Chain drive for CVT users

[eflo16003]

I just had a quick question about the chain and sprocket set-up for a CVT car. Does anyone have experience using a double-pitch roller chain? Would you recommend using one? What are the downfalls of using such a chain? Thanks for the help

[eflo16003]

I just had a quick question about the chain and sprocket set-up for a CVT car. Does anyone have experience using a double-pitch roller chain? Would you recommend using one? What are the downfalls of using such a chain? Thanks for the help

[Hector]

Usually in these broad, open-ended questions, it's best to start out explaining why you want to try something, along with your Pro/Con list. I'm not saying this to be mean, but I promise you'll get better results and more feedback if you prove to everyone that you've done some research on your own first.

[eflo16003]

Upon doing research for a chain and sprocket drive for a CVT motor I came across a chain called a double-pitch roller. The advantage of using a double pitch chain is that it has half as many links within the chain, meaning a reduction in mass. But on the down side it is unable to hold larger tension loads. Therefore my question refers to the reliability of this type of chain for an fsae car. I could not find any load tests for a specific chain. Also, because this chain only makes contact with every other tooth within the sprockets, would this present a problem in any manner? In addition, would it be possible to move the chain one tooth over and in theory have a new chain?

[eflo16003]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by eflo16003:
In addition, would it be possible to move the chain one tooth over and in theory have a new chain? </div></BLOCKQUOTE> meant to say sprocket, sorry.

[Tom W]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by eflo16003:
Therefore my question refers to the reliability of this type of chain for an fsae car. I could not find any load tests for a specific chain. </div></BLOCKQUOTE>

Reliability you would probably be ok because these cars run for such a short amount of time, generally you can get away with an under-specced chain. On the other hand you could ask Stutgartt about how much of an effect a poorly timed chain failure can have.

I only read the first link that came up when I googled double pitch chain but it included maximum allowable loads from Tsubaki, if you know your peak torque and gearing then it shouldn't take you long to figure out the load you will be putting through this thing.

Surely the bigger problem with these though is that your sprockets have to be twice as big. Even if you disregard packaging considerations and purely consider rotating mass doubling the size of your sprockets sounds to me like it is going to add more weight than you save through a few chain links...

I have also been told that equal sized industrial chains have less load carrying capability than equal sized bike chains. You probably need a pretty good reason to do anything other than standard, after all getting custom sprockets with custom splines isn't exactly the easiest thing in the world.

[Hector]

Welcome back eflo!

I'd probably stay away from double-pitch chains for now. As you design you'll find that a quick way to reduce weight is to go to the smallest front sprockets possible, then size your rear sprocket for whatever ratio(s) you want to run. This reduces sprocket weight (front and rear), chain weight, and makes packaging easier. That being said, the most common sized front sprockets you'll see on an FSAE car is between 11-16 teeth. I'd be very worried about chain wrap angles of a double pitch chain on sprockets that small. Generally, anything under 15 teeth is not recommended in long lifespan conditions. We can use smaller sprockets because FSAE is all about short life, high performance vehicle, but most teams are still pushing it pretty close with the small front sprockets.

We frequently wear out 520 motorcycle chains that only run short distances. A common misconception is that chains "stretch" over time. That may be somewhat true, but the "lengthening" effect occurs when the chain joints wear out, inducing slop. Take a "stretched" chain and try and bend it sideways, in it's non-bending direction. You'll see that and old chain bends quite a bit more than a new chain because of the wear.

One more thing to look at is benefit-to-risk ratios. Stuttgart is a kickass team with a lot of wins and top finishes under their belt. However, in recent history they had to end a very good endurance race right at the end when they threw a chain (or so it seemed from the video). Some things can brake on your car and you can limp on to a finish. A chain is not one of those things.

All-in-all, I say that this is a terrible place to try and save weight. We frequently wear out or brake 520 chains after only a dozen hours of testing or so when running sprocket sizes of around 12 or 13 teeth. I can only imagine how a double pitch chain would hold up to the stress. If you do end up trying it, make sure to be helpful and let us know how things turn out, as we've been pretty helpful to you.