Its all to do with power and torque, from another forum on this setup.....

Quote..

Well the 1.5Hp induction motor with variable mechanical drive would have (basing torque on 1.2Kw)

2880RPM 0.8kW and 3.94 Nm

1440RPM 0.8Kw and 7.9 Nm

720 RPM 0.8Kw and 15.78Nm

The 1.8kW Servo would have,

3000RPM 1.8kW and 5.7Nm

1500RPM 0.9Kw and 5.7 Nm

750 RPM 0.45Kw and 5.7Nm


As you can see, I would be losing a lot of power in the lower ranges but retaining constant torque, what is needed is both torque AND power.

It can be done but i would need to fit a 3.8kW servo to match the existing motor without losing performance, this is too expensive and they only run to 2500rpm.

I have just been advised that the encoder module CAN use the motor encoder ok, as long as the motor and spindle are at 1:1 ratio.

Will refit the original motor.