We are building a 6wd chassis. A design constraint is that the wheel/sprocket assemblies must fit within a 1.75" width aluminum tubing. We would like to run two chains (#25) from the center driven wheel to the two outer wheels; this requires two sprockets on the center wheel axle. However, spacing is pretty tight.
We have 1 inch wheels and 2 #25 chains that have a collective width of .64". This leaves .11" to be divided between the three areas that need to be spaced: between the wheel and first chain, between the two chains, and between the second chain and tubing wall. Therefore, each space would be about .037". Is this too close to prevent the chains from rubbing or causing some sort of disaster?
Alternatively, we could run one chain between all three wheels. Would the addition of idlers (to increase center sprocket wrap) have any serious impact on speed/power of the drive?
Thanks
According to Vex’s product drawing, #25 chain has a width of 0.354". Therefore 2 runs of chain would have a width of 0.708". Add that to a 1" wide wheel (check that it’s actually 1" wide at the hub, not the tread), and you get 1.708", theoretically leaving 0.042" to be divided between everything. That’s pretty tight.
If you replace that with one run of chain, you get 0.396" of space to space everything out, which to me sounds much more comfortable. Using one chain run is a bit more dangerous (if it breaks you lose two wheels instead of just one), and puts more load on the chain (powering two wheels). However, as long as the chain isn’t too tight, using sprocket idlers or even plastic bushing idlers shouldn’t add a noticeable amount of inefficiency.
Chain varies a bit between manufacturers, Vex chain gives one width, McMaster lists it at 0.3" width. Also remember to include the width of the master link if you’re using one because it sticks out from the chain.
If you break a chain in FTC you’re doing it wrong. Idlers should solve your problem.
Oops…missed that this is for FTC. One chain run with idlers will definitely be fine.
There was a thread on small cheap idlers for FTC a few weeks ago.