On the CNC front, I think I've got it worked out in my mind how to put the aluminium frame together. I've purchased some 608 bearings ( it turned out that these are the same size as used in skateboards, so they're pretty cheap ). They have an 8mm ID, and 22mm OD - so they will fit nicely on the face of the frame (25.4mm). The 8mm threaded rod that I'm using for the leadscrew will rotate in the bearing, being driven by the motor.
On the topic of motors, I'm shying away from the stepper motor approach. There's a nice geared motor with encoder available that I think should give more torque, faster rotation and less vibration than a stepper. The question is, can a motor be controlled well enough to "step" a few encoder positions at a time? Time to experiment....
|What to do with old mice...|
With this setup, I did some basic PWM experiments in controlling the motor. Reasonably successful. There's no full H-bridge here, just a single BD682 bipolar transistor driving the motor.... so it's forward only.
Convinced that this is the way to go, I ordered some parts from Futurlec.com.au. A PIC development board with a 16F628A, a L6203 mosfet H bridge, and a few other sundries. It's effectively the setup described in Microchip's servo application note AN696. Oooh, just found another - AN532. Both useful info on concrete implementations of a PID control loop. The gear finally arrived today (ordered 1st Nov). Futurlec are cheap, but you gotta have some patience. Probably better that they didn't arrive until after the semester was over anyway.
|PIC16F628A development board and L6203 H-bridge|