I became part owner of a 1980's tennis ball machine last year and used it for it's intended purpose - yes I like tennis! - for a few months.
Then one of the motors stopped working and on taking it apart it seemed like the control circuit for it was not working for some reason. I have ordered a replacement - or at least an equivalent - but at the same time I am dreaming of making my own control system which can be wirelessly controlled by a phone via the arduino. I can cope with the programming and wifi control (famous last words) and I've been googling the electronic side but I thought I'd post the project here for advice as I'm no electronics expert.
The current system is this. Despite me being in UK the machine basically runs on 110VAC (there is a 220 to 110 transformer).This is rectified to DC to drive the three motors. The motors are 90V, 0.3A, 1/3 HP. One is to drive the oscillation and the ball feed, the other two are to drive the rotating wheels which fire the balls out (really fast!). There are two control circuits - one is a basic speed control for the oscillation/feed, the other is slightly more complicated comprising two pots - one for the overall speed of, and another for the relative speed between the two wheels. This controls backspin, topspin and speed.
It's actually quite simple I think and this can be taken care of in software.
So basically I want to control 3 DC Motors. After research I think (tell me if I'm wrong) that I can control these using PWM and N Channel Mosfet transistors - the motors only spin one way. So I'm thinking I can convert the mains feed to 90V DC using a high quality(!) off the shelf part and then do something similar to this tutorial
So my questions are will this work? Is there anything else I need to know and how do I choose the appropriate transistors and diodes if I need them. I was looking at a 100V N channel 1A mosfet (3 pin) - will this be ok or do I need more current in case there is a surge on the motor? I'm quite surprised at how low current the motor is - it looks quite chunky. Also I don't know much about the gate voltage threshold - do I need to watch out for this?
A bit of basic advice with the diode, resistor and need for an opto isolator to protect the arduino would be handy. Plus is PWM going to be OK for this purpose, can I damage the motors, are there any limitations? Do I need to condition or smooth the power or changes in speed or anything?
If anyone can give me any tips I'd be very grateful - you can come and have a go on it if you like when I get it working! It's in West Dorset.