[KenWittlief]

if you are looking at characterising a drive train with a robot moveing straight forwards and backwards, the friction would be pretty low

The constant would be somewhere around 0.1 or less. I have to point out, the equation for kinetic friction is the constant times the normal (usually downward) force.

Lets take the most simple example. A robot with two side by side drive wheels and two nylon skidplates for balance. The main friction will be the skidplates, and the value will be their co-effecient of friction on the suface (carpet) times the part of the weight of the robot that is on the skid plates.

If the coeffecitent is 0.1 and you have a 50Kg robot, and half the weight is on the skid plates, then the kinetic force is 0.1 * 50/2 * 9.8 or ~ 25N

The reason this is the most simple example is this friction will be the same no matter which direction the robot is going - straight, turning, spinning....

A more typical robot might have 4 wheels, using skid steering. In this case the forward and reverse coeffecient of friction might be much lower, say 0.01, but when the robot turns the tires have to slide (skid) sideways, which could have a coeffecient closer to 0.9 or 0.95.

It gets complicated very quickly.

But remember, kinetic friction is not a function of velocity.