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#1
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pic: Offseason 8W Tank Drive
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#2
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Re: pic: Offseason 8W Tank Drive
Seems like it would be tough to work with in the pit if it would need to be worked on. I'm basing this by the number of gears.
Can you post some specs? looks cool! |
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#3
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Re: pic: Offseason 8W Tank Drive
Sure!
The drive channels are two pieces of 1"x3" C-channel, with the two sides connected by a single 0.090" bent sheet metal piece. You could also replace this bent sheet metal piece with the front/back rails of the 2014 VEXPro Drive in a Day or the 2015 kitbot end rails (at least as much as I can tell from the drawings). The gearbox is mostly just a repackaged Ball Shifter. The only trick is that two of the CIMs are on a separate first stage reduction and then connected to the rest of the gearbox with a 9mm HTD belt. These then drive 8 4" Colsons on dead axles. Here are the drive numbers: ![]() Weight seems to be about ~40 lbs, including motors and chains. |
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#4
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Re: pic: Offseason 8W Tank Drive
What program are you using for those drive numbers? AFAIK, it's pretty much impossible to pull 90 amps per CIM on a 6CIM drive under any circumstance with the batteries we use in FRC.
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#5
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Re: pic: Offseason 8W Tank Drive
Quote:
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#6
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Re: pic: Offseason 8W Tank Drive
Quote:
http://www.chiefdelphi.com/media/papers/2755 |
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#7
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Re: pic: Offseason 8W Tank Drive
Quote:
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#8
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Re: pic: Offseason 8W Tank Drive
Quote:
FWIW, we found that the 1.3 CoF was a little on the high side for normal traction wheels. |
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#9
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Re: pic: Offseason 8W Tank Drive
Quote:
I know the calculator on the WCP website does take battery voltage drop into account, which is nice, but their "max pushing force" calculation uses the static COF even for a traction-limited drive, which is not-so-nice. |
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#10
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Re: pic: Offseason 8W Tank Drive
Quote:
http://www.chiefdelphi.com/media/papers/3038 |
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#11
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Re: pic: Offseason 8W Tank Drive
A quick question, the sheet piece as shown is made out of 0.090" Al 5052-H32. I know other teams, such as 33 and 67, have had success with thinner sheets. Would trimming down to 0.063" be a wise decision?
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#12
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Re: pic: Offseason 8W Tank Drive
You can go even thinner. We're experimenting with 0.050" 2024-T3 this offseason, and it should actually be stronger than .090" 5052-H32. We get this added strength by not drilling lightening holes. Your robot is really only as strong as the smallest cross-sectional area (in tension and compression). So by eliminating lightening holes, the smallest cross-sectional area ends up where the axle holes are. It ends up almost the same weight, but almost twice as strong (ballparking, of course).
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#13
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Re: pic: Offseason 8W Tank Drive
Quote:
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#14
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We use a 0.125" bend radius. It's a bit tighter than aviation requires, but it's good enough for FRC, especially if you bend against the grain. We've reached the limit of our brake, but fortunately it's big enough for a robot.
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#15
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Re: pic: Offseason 8W Tank Drive
Quote:
Just one comment: Your "combined motor stall current" figure seems to be purely determined by motor selection, as it doesn't vary with changes to internal battery resistance or circuit resistance. The current displayed on the "stall conditions" graph, on the other hand, does seem to be calculated from the relevant values. Is there any reason for this? |
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