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Unread 01-11-2004, 22:30
Wayne C.'s Avatar Unsung FIRST Hero
Wayne C. Wayne C. is offline
hey- I think we did pretty good?
FRC #0025 (Raider Robotix)
 
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Re: What teams have desgined a 6 wheel drive system?

Quote:
Originally Posted by JVN
Wayne,
First off, I'd like to say I'm a huge fan of your team's machines. You guys are great.

The amazing turning ability of your machines is DEFINITELY linked to your "wide" wheel configuration. It's all physics (you can see it in Chris Hibner's whitepaper, I linked in my previous post).

I disagree with you on one point:
I would argue that your 6WD configuration isn't helping you get more traction. For the most part, surface area isn't a factor in tractive force. (F = mu x N) <-- No "A"

For our applications (rubber on carpet) these are NOT perfect surfaces, and cannot be expressed perfectly with the above equation. They are intertwining meshes. This would help explain getting "more" traction using 6WD.

However, I would argue that you're not getting very much more.
Is there any chance you'd be willing to help with a little experiment?
It is for the mutual sharing of knowledge to benefit the entire communitty.

Wayne, do a straight up pull test with one of your robots. Record some values for it's maximum linear force. THEN, have one of your kids remove the 2 middle wheels from your drive modules (put them on top of the robot somewhere, so the normal force doesn't change). Now try the pull test again.

I hypothesize that your second test will be within 10 lbs of the first test (if not closer).

If you participate in this little experiment, I know I'd be (along with many others) very interested in the results.

Thanks,
John

PS - Your gearbox isn't any more over-powered than the rest of ours! 2 Drills + 2 Chips = 1552W = 2.08 Hp. How you guys manage to gear it so fast, yet still push so hard is beyond me. Up here on 229, we're genuinely convinced you guys are defying physics somehow. Are you sure you don't have 2 extra drills tucked inside that thing somewhere?

John- you're probably right on the physics of it all. One thing that I do notice is that the rubber of the tires is quite soft and wears quickly- possibly just enough to naturally create the surface needed. In any case it works. And when the wheels get some pressure pushing back on them they probably flatten a little and grab better. I'm not sure I want to test it however although all this discussion gave me an idea about recycling some of the old tires we have layiing in the shop.

As for experiments- it IS more fun to just have the machine throw Big Mike around.......

WC
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