4 Wheel Drive Too Much Traction

[Taylor]

Originally Posted by JesseK

In no particular order, you could do one or more of the following:[list=1][*]Make a 'lessons learned' so your team never designs a wheel base that is longer than it is wide

Can you please explain your thought on this? It's common practice for teams to have robots longer than they are wide - 48 had a (in)famously long robot last year, and they were multiple regional winners. I agree that wider bases have less scrub, but never longer than wide?

[JesseK]

Originally Posted by Taylor

Can you please explain your thought on this? It's common practice for teams to have robots longer than they are wide - 48 had a (in)famously long robot last year, and they were multiple regional winners. I agree that wider bases have less scrub, but never longer than wide?

If the team doesn't understand the fundamentals of the forces of scrub in a skid steer drive train, then it's probably best they steer clear of longer wheel bases (w/o dropped centers) until they do. Team 25 won Einstein last year, and they typically have the same setup (8WD, all touching the ground, all long configurations from year to year). The difference is, they understand what works, what doesn't, and why.

[Racer26]

I think we're going to see alot of robots with this approximate design (chute with indexer, dropping into a linear shooter at a ~30deg angle).

This particular robot seems much heavier than it needs to be though... Why two gearboxes to a side unless you were putting mecanums on it? The whole chassis appears to be steel tube and bent sheet steel, which, might be more viable this year than ever before, with the reduced perimeter, but still.

[Lil' Lavery]

Originally Posted by Taylor

Can you please explain your thought on this? It's common practice for teams to have robots longer than they are wide - 48 had a (in)famously long robot last year, and they were multiple regional winners. I agree that wider bases have less scrub, but never longer than wide?

Wheel base, not robot/frame. I believe 48 had a dropped center, so their wheel base was still wider than it was long.

[Ether]

Originally Posted by Taylor

I agree that wider bases have less scrub, but never longer than wide?

Yes, under certain conditions wheelbase can be longer than trackwidth

For the robot pictured, if you make the following simplifying assumptions:

1) all four wheels identical and driven independently with the same torque

2) coefficient of friction of the wheels the same in X and Y directions

3) Center of Mass lies on the the longitudinal axis, somewhere aft of the geometric center of the 4 wheels

... then the analysis becomes straightforward:

http://www.chiefdelphi.com/forums/sh...ad.php?t=99089


JesseK's advice is good though:

If the team doesn't understand the fundamentals of the forces of scrub in a skid steer drive train, then it's probably best they steer clear of longer wheel bases