The Redpoint uses a brushed DC motor. They all drift. Since the controller is open-loop - meaning there is no feedback from the platter (using a tachometer type device to send corrections to the controller), the speed will invariably drift due to stylus drag, thermal changes in the controller components and the motor itself.
I've been down this road, and have tried various open and closed-loop DC and AC controllers (Mark Kelly designs), as well as offerings from Origin Live and Walker. All are compromises - brushed DC motors are very difficult to control, and AC motors introduce the issue of cogging and vibration transmission.
Your best bet would be to implement a different controller architecture altogether. Talk to Thom at Galibier Design. His latest controller is a brushless, electronically commutated design, with hall-effect sensors around the motor spindle itself sending instantaneous feedback to the controller electronics. It is one of the most significant upgrades I've ever made to my Galibier, and Thom should be able to help you out.
I've been down this road, and have tried various open and closed-loop DC and AC controllers (Mark Kelly designs), as well as offerings from Origin Live and Walker. All are compromises - brushed DC motors are very difficult to control, and AC motors introduce the issue of cogging and vibration transmission.
Your best bet would be to implement a different controller architecture altogether. Talk to Thom at Galibier Design. His latest controller is a brushless, electronically commutated design, with hall-effect sensors around the motor spindle itself sending instantaneous feedback to the controller electronics. It is one of the most significant upgrades I've ever made to my Galibier, and Thom should be able to help you out.