The numbers produced in the >c a b calibration output should be the maximum azimuth and elevation speeds in rad/s, and these are used to scale a 'target' slew speed into a commanded [0,255] speed. The nominal slew speed (in state.cpp's SlewSchedule::step hdot) is 1rad/min, which is intended to be a bit larger than the actual maximum, so that the slewing algorithm will calculate a speed >255 in at least one axis, and scale this down to the maximum 255 in one axis or the other. You should, therefore, see chatter like:
#FollowingSchedule: overspeed by %g: scaled to (%g,%g)
in the log (this comes from activities.cpp).
On reflection, 1rad/min might be too low. Try editing line 92 of state.cpp to change hdot to, say, 1.0. Can you post the lines produced by:
I think the Arduino was happy to be powered from the USB but I guess its safer to have power from the wall.
At present, when the SRT is asked to go to its home position, it does this (with what seems to be) at full speed drawing between 1-3 amps. When it is asked to go to an az alt coordinate, it travels very slowly.