Quote:
|
Originally Posted by Wayne C.
John-
Although it seems to make sense and would make design interesting we have never moved any of the center wheels from our machines out of line from the rest. We want the deep grab traction for the motors and pushing power. And I think any who play us will agree that the machines are speedy and maneuverable. We use two joystick tank drive on the machines and they can spin in place with no problem at all.
Perhaps the answer to this is the fact that we have such wide wheels (custom made from Skyway wheels) and a gearbox with great power. We are probably horsing the machine around so much when we turn that the coefficient of friction on the center wheel is negligible. We usually give the machines the "Big Mike" test- if they can shove him away they are strong enough. If we lowered the center wheel we negate the traction we are looking for back to 4 wheel drive.
WC
|
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?