As far as traction I was mostly referring to the width of the wheels. In my mind I was comparing them with wide tank treads or a 3" inch wide natural rubber wheel that we had custom wrapped with 60 durometer natural rubber a couple of years back. I realize that the normal force will not change because the weight of the robot is limited so widening the wheels only spreads out the normal force on a wider surface area. I haven’t really experimented with this so I don’t know what the trade off is. I know that there would be a point of dimenishing return as far as increasing the tread contact area to normal force ratio. I just know what I have observed which is I have seen tank tread and wide wheeled robots winning the pushing battle against the narrower wheeled robots. My imppresion was that the wheels on your frame were of the narrower variety. This is purely subjective. I would be interested in knowing the width of said wheels.
I would also love to do some testing with comparing different traction device and finding out what the return is on increasing the traction surface area realtive to the normal force. If my team does this experiment we will post the results of our findings.
As far as the different gear ratios being traction limited I agree that a slower ratio would definately give you more accurate control. I would love to see the spreadsheet of speeds when you get back home and have a chance to post them.
I agree with you EricH that the four speed in this type of shifting is easier to design then a three speed. I would love to see someone design and build a squential shifting three speed ball shifter I think that would be sweet. If I ever get the time to actually sit down and dore more inventor work I will make one and post the pics. One of the down sides of having a full time job and other demands on my time other than robotics.