Smaller Mecanums

I always felt that the mecanum wheels we use on P21 were too large; they’re about 100mm diameter. I think they are not really suited to delicate autonomous manoeuvres.

Over Christmas I decided to gamble on buying a set of these from Pimoroni…

Pimoroni mecanum wheels

These wheels are cheaper than ones I’ve seen before (£24 for a set), and are about 36mm diameter.

I say gamble because the website doesn’t specify the size of the hexagonal hole on the back of the wheels. I hoped the hole would be the right size for the hubs we use on our robots…

Excuse the nail varnish (aka thread lock)

Unfortunately the holes on the wheels were too small, so the hub didn’t fit.

I thought about 3D printing a new hub to connect the motor shaft to the wheel but didn’t think I could make it strong nor accurately enough.

I decided to enlarge the hole in the wheels. I preferred this method as this keeps these wheels compatible with the hubs we use on all our robots. Well, assuming I could make it work of course; this is what you might call a high risk / high reward approach.

I 3D printed a jig to hold a single wheel, with M4 bolts to clamp the wheel in place. The jig can be screwed down to the spoil board on the CNC router at Exeter FabLab.

Next, I created a tool path in Fusion 360 to machine 0.7mm from each face of the hexagonal hole…

Fusion 360 tool path

Amazingly, this all worked. I was able to machine off 0.7mm from each face of the hexagonal hole on Exeter FabLab’s Denford router. The cut is just right, the hubs are a nice snug fit in the wheels.

The wheels now fit our standard hubs

Hopefully, I can get some time to test these new wheels in the near future.

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