pic: prototype drivetrain v2.1

This is the solution to driving the suspension. The nylon round stock can be adjusted via the slits in the suspension carriage. This not only allows each chain run to be tensioned to the proper tension, but also allows the suspension to pivot while keeping the system under tension because the tensioners pivot along the same center of rotation as the carriage.

Any comments?
Should the bushings be brass or nylon?

This drive design does not need suspension.

Why not? It is incorporated as an innovative element in case it becomes necessary in the future. It is possible this system will never be built.

I am not sure if this is what you are trying to convey in your above image so if not consider this. Using your pivot shaft as a jack shaft will enable the chains to freely rotate and stay tensioned throughout the range of suspension. You can determine the center distances for chain runs with an even number of links and then do not require external tensioners. Here is even an calculator to do it for you. http://www.botlanta.org/converters/dale-calc/sprocket.html

As for if this drive needs a suspension or not totally depends on your team and it’s engineering decisions regarding the application for this drive. Keep thinking outside of the box it will serve you well in the future.


There are no absolutes in engineering decisions. People and organizations value different things and out of context it would be wrong to make assumptions on the necessity of a feature.

last year we did the same type of thing with our prototype, we had a delrin tube tensioned with a zip tie, the tubes 1/4 inch thick wall was completely destroyed by the chain in about 15 min, if you do that, you are going to need some large diameter nylon.

your chain bearings could be nylon, depending on how hard they push against the chain. Nylon will be better than delrin or teflon in terms of wear. Brass could work too, but it might be excessively loud. You could use two idler sprockets and not have to worry about anything.

Thank you very much for your feedback!

The goal was to show how I intend to keep the chain under tension while it is pivoting. The nylon spacers are adjustable so that they can act as chain tensioners. When the carriage moves up and down, the tensioners will as well, theoretically keeping the chain under tension. If any one knows whether or not this will work, please let me know.

The bushing question was in reference to the bushings on the carriage that are currently brass. I guess a better way to phrase it would be to ask whether brass or nylon has a lower coefficient of friction with aluminum.

The solid/plain surface bearings (which are different from bushings) that the suspension pivots on could be made from brass, with a ground steel shoulder bolt being used as a shaft, which would be very strong and durable. Better yet they could both be purchased parts. If the shaft is aluminum I would use a nylon or delrin bearing so that the bearing wears faster than the shaft.

We like doing all of our own fab work, so I’ll swith the material to nylon. Thanks for the help!

Good deal. Look at 7075 or 2024 for the axle, with a good lathe you’ll be able to get an excellent surface finish and great strength. I don’t know if you have one, but a HSS reamer to do the inside of any polymer bearing is much much much easier/faster/idiot proof than boring it out.

We usually just drill it out on a lathe, and all of our machining is very high quality because we have access to the Milford Proving Grounds machine shop. I guess we could ream it, but it’s unlikely anyone will remember to do that by the time this gets made, if it even does, in September/ this summer.

Reaming doesn’t really take much longer than drilling, I don’t see any reason not to do it.

Remembering. Many of the build team members are so used to working in our school’s “shop” where we have no reamers, that when we are in a real shop, we just go straight for the drill bits because we’re used to them. If we remember to ream, there is no reason for us not to.

We work in our school’s shop as well, and purchased the few sizes of reamers we routinely use; they were inexpensive and well worth it.

Alright, I’ll talk to our… I’m not really sure who would make that decision…

I’ll figure that out at our next meeting, along with the answer :D.

Drill bits are great for clearing material out and for making holes where fasteners can pass through, but a drill bit will never come close to surface finish or precision of a reamer. Say you’re making the bearing for a 1/2" axle, I would drill with a 0.4921 jobber bit then ream to 0.5010, a HSS reamer in that size is $21 from McMaster and has a tolerance of +/- 0.0003" an impractical tolerance for drilling or boring, but anyone can do it with a reamer.

Best of luck!