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#16
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Re: pic: Butterfly Drive
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We took inspiration from 148's strafing module (from their 2014 robot, Vader). The module itself spins on the axle that's powered by the CIM. So when the CIM is powered, the module spins down until a wheel contacts the wheel. The CIM will exert enough force to push down the module enough to have the ground exert a normal force on the wheel (which is what traction is dependent on) before the torque of the CIM spins the omniwheel. At least that's how I understood it while designing this. We haven't actually done more serious math outside of a simple free body diagram. If someone from 148 or anyone with experience with this type of strafing module could explain more/clarify/prove me wrong, that would be awesome. |
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#17
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Re: pic: Butterfly Drive
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We struggled with tuning the amount of force our strafing modules needed in 2015, but that was going over the bump + with and without totes, so it had to move more weight / accelerate more mass than just a robot and that weight varied quite a bit. I looked at 148's design when thinking about ours, but we had one shot at getting it right (we swapped our drive from mechanum to this at state champs) so I ended up going with 2 strafe modules, held down with gas shocks counter balanced by surgical tubing so we could adjust the downward force. The 148 solution is lighter and more elegant, but more difficult to get right. |
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#18
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Re: pic: Butterfly Drive
Hm... so I think the main issue revolves around when the tractions are down and the robot gets hit on the side, which might damage the modules, and the shaft especially over time. In addition, the way the piston is mounted probably also causes it to receive a lot of force on impact.
I might consider another design of the Butterfly, although I might move on to intakes or something other than drivetrains, because I've been doing that a lot. But anyways, here's what I was thinking about the new design:
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#19
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Re: pic: Butterfly Drive
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For those more knowledgeable than I: Is my understanding correct? Edit: As far as I can tell, it would follow from this understanding that, in theory, a tilt angle from horizontal of greater than the inverse tangent of the wheel-to-ground coefficient of friction would guarantee that the wheel wouldn't slip (Well, until the point at which the linear relationship between torque and normal force ends because there simply isn't more weight available for the strafe wheel to support). However, in reality, friction is also a fickle beast and is highly dependent on the exact conditions of the interaction at any given time. Last edited by Greg Woelki : 14-11-2015 at 23:41. |
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#20
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Re: pic: Butterfly Drive
Yeah you're right. I remember discussing this with someone when we watched the reveal video for the first time in 2014. But I completely forgot this time around, even while reviewing this CAD...
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#21
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Re: pic: Butterfly Drive
Have you considered putting springs on the modules to hold them in place without air pressure?
There's nothing quite like losing air pressure in the middle of the match and being unable to drive. |
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