Need shifting transmission layouts/ideas

[sanddrag]

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.

[JVN]

I couldn't pass up the challenge.

12:50
50:32 or 32:50
21:64

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:
http://team229.org/photo/single/2723
http://team229.org/photo/single/2744
http://team229.org/photo/single/2743
http://team229.org/photo/single/2829

[sanddrag]

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.

[Ianworld]

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:
http://www.billfredinthenighttime.com/694.wmv

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.

[Andy Brockway]

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.

[Greg Needel]

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.

[Andy Brockway]

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