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 what is integration if not a compromise?
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By: Scott Kozutsky
New: 17-06-2016 18:33
Updated: 17-06-2016 18:33
Views: 762 times
Discussion
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18-06-2016 01:08
Jay O'Donnell
Re: pic: OmniSwerve Pivot Top View
Maybe I'm missing something, but what's holding the CIMs in place?
18-06-2016 01:10
Greg Woelki
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Jay O'Donnell
Maybe I'm missing something, but what's holding the CIMs in place?
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18-06-2016 02:00
Jay O'Donnell
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Greg Woelki
Friction. It appears to be a clamping design (look at the standoffs).
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18-06-2016 02:29
asid61
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Jay O'Donnell
That's what I assumed. Is this actually a design that teams use? I don't know if I could ever trust it.
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I would feel safer if the CIM was clamped on the front and back endcaps instead of the black body, but as a concept I think it can work.
18-06-2016 18:48
Joey Milia
Re: pic: OmniSwerve Pivot Top View
Yeah I would be worried about CIM diameter tolerances and the effect they would have on the gear mesh. Clamping on the aluminum ends might work but the rubberized black body is probably too variable.
19-06-2016 14:48
Greg Woelki
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Joey Milia
Yeah I would be worried about CIM diameter tolerances and the effect they would have on the gear mesh. Clamping on the aluminum ends might work but the rubberized black body is probably too variable.
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19-06-2016 15:31
Scott Kozutsky
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Greg Woelki
Rubberized?
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19-06-2016 15:45
Greg Woelki
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Scott Kozutsky
The casing probably isn't adequately concentric with the shaft so the gear spacing could be pretty significantly off. That said, peoples get away with 10-32 screws in loose fit holes for gear spacing on drive gearboxes (when they don't use the flange for more precise centering). It might take a little finicking but I think it's certainly doable to use a clamp like this. As I understand it, gears can handle pretty significant misalignment if they aren't expected to run for very long.
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22-06-2016 00:54
Joey Milia
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Greg Woelki
Rubberized?
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The problem isn't the lack of concentricity, the outer casing isn't spinning so it doesn't matter. What does matter is the very loose tolerance (only max is stated, not an actual tolerance) on the outside diameter that you're clamping onto. If you assume nominal is 2.5" and max is +36 thou thats quite a large tolerance. However if you were to measure all of your cims and find them all to be the same then you could probably get away with it and be fine.
EDIT: ok concentricity kind of matters but becomes kind of irrelevant once you clamp the motor down. And lack of it could even be used to adjust the center distance to correct it.
22-06-2016 02:59
DaveL
Re: pic: OmniSwerve Pivot Top View
This is a great design!
I like that its compact, has a lot of power and uses a wide base of support.
Like others have said, mounting the CIMs to their faced plate is the tried and accepted way to go, but I like the way you are thinking.
I am a little surprised you went with omni wheels. My guess is that they won't have the friction to transfer the power of the CIMs during high acceleration. Changing to a tread wheel would fix that. If you are short on resources, build one module and mount it up front. Then independently power the non-steering rear wheels. That would be one fun trike. For more fun, add omni wheels to the rear so you can slide your turns.
22-06-2016 10:01
Chris is me
Re: pic: OmniSwerve Pivot Top View
I don't really see the benefit of clamping the CIM versus just face mounting it to the outer plate with a clearance hole on the inner plate. It's a little more compact I guess.
Clamp mounting the CIMs is something that does work, but I've never done it where the clamping action is used to hold a gear mesh together. In 2013 my old team mounted CIMs to a Frisbee shooter by clamping on the outside and it held all season, but there were no gearboxes to worry about.
22-06-2016 13:00
JamesCH95
Re: pic: OmniSwerve Pivot Top View
Are we all ignoring the fact that this is a swerve drive with omni wheels?
Might I ask the obvious question: why swerve with omni wheels?
22-06-2016 13:06
Chris is me
Re: pic: OmniSwerve Pivot Top View
Another thing - I don't really like the lightening pattern on the gear. The spokes don't do a ton for the gear's strength, and a spoked lightening pattern like that requires milling whereas a no-spoke lightening pattern could potentially be turned.
If you are going to do a spoked lightening pattern, at least make it six spokes and have the spokes align with the hex points. That way the additional material is behind the stress risers and not just in random places.
In either case, I would leave a bit more material around the hex (maybe .875 diameter?). The material left around the gear teeth should be fine. If the thin part of the gear is at least .15 thick or so you should be fine. These are "gut numbers" not backed up by real math or engineering, just experience, so take them with a grain of salt.
22-06-2016 15:51
Aren_Hill
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Joey Milia
I believe the black portion of the CIM is steel with a black rubber coating on the outside, thus my use of rubberized.
The problem isn't the lack of concentricity, the outer casing isn't spinning so it doesn't matter. What does matter is the very loose tolerance (only max is stated, not an actual tolerance) on the outside diameter that you're clamping onto. If you assume nominal is 2.5" and max is +36 thou thats quite a large tolerance. However if you were to measure all of your cims and find them all to be the same then you could probably get away with it and be fine. EDIT: ok concentricity kind of matters but becomes kind of irrelevant once you clamp the motor down. And lack of it could even be used to adjust the center distance to correct it. |
-Aren
22-06-2016 16:10
Scott Kozutsky
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Chris is me
Another thing - I don't really like the lightening pattern on the gear. The spokes don't do a ton for the gear's strength, and a spoked lightening pattern like that requires milling whereas a no-spoke lightening pattern could potentially be turned.
If you are going to do a spoked lightening pattern, at least make it six spokes and have the spokes align with the hex points. That way the additional material is behind the stress risers and not just in random places. In either case, I would leave a bit more material around the hex (maybe .875 diameter?). The material left around the gear teeth should be fine. If the thin part of the gear is at least .15 thick or so you should be fine. These are "gut numbers" not backed up by real math or engineering, just experience, so take them with a grain of salt. |
22-06-2016 16:18
Scott Kozutsky
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by JamesCH95
Are we all ignoring the fact that this is a swerve drive with omni wheels?
Might I ask the obvious question: why swerve with omni wheels? |
Various Reasons
22-06-2016 21:19
Cothron Theiss
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Scott Kozutsky
The design assumed use of a CNC router so that would be used to do the pockets (multiple passes, depth of cut isn't that great but its certainly doable). I also made sure not to pocket it all the way through so there is 1/16 of material left on the bottom which should adequately handle the torsional shear between the hex and the teeth. The diameter of material surrounding the hex is .8 which should be ok as there will be relatively less stress acting on it (3.25in omni wheels can only transmit so much torque compared to 4 in nitrile for example). 7 spokes is a byproduct of our team name, not the best engineering solution but we'd probably keep it anyways.
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22-06-2016 23:04
Scott Kozutsky
Re: pic: OmniSwerve Pivot Top View
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Originally Posted by Cothron Theiss
Have you run any simulation or FEA to confirm that this gear won't fail? Also, have you designated a material for the gears? (I apologize if you've already listed he material and I just missed it.)
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