pic: GBX-150, CIM-mounted swerve

[asid61]

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[marshall]

I'd switch the turning encoder out for one of the versa planetary integrated ones but other than that, this looks cool. Good work!

[GeeTwo]

Independent of the swerve aspect, the idea of mounting a wheel based only on the two 10-32 mounts on the face of the CIM is a bit scary. Mounting that arm with a 6-32 and putting a swerve mechanism between there and the wheel have a bunch of alarms going in the back of my neck.

I've seen plans for a VP-compatible cycloid drive, but I don't recall that it's been built, much less made a COTS item. Did you include that in your machining requirements? Is there any advantage of the cycloid drive (vs planetary) in this application other than the obvious weight/space savings?

[asid61]

The main forces on the CIM are thrust loads against the face rather than shear forces, and she shear forces are limited by wheel friction. I'm more worried about the attachment arm. Looking back, I think I can redo the design to use no friction locking at all and use traditional plates, so I might try that next.

VP cycloid should be included in the machining bill, you're right. I like the height savings it provides, mainly.

[GeeTwo]

Originally Posted by asid61

The main forces on the CIM are thrust loads against the face rather than shear forces, and she shear forces are limited by wheel friction.

The thrust load isn't the concern, especially as it's compression. However, if the CoF of the wheel on carpet is greater than one*, the shear forces are potentially greater than the thrust load. What really concerns me are shock loads.


* Except for Lunacy swerves, this seems to be the rule rather than an exception.

[Bryce2471]

Looks very cool. I'm glad to see you are still iterating on your swerve designs.

What I can't gather from this picture is how the primary bearing setup would work. Could we get a cross section view, or an explanation for that?

[asid61]

Originally Posted by GeeTwo

The thrust load isn't the concern, especially as it's compression. However, if the CoF of the wheel on carpet is greater than one*, the shear forces are potentially greater than the thrust load. What really concerns me are shock loads.


* Except for Lunacy swerves, this seems to be the rule rather than an exception.

That's a good point; I hadn't thought of it that way. Looking back on it, the whole clamping mechanism is a cool gimmick, but not something I actually need... I could also reduce the weight somewhat with other constructions I think.

Originally Posted by Bryce2471

Looks very cool. I'm glad to see you are still iterating on your swerve designs.

What I can't gather from this picture is how the primary bearing setup would work. Could we get a cross section view, or an explanation for that?

Thank you!
The bearing setup is definitely an oddball one. Here's a link to the 2015 Offseason folder with the CAD, if that helps:
https://workbench.grabcad.com/workbe...1Z2b-tQWAq3gUh

Essentially, a plate is screwed into the CIM and firmly attaches to the inner race of the 6711 bearing. The outer race of the bearing is pressed into the 64t turning gear and captured with the flanged buttonhead screws seen in the picture.

[Aren_Hill]

I like the concept, as someone who has utilized the large steel sleeve of the CIM structurally before.

I will warn against taking any loads with the face of the CIM, this is a rather thin wall cast component, which I have seen break in normal mounting configurations.

See if you can find a way to clamp higher up on just the steel sleeve, for both parts, the module rotation and the main frame mount. It'll be interesting to accomplish that and still properly pilot the CIM for the gear mesh.

Also I have next to zero confidence in that wheel/tread setup surviving for a match, once you get past a certain point there is simply not enough contact to transfer the forces required without extreme wear, one of the reasons I stopped at the ~3" diameter territory with my designs.

[Mechvet]

R30 (as of 2016) allows modifying a motor housing for the purposes of mounting, which certainly opens the door for structural mounting of a CIM.

It may be possible to entirely replace the output shaft plate of the CIM with your main anchoring plate. Only restrictions I'm seeing from the rulebook would be ensuring that your design is not lighter than the original, and that the electrical and mechanical operation of the motor have not been modified.

[Richard Wallace]

Originally Posted by Aren_Hill

I like the concept, as someone who has utilized the large steel sleeve of the CIM structurally before. ...

.

+1

That CIM sleeve is a beefcake. See linked cartoon-CAD of our 2016 winch. (We ended up using an igus bearing, not the PTFE called out in the cartoon. Metric 64mm i.d. fits nicely over the CIM sleeve paint. See picture of the innards also.)

My theory as a motor designer: if you have more than the minimum steel required for magnetic flux, the excess should perform another useful function to justify its weight, cost, claimed space, etc.

[Cothron Theiss]

Originally Posted by Richard Wallace

+1

That CIM sleeve is a beefcake. See linked cartoon-CAD of our 2016 winch. (We ended up using an igus bearing, not the PTFE called out in the cartoon. Metric 64mm i.d. fits nicely over the CIM sleeve paint.)

My theory as a motor designer: if you have more than the minimum steel required for magnetic flux, the excess should perform another useful function to justify its weight, cost, claimed space, etc.

Ok, so does anyone have a spec for the wall thickness for a CIM? Mini CIM? Bag CIM? I'd love to see more and more designs delving into this somewhat uncharted territory of using the CIM body as a mounting point.

[Aren_Hill]

Originally Posted by Cothron Theiss

Ok, so does anyone have a spec for the wall thickness for a CIM? Mini CIM? Bag CIM? I'd love to see more and more designs delving into this somewhat uncharted territory of using the CIM body as a mounting point.

I think last time I measured it was ~0.090" thick, it's not going anywhere.

[asid61]

Originally Posted by Aren_Hill

I like the concept, as someone who has utilized the large steel sleeve of the CIM structurally before.

I will warn against taking any loads with the face of the CIM, this is a rather thin wall cast component, which I have seen break in normal mounting configurations.

See if you can find a way to clamp higher up on just the steel sleeve, for both parts, the module rotation and the main frame mount. It'll be interesting to accomplish that and still properly pilot the CIM for the gear mesh.

Also I have next to zero confidence in that wheel/tread setup surviving for a match, once you get past a certain point there is simply not enough contact to transfer the forces required without extreme wear, one of the reasons I stopped at the ~3" diameter territory with my designs.

Thanks for the advice. I thought the face was machined, but if it breaks that easily it looks like I'll have to rethink a lot of it. I'm currently working on an iteration of this idea that should be stronger while pushing the weight under 5lbs (finally).
Does the tread just come off such small wheels, or is there another problem? I was thinking of just using a colson if what you're saying is the case.

Originally Posted by Mechvet

R30 (as of 2016) allows modifying a motor housing for the purposes of mounting, which certainly opens the door for structural mounting of a CIM.

It may be possible to entirely replace the output shaft plate of the CIM with your main anchoring plate. Only restrictions I'm seeing from the rulebook would be ensuring that your design is not lighter than the original, and that the electrical and mechanical operation of the motor have not been modified.

I recall seeing old threads about a team machining the paint off the CIM to make it shiny, but I want to avoid machining more COTS components than absolutely necessary. That being said, replacing the front plate of the CIM would be an elegant solution.

[Cothron Theiss]

Originally Posted by Aren_Hill

I think last time I measured it was ~0.090" thick, it's not going anywhere.

Ok, thanks. I've only opened a CIM once, and I wasn't paying attention to the sleeve as much as the internals.

[Aren_Hill]

Originally Posted by asid61

Thanks for the advice. I thought the face was machined, but if it breaks that easily it looks like I'll have to rethink a lot of it. I'm currently working on an iteration of this idea that should be stronger while pushing the weight under 5lbs (finally).
Does the tread just come off such small wheels, or is there another problem? I was thinking of just using a colson if what you're saying is the case.



I recall seeing old threads about a team machining the paint off the CIM to make it shiny, but I want to avoid machining more COTS components than absolutely necessary. That being said, replacing the front plate of the CIM would be an elegant solution.

A colson would work better as the bond to the polyolefin core is very strong, but it would still wear out faster than you'd think.

Replacing the ends of motors has been on my "i'd like to do this..." list, but I never have as I'd likely lose the rules argument, you are getting a weight/performance advantage when you integrate the motor into the structure like that. And I read "modified to facilitate mounting" as "mess with it some if need be, but don't replace it".

I had a concept once that would replace the dead axle of a window motor with a powered shaft through to get an on-axis steering motor, but never made it past that as I'm pretty sure I'd lose the legality argument.


-Aren