8WD drivetrain?

[DonRotolo]

Originally Posted by sanddrag

Friction has little do do with surface area in theory. Perhaps in the real life application of FRC is different? Do more wheels equal more traction in FRC or do they just equal more weight? Will a robot with its left and right sides lined with wheels be harder to turn than the same robot with the wheels only at the ends? I'm actually not sure on this one. Simple friction theory says there will be no difference, but there is the tread/surface interaction factor to consider in real life.

The independence of friction to area is valid only for hard surfaces. In cases where there is deformation (such as with carpeting or skyway wheels) then frictional force is dependent upon surface area - this is what you're getting at with your comment about "tread/surface interaction"

In FRC, more wheels means somewhat more traction, but there is a diminishing return, since the Normal force (robot weight) is constant, meaning each contact patch is being pressed into the carpet less forcefully as you add more contact patches.

As you gain too much traction, the power of the motor can become insufficient to cause sliding motion, which is often required to turn an FRC robot. (Note that cars use steerable wheels to help avoid this issue). The hyper-grippy tank tread issue.

The wheels at the furthest points from the center of rotation will need to slide the most. If a robot had all eight wheels clustered around the middle of the robot, it would be easier to turn than if the wheels were clustered in the corners. Having the wheels in-line or offset is immaterial, their distance from the center of rotation is all that matters (as far as placement goes). That is why a tank tread design needs a slight high spot to turn, and why it's generally located in the middle of the side. Having the center of gravity near there helps, too.

"Easy to turn" is so relative, but with careful design, such a bot could be indeed quite nimble.

Don