Wavetrac Differential

[Tyler Jones]

Hello,

My name is Tyler Jones, I'm the Project Director/Controls Team Lead for the Iowa State University FSAE team.

Our 2014-2015 car runs a Torsen T1 differential with a custom gear housing. We are having problems with the car unloading the inside rear tire in tight corners which is an issue since the Torsen differential essentially becomes an open differential when a wheel is lifted. We are considering switching to the Wavetrac differential to mitigate this issue. In order to pursue this further I need to obtain some models or drawings of the Wavetrac's internals to begin designing a custom gear housing as soon as possible, but after contacting them directly Wavetrac is reluctant to give out any drawings showing the internal workings of their differentials. Hopefully a team that currently uses the Wavetrac differential or has used one in the past may be able to share any models or drawings they have of the internals?

Additionally I had some questions about the FSAE stub shafts that RCV Performance sells for the Wavetrac differential. I determined that the spline on the male stub shaft has 33 teeth vs 27 teeth for the female spline in the Honda Civic model Wavetrac suggested for FSAE use. Can anyone confirm which model the RCV stub shafts are compatible with?

Link for the stub shafts:
http://www.rcvperformance.com/produc...aspx?sku=D5253
http://www.rcvperformance.com/produc...aspx?sku=D6768

Link to Wavetrac:
http://www.wavetrac.net/

Attached are the drawings of the models Wavetrac says they have sold to other FSAE teams.

Civic Wavetrac.jpgVW Wavetrac.jpg

Thanks!

[Drew Price]

It looks to me from their video that it's a helical ATB like a Quaife / Torsen, but with a ramp clutch like a Gripper / Guard.

Cool idea, it looks pretty compact. Was the tech rep not able to tell you which diffs their little stub tulip flanges worked with? Might be best to get the info right from the source.

Does something preclude you from tweaking your roll stiffness distribution enough to keep the inside rear on the ground?

[Tyler Jones]

It looks to me from their video that it's a helical ATB like a Quaife / Torsen, but with a ramp clutch like a Gripper / Guard.

Cool idea, it looks pretty compact. Was the tech rep not able to tell you which diffs their little stub tulip flanges worked with? Might be best to get the info right from the source.

Does something preclude you from tweaking your roll stiffness distribution enough to keep the inside rear on the ground?

I'm waiting on a response from RCV about the stub shafts and the Wavetrac rep couldn't help any more than providing me with those drawings.

Our suspension guys are trying to tune the car to keep that inside rear planted but it has been a recurring issue with the past two or three cars. Either way I think the Wavetrac is a better design than the Torsen anyway, so if I can find the resources I would like to switch even if we solved the lifting issue.

[CWA]

Hi Tyler,

There will be plenty of people here able to give suggestions on the diff queries you have I'm sure. As Drew is, I am curious to know a bit about your base chassis and what options you have available to you that may potentially help with this issue.

Can you give some info on your suspension setup. What steering axis angles do you have (caster, KPI) and what steering axis ground level offsets do you have (scrub radius, caster trail)? Do you have any scope for adjustment?

What is your Front/rear static weight distribution? What is your estimated CG height? What are your front and rear wheel rates? What are your front and rear 'roll centre' heights? Do you have anti-roll bars fitted, front and/or rear? If so, what is their contribution to wheel rate? Do you have any adjustability for any of these parameters?

Have you had the car on scales to check for cross-weight imbalance? Does your suspension actually move as it should; or do you have lots of friction in it?

[Tyler Jones]

Hi Tyler,

There will be plenty of people here able to give suggestions on the diff queries you have I'm sure. As Drew is, I am curious to know a bit about your base chassis and what options you have available to you that may potentially help with this issue.

Can you give some info on your suspension setup. What steering axis angles do you have (caster, KPI) and what steering axis ground level offsets do you have (scrub radius, caster trail)? Do you have any scope for adjustment?

What is your Front/rear static weight distribution? What is your estimated CG height? What are your front and rear wheel rates? What are your front and rear 'roll centre' heights? Do you have anti-roll bars fitted, front and/or rear? If so, what is their contribution to wheel rate? Do you have any adjustability for any of these parameters?

Have you had the car on scales to check for cross-weight imbalance? Does your suspension actually move as it should; or do you have lots of friction in it?

You will have to wait for the suspension guys to get back to me, most of that's a little beyond my depth of knowledge. I can tell you that the weight distribution is approximately 49% front (was designed for 45% and was measured at 45% at Formula North but managed to change at FSAE Lincoln, not sure if ride heights changed or what) and that we have tested most configurations for ARBs and are currently between no ARB front and rear or a soft ARB front and no ARB rear.

I will get back to you as soon as I have the other technical info.

[craigorydean]

Hello Tyler,

My name Is Craig Kellermann. I am team member from the University of Texas-San Antonio. By any chance have you looked at what offering could be had else where on the applications of differentials.(Taylor, Drelxer, Front diff. from atv, spool, ext). What I stated maybe options to look at depending on what you actually see as you problem.

I personally would really look at your whole drivetrain and see what is your goal of this sub-system and see if changing to that differential is meeting your goals. First, you may have to sit down and really see what problem you are trying to solve as a whole. If the only problem is that you want to "Close" the Differential a little bit. Then so be it but i think you have a list of problems like "Closing" the Diff ,having a solid model, spending $X,XXX dollars, weighing XX lbs, and having some bias ability during cornering. Once you have those thing figured out maybe a new solution will present its self.

After this past year I have nothing but great things to say about taylor racing products as they were a key reason why we were on of only 17 or 18 teams that finished enduro at lincoln.I know our team currently has a model for a Taylor Racing MKII diff.(This is the Diff we use), if you decide to go with that option I would be more than glad to get the solidworks file to you.

[Tyler Jones]

Hello Tyler,

My name Is Craig Kellermann. I am team member from the University of Texas-San Antonio. By any chance have you looked at what offering could be had else where on the applications of differentials.(Taylor, Drelxer, Front diff. from atv, spool, ext). What I stated maybe options to look at depending on what you actually see as you problem.

I personally would really look at your whole drivetrain and see what is your goal of this sub-system and see if changing to that differential is meeting your goals. First, you may have to sit down and really see what problem you are trying to solve as a whole. If the only problem is that you want to "Close" the Differential a little bit. Then so be it but i think you have a list of problems like "Closing" the Diff ,having a solid model, spending $X,XXX dollars, weighing XX lbs, and having some bias ability during cornering. Once you have those thing figured out maybe a new solution will present its self.

After this past year I have nothing but great things to say about taylor racing products as they were a key reason why we were on of only 17 or 18 teams that finished enduro at lincoln.I know our team currently has a model for a Taylor Racing MKII diff.(This is the Diff we use), if you decide to go with that option I would be more than glad to get the solidworks file to you.

I'm aware of most of the options available for FSAE differentials. From what I have found we can choose between:

• A spool (causes understeer)
• Detroit Locker (causes understeer)
• A Cam and Pawl a.k.a. front diff from atv (also causes understeer but doesn't work with a lifted tire)
• Torsen (<$1000, bias adjustable, doesn't work with a lifted tire)
• Quaife (<$1000, bias adjustable, doesn't work with a lifted tire)
• Wavetrac (<$1000, bias adjustable, works with a lifted tire)
• Taylor (>$2000, bias adjustable, based on Quaife so doesn't work with a lifted tire?)
• Salisbury-style differential (expensive, bias adjustable, can be made to work with a lifted tire)
• Drexler (>$2000, bias adjustable, can be made to work with a lifted tire)
  
  

Goals in order of importance:

1. price <$1000
2. bias adjustibility
3. works when one wheel is unloaded
4. weight < ~10 lbs (not a huge driving factor here)

The Wavetrac is cheap (~$600), the bias can be adjusted by changing the material of the friction plates, it works when one wheel is unloaded, and with a custom housing the weight increase over the Torsen would be negligible. The only drawbacks that I can see are the lack of the drawings necessary, the time invested in designing a new housing, and having to partially disassemble the housing every time you want to adjust the torque bias.

Feel free to bring up any negatives to the Wavetrac I haven't thought of, but from what I can see it it meets all my goals.

[Tyler Jones]

Hi Tyler,

There will be plenty of people here able to give suggestions on the diff queries you have I'm sure. As Drew is, I am curious to know a bit about your base chassis and what options you have available to you that may potentially help with this issue.

Can you give some info on your suspension setup. What steering axis angles do you have (caster, KPI) and what steering axis ground level offsets do you have (scrub radius, caster trail)? Do you have any scope for adjustment?

What is your Front/rear static weight distribution? What is your estimated CG height? What are your front and rear wheel rates? What are your front and rear 'roll centre' heights? Do you have anti-roll bars fitted, front and/or rear? If so, what is their contribution to wheel rate? Do you have any adjustability for any of these parameters?

Have you had the car on scales to check for cross-weight imbalance? Does your suspension actually move as it should; or do you have lots of friction in it?

You will have to wait for the suspension guys to get back to me, most of that's a little beyond my depth of knowledge. I can tell you that the weight distribution is approximately 49% front (was designed for 45% and was measured at 45% at Formula North but managed to change at FSAE Lincoln, not sure if ride heights changed or what) and that we have tested most configurations for ARBs and are currently between no ARB front and rear or a soft ARB front and no ARB rear.

I will get back to you as soon as I have the other technical info.

Okay, here is the response from one of my suspension guys:

"Man that is a lot of questions, I don't have access to all those numbers at the moment and I might hesitate a little bit to put that much info on the forum (probably not a big deal, but he's asking for almost our whole design haha). I can answer all of those though, and it sounds like he is wondering whether the front wheel motion in steering is jacking the inside rear too much, and also if our bar setup is lifting it. I wouldn't suspect too much jacking from the front (although I wouldn't totally rule it out) since we have 3 deg of caster and about 0.8 inches of scrub radius, which doesn't displace the wheel downward very much (a lot of caster would be more like 5-7 deg). Wheel rates are about 112 lbs/in on all corners, and since we've tried almost all the bar combinations I don't think he can help us too much otherwise. It's got low friction and it's good on the scales, so we can pretty safely rule those things out."

[CWA]

Goals in order of importance:

I would have said that your priorities would at least be more like:

n: Works when one wheel is unloaded
n+1: Price
etc..

You already have a diff which doesn't work when one wheel is unloaded (and to you right now, technically it is free). The diff has been deemed unacceptable because it does not perform. So I assume, based on this reasoning, you would not deem another diff that also does not work when one wheel is unloaded as acceptable either, regardless of how much it costs.

So you won't be buying a another, different diff that also doesn't work when it is unloaded. This means you can cross a load of options off that list straight away. In fact, I don't see how "Works when one wheel is unloaded" is not your first priority, because it is your only prerequisite.

But ignoring my pedantry, it may be possible that you have some chassis tuning options available to you that actually negate the need to replace your existing diff completely. Once your suspension guy can post up some info, this can be determined. It might save you some time and money.

[EDIT - I've just seen your reply r.e. suspension settings - I'll take a read now..]

[Tyler Jones]

I would have said that your priorities would at least be more like:

n: Works when one wheel is unloaded
n+1: Price
etc..

You already have a diff which doesn't work when one wheel is unloaded (and to you right now, technically it is free). The diff has been deemed unacceptable because it does not perform. So I assume, based on this reasoning, you would not deem another diff that also does not work when one wheel is unloaded as acceptable either, regardless of how much it costs.

So you won't be buying a another, different diff that also doesn't work when it is unloaded. This means you can cross a load of options off that list straight away. In fact, I don't see how "Works when one wheel is unloaded" is not your first priority, because it is your only prerequisite.

But ignoring my pedantry, it may be possible that you have some chassis tuning options available to you that actually negate the need to replace your existing diff completely. Once your suspension guy can post up some info, this can be determined. It might save you some time and money.

[EDIT - I've just seen your reply r.e. suspension settings - I'll take a read now..]

That is the reason I came into this thread with the Wavetrac in mind. The only other option that met that prerequisite was a clutch-style lsd and they are too expensive for our budget. As for using the "free" differential we already have, we like to keep our cars together each year so the 2015-2016 car will need a new differential either way. As for chassis tuning, our suspension team leads seem to think we are out of options since we have already tried all arb options and 3 or so different spring setups. There is more to look into there, but I think the Wavetrac would be beneficial even if we tuned to keep that wheel planted in most situations. However, as you said, it would save us time and money which are both pretty big concerns for our team. If you have suggestions to keep that wheel planted I will definitely relay that back to my suspension guys.