Need shifting transmission layouts/ideas

I should be able to do this myself (since I have before) but I can’t come up with anything I like that works well. I need some new ideas because nothing I’ve come up with has enough reduction while still maintaining elegant but simple design. So, I’m asking for help.

We need a 2 speed dog shifting transmission that accepts two small CIM motors as the input. The no load output speed in high gear must be in the range of 450-500 RPM (slightly higher or lower is okay) The difference between high and low gear needs to be in the range of about 2.5:1. The gears will be 20 pitch. The goal is to keep it as small, as light, and as cheap as possible.

So, if anyone has a good layout that will get me down to this RPM, I’d love to see it.

By layout, I mean gear placement and tooth counts.

Thanks so much.

I couldn’t pass up the challenge.

50:32 or 32:50

244% Reduction difference.
High Gear RPM approx 548 RPM
(assuming 81% speed loss from free speed.)
All gears available from Boston Gear, as standard parts.

On 229, we used a similar layout in 2004.

See attached for gearing calculations.

Inspired by:

Sanddrag.xls (46 KB)

Sanddrag.xls (46 KB)

Thanks John. I’m, still confused as to exactly what the layout looks like and what drives what. Do you think you could whip up a hand drawing or MS paint drawing that kind of follows the idea of my attached pic? That would make it much easier for me to understand. Thanks.

I wanted to use a layout like the andymark but I’d have to go huge on all the gears to get the reduction I want. If you could further illustrate your layout, that would be great.

Note: I don’t believe the gearbox in the attached pic will actually work because that picture is not to scale and I think the gears will hit somewhere. I don’t remember because I made it so long ago, but I think there was some sort of problem.

If I may suggest, you could use a shifting system similar to the one my team used last year and probably the one we will use this year. A video of it in action can be seen here:

Its not as high quality as a dog shifter, but it does work, and you could build it in 4 days starting now(2 days to get parts from mcmaster, one day to machine and one day to put together.) We used a 2 inch pulley to a 4 inch pulley for low gear and a 3 inch to a 2 inch for high gear and got RPM’s I believe in the range you’re thinking of. I don’t have my spreadsheet on me so I could be wrong. As for an actual dog shifter, i’ve never built one so I Can’t help you there.

My 2005 gearbox comes close to your specs. 522 rpm in high, 233 rpm in low. This is a 2.2:1 ratio. It is in the White Papers. Team 716, 2005 Dual Speed Gearbox.

It is simple and quick to build.

Andy your gear box looks really nice and clean. do you have any ideas as far a weight of it, the cim interface gear looks massive. I do like the concept for the first stage being outside the box.

The CIM interface gear is 72 tooth, the stock gear weighs 1.6 lbs but with simple lathe work I shaved it down to .85 lbs. With more work it could lose quite a bit more. Overall the gearbox with the CIMs weighs in at 9.25 lbs. I am currently building a set for this year. The outside the box gear design was adapted from an idea that Greg Perkins concepted.

more on my gearbox was discussed here