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

[CD47-Bot]

Thread created automatically to discuss a document in the White Papers.

Dual-motor, dual-speed drive transmission design by dlavery

[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

[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

[Andy Baker]

Originally posted by dlavery
We... are... attractive... heavy... doofus,... Both Andy and I.

-dave

I agree.



Also, I commend Andy Brockway and Dave for following through with "the challenge" of creating a design and posting it in detail. These guys are helping to "raise the bar" in FIRST.

Andy B.

[Andy Brockway]

We fall into the second category with one exception, we have an experienced machinist to run the manual lathe.

We are adapting our 2003 gearbox for shifting and hope to have it in the bot for the Fall season starting with River Rage. If so I will post the design later this year.

Thanks for your support!

Andy

[patrickrd]

That's slick... I like it. I wonder if I can convince some of the high school kids on our team to try and machine something like this instead of sending out the engineers to do it. How is the shifting? I was wondering if it is able to shift at high speeds, or only at rest or slow speeds? It looks like you might damage the gears if you try at high speeds.

- Patrick

[dlavery]

The design we developed, like the TeknoKat design, actually prefers shifting on-the-fly over shifting while stopped. One of the things that makes this possible is the chamfering on the tips of the teeth of the shifting gears, which tends to guide the teeth into a proper meshing configuration as the shifting gear moves (we were also careful to break any sharp corners on the edges of the entire tooth with a needle file, to further reduce the chance of binding).

If you were designing a transmission that was going to see hundreds of thousands, or even millions, of operational cycles, then you wouldn't do it this way. But given that this system is probably only going to see a few hundred shifts at the most, the abuse heaped on the gears with this design should not be too much of an issue.

-dave

[Matthew_H]

What was your approximate build time on these dual motor gear boxes. We are try to build the technokats design this fall to see how long and what modifications we need to make for our application. We do have a CNC lathe but our CNC mill is broken but we hope to repair it within the next month. This is being built with our machine shop class at our school so we have one experience machinist along with 5 students working with our robotics team. These designs are going to help us greatly in generating ideas with our students and engineers on ideas for future parts. This is top notch work.


Matthew Hillis
Ubergeeks

[Matt Reiland]

Originally posted by Matthew_H
What was your approximate build time on these dual motor gear boxes. We are try to build the technokats design this fall to see how long and what modifications we need to make for our application. We do have a CNC lathe but our CNC mill is broken but we hope to repair it within the next month. This is being built with our machine shop class at our school so we have one experience machinist along with 5 students working with our robotics team. These designs are going to help us greatly in generating ideas with our students and engineers on ideas for future parts. This is top notch work.


Matthew Hillis
Ubergeeks

Matt,

We did something similar to what you are thinking last year. The technocats design (with a little modification) can be completed without much CNC work. The hard parts of the design are the Shift Dog, the output shaft, and the 2 output gears. The output shaft can be done on a manual mill and a manual lathe without too much hassle. The dog & output gears are also somewhat difficult but they could be done on a manual mill with a rotary table to get the angles right. Once these 4 pieces are complete the rest of the parts can be done fairly easily on manual tools. I would start with those four pieces and modify the design to your needs after that.

Matt

Just drop a message here if you need help and I am sure you will get it.

[dlavery]

OK, so I finally got my act together and cleaned up the last two drawings, and folded them in with the rest of our white paper describing of our updated gearbox design. The "Mark 2" version of our gearbox is smaller, lighter, has fewer moving parts, and is easier to manufacture than the previous version. It is also updated to incorporate the new Bosch motors included in the 2003 FIRST kit of parts. The updated design has been posted in the White Papers section of the board.

We used this gearbox design successfully during the 2003 season in Richmond and Annapolis, and it performed well. We also used it this past weekend at the Maryland State Fair competition, when we were running and our treads weren't binding (due to a different, and completely frustrating, problem - next year we go with WHEELS!!!). Anyway, we hope this is useful. Let us know if you use, or improve upon, the design. Have fun!

-dave