pic: Swerve Render



I was naturally hesitant to use a bevel gear beside the wheel design, because the the exotic parts and CNC machining it generally requires. I finally decided to CAD this yesterday when I saw how much it could reduce the custom part count. (inspired by asid61’s latest designs)

This has a plastic wheel, plastic encoder mount, three aluminum plates, and an aluminum gear that have to be cut custom.
Three gears have to get their bores modified, and some spacers have to be cut to length. Edit: The vertical drive shaft requires some lathe work as well.

The drive is a 4:1 gear ratio on a 2.75" wheel for 16fps free speed.

The encoder is an absolute magnetic USD encoder with a one to one total gear ratio. I could use a CIMcoder for drive, but it would be a bit sketchy.

I really like your take on the bevel-beside wheel. It looks like it saves a lot of weight and space while eliminating some of the weaknesses in my design by putting the bearing around the turning gear and the spur gears below the turning gear. Overall this looks pretty robust.
It looks like you’re missing a way to hold the CIM pinion on the shaft short of welding it on there, which I believe you can only do with a steel 11t pinion. Did you have another plan in mind?
Which gear did you need to make custom from aluminum? Or did you just mean modifying the turning gear?
What bearing are you using for the module rotation?

Thanks!

It looks like you’re missing a way to hold the CIM pinion on the shaft short of welding it on there, which I believe you can only do with a steel 11t pinion. Did you have another plan in mind?

Correct. No method for this is in the CAD because I am not really decided. I was thinking of using loctite so that that it could be removed with a press and heat. What do you think is the best solution there?

… did you just mean modifying the turning gear?

That is what I meant.

What bearing are you using for the module rotation?

Silverthin bearing with 0.25" x 0.25" cross section and 3" ID. This way the outer race can be clamped to the upper plate with 0.25" long shoulder bolts.

I know 1296 tried welded CIM pinions last year to save space in the same kind of situation (shaft needed to be cut short). Loctite could work I think, but I was imagining something with maybe a pin through the gear and shaft in addition to the keyway.
Those Silverthin bearings are pricey (albeit highly convenient)! I know teams that used them way back in the past have gotten sponsored.

Can you shed some light on the wheel itself? Also, any chance for the full CAD?

Retention Compound (also made by Loctite) should work well. It can fill much larger gaps than threadlock.

Correct, we lathed the pinion in half and welded in addition to cutting the cim shaft down, only down side is that you can’t remove the pinion.

I was worried about this. I requested a quote from Silverthin but have not heard back yet. I know the equivalent bearing from VXB is $81.77!

The wheel is to be made from ABS (either on a printer or lathe) and the tread is polyurethane tubing from sun-ray that would be pressed on and bonded with a silicone adhesive like shoe goo. The basic layout and shape of the wheel should be visible in the cross section view.
Here is a link to the CAD. If you need STEP files let me know, and I can put that up too.

I like this idea, but I’m not sure how removable it would be.

Is there a STEP format file in the folder? I can’t seem to find one.

Huh. That’s interesting. So if/when the tread wears out, do you plan on just switching out the entire module or just the wheel?

There was not, but I just added one! Here is the link directly to the step file.

Yes. Or we could swap out the lower caster part, which ever is easiest. (I’m guessing just swapping out the wheel will be fastest because it only requires one bolt.) Then the old wheel can get new tread, so it can be used again later.

Are you concerned about thrust loads generated from the bevel gears at all? I can’t tell what bearings you’re using on your drive shaft. Especially with the draft shaft being a nut/bolt combo, it seems like those thrust loads could slowly loosen the nut and creating play in the drive shaft.

Do you mean the wheel shaft or the vertical shaft?

If you mean the vertical drive shaft, I am not worried about thrust loads because it is supported by 0.375" ID 0.875" OD flanged bearing, and I think it will be more than strong enough.

If you mean the wheel shaft, I am not worried about thrust loads from the bevel gears, because I am much more worried about the thrust loads from driving forces on the wheel.

Also none of the shafts are a nut/bolt combo. the vertical shaft is a solid aluminum live axle, the wheel shaft is a hollow steel dead axle with a bolt through the middle of it.

Heat and some force should get it off without too much issue. CIMs are relatively cheap and reliable anyway.

This would likely be a custom part, but you can definitely do press-fit CIM pinions. I prefer press fit to keyed pinions personally, whenever possible.

Otherwise, Loctite or something would probably hold on. I wonder if you could even put a snap ring groove into the output shaft of the motor?

I just remembered this:
http://www.andymark.com/product-p/am-0556.htm
15t 32p press-fit for a CIM shaft. If you switch to 32p on your first stage, that’s doable.

Good to know.

Yes. This is what I originally planned to use, but I could not find a good 32dp mating gear. The WCP ones only come in 20 and 40 tooth, which are not great sizes for this.
I guess I could look into modifying a SDP/SI gear, but I wanted to keep machining work down on this design.