P =Mn/9,55, .(M = torque in Nm, n = rpm) -> W= Mnt/9,55
or
W = Fd, (F = force in N, d=distance in m) -> P = F*d/t
t = time in s
In all cases above the multiplications should really be integrations because the numbers not being constant
Measuring force by mounting a stringauge should be possible. Preferable on the chassis then on the pushrod. Rotaion can be measured by a ir sensor detecting sections of the wheel