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Unread 05-01-2017, 03:11 PM
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AriMB AriMB is offline
The Philadelphian emigrant
AKA: Ari Meles-Braverman
FRC #5987 (Galaxia)
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Re: Championship Robot Mechanism Pictures 2017

Quote:
Originally Posted by wesleyac View Post
1640's CVT swerve is really cool, but I'm having trouble visualizing how it works - it looks like the belt is changing size, but I assume that there's something else at play. Can someone explain how it works? I've looked at their wiki but I still don't get how the constant velocity pulley operates...

Also, does it automatically shift in software, or does the driver manage the shifting? If it's software, what parameters are used to decide what gear to be in?
I'm not associated with 1640, but I've been watching videos of their CVT for almost a year now and I think I understand how it works. (Also from the description here) Someone from 1640 can come and correct me if I'm wrong.

The first reduction from the CIM is a V belt. The pulley attached to the motor is spring loaded so that tension on the belt slides the belt towards the center of the pulley and the top half of the pulley up. This decreases the diameter of the driving pulley. The servo on top of the module opens and closes two rollers around the belt, which tightens and loosens the tension in the belt. This changes the diameter of the driving pulley, which changes the final gear ratio. A large encoder disc is attached under the driven pulley, and an optical sensor reads the pulses from that to measure the drive speed. I would assume they then use some function of speed to determine the optimal drive ratio, and therefore the desired tension on the belt, and use that to set the value for the servo position.


EDIT:
Quote:
Originally Posted by Noudvanbrunscho View Post
https://youtu.be/PEq5_b4LWNY here is a video explaning How cvt works. I am wondering How iT worked out for team 1640, What the pro's and cons are.
I imagine one con is that the V-belts carry little force back to the motor, so they can't push very hard in a pushing match. This probably isn't a big problem for a swerve, considering you can just put all your wheels at 45* angles and no one can push you anywhere. It might even be a pro if they explore using 775pros instead of CIMs for the drive motors in the future.
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Last edited by AriMB : 05-01-2017 at 03:14 PM.
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