pic: 2.5in gearbox

A single speed gearbox that uses 2.5in Colson wheels. It runs at 13.95 ft/sec free and 11.30 ft/sec adjusted with a 4.17:1 reduction.
Feedback would be appreciated.

Looks good so far!

What led to your choice of 2.5" colsons?

What gears are you using? I ask this because at smaller tooth counts for a more compact gearbox, you might be approaching the limit for some materials, such as aluminum. (note: I have done zero calculations for a smaller box. I’d suggest running some lewis gear numbers to see if you’re inside the gear’s envelope)

Am I correct in assuming that the two sprockets inside the gearbox mean this is for a WCD setup? If that’s the case, how are you planning to mate this gearbox to the frame rail?

If this is for an FRC robot, you may want to make sure the wheel is easily replaceable.
Anecdotally and from some experience, when using the belted wheels, an 8 inch wheel would last most of a season. 6 inch wheels tended to last an event pretty well, and 4 inch wheels I think needed tread change each day.

Aren Hill made a neat little swerve module several years ago that used a small wheel. While the module worked well, I think fast tread wear was a concern of that system.

One other possible critique, you may want to look into narrowing the gears. With the lower relative torque in your system, you could likely reduce the gear widths and further improve your packaging space. If you are using COTS gears, then I can respect the extra width vs. simplicity of application.

It appears as though you have sprockets to run to other wheels. What size chain are you using?

The gearbox would be mounted using the lower 10-32 bolts that would mount the CI’M motors, in total there would be 3 10-32 bolts holding the CIM motors and the gearbox on.

I used 2.5" where’s because my personal philosophy is that the smaller the wheel you design for the small your gearbox can be. I posted this because I fear I am missing some torque related risks of small wheels.

The chain is 25 because small wheels should (if I did my math right) require less torque to move and rotate.

Are there any disadvantages of 2.5in wheels I may have missed? (assuming that high centering is not an issue)

Possibility of getting caught on field elements or uneven flooring notwithstanding, a concern when using really small wheels is tread wear. If you think about it, 2.5" wheels are traveling the same distance with much less tread. Now the Colsons are wonders for durability, but they will still wear down pretty quickly and become slicker sooner. But if it’s a WCD setup, you should be fine to replace wheels often.

Doesn’t that mean that you would have to assemble the gearbox directly onto the drivetrain, instead of assembling it somewhere else and mounting it on? That would be more annoying imo. From what I can see, there’s space to add some mounting holes and avoid that complication.

It looks like the gearbox can be assembled off-bot, but you attach it using 1 screw each from 2 CIMs. I like this design; that’s a really good use of screws.

It can but partial disassembly will be required to install.