4" vs. 6" + 8" Diameter Wheels

[Ether]

Originally Posted by James Critchley

It is an increase in total mass of the robot or mass distribution of the wheels that contributes to any performance degradation.

YMMV, but I think it's clearer to explain it the following way:

The equation for vehicle acceleration in the PDF file attached to this post can be re-arranged as follows:

a = (tau/r) / (I/r² + (1/4)*(M_v+4*M_w))

or, substituting K*M_w for I/r²

a = (tau/r) / (K*M_w + (1/4)*(M_v+4*M_w))


Since tau/r remains unchanged when you change the wheel radius (if you change the gearing accordingly), what remains is

a) the total vehicle mass M_v+4*M_w, and

b) the mass of the wheel times the mass distribution factor of the wheel (K*M_w)

Since neither (a) nor (b) is likely to remain the same when you change wheel size, there will be a change in vehicle acceleration.

The equation also gives a way to estimate the change.