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Originally Posted by BrendanB
This is extremely cool! How is the drive system when it is a competition weight? IE 150lbs total with bumpers and a battery?
Very cool design overall to give yourself the lateral movement.
EDIT: Could you post some more pictures of the wheel pod? Is that a custom gearbox or a CIM-sim from AM?
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We haven't tested this one with full weight yet, but we will. The previous prototype from the video worked well at close to full weight. That will be interesting to see, actually. The gearing is conservatively slow on the 9th wheel, so my guess is that it will strafe pretty similarly at full weight.
We should be able to eventually take some closeups of the actual wheel setup, but for now I can provide some CAD shots of the gearbox module. By the way, I designed the 9th wheel piece, but one of our students can take credit for the rest of the CAD design.
This is a custom 3 stage box that is basically a Toughbox plus a CIM-Sim. This is not the newest version (it's on a USB drive at school), so some minor differences exist. In particular, I swapped in the 60T gear from the CIM-Sim when AndyMark released that product. I LOVE that gear. The actual gearing is something like 60:15 / 50:14 / 50:16.
The thing is a puzzle to put together. I probably got carried away a bit in my efforts to make it as small as possible; notice the two holes on top of the gearbox for holding the top pivot brackets on - it is necessary to put the screws in there first, then assemble the rest of the gearbox, then tighten them last by poking the allen wrench between gears. It's a good thing the side plates were bent perfectly at the shop, because they need to be to fit together. Maybe for the next version we can think of something a little easier to make.
We thought about pushing the 9th wheel straight down instead of pivoting it off the back rail/bumper, but we never came up with a clean way to do that without adding a bunch of structure and weight in the back.
Quote:
Originally Posted by AdamHeard
I figured this would be necessary for nice performance, about how much power are you applying to counteract the drift?
Are you doing it on some guesstimated value, or using a gyro to hold a heading?
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We're using both a fudge factor and a gyro. Maybe Josh will comment more on his programming. The programming presents some interesting challenges, to be sure.
It takes more power from the straight facing wheels than I would have expected. On last summer's 7 wheel version, the straight omni's couldn't keep up with the sideways wheel if we had it in low gear. In the new one, the 9th wheel is geared slower and the one speed drive is faster than the low gear we used last summer, so I think the 9th wheel's speed limits our strafing speed now. Josh, feel free to provide better info on that.
Picking the gear ratio for the 9th wheel is an interesting problem. Ideally, it would be nice if the 9th wheel accelerated the robot around in a circle at the same rate that the main drive's omnis accelerate into a turn in the other direction. That would reduce the amount of correcting needed based on the gyro feedback.