pic: Poly-carbonate 2 Speed Gearbox

[Chris Endres]

Very nice.

However, you're going to want to watch out for possible deformation of the plates under load, especially the plate that CIMs are mounted to.

[Chris is me]

If you want to be extra safe against deformation, you'll want to upgrade to 3/8ths polycarbonate. 1/4" probably deflects too much, even un-lightened.

It doesn't end up saving you weight over an optimized aluminum gearbox, but it's hard to do gearboxes with polycarbonate.

[cbale2000]

Originally Posted by Chris is me

If you want to be extra safe against deformation, you'll want to upgrade to 3/8ths polycarbonate. 1/4" probably deflects too much, even un-lightened.

It doesn't end up saving you weight over an optimized aluminum gearbox, but it's hard to do gearboxes with polycarbonate.

Having built several polycarbonate gearboxes I would have to agree with this. If it were designed like an actual box, where you have polycarbonate connected on all 6 sides supporting itself you might be able to get away with 1/4" (as my team has in the past), but if you plan to support it like that, you'll definitely want to go to 3/8" for rigidity.

You might also consider mounting another plate of polycarbonate between the gearbox and the output sprocket. Having less distance between plates should improve the rigidity.

This is what we built a few years back. Note that the aluminum plate was eventually replaced with polycarbonate. Also worth noting that the gearbox is still around 8 years later. The gears failed a while back, but the box is still in great shape.

[jkelleyrtp]

Very nice, I've been researching good plastics for gearboxes and found that acetal and thick polycarb will work fine, but polycarb does have more flex in it. I'd recommend some sort of bracing/stand for the cims to hold them in place during load (as said above).

Also, 254 has made a plastic-based gearbox and made their mounting frames out of acetal.

[asid61]

If you could do a stress test on the holes compared to the WCP gearbox plates, that would be interesting to see.

[Cory]

Originally Posted by jkelleyrtp

Also, 254 has made a plastic-based gearbox and made their mounting frames out of acetal.

It wasn't worth it though and I'm pretty sure the solid delrin plate was just about as heavy as a pocketed aluminum plate...and substantially less rigid.

[kiettyyyy]

Originally Posted by Cory

It wasn't worth it though and I'm pretty sure the solid delrin plate was just about as heavy as a pocketed aluminum plate...and substantially less rigid.

On top of that, I recall having issues with being unable to draw heat out of the CIM motors since we used delrin plate.

We did a test with the same gearbox under the same load using pocketed aluminum plate. It resulted in having a cooler motor over the same testing duration.