classes. Only the 1/8th scale buggy and truggy classes tend to have a 'traditional' 4WD driveline with a centre differential. 1/8th on-road, 1/10th on-road (both narrow / wide, electric / nitro) & 1/10th 4WD off-road can make use of one way couplings. Sometimes this is in conjunction with a differential on the front axle, sometimes instead of it. Sometimes the coupling is before the differential in the driveline, sometimes there are 2 couplings, one for each wheel. Each implementation has different handling effects and experienced drivers may change configuration depending on the circuit and tyres. This is especially true in the 1/10th on-road classes.

As an aside, the most successful 4WD Group B rally car, the Peugeot 205 T16 employed a one-way coupling between the centre and front diffs at some point in it's development history.

There is an additional vehicle dynamics effect at work in an RC car compared to a typical full size vehicle. Usually the brakes are implemented inboard, either as a single disk brake working on the transmission, or by using regenerative braking of the electric motor. With a one-way coupling this means the braking effect is limited to the rear axle, essentially creating a 100% rear brake bias. Any competent analyst will recognise this has an oversteer balance effect. RC cars do not gain as much laptime on the brakes as full size cars and tend to lose speed through tyre scrub as much as anything else. Certainly they do not brake much in a straight line. In this respect they have much in common with most karts, which have a single rear axle brake.

Regards, Ian

01-17-2014, 09:07 PM

Gentleman,

I'm back to stir the pot.

And I'll keep the pot stirring, because differentials are a major performance factor in FSAE (potentially bigger, IMO, than many FSAEers realize), and a "Weismann" style diff does not seem to have been used in FSAE yet.

... Z's post [previous page] caught my attention ...
A few years back we came up with a new Weismann Locker for offroad racing trucks...
... but made it only one-way drive ...

What Chris describes in that section seems similar to what I was suggesting for FSAE back in 2005. Namely, a pair of one-way clutches that can drive each rear-wheel forwards, but not backwards.

The best that I can interpret from reading Chris's posts is that the "Weismann (Un)Locker" is much stronger and smoother than off-the-shelf spragues or ratchets. But that seems to be only a matter of detail design, material quality, etc. Otherwise, it seems the basic operating principles are exactly the same. (Chris, please correct me if I am missing something big).

As Chris notes, these can be built into a central "differential-like" unit, or they can be individually mounted in each rear-wheel-hub [Edit: "in each rear-wheel" for usual FSAE, or in ANY wheel if you are going 4WD]. And as both Chris and Ian point out, for lighter weight vehicles like RC cars, these one-way clutches can actually be built as "ratchets". IMO, FSAE cars are small enough that the right design of ratchet would work acceptably (hint: consider a larger diameter version of a bicycle's rear-hub-ratchet mounted either side of your rear sprocket...).

Very briefly, the advantages are that they act like an open-diff on corner entry, so giving good turn-in (both wheels are "free-wheeling"), and like a spool on corner exit (engine drives both wheels at same speed, so straightening the car). And they could potentially be made quite cheaply...
~~~o0o~~~

And lastly,...
In my opinion, the rear differential that was in the car that the late Allan Simonsen was racing in caused his fatal crash at Le Mans ...
... his car drifted out and up onto the curb.
Because his car was so stiffly sprung, as the left [right-front?] wheel climbed the curb, the right rear wheel came off the ground as well...
... the unloaded right [rear] wheel then sped ahead of the wheel on the ground ...
... As the car ran down the curb and back down on the track, the right wheel then touched the ground and instantly shot the car off to the left.

I have put in bold what, IMO, is the root cause of the problem here. If Simonsen's car had a SOFT TWIST-MODE (and even if it had stiffer Heave, Pitch, and Roll modes), then the right-rear-wheel would never have come off the ground, and no problems, regardless of his diff type.

[Mini-Rant] The earliest wooded carts, from many thousands of years ago, were deliberately built with soft Twist-modes. Quite naturally, the first steam traction engines of the 1800s had the same. Same again with all farm tractors, forever, and multi-axled trucks, and forklifts, and ride-on-lawnmowers, and ... countless other vehicles.

But NOT RACECARS. Oh, noooo... Instead, the experts will ask you about your "Front & Rear Ride Frequencies", and get you to do 59 different damper calculations, +++.

But soft Twist-modes, oh, noooo..., that's black magic..., the work of the devil!!! [Mini-Rant Over :)]

Magic is term that the less educated use to describe things they can't comprehend.

Chris W

Z