New spindle idea for my machine - DC 1HP

[HiltonSteve]

Been playing with the Spindle2 board today and have interfaced it with my controller, got it all working but I have got a little bit of discrepancy with the volts coming out of it and the programmed spindle speed.

Configured my spare A axis to output to the Spindle2 board and ended up with my spindle motor tuning set at 1000 steps per unit and velocity at 130, tried tweaking above and below these but these settings seemed to give me the best output voltages from the Spindle2.

Set the max speed in mach (pulley selection) to 6500.

I now get 10.00V exactly from the Spindle2 board when I program the speed in mach to S6500, but when I set it to half (S3250) I get 5.7V. Tried lots of different values in the motor tuning settings which do change what voltages you get but 5.7V is the lowest I can get it to when the speed is programmed at 3250, I would like to see it closer to 5V but can not see any other settings which influence it. Have i missed something??