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Unread 09-05-2015, 14:17
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Bryce2471 Bryce2471 is offline
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AKA: Bryce Croucher
FRC #2471 (Team Mean Machine)
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Re: pic: Small CIM in wheel swerve

Quote:
Originally Posted by GeeTwo View Post
If you used a worm gear for steering, it seems to me that you could orient both motors horizontally and get the module height down to the wheel diameter. You'd also save some weight on a second gear stage at a bit of loss of steering efficiency.
I would like to use a worm gear, but I have no idea how to make a large custom worm gear, and I assume that a COTS gear that large would be incredibly expensive. Perhaps worth looking into though, since this was just a CAD experiment anyway
Quote:
Originally Posted by InFlight View Post
Bryce,
Really nice concept once again.

Are you using a Silver Thin Bearing to support the the pivot assembly?

The planetary drive inside the wheel is a great idea, are there two stages there for ~9x reduction?
Thanks, right now it uses a bomb squad style slew bearing.

I kept it to one stage in this design, but it's likely geared too tall for most situations. It's a 5.33 to one reduction on a 3.5'' wheel.
Quote:
Originally Posted by InFlight View Post
With a large steering gear like that you can't use an absoule encoder.

Team 141 at championships had a similar large steering gear setup. They used an incremental encoder to count steering input revs, but also had a pivot extension that triggered a proximity switch to calibrate the nominal forward position.
We have run an incremental encoder with a homing index in the past, and would probably never go back... It's a real pain, and the drift robs a lot of a swerve's efficiency.
Quote:
Originally Posted by Scott Kozutsky View Post
It appears there's an absolute encoder on the top of the entire module, likely connected by bent polycarb like 3928 and 2451 before them.
Correct, although I'm still debating how the wire routing will work...
Quote:
Originally Posted by Ether View Post
If your sample time is fast and stable enough that the encoder could never turn 180 degrees from one sample to the next, then "all ya gotta do" at each sample is assume the encoder turned through the shortest angle, and keep track of zero crossings.
You also need to have a good home position. Which would likely involve putting the swerve slightly to one side of "Straight" before every match, so that it's "zero" would be the real zero of the swerve, to begin with.
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