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H-Drive Strafing issues
Hey CD
So we are experiencing traction trouble with our H-Drive chassis. When we attempt to strafe, sometimes the wheel just turns and doesn't catch on the ground. We were doing it on polished cement, so that may be an issue, but what to do you all think, what should we do? |
Re: H-Drive Strafing issues
When we did this in 2015, we found that on carpet, the robot sinks significantly into the carpet for the wheel to catch. You should probably try this out on carpet and see if this is the case. If it is, great! If it still doesn't catch, you may need to lower your center wheel.
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Re: H-Drive Strafing issues
Carpet will most certainly help, what wheel is your strafing drive?
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Re: H-Drive Strafing issues
Is the strafing wheel at a set position? Is there any way you can increase the amount of normal force on that middle wheel? Carpet will almost certainly help. But it probably won't fix the problem.
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Re: H-Drive Strafing issues
The center wheel has no applied force on it, but we do have the majority of our heavy weight items (battery, etc.) toward the center wheel. It is just an Omni wheel with rollers. We should be taking it up to the practice field soon
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Re: H-Drive Strafing issues
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In 2015 our strafe wheel was in a spring powered suspension setup to keep it in contact with the ground. I don't know what your setup looks like, but it's very difficult to keep weight on a fixed center wheel without lifting up other wheels. One of the best methods I've seen is what 148 did in 2014 with their "rocker" module. Perhaps someone from their team can elaborate on it further.
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Re: H-Drive Strafing issues
We tried strafe with H-drive in 2015, using a hard chassis mount. No matter how high or low we put it, it never worked right. Off season, we used a pneumatic cylinder to apply a steady force to it, and it worked first try. Springs can also work, I understand. The force on that wheel should be roughly between 20% and 35% of the weight of your robot, depending on how much strafe force you want and how much forward drive force you're willing to give up while you strafe.
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Re: H-Drive Strafing issues
Is the center wheel rigidly mounted to the frame, or is it articulated? An articulated strafe wheel will do a much better job contacting the ground. One COTS way to do this with VersaFrame would be to use a drop drive module with only one wheel in it (I've never tried this, it just seems like it would work).
If your frame uses VersaBlocks, be sure you don't accidentally have the drop center in the wrong direction. A picture would really help here. |
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When we did our H-drive in 2011 (which worked very well), our center wheel was on a simple suspension system. We put the center wheel on a swing arm and used a gas strut from McMaster Carr to provide the spring and damping. The trick was to size the gas strut to provide 1/5 of the robot's weight to the center wheel.
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