White Paper Discuss: Dual-motor, dual-speed drive transmission design

[dlavery]

Originally posted by Andy Brockway
Dave,

So our team has decided to take the plunge and build a 2-speed transmission. We are looking at Andy Baker's through the center of the shaft and your over-the-top shifters.

I was wondering if you used this design during the 2003 season. If so, were there any problems with reliability and did it require maintenance. I see that there is quite a moment generated between the position of the air cylinder and the center of the gear.

Thanks for sharing your design.

Andy

We did use this design for the 2003 competition, updated to incorporate the larger Bosch motors in the 2003 kit. We only had one problem with it, which was a manufacturing problem and not a design issue (we traced it back to a cold braze on one of the gears during construction). Getting it fixed took some time, and kept us from moving during the first day at the Richmond competition while the machine shop and we tried to repair the braze. Once that was fixed, it was trouble free. It worked fine for the rest of the Richmond competition, and in Annapolis. There were no problems with the over-the-top method for moving the shifting gear - the piston rod is large enough, and the forces involved are small enough, that we never had any binding problems or excessive friction associated with shifting. We never broke a gear, or stripped a gear tooth, or bent a shaft. Maintenance was limited to just keeping the thing lubricated. I will be posting a white paper with the updated 2003 design shortly (if I can just get around to finish cleaning up some of the drawings).

The fundamental differences between the Teknokat design and ours center around the resources required for fabrication. If you have a CNC machining capability, or a good machinist and shop with adequate time, and can manufacture the dogs, dog gear, and drive shaft, then the Teknokat design is very attractive. It is lighter, smaller, and has more efficient power transfer than our design (one less stage of spur gears).

Our approach was driven by a complete lack of CNC capabilities (our machining capacity is limited a manual benchtop mill and lathe), and relatively inexperienced machinists (i.e. students with about two months of experience). So we had to come up with a design that they could manufacture fairly quickly, and that would tolerate some imprecision in construction. The result is that our gearbox is built sort of the same way the Russians build rockets - big, heavy, inefficient, old technology, but really simple, easy to maintain, and really robust.

Based on whatever resources you have available, you will have to look at the trade off between "smaller, lighter, efficient, requires higher manufacturing capability" or "big, heavy, clunky, but can be built by any doofus with a small shop in his garage"

Use whatever design(s) you can, but then adapt and customize them for the resources and capabilities you have on your team. Make modifications, updates and improvements to the designs - that's the fun part! And then post your improvements back to the community. Both Andy and I would love to see you post a new, better gearbox design next year - and if it happened to be based on some element of our designs that you have improved, that would be great!

-dave