Re: West Coast Drive, WCD
 

Is 1/16" thick enough for the aluminum frame or should 1/8" thick tubing be used? Would it be a problem to use flanged bearings in such a thin tube?

Re: West Coast Drive, WCD
 

How difficult is it to create a WCD? By the looks of it, it can be easily made from parts from the KoP.

Re: West Coast Drive, WCD
 

To make a WCD you would want to make the frame out of 2x1x1/8" Tubing. Bearing blocks can be made in house with a milling machine and a drill press. Hex shafts and hex bearing can be bought off AndyMark and you can use pretty much any Gearbox that you choose.

Anyone can add to this list.

Re: West Coast Drive, WCD
 

Revival of a long dead post yet I have one question that does not seem to be answered.

The dropped center axle. I can see how that helps with turning since the robot can rock back and forth depending on direction yet I fail to see how only have four of the six tires actually pushing is beneficial if you get in a pushing match?

Thanks in advance

Cheers

Re: West Coast Drive, WCD
 

In the big picture traction (and pushing power) is not dependent on surface area in touch with the ground.

As you add more wheels, each wheel carries less weight, and the traction from that wheel decreases. Adding a million wheels to the robot won't make it super high traction.

If you have 4 wheels, each being pushed into the ground with 30 pounds, you should have the same traction as 6 wheels each being pushed into the ground with 20 pounds.

All that said, the interaction between tread and carpet isn't doesn't work with an ideal model of friction. Increasing surface area in contact with the ground does actually increase traction, but only by a very small amount.

Re: West Coast Drive, WCD
 

The other two wheels may actually be contacting the ground. This depends largely on how much drop you've put into the system, but you may get some extra push out of them.


The other factor is that (in an ideal world) you get the same, or nearly the same force out of four wheels pushing as you would with six. The reason is that the normal force is distributed over fewer points, thus the portion of the normal force on any given point is greater, thus roughly balancing out the loss of two wheels.

Re: West Coast Drive, WCD
 

This statement should carry a huge asterisk.

While it is very true that simplifying friction as F=(mu)*m*g does mean that friction does not depend on the surface area, this is not really the case. In reality, tread digs into the surface of the carpet, so in addition to the (mu)mg friction, you're going to see some additional component that's proportional to surface area. The simple (mu)mg model was true in years like 2009, or would be true if we played on smooth surfaces or with smooth wheels, but unfortunately (or fortunately, in the case of 2009), that's not the case. There's a reason why no team plays with 1/4" wide wheels, and some teams make their wheels 2" wide or wider.

By the way, this question "does surface area effect friction?" used to be an absolutely huge topic of debate in the olden days of CD. I believe Paul Copioli (and many of the greats) have some good posts on the subject. So if you're interested in a more full story, search away.