#25 Chain Drive System Questions

[cbale2000]

Our team is looking to build a drive system using #25 chain to drive the wheels. We have some experience using #35 chain in drive systems but in an effort to keep the drive base as light as possible and since there is no defense this year, we figured #25 chain would be adequate.

Having never used #25 chain for drive systems, I'm trying to figure out a few things for the design:

1. How do you calculate spacing between sprockets to minimize the need tensioners? Is there also a way to take idlers into account?
2. We would like to run 3 wheels from a single chain to minimize the width of the drive base, is there a minimum chain contact area on the sprocket that is needed to avoid slipping?
3. We've used a chain break tool to splice #25 chain and avoid master links in the past on various mechanisms, is it still ok to do that with a drive system?
4. Is there anything we should watch out for that is different when using #25 chain on drive systems compared to using #35 chain (or in general for that matter)?

[lbarger]

1) There are calculators available on-line for simple chain configurations. i.e. between two sprockets. If those sprockets are the same size, you only need to space the axels in 1/4" increments for #25 chain. If you use a half-link you could work on 1/8" centers. However, to drive 3 wheels from a single chain is significantly more complicated and may require the use of CAD for your specific configuration.
2) Obviously, the more wrap you use on a sprocket, the less likely it is the chain will be able to jump. The general rule of thumb I use is 120 degrees of wrap, but geometry does not always allow that. With reduce load on the chain you can use less wrap on each sprocket, but I caution against going with less than 90 degrees of chain wrap.
3) I've always used master links. When properly installed I have never had an issue with them. Simply need to make sure the retaining clip is properly engages with the grooves on the posts.
4) #25 chain can no handle the loads that a #35 chain can. You need to make sure you do not over load the chain and cause it to yield/stretch/fail. As with any chain proper alignment of sprockets is critical for keeping chains on sprockets. My experience is that #25 tends to 'relax' or stretch more than #35 chain after some use. I attribute this to the greater number of links for a given length and wear at each of those links. Keep loads reasonable should help with this. Fortunately this year's game should not involve a lot of pushing so managing your chain loads should be fairly straight forward.

[Jeffrafa]

As Lee mentioned, for 2 sprockets it is pretty easy to calculate center distance. For 3 or more on the same chain, it gets quite a bit more difficult.

Dr Joe created a useful excel spreadsheet for calculating this, check out his whitepaper: http://www.chiefdelphi.com/media/papers/1598

Its not the most intuitive interface, but will let you find the appropriate spacing to avoid half-links, and get a tight chain. It also creates a plot to visualize the chain run to make sure it matches your design intent.

[cbale2000]

Thank you both for your quick responses, all of this will definitely help our design.