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CVTech Mounting Distance

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sandres913 View Drop Down
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    Posted: 2012-Apr-27 at 5:17pm
Watched some YouTube videos of other teams and of our own car, and I came across the infamous belt squeal. Last year our car sounded like it was killing cats when it wasn't moving, which we kinda hing-a-ding-a *cough cough* "fixed." With an angle grinder. Yeah.

This year we're modeling eeeevery little thing before we make it and it just ran through my mind that mounting distance. Is everyone using the center to center distance CVTech displays on their site? Or are you giving it more space to slip without killing kittens? This will be our second year with CVTech, so we've got more experience with the tuning than we do the mounting, just wondered if anyone else had any opinions on it! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-27 at 10:48pm

The four cars I have worked on all have had the C-C distance given from CVTech. Like you, we either get the squeal or the slow creeping at idle. Not really the biggest issue but if I were to do it again I would make the CC a tiny bit smaller than the one supplied, maybe around 1/16th or 1/8th...not sure


EDIT: When we talked to Bill from Gaged at comp last year, he mentioned that his cvt belts had a pretty "big" manufacturing tolerance which I had never considered. The CC distance he gives for his CVTs should only be used as a starting point. Ideally, you should have an adjustable CC distance. 



Edited by jeiB - 2012-Apr-27 at 11:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike-UPRM Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-28 at 12:29am
Heres a pic of our motor mounts, you can see the make it easy for the motor to be moved forward or back. This makes it possible for the CVT distance to be adjusted a little bit, that said we started with the distance that CvTech lists and  where not able to test the adjustment but maybe this can give you an idea if you have not designed or build the motor mounts yet. 





Edited by Mike-UPRM - 2012-Apr-28 at 12:32am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-28 at 9:57am
Thanks for the quick replies guys!

Originally posted by jeiB jeiB wrote:

The four cars I have worked on all have had the C-C distance given from CVTech. Like you, we either get the squeal or the slow creeping at idle. Not really the biggest issue but if I were to do it again I would make the CC a tiny bit smaller than the one supplied, maybe around 1/16th or 1/8th...not sure


EDIT: When we talked to Bill from Gaged at comp last year, he mentioned that his cvt belts had a pretty "big" manufacturing tolerance which I had never considered. The CC distance he gives for his CVTs should only be used as a starting point. Ideally, you should have an adjustable CC distance. 


jeiB - that's kinda what I started thinking about, as we ran into this issue of using exact values and not leaving and room for motion on a few other parts, a few errors on my part. Live and learn! Thanks for the tip!

Originally posted by Mike-UPRM Mike-UPRM wrote:

Heres a pic of our motor mounts, you can see the make it easy for the motor to be moved forward or back. This makes it possible for the CVT distance to be adjusted a little bit, that said we started with the distance that CvTech lists and  where not able to test the adjustment but maybe this can give you an idea if you have not designed or build the motor mounts yet. 




Mike - first, that rear end looks beautiful. And genius. And the mount is so simple! We kind of had an "adjustable" C-C distance last year, with all the angle grinding and drilling and whatnot. I kinda wanted to lock it down this year to eliminate the uncertainty we had last year, so we wil probably still go with the plate method and just give it a few extra mm's or so
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LukeS Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-28 at 4:44pm
We work closely with a Jr Dragster company and they mentioned that every belt will be slightly different.  The belts also stretch over time.  Your center to center should be adjustable.

Our engine actually sits in a track and we have a 3/8" fine thread bolt for changing the center to center accurately.  That way the engine and gearbox are always in line and all we have to worry about is center to center.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike-UPRM Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-29 at 1:20pm
thanks for the compliment sandres913. Hope it could help you out.Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-30 at 3:40pm
Don't forget to shim for the correct space between primary sheaves to prevent screamers. The belts may vary in this dimension too. Not to mention, the sheaves can wear down during a season, depending on the materials and the conditions you're exposing them too. Then there's your idle setting on the engine and the corresponding CVT engagement speed you've set your preload for. This is all per my notes from Aaen's handbook. My point is that there's quite a few adjustments and alignments that can be off to cause a screamer. C-C is the most-often screwed up one. I advise every team to make a Go-NoGo gauge from scrap material to ensure proper C-C.
 
Pay attention to the fact that Aaen's tuning procedure starts with checking that the transmission is properly aligned. It is not just good advise... it's the only way to make changes to tuning parameters without ending up with worthless results.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-30 at 3:45pm
Originally posted by p.lewis p.lewis wrote:

 
Pay attention to the fact that Aaen's tuning procedure starts with checking that the transmission is properly aligned. It is not just good advise... it's the only way to make changes to tuning parameters without ending up with worthless results.


For this part, I am guessing you mean the driver to driven alignment. We leave the driven floating on the shaft. You just have to be careful your key does not fly out!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-30 at 10:52pm
Originally posted by p.lewis p.lewis wrote:

Don't forget to shim for the correct space between primary sheaves to prevent screamers. The belts may vary in this dimension too. Not to mention, the sheaves can wear down during a season, depending on the materials and the conditions you're exposing them too. Then there's your idle setting on the engine and the corresponding CVT engagement speed you've set your preload for. This is all per my notes from Aaen's handbook. My point is that there's quite a few adjustments and alignments that can be off to cause a screamer. C-C is the most-often screwed up one. I advise every team to make a Go-NoGo gauge from scrap material to ensure proper C-C.
 
Pay attention to the fact that Aaen's tuning procedure starts with checking that the transmission is properly aligned. It is not just good advise... it's the only way to make changes to tuning parameters without ending up with worthless results.

@_@ gahhhh I didn't even consider the side-to-side value...but you are correct. I've been through Aaen's a gajillion times last year I should've remembered that part! >_<

Originally posted by jeiB jeiB wrote:

Originally posted by p.lewis p.lewis wrote:

 
Pay attention to the fact that Aaen's tuning procedure starts with checking that the transmission is properly aligned. It is not just good advise... it's the only way to make changes to tuning parameters without ending up with worthless results.


For this part, I am guessing you mean the driver to driven alignment. We leave the driven floating on the shaft. You just have to be careful your key does not fly out!

O_O floating? how's that work out? Right now, I've got two bearings in the box (for axial load) and one bearing at the end of the shaft to better support the driven (the input shaft had to be almost 16" long...) I had put snap-rings in my design because I wanted to be sure that thing wouldn't move, because if, IF, we get it to fully shift, there will be a quarter inch clearance between that and the trans case....not the best setup ever, but you work with what you're given...but Floating?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Apr-30 at 11:09pm
 
Originally posted by sandres913 sandres913 wrote:


O_O floating? how's that work out? Right now, I've got two bearings in the box (for axial load) and one bearing at the end of the shaft to better support the driven (the input shaft had to be almost 16" long...) I had put snap-rings in my design because I wanted to be sure that thing wouldn't move, because if, IF, we get it to fully shift, there will be a quarter inch clearance between that and the trans case....not the best setup ever, but you work with what you're given...but Floating?

16in sounds very long. Im curious now!

Anyways, if the driver is bolted to the engine, there is NO way you can pull the driven off with the belt on, correct? THere isn't enough lateral give in the belt to pull off the driven off the shaft (in our setup but Im pretty sure its the same for 90% of the cars out there).

I would suggest to unbolt your driven and test if you can pull it off with the belt on. If you can't, then go for a test drive, I can assure you that you will feel the difference Wink

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Post Options Post Options   Thanks (0) Thanks(0)   Quote elija.wattson Quote  Post ReplyReply Direct Link To This Post Posted: 2012-May-01 at 6:42am

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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: 2012-May-01 at 8:25am
The alignments I'm talking about are parallelism, offset, and C-C. Yes, floating the driven is a good way to let it self-align the offset, but if your shafts are far from parallel, the belt may cause the driven to track like a belt sander and/or make some lateral loads. Therefore, I'd limit how far you let the driven float so that it doesn't run too far away from your desired offset. Obviously, the real solution is to adjust the shafts to parallel.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-May-01 at 9:45am
Originally posted by jeiB jeiB wrote:

 
Originally posted by sandres913 sandres913 wrote:


O_O floating? how's that work out? Right now, I've got two bearings in the box (for axial load) and one bearing at the end of the shaft to better support the driven (the input shaft had to be almost 16" long...) I had put snap-rings in my design because I wanted to be sure that thing wouldn't move, because if, IF, we get it to fully shift, there will be a quarter inch clearance between that and the trans case....not the best setup ever, but you work with what you're given...but Floating?

16in sounds very long. Im curious now!

Anyways, if the driver is bolted to the engine, there is NO way you can pull the driven off with the belt on, correct? THere isn't enough lateral give in the belt to pull off the driven off the shaft (in our setup but Im pretty sure its the same for 90% of the cars out there).

I would suggest to unbolt your driven and test if you can pull it off with the belt on. If you can't, then go for a test drive, I can assure you that you will feel the difference Wink

 

It's...it is what it is. It's got a ways to travel to get to a miter box which leads to a spur box before it shoots to a diff. I wasn't all that crazy about it until I did the calculations, and I can live with it for this year. Next year will be my senior year so I've got a few ideas that don't involve the CVTech!

That makes sense about the belt though. I'm definitely keeping two snap rings on it, because the last thing I want is that driven to slam into the spur box! >_< I might try taking the outer snap-ring off though...after the race! Wink

Originally posted by p.lewis p.lewis wrote:

The alignments I'm talking about are parallelism, offset, and C-C. Yes, floating the driven is a good way to let it self-align the offset, but if your shafts are far from parallel, the belt may cause the driven to track like a belt sander and/or make some lateral loads. Therefore, I'd limit how far you let the driven float so that it doesn't run too far away from your desired offset. Obviously, the real solution is to adjust the shafts to parallel.

Right, that's what I would think, let it be a little free, but just free enough within the confines of our limits. And we're engineers! Just make the assumption that everything's parallel and neglect friction! LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: 2012-May-03 at 8:02pm
Originally posted by sandres913 sandres913 wrote:

And we're engineers! Just make the assumption that everything's parallel and neglect friction! LOL


You know, it's been almost 6 years since I got my BS in ME and now I think that all those homework problems where everything is perfect are borderline worthless. Fundamentals and theory are great. You have to teach that. But why can't a professor add a Part B more often where they ask "What if your beam is thicker or thinner by 0.040 inches?" Most of the time you've solved the problem symbolically almost completely to the end, so redoing it with a small change in a value is no big deal.

In the real world, the nice engineering calculations take you maybe 25% of the way to the solution and then you need to deal with the question of what to do about real world uncertainty, loose tolerances, supplier quality issues, etc. Baja teaches you this. Your future employers want you instead of your classmates because of this.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Jul-26 at 10:06am
Thought I'd throw what happened back onto this post, since I started it anyway!

I put the C/C distance at 240mm, and floated the CVT. It didn't work out too bad until acceleration and tractor pull, when everyone could see how far we (didn't) make it. Assembly-wise though it was much easier. We definitely weren't getting anywhere near the full shift-out though. We're going to re-assemble the destroyed right-rear of the suspension, throw the GoPro on the frame to watch the CVT and do some laps. My guess is that, since I allowed the CVT to float, I'm not getting the full ratio because it needs the belt to develop an "angle" between the primary and the secondary, instead of remaining, for all intents and purposes, straight up and down.
We'll probably run some laps with it in the current form, then shim the engine up 2mm and see how it reacts. I'll post some more information once we do that so there's more info for teams to search for in the future

Once the cover comes off the CVT, I'll be able to see about that 16" shaft, expecting to see virtually no deflection (<0.125" at least!). The whole miter to spur to diff worked out pretty well after all. Definitely needs seals though. Sealed bearings don't seal in gear oil. Lesson learned LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Jul-26 at 1:32pm
DON'T TAKE THE SMALLEST SIZE FROM cvtech  !!
Last yr, in the greed of lowering the C-C, we chose the smallest belt size.
And guess what, it wasn't even big enough to accomodate the 2 pulleys.
It was ridiculous.
We then bought an awfully expensive milling machine belt :(

I know it's desirable to minimise the C-C, but think wisely :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Jul-26 at 1:38pm
The 242 belt is nowhere near the smallest size was the largest they offered at the time we ordered it. Tried to get the 299 this year but they claimed to have never received our order over fax, and we only found that out on about the 4th time we called them.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Vladmir123 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Aug-17 at 1:45pm
please could u tell me what kinda final drive u guys run ? and how much adjustability do u allow for the CVT ?

BTW great rear end design
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