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I am trying to control the spindle-speed of a small lathe and would appreciate any suggestions or advice. Have any of you done something similar?
The lathe is very small though it is adequate for what I machine - steam engines. I have replaced the motor with an ex-kitchen-processor motor, which is brushed,and series-wound for 240-volts AC. The speed control is of triac-type and is quite gutless at low speeds. Hence this project ...
My 'new' motor drive comprises 60 or 70-volts DC, released into the motor by a MOSFET transistor in PWM bursts. For feedback, I have a holey disc on the motor-shaft, viewed by an opto-interrupter. The pulses are cleaned-up and integrated by capacitor to a speed-dependent voltage.
Having just acquired an Arduino Uno, it seemed like a good project to play with. Basically, the Arduino compares the feedback-voltage with a set-speed potentiometer and outputs PWM to the MOSFET. Hopefully, when a load is applied at low-speed, the PWM bursts will be wider to apply more power. Hopefully ...
I have been trying PID, based on a method by Tim Hirzel, but cannot achieve a really smooth control throughout the speed-range - probably I am missing something small-but-very-significant.
Can any of you help, please?
Geoff Thailand
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