Torsen University Special Output(12000)

Hi all, new team with limited funds and experience here, we have a torsen university special(center diff from the audi quattro) and we are looking into ways to connect the output splines to cv joints, we are essentially price restricted to junkyard finds, so the only option i know of is using the actual rear output shaft from the quattro center differential,i have been able to find pictures of this and have a rough guess that it is approximately 7 inches long, this is enough to get us from the center of the diff to the outside of our diff case, however i ma really just guessing that is how long it is based on its relative length compared to the differential in the picture, does anyone who has pulled one of these have measurements? I have also read that in some later years the quattro system used a torsen in tr rear axle as well, does anyone know if those splines are the same as the splines in the 12000? or for that matter if there are any other production cars(s2000, miata, brz, supra, ect) that use a torsen with the same output splines in the rear that have cvs already attached to the output shafts? also, if there are no cars that have those output splines in the rear has anyone found a car with a reasonably light bolt up cv housing that could be modified to bolt onto the center differential output shaft? my thought was that if we couldn't find cvs that have the same spline or a bolt up housing we would take the cvs off a civic or some other similarly light car and key the shafts and use a through bolt to attach them(drilling a hole in the center differential output shafts). any input from teams who have modified cvs from existing cars would be greatly apprecuated, or any other thoughts at all for that matter
Thanks
John

ps please dont give me the "google it" line or the "teams these days dont do any research they're so lazy" the have a team of three people, and a budget of "whatever is in johns pocket", along with a college that was super excited to have us build a car but would only give us the money to have the frame tubes cut, and wouldn't give us a place to work, and then after they found out where we were working(at a local welding school that offered us space) kicked us out because of insurance reasons, eg they were really excited to have us build a car but we couldn't actually build it(yes im not joking that is actually how it happened no bullshit)

Good justification.

If you're really that limited on budget, I might suggest you look into using a spool drive in the back instead of a diff (rear wheels locked together with a simple drive hub with a sprocket on it.)

Lighter, simpler, and much much cheaper, as you may well end up spending literally days at a junkyard tearing an entire transmission apart to get the shafts you need, then you still have to modify them into something you could use.

Lots of info here on the pros and cons of a spool drive and some of the tricks you can do with the suspension to make it drive decent.

Hint - set the car up to intentionally lift (or nearly lift) the inside rear tire off the ground during turns....

thought about spool drive, but really whats the point in irs if youre gonna lift one of the wheels anyway, and really if youre gonna go through all the trouble of designing a mini f1 car whats the point of not putting a proper diff in it(yeah i know teams have done great with them but theres some more back story to this and we have bigger plans later on, like hill climbs where we go allot faster than 80mph, and in that situation i dont feel safe with a spool)? besides i already have the diff, and ive got a case designed, and a spool wouldn't be any less complex than the case ive got designed, the car is 90% mechanically done the only real remaining hurdle is the half shafts.

side note, as anyone experimented with using abs sensors to drag one of the brakes if the diff starts to spin one of the wheels(torsen acts open if one wheel lifts)?

No idea with the shafts, but to echo what Drew said, just run a spool, you're not building a mini-F1 car. You'll also find a great deal of evidence for not running IRS on these forums as well.

Monash were running a spool for several years whilst winning the FSAE-A comp, and doing hillclimbs. I'm sure there are others who are similar.

As for the ABS idea, it has also been discussed on here and I think the general consensus is that it's not worth it. The units themselves weigh more than nothing and if you are designing for a torsen then you need to design to keep both rears on the ground under acceleration.

well point taken, but in lieu of someone handing me a spool that will bolt in, it would be more of a hassle to rebuild the whole rear end, because like i said i have the torsen right here next to me on my desk, and all our suspension is designed and built to keep the wheels on the ground

You do know you can buy a double-ended, splined shaft with the proper geometry off the shelf for not that much money, right? You can then chop the stubs to whatever length you need and weld on the mounting cups for whatever CV's you want to use. Our first and second cars both used this solution with VW Rabbit parts grafted on to make our inboard stub shafts. The inner CV, axle (modified length - simple), outer CV, bearing, and hub were all VW Rabbit. It's certainly not the ultimate in lightness, but it'll get the job done, and you can always whittle parts down as you see fit.

Worst case, you get some shafts cut for you, or you get a cutter made and you do it yourself. These diffs used to be much more supported prior to the invention of the Taylor Race line of products. Honestly, considering how much time and manpower you're probably going to have to expend to get this solution working, there may be better alternatives.

For product links and discussions on this forum, you CAN use the search feature. http://fsae.com/groupee_common/emoticons/icon_wink.gif Haha. In fact a discussion and confirmation of the pressure angle of the Torsen spline popped up just the other day in a thread (it's wrong on the spec sheet for the University Special).

Also, I agree with Drew, and take it a step further. If you're on a super tight budget, there's no shame in a spool... but why not take it a step further and just use a "solid" rear axle (ala karts) and skip all of the fancy articulating driveline bits? BAM! I just saved you a bunch of money and a bunch of time in design and fabrication. http://fsae.com/groupee_common/emoticons/icon_smile.gif Also, you don't have to "lift" the tire either, it just nice if it unloads on turn entry. If you spend some time reading through the thousands of man-years of experience put forth on this forum, you'll quickly realize that there's a lot more to designing and building a vehicle like this than insisting on "It must be this way because [insert shortsighted view here]...". Systems engineering is all about making compromises. Budget and perceived "maximum" performance is a tradeoff that has to be made in almost any system. If it was as simple as "maximize" or "minimize" every vehicle feature, then the cars would all look the same. Clearly, this isn't the case at all in FSAE. Basically, if your resources don't allow for something fancy like a diff and its requisite axle components, then it's not that tough to figure out viable alternatives that will still be competitive within the scope of the FSAE rules. In fact, if you can think it up, there's probably already "prior art" that you can find as inspiration to springboard off of.

-Kirk

yeah i had seen the paradgrim splines, but with those theyre barley long enough for my purpose and all i would be left with is a part that looks almost exactly like tr rear output shaft for nearly 3 times the cost, plus i would still have to machine it, and yes i have used the search function, the question had been danced around, eg "how can i spin the wheels of my car" but the answers typically proposed to those peopleare along the lines of "open a book jackass", i was looking for some specific information that i figured some teams had perhaps come across by trial and error, or experimentation and that they might be willing to pass along to a non funded start up, car manufacturers dont typically list spline data on there parts ordering forms, i figured that some team may, through trial and error have found that say an s2000 had the same spline. Yes, i understand that it isnt a mini f1 car, but it is a quick and easy way to describe in a general sense what the project is to a layman(not that members on this site are laymen) so i tend to use that by habit, and yes i don understand that i dint have to "lift" the tire however if you merely unload it it will drag and wear quite a bit, and even though these cars arent mini f1 cars, i think they're a bit more than shifter karts, but let me reiterate that i already have a diff and independent rear suspension built so a solid rear axle is not going to be used, nor a spool, it is just a question of what method will be used to get the diff to the uprights

I got kind of lazy towards the end of the thread here and didn't read all of it. Not enough punctuation for me...

It sounds like you don't have much money but have a mostly complete car. If you are planning on competing this year (cutting it really close). I would suggest the aforementioned spool. The biggest hurdle you will face at your first comp is just finishing most the events with everyone willing to do it again next year.

If you really want to use the Torsen and have time to waste* you could machine your own output shafts and cv housings out of some steel and hope for the best. Machine extras because they will probably wear out. Then you just need to find some appropriate length half shafts from a civic or what ever you can. I don't have any experience with the actual Audi diff, but what I can tell you is that you are going to have a hell of time trying to get anything that came out of 2 ton car's drive train (excluding the diff) to package nicely.

Once again I advocate using the spool. There are thousands of other things to worry about as a new team and the simpler you can make things the better. On a side note a shifter kart would probably place top ten if not win most the dynamic events at comp, so they really aren't a bad place to look for ideas.

* I say wasted time because the diff would be a very low priority for me if I was in your situation.

I'll make a suggestion as a (newbie/lurker).

Try to find an MX-5 at a junkyard (NB or 2nd generation as you might call it will likely give you a better chance of success). These cars came with Torsen differentials as options (94-95 were type 1, 95-02 were type 2's), it will absolutely not be the ultimate in lightness but it should be good enough for your application, take the shafts with it too.

Modify the shafts and you should be good to go with a reliable (people have ran a lot of power through these things in less than kind environments (read drifting) so it should be strong enough) and (relatively) plug and play assembly.

There's a lot of information on the relevant MX-5 forums about identifying the differences so take a look (google it).

I appreciate this might not be the answer you were essentially looking for but at the same time this is what I would do if I was in your situation.

Also, whilst you're under the MX-5 taking the diff and all associated shafts, take a look how Mazda got the drive to the uprights and copy that if you're really that stuck for time.

I'll also make the point that if you're talking about an original Audi Quattro then you've got yourself a Torsen MK1 so you'd be wise to check an earlier 94-95 MX-5 for a MK1 Torsen and hope to hell the shafts from that match the Audi diff. Personally I'd sell the Quattro diff and just get the whole assembly as I suggested from a MX-5.

(Worth noting that I don't have experience with the USpecial diff so I don't know it's specifics)

Good luck http://fsae.com/groupee_common/emoticons/icon_smile.gif

I understand you want to run the Torsen "because you have one." Here is where everyone else is coming from. To get the Torsen diff working:

1. I hope the system is designed already, if not then you have a good bit of work cut out for you!
2. Spec splines, find someone to make them, spend perhaps $500 total (if you call around) on getting shafts done with heat treating and splines. Alternatively, buy a cutter and spend enough time on a mill to make you want to take the cutter to your wrists, and pray to god you don't remove too much material; regardless, the cut splines will have unfavorable grain alignment and stress risers that are much more likely to fail.
3. Now get some CVs. Let's assume you can make some from a Geo Metro work, and you're only out maybe $200 for the pair.
4. What's the rest of the Torsen housing supported by? Figure another $200+ for more machined parts and billet. I hope you have a CNC or perhaps a time machine...
5. The hubs are probably also going to need to be splined for your halfshafts. Find someone with a wire EDM, do all the machining except the splines yourself, and budget another $400.

So as you can see, the money you have dropped on the Torsen housing is but a small drop in the bucket. I can also tell you from experience that you will find all kinds of surprises in design oversight; it will take probably 1-2 years of breaking things before you get something worked out that's reliable. Also, please do yourself a favor and don't bother with through-bolts or keyways! Baja might be able to get away with that, but the only way you could in FSAE is maybe if you're running a 10 HP Briggs and quad off-road tires. A hard clutch dump on slicks will shear splined axles if they aren't done right.

As for hillclimbs, spools are much happier at high speeds than low speeds, so that shouldn't be an issue. Besides, you can save up for properly setting up a Torsen in there next year, right? May be a better option than having a car with a Torsen that isn't connected to the rear wheels...

thanks for all the advice guys =D those last few were really helpful,

adambomb, yes, i have the system designed already, and have access to the machining equipment, well i have it mostly designed, i havent taken all the weight out but for the most part, its done, im really concerned about having somebody cut the splines cause that's a serious cost and that doesnt even include the hardening, which im not entirely comfortable with, i think the actual oem audi output shafts will be nearly perfect, and i can use the flange to bolt the cvs to, i like the geo metro idea, i was looking at vw rabbits as well, the rabbits are almost the perfect length so i may deal with the excess weight, although ill take a look at those geos, as for the hubs, those are already done, we actually got them from another team, they use six circular keyways cut onto the shaft, and to me, they seem good, wed just mill the other cv out to the same dia and cut the keyways, then cut the threads for the center bolt and viola, a (hopefully) functioning driveline

btw sorry about the lack of punctuation, i tend to type fast and disorganized, in an attempt to get all my thoughts down =D

on a seperate not i have one more question, in the rear we plan on mounting the pushrod to the lower a-arm, in order to get the angles right and keep the actauation as vertical as possible, i was planning on mounting it about halfway down the aarm, aside from the fact that i need to account for the change in travel and the fact that i will get roughly a half pound more of unsprung weight, is there anything structurally wrong with that?

thanks again for all the advice
john

Quote:

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we plan on mounting the pushrod to the lower a-arm... i was planning on mounting it about halfway down the aarm ... is there anything structurally wrong with that?

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There is nothing structurally "wrong" about it, as long as your lower control arm is designed to handle the bending load. Typically, long slender members do not carry bending loads well, especially when applied at the center of an unsupported span.

I would strongly recommend against mounting the pushrod anywhere on your a-arm except as close as practically possible to the outboard joint. If you are using bell cranks (rockers), the angle of the pushrod does not matter, since it can be compensated for in the motion ratio.