pic: 2-Speed Gearbox



This is my first complete CAD for a 2-speed gearbox. Overall reductions are 4.89:1 high, 14.29:1 low. On 4" wheels, that’s 5.44fps and 15.9fps. Currently, it is designed for 2 CIMs, but I am working on a 3 CIM version. Also, the picture shows 2 different plates, but the back plate can actually be used in place of the front plate. The goal of this gearbox was to be as small and light as possible. In the shown configuration, the plates are about 8% lighter than the plates on a comparable WCP shifter.

(I will post a STEP file soon)

Here’s the STEP file: https://drive.google.com/file/d/0B4POpKC2IAD9ZFR0Y3ZFMzcxZW8/edit?usp=sharing
Any suggestions?

No technical suggestions, but than I am a software guy. Gearbox looks really good though! At ~8% lighter than a wcp dog shifter, this would be 1.9 pounds with a pancake attached! Also, no “Black anodized for superior performance”? :stuck_out_tongue:

Your pocket shapes are odd. There’s no need for bearing retention screws on the top shaft. The top two standoffs may be unnecessary.

Sorry, I was a bit unclear on the weight improvements. The weight of the plates on this gearbox is 8% less than the weight of the plates on a dog shifter, so .46lbs vs .5lbs. If the larger gears were milled out, weight could be reduced more.

Some of the weird geometry is necessary because of the odd positioning of the gears, some of it is simply to add character. The “retention screws” are actually mounting points for an encoder.

You may need slightly larger fillets in the pockets to allow for a bigger endmill to work around. I would think a .125" radius would be nice for at least a 1/4" endmill, but more experienced machinist could chime in on a nice cutter size. The larger fillets will also reduce stress concentrations, strengthening the plates.

Agreed. A .250 endmill is where you want to be for these sorts of plates. It’s actually significantly stronger than a 3/16th endmill. Even if you’re waterjetting the plate, I’d use a minimum radius of an 1/8th. There’s a few lightening pockets that can’t be cut on your plates, even with radiused corners.

If you’re planning to mill the plates, it can be helpful to make the radius 0.126 inches. The extra thousandth makes generating the toolpaths a lot easier. That way, the machine doesn’t have to go to a specific point, stop, and change direction; instead, it cuts the fillet as an arc.

I like the design. I’m guessing the upper shaft is .375 hex like the WCP shifter.

The wall thickness on your threaded holes is scary thin. A general rule is to use a circle that has twice the diameter of the hole. Also, the holes should be at the center of their fillets. It’s stronger that way.

If you’re really looking to save weight, you can get rid of the top set of standoffs and make the closer plate a lot smaller.

Thanks for the suggestions! You’re right about the upper shaft, the shaft is identical to one you’d get in a WCP 2-speed. I’ve been making some adjustments, like centering the holes and adding material around them.

Edit: The larger fillets make the space around the holes much better, I might post a new screenshot soon.