pic: It's the MiniCrab!

CD-Media: Photos
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This is a scan of the underbelly of the MiniCrab, an edubot with crab drive capability. It’s hard to tell what’s what, but basically the crab drive is on a caster platform. It uses 2 wheels so it can switch between crab/skid steering. Anyway, I hope to post some video of this baby in action, but I can’t test it till we get our new edu RC :frowning:

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So for those who want to know the specs:
I used 2 of the Hitec servos from last year’s kit bolted to the top of the Wheel Assembly, and one of the edu Motors on the inside of the chassis on the side of the wheel assembly. The fact that the servos are used to pivot the wheels makes it much simpler to map the input angle to the wheels.
It only powers 2 small wheels, which are slightly lower than the 4 casters on the frame so they’re touching the ground more.
I can’t test it til’ we get our new edu RC, since our last one was busted.

Oh, and we’ve dubbed it the “MiniCrab”. I just can’t wait to run this baby!

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I love all the atention crab drive is getting. Expermentation is the best

However I would suggest you mounted both the drave motors semectrical instead of mirrored like they are, it will swerve smother with little or no body rotation and center the wheels more, your motors are fendered so you dont need Arakeen correction

Good Job, keep it up

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Actually they are simmetrical, they just are pivoted a bit in the pic, and it’s kinda hard to tell. Anyway, I think I’ve got the programming ready. Anyone know what kind of math functions we’ve got available? I need Arc (Arc Tangent) or A function for ArcSin (sin -1) would be great. Right now it’s progged to use Arc. Most languages have it built in… not sure about MPLAB.
I’ll post some video of this thing in action once it gets up and running.

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Interesting… I just barricaded myself in my room for the weekend and successfully built a crab drive much like yours, only with 4 wheels and two chain systems… The chains are struggling to turn those wheels, as the rubber does a very good job of preventing turning, so I’m experimenting with different gearing of the chains…

P.S.- I figured out a way to drive these suckers without any extra programming- I was sitting in my room with two edubot controllers, two isaacs, and two joysticks when I realized just hook up one edubot controller to the wheels themselves, and the other one to the turning mechanisms, and presto, insta-crab… This lets me test the bot out to make sure it works before our team actually starts to program it… (we have multiple edukits since we had a robotics class last year)

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