In Board--or Out?

[jack]

just wondering how many teams have/are running outboard rear brakes? why is in board better than out (other than weight) or vice versa. how about front brakes? just want to know what you people think.

JACK
www.etec.wwu.edu (http://www.etec.wwu.edu)

[Sleeque]

Either inboard or outboard brakes work okay, but the arguments in my book for a single inboard brake is as follows.
1. Weight and packaging. It is a fairly simple matter to put a single disk on the opposite end of the differential carrier but you must use a locking or locked differential.
2. Inboard reacts the brake loads directly into the chassis, outboard requires the brake torque to be passed into the chassis structure via radius arms or the A arms.
3. Reduction in spng weight. When the rotor and caliper is moving with the wheel, that weight must be controlled and damped.

I hope this helps
Slan Leat

Sleeque

[Brent Howard]

We run a 4 brake system because it provides even braking and the judges like it. We had a 3 brake inboard system before and they didn't like ti too much so we switched. I'd go with the 4 brake system over teh 2 front/ 1 rear set-up simply because the judges like it.

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Marshall]

We simply found that 4 brakes was a complete waste for our car. The rear brakes do so little that we found that the diff generated as much heat as the rotor. Putting something on the car because "the judges like it" is not the way to win. The way to win is to prove to the judges that you made the right decision.

Marshall McLean
University of Western Ontario
http://www.cockyracingguy.com/pictures/tripodsig.jpg (http://www.cockyracingguy.com)
UWO FSAE Racing Team (http://www.engga.uwo.ca/sae/)
Western Ontario Sports Car Association (http://www.wosca.com)

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Brent Howard:
I'd go with the 4 brake system over teh 2 front/ 1 rear set-up simply because the judges like it.
<HR></BLOCKQUOTE>

Wow. First, I seriously doubt that the judges would prefer outboard to inboard, unless you run an open diff? Were there any cars in the design finals with outboard rear brakes? I'd be suprised. Secondly, the judges sure don't like it if you do something without knowing why. We've resisted judges opinions before, and from my experience they are usually right. But you've got to understand why they are right or else you are just lost.

-Charlie Ping
Auburn University FSAE 1999-present

[Scott Wordley]

Charlie,

Brent never mentioned anything about outboard brakes. Its possible to have dual inborad brakes at the rear.

Regards,

Scott Wordley & Roan Lyddy Meaney
Monash FSAE Wingmen
http://www-personal.monash.edu.au/~fsae

[Charlie]

Good point. You may very well be correct, however I would still infer from his post that he meant outboard.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> We had a 3 brake inboard system before and they didn't like ti too much so we switched. <HR></BLOCKQUOTE>

-Charlie Ping
Auburn University FSAE 1999-present

[Superfumi]

Knowbody said anything about inboard rear brakes stressing the driveshafts? Torque from outboard brakes would be reacted at the tire-road interface (ie is not reacted through driveshafts)

[Schumi_Jr]

Aren't your driveshafts designed to be stressed?? If you have enough torque at your engine, you can theoretically produce more torsional stress in you driveshafts in acceleration than breaking (wheel loads). I see no real argument for outboard rear brakes in FSAE...

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae (http://www.eng.uwaterloo.ca/~fsae)

[Mark Ortiz]

I think the usual choice of a Zexel-type diff for FSAE is sound, but just as a point of discussion, a single brake works fine with an open diff. In fact, it works most like well-matched individual brakes when the diff is open. Or at least that's true as long as neither wheel locks. If one wheel locks, we can add more braking force on the other wheel with individual brakes, whereas with a single brake through an open diff, the rolling wheel is limited to the torque of the locked one.

This is largely academic, because if one wheel locks, we probably want to release the brakes anyway, to avoid flat-spotting the tire.

Frictionally connecting the two wheels is good in terms of avoiding flat-spotting. One penalty is that the diff locking force tries to resist attempts to turn the car. This tends to add understeer on turn-in if we are braking, which is probably undesirable for autocross, though it might actually improve trail-braking behavior on an oval or a road course.

In practice, single rear brakes acting through Zexels seem to work just fine.

[formula_geek]

Mark-

If we were running open diffs (obviously not), couldn't there be an issue when an inside wheel becomes very unloaded? Wouldn't the inside wheel be turning backwards at the same speed as the wheel that is moving forwards, while the rear brake is simply stopping the carrier?

Curious,

Travis Slagle
KU FSAE

[MercerFSAE C. Burch]

As the suspension group leader for our new team here at Mercer, I've been doing a lot of research on the brake system. Looking at a book titled the "Brake Handbook", by Fred Puhn, and using a few numbers applied to some of his equations, it really seems that adding an extra brake to the rear would be useless. According to Puhn, about 2/3 of the braking is at the front, while only 1/3 of the braking is at the rear! That would seemingly make a three-rotor setup ideal to our needs!

I also ran some numbers through his equations for heat generation and found that the heat generation that we need to produce is far smaller than what 3 solid steel rotors of about 7 pounds each could handle. I haven't found a really good reason for why teams are cross-drilling their brakes... they're probably hurting performance by reducing their swept area. The additional cooling is not only not needed, but even if they did, it would be much better accomplished by using air ducts rather than weakening their rotors with holes. I haven't found any pictures from any formula car series that uses drilled discs.

If anybody else is in the know and has experience, which I'm not and I don't have, I'd appreciate their comments.


-Chris

[Matt Thio]

Using inboard brakes can be just as effective as an outboard configuration if done properly. Even eliminating the need for a separate inboard rotor can be made, by utilising the rear sprocket itself as a braking surface.

[James Waltman]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Matt Thio:
...utilising the rear sprocket itself as a braking surface.<HR></BLOCKQUOTE>

Matt Thio,
Have you done this before? I know that some teams have done it but I hear that it is a nightmare to keep the braking surface clear of chain lubricant. If you've done it could you share how you solved this problem?

James Waltman
waltmaj@cc.wwu.edu
http://dot.etec.wwu.edu/fsae/
Formula SAE
Vehicle Research Institute at
Western Washington University

[terc04]

wouldn't the heat from the rotor also cause chain stretching problems?

[Scott Wordley]

I saw someone mentioned the possibility of running the rear brake on the drive sprocket. We have actually done this for two years now. I think we may have been the first team to do it, please correct me if you know otherwise. I think Sydney Uni (Matts team) also did it this year. We've found it works fine. We actually built a test rig in the first year to check stopping power and temperatures etc. It all checked out fine. Saves heaps of weight as there is no rear rotor, less mounts etc. The things you have to think about are chain lubrication and keeping the heat away from your diff. See the photos below, the test rig rotor was actually glowing red hot in this shot.

http://www-personal.monash.edu.au/~fsae/brakeonsprocket.JPG

http://www-personal.monash.edu.au/~fsae/braketest.JPG

Regards,

Scott Wordley & Roan Lyddy Meaney
Monash FSAE Wingmen
http://www-personal.monash.edu.au/~fsae

[awhittle]

A few points

1) the loads on the axles when acelerating will always be higher when accelerating then braking. The weight on the rear tires once the weight transfers times the rolling radious times the cof will determine the max loads on the axle.

2) This all changes one more huge set of assumptions one you start turning in.

3) Torsen diffs act as an open dif once the inside unloadson turn-in but that may be a good thing.

4) a Torsen will behave as a poor mans ABS in the rear as long as there is load on all three peices of the equation the diff and two tires. If any of these three goes to zero load...all three go to zero torque.

5) if you question any of the above, just up the rear roll stiffness and remove front roll stiffness so that you can carry a inside rear tire at mid turn and try rolling on the power.

6) clutch pack diffs and spools change all of this to a new set of problems and advantages.

Hope this helps

AW

[JDF]

Tennessee Tech will be running a combination rotor/sprocket this year (I'm calling it the sprotor). Can't say much else about the design of the diff, except that it will be a huge departure from the 30 pound monster we had last year. Still trying to find a 12 tooth front sprocket before I can finalize the design of the rear....

I was a little dissapointed to hear that the idea had been used before, but what we have in mind will still hold a lot of originality.

JDF
Tennessee Tech

[Matt Thio]

It's not a nightmare. An O-ring chain was used in order to reduce the amount of lubricant required. The Mechanical LSD was mounted with two CNC machined aluminium mounts either side of the differential. These aluminium mounts also housed roller bearings. diff mounted Turnbuckle-type adjustments were also used to keep chain tension, and the brake caliper is mounted directly to the aluminium diff mounts. Just be cautious not to heat the diff too much. I'll try and post a picture of USYD's soon, but the one already here looks nice as well.

[Frank]

we ran a strain gauge on a drive shaft..(radio transponding strain gauge $5000 US)

the torque on acceleration is limited by the clutch

the torque on de-acceleration is due to the INERTIA of the components from diff to tyre being brought to a halt rather suddenly

the result.. giant spikes on torque during aplication of the brakes.. (for us it was about 5 times the static breaking load) ((although we had rather heavy wheels.. 5kg))

just something to think about

http://fsae.com/groupee_common/emoticons/icon_eek.gif

[Frank]

that last post was meant to say "braking" as opposed to "breaking"

interestingly we broke a GKN shaft...

dont use their drawing for the circlip groove..

a circlip groove shouldn't be deeper than below the splines

several aussie teams broke the same shafts (repetitively) until they changed the design of the circlip groove

[Frank]

that was meant to be 15 times the static load
NOT 5 times the static load

[Charlie]

You can edit your posts. Click the pencil & paper above them.

-Charlie Ping
Auburn University FSAE 1999-present

[jack]

i was wondering if you guys make or buy your "sprotors"? can you buy those, do you frankenstien together a brake rotor and sprocket? does any one make/design their own?

JACK
www.etec.wwu.edu (http://www.etec.wwu.edu)

[tool]

Originally posted by Mark Ortiz:

In practice, single rear brakes acting through Zexels seem to work just fine.


Can someone comment on the effectiveness of single inboard rotor while using a Quaife differential?

[Christopher Catto]

I agree 100% with comments about two outboard rear brakes being generally unnecessary in FSAE.

I think however many teams, including my uni, have used two outboard brakes because it has proved reliable and performing so long as the rear brakes have not added much weight. This means using an AP 2pot (non-floating) calliper for the rear of a racing bike or some really tiny scooter brake calliper, and very thin discs. We never had any issues at the rear because the systems were decoupled. you can see this as a waste (if you were for example Colin Chapman) or as a big time saving if you have to get the other stuff done, like a damn bullet proof cost report.

Reasons for not using inboard brakes are in my opinion lack of time to tune diffs and/or sprotors. Ok, so this should not happen but I can say that in Detroit 05 we did very well with 2 rear outboards. Car braking was awesome (i disagree about opinions that rear brakes are not much use, ok maybe in SOME fsae cars they may not be but I think if you have a large rear bias to improve your yaw response then you will find rear brakes are actually damn important under braking especially if you want to keep understeer at bay) and I don't think our rear upright hub and brake assembly was any heavier than those of teams who fashioned their uprights as if they were for a GP2 car. at the limit then yes, the outboard design is heavier of course!

In retrospect I think that for us, having two outboard rear brakes freed some time for other stuff. If we could re-do things then maybe yes, we'd invest more time in diff setup but truth is, we just had little money and time due to all sorts of reasons.

It's really a bit like: do I want a nice big house or do I want a small town house and one in the countryside. I think if you are clever enough you can make any system works and dare I say that you make your choice as to where you want to cut corners.. realistically!

last thing. we thought outboard brakes was a nicer learning experience for us since most of us are now working at racing teams where inboard brakes are not used. This sounds like madness but again, we chose other things based on what it would teach us for life, hence no weird cvt which we think is bollox on racing cars unless you had the budget of Williams when they developed it.

[Steve O]

I'm on the inboard brake bandwagon here. It decreases unsprung mass, decreases rotational mass, and has far less parts to buy/mount to the vehicle. Another benefit of running the inboard brake that hasn't been mentioned is additional clearance inside your wheel hub to put your ball joints right at your tire centerline.In our fronts with the outboard brakes, the rotors and calipers get in the way of that.

To be honest,though, I'm not sure I am sold on the sprocket rotor. I think heating up your sprocket is just asking for trouble. You are going to get warping from jamming the acceleration load on it once it starts to heat up. If you are driving hard enough your brake rotors will start to glow. If they aren't you are either driving like a sally and backing off way to early before corners or your rotors are not properly designed (either designed for too much load or you aren't transferring enough heat). I'm also not sure how much it really saves you. Eliminating an entire extra brake saves weight because of the assembly, eliminated your 1 rotor doesn't save that much as long as your rotors are not over engineered. We use aluminum rotors front and rear and they hold up just fine, weigh almost nothing, and have better heat dissipation than cast.

One last comment on the judges. Their task is to judge your engineering of the vehicle, not what the vehicle would have been if they were to engineer it. The most important thing to them is that you thought about what you put on the car and not just said "oh this looks good", or especially, "oh this looks good because 'team A' did it last year." You can do anything you want on the car as long as it does not jeopardize safety. With the judges, it is 90% about what you say about what you did, and not really about what you actually did.

Steve

[flavorPacket]

We went from a single to dual outboard brakes and lost weight.

[John Valerio]

Originally posted by Steve O:
We use aluminum rotors front and rear and they hold up just fine, weigh almost nothing, and have better heat dissipation than cast.
Steve

hi again steve, make sure you have something to say to the judges about high temp wear rates. we were hit with that one, and the old "limited FSAE driving time" argument didn't hold much water.

back on topic, as far as the braking configuration goes, this year we're switching from 3 AL-MMC rotors to 4 outboard cast iron rotors. we're tired of a crappy pedal feel from Al-MMC rotors, and also tired of making compromises in other areas to get the damn thing to trail brake well. as far as dual diff mounted rotors goes, we're using fairly small cv-joints that we dont want to reverse torque, and a diff that we want to be able to adjust quickly and keep additional heat out of.

[drivetrainUW-Platt]

Originally posted by formula_geek:
Mark-

If we were running open diffs (obviously not), couldn't there be an issue when an inside wheel becomes very unloaded? Wouldn't the inside wheel be turning backwards at the same speed as the wheel that is moving forwards, while the rear brake is simply stopping the carrier?

Curious,

Travis Slagle
KU FSAE

I was a corner worker for Autocross and yes, there is definitely air underneith the rear unloaded wheels on some cars and yes things will start rotating backwards with a single center diff mounted disk.

My argrument is that with inboard disks mounted on the diff you have to worry about heat and oil, both in the diff and on the disk. The problem with duel inboard disks is what do you mount them to? You can make splined adaptors and longer axles but if you are using stock CV joints and an ATV differential thats a lot of extra work.


We run them on the outer rears because they are far away from oil leaks and the disks can be mounted to the wheel hubs.

[Vinnie]

I also ran some numbers through his equations for heat generation and found that the heat generation that we need to produce is far smaller than what 3 solid steel rotors of about 7 pounds each could handle.

ok let me share some experience with you: we recently tested the 3 brake disc setup of the previous car. after 8 (30s laps) the rear brake temperature was 430 degrees celcius, the front brake temperature only 180 degrees celcius. and we hadn't even driven a fourth of an endurance distance. so you can guess what happens when you drive an endurance distance; exactly temperature gets too high and your brake fluid is boiling; that happend in the endurance at FSG. so I don't know how you calculated that your discs could handle the heat, but i doubt if it is accurate; did you take into acoount that your discs getting hotter each time you brake (until it reaches an equivilency in cooling and heating off course)


I haven't found a really good reason for why teams are cross-drilling their brakes... they're probably hurting performance by reducing their swept area. The additional cooling is not only not needed, but even if they did, it would be much better accomplished by using air ducts rather than weakening their rotors with holes. I haven't found any pictures from any formula car series that uses drilled discs.

We also tried out brake ducts; the rear brake disc temperatures came to 370 degrees in stead of 430. still too hot for only 4 minutes of driving if you ask me. thats why i think its good to have cross drilled brake discs, if you put many tiny holes in the brake disc it will create a lot of cooling surface, but also heat up your brakes sooner as the heat capacity is less. however more cooling surface means that the equilibrium of cooling and heating is reach sooner, which prevents the disc temperature to become too hot. other theories about cross drilled brake discs, which I don't know for sure whether it true or not, but they seem very likely:
<LI> brake dust removal
<LI> holes create an additional brake bite

and what about the unsprung rotating mass? another advantage of cross drilled rotors is weight. another thing: beaware for placing the brake disc inboard; engine temperature and almost no cooling air flowing past will result in very hot rear brakes...

cheers, Vincent
Delft 05/06/07 class 3/steering/braking
OBR 08 brakes/tyres/race eng

[Christopher Catto]

Two brake manufacturers I have been in contact with for work reasons both told me that cross drilled brakes are a gimmick for show. Basically they decrease disc life by about 20% due to earlier onset of cracking. You'll find very few race cars run drilled (if they do, they're not a serious team). Where I work now we don't have drilled and many of the cars I've seen so far do not, apart from stock Porsche GT3s that are sold to customers, also (he he) on looks.

What I have used is slots to clean pads. The best is a groove but if you're making your own discs this is a separate process from the usual laser cutting or general machining. Or you can use wavy dics like motocross to be aggressive on the pad.

As for Steve saying that the brakes will glow, well, I'm not sure at what temp steel glows but I bet it's more than 650C, which is the most temp I've seen on steels before you start having a few problems. I've only seen discs glow on F1, ALMS and some other hard racers. No disrespect to formula SAE but to make steel glow you'll need 18 gauge discs or something! Fair play if your car is that well specced to make them glow. If you're using brakes that hard you're so efficient that you're a bit marginal on reliability. A bit like running your oil and water temp right at the limit.

I think some teams have got away with bad sprotor design simply by not being fast enough or hard enough on brakes. In hot May-July conditions the temps on rear discs may well be enough to boil stuff like some have experienced. As for pushing your upright hard points further out in theory this is better although I would doubt this has much of an influence on the rear end unless you have a wide chassis and are tight on wishbone length. I used to think about this all the time but then I just moved on to be less anal about stuff. http://fsae.com/groupee_common/emoticons/icon_razz.gif

[Composites Guy]

Vinnie, from pencil and paper calculations (and not experimental evidence) I find it odd that you'd measure such a large front/rear brake temperature difference. For the car I am designing I figure that each front brake rotor should take just about the same amount of energy input as the single rear rotor due to the forward weight transfer under braking. What sort of weight distribution or weight transfer are you seeing?

[Buckingham]

Two brake manufacturers I have been in contact with for work reasons both told me that cross drilled brakes are a gimmick for show

We tested multiple cross-drill patterns and found that a specific pattern doubled the overall heat transfer coefficient (experimentally measured on a controlled brake dyno). The installed result was a drop in on-course average temp of 100 degC.

But then again, FSAE rotors typically aren't vaned. I can see how if a rotor is already vaned like on larger vehicles, cross-drilling might be useless.

[Sam M]

We went from a single to dual outboard brakes and lost weight.

flavorPacket, can you elaborate on that a bit? ie rotor diameter and thickness before/after, calipers before/after? Would you say that most of the weight savings came from the actual brakes (rotor and caliper) or the packaging?

I've heard this said before but I'm curious as to exactly how it is done.

[flavorPacket]

i didn't design those systems, so I can't give you specifics. We lost about 1lb overall

[Vinnie]

For the car I am designing I figure that each front brake rotor should take just about the same amount of energy input as the single rear rotor due to the forward weight transfer under braking.

you should think so, that that is the case, but it isn't really. the location of the disc has a major influence on the cooling they get from the air.

keep in mind that a single rear disc is placed behind the engine, therefore it receives warm air from the engine. secondly there is almost no cooling air that reaches the rear brake disc.

with OBR's last years car, the rear brake disc is totally surrounded by the chassis, brackets, scatter shield etc, so there is not much cooling air that can possible reach the rear brake disc.

cheers, Vincent
Delft 05/06/07 class 3/steering/braking
OBR 08 brakes/tyres/race eng

[Boston]

Whether or not to use dual outboard brakes depends almost entirely on whether or not you determine your choice of differential biases torque undesirably with a braking input.

You can forget about the idea that the rotational inertia of dual outboard brakes has a significant impact on the overall inertia of the vehicle. Do the calculations:

Rotational Energy = (1/2)*I*w^2
Translational Energy = (1/2)m*v^2

Where I = moment of inertia
w = angular velocity
v = translational velocity
m = mass
and v = w*r

Your CAD package should be able to determine your exact MOI. Unless your rotors are much too large, you will find that the rotational inertia converted into translational mass to be very small.

[murpia]

Originally posted by Boston:
Whether or not to use dual outboard brakes depends almost entirely on whether or not you determine your choice of differential biases torque undesirably with a braking input.
Consider WHY your diff might torque bias with a single rear brake:
Either 1) the braking surface has a split mu effect,
or 2) you have load transfer at the rear axle.

In the case of 1) then the car behaviour won't be much different to a twin rear brake, except the low-mu wheel might not lock up so easily. This could be a good thing, although if you have twin front brakes on the same split-mu, it gets complicated...

In the case of 2) you will get more braking at the higher loaded (outside wheel) generating an understeer yaw moment. This may or may not be a good thing, it depends a lot on the rest of the setup.

Personally, I don't like the idea of transmitting brake torque through CV joints, for mechanical reasons. Also, I find it easier to analyse the behaviour of twin outboard brakes, as the interaction with the differential is less critical. That doesn't mean that a single rear brake can't be made to work, it just needs good analysis.

Regards, Ian

[Chuckster]

Some more info: Current design C and D-sports racers and F-1000 have 100% gone away from single inboard rotors to 2 outboard rotors. There are no current designs using a single inboard brake anymore that I know of.

Some reasons I can think of for why:
inadequate braking with one rotor and caliper. One early design DSR I had direct experience with had fluid boiling problems until he added a second caliper on the single rotor to share the heat. Already had extensive rotor cross drilling and ductwork. Had the correct rotor material (cast iron)

One CV or axle failure puts one at risk for no rear brakes at all with a single inboard and anything but a spool or something like a spool. There are real World examples of this event happening.

Diffuser space is at a premium and additional inboard stuff like a brake can detract from that space.

Risk of losing rear inboard brake if a diff O-ring or other seal leaks.

Now, that said, do I think you can make a single inboard brake work properly and get rated highly by judges on an FSAE? Maybe-there are solutions to the shortcomings that I mentioned above. Example: solid rear axle-no IRS.

[Malcolm Thomson]

Hi,

Interesting topic! This is our teams first year in competition, an we still have a lot to learn about what works an what doesnt.

The team is short of people so calculations have been a bit limited, however we judged that the reduction in un-sprung weight through moving the brakes in-board, and thus running with lighter, smaller uprights, was worth going for.

We are running a Torsen LSD from a Honda EK9 Civic Type R, and the non-OEM CV joints are made from billet steel, opposed to the lightened machined down Honda items. There was enough meat on them to shave off 200g each and fit a disc each side, with the calipers mounted on the team designed carriers.

We're going to run laser-cut solid discs, and should have time to investigate cross-drilling or slotting on the track.

We'll monitor brake temps and try and rig up some strain gauges between CVs and driveshafts to analyse the effects of torque reversal. I'll post some findings when we get the testing done.

Of course... we've got to get the car built first!

Here's a couple of images

http://i582.photobucket.com/albums/ss269/mjt4/diffwithbrakes.jpg

http://i582.photobucket.com/albums/ss269/mjt4/sexydiff.jpg

[Fred G]

Looks good,

I take it, the cream coloured diff holder connects to the engine? What material have you selected for this task?

Why are the brake calipers where you positioned them? What was the design direction on this? Could they go lower to reduce your cog?

Cheers,
Fred

[PatClarke]

I just love when these old threads come back from the dead

Pat

[Adambomb]

That setup looks VERY similar to what we run. And it does work well. As for caliper positioning, I'm guessing it's for brake bleeding, seeing as how most calipers have their bleeders at the "top" (relative to that pic).

[Pete Marsh]

I curious what sort of engine configeration has the sproket in the middle like that with structure either side of it?

Pete

[TorqueWrench]

That actually looks nearly identical to the setup our team will be running in 2011.

I know for us its going to be a Supercharged Polaris Sportsman 500 with a CVT transmission and we will be putting the differential in the very center of the car through jackshaft layout.

[Malcolm Thomson]

Hi,

Great to see some of you have like-minded designs!

The caliper placement is indeed for brake bleeding, though theoretically you could place them wherever you want. This placement also ads with packaging in my view, as it keeps the calipers out of the way of any other components with plenty clearance for adjustment.

The diff is actually off centre by about 115mm, with 180mm difference in driveshaft lengths.
I realise this will make for differing torque reactions side to side, though fundamentally...(I may be showing my inexperience here, please correct me if so!) I don't think it will have a significant effect.

Please enlighten me if you think I am missing something crucial here, though I have seen this system working succesfully on a few ford sierra diff based hill climb and sprint cars.

Cheers,

Malcolm

[Fred G]

Hi Malcom,

I'll let you determine what constitutes a significant effect. But some things to consider:

- Will the driver notice an affect? Consciously or sub consciously?
- Will my diff choice having influence on torque steer?
- How could I change the property of the drive shaft to equal out the torque distribution if torquesteer is an issue?

Personally, I'm a fan of equal length. It's cheaper to have spares http://fsae.com/groupee_common/emoticons/icon_smile.gif Less calcs/ testing to consider when determining torque distribution. I don't doubt that unequal length work.

Keep up the good work,

Cheers,
Fred

[Malcolm Thomson]

Hi Fred,

thanks for the input.

I have to confess to being a bit of a novice when it comes to differentials, and being time-limited (designing the braking system and in charge of engine development + intake design(my final year project))a lot of things will have to be found out through testing this year.

In terms of changing the driveshaft properties to counter torquesteer:

The torsional stiffness of the shafts is assumed to be equal in the first instance, that they are of the same cross sectional area, material,and modulus of rigidity.

The torque applied at the differential can be assumed to be equal for a straight line acceleration (for the purposes of calculation), assuming equal grip at both tyres.

The lengths are fixed, and the angle of twist
is dependant on the dimensions of the shafts. This means the longer shaft will twist more than the short one and the vehicle will torque-steer towards the side of the longer shaft. To balance this out, as far as I understand, you need to change the CSA of either of the shafts so that the angle of twist at the wheel hub is the same for both sides.

Does this sound correct to everyone? Correct assumptions made?

Unless we encounter severe problems with drive-ability, we won't be manufacturing a set of perfectly torque balanced shafts, as the goal for our first year of competition is simply to get a car built that completes all of the dynamic events, and score maximum points in the static events.

Cheers,

Malcolm

[Hector]

Yep, your general assumptions sound good, and changing the cross section area of the shafts is what most teams due to make torque steer equal.


Unless we encounter severe problems with drive-ability, we won't be manufacturing a set of perfectly torque balanced shafts, as the goal for our first year of competition is simply to get a car built that completes all of the dynamic events, and score maximum points in the static events.

This is a noble goal. Torque steer DOES have an effect on the handling of the car, but not enough that you should worry about it if you simply want to build a solid first-year car. Next year you can start picking apart all the little details that make you fast.

Cheers,

Hector

[murpia]

Originally posted by Malcolm Thomson:
Hi Fred,

thanks for the input.

I have to confess to being a bit of a novice when it comes to differentials, and being time-limited (designing the braking system and in charge of engine development + intake design(my final year project))a lot of things will have to be found out through testing this year.

In terms of changing the driveshaft properties to counter torquesteer:

The torsional stiffness of the shafts is assumed to be equal in the first instance, that they are of the same cross sectional area, material,and modulus of rigidity.

The torque applied at the differential can be assumed to be equal for a straight line acceleration (for the purposes of calculation), assuming equal grip at both tyres.

The lengths are fixed, and the angle of twist
is dependant on the dimensions of the shafts. This means the longer shaft will twist more than the short one and the vehicle will torque-steer towards the side of the longer shaft. To balance this out, as far as I understand, you need to change the CSA of either of the shafts so that the angle of twist at the wheel hub is the same for both sides.

Does this sound correct to everyone? Correct assumptions made?

Unless we encounter severe problems with drive-ability, we won't be manufacturing a set of perfectly torque balanced shafts, as the goal for our first year of competition is simply to get a car built that completes all of the dynamic events, and score maximum points in the static events.

Cheers,

Malcolm

There is a load of info here (http://fsae.com/eve/forums/a/tpc/f/125607348/m/99510106241), here (http://fsae.com/eve/forums/a/tpc/f/125607348/m/1466038355) and here (http://fsae.com/eve/forums/a/tpc/f/125607348/m/26910051431) regarding the need for equal stiffness driveshafts and the effect (or not) on torque steer.

Regards, Ian