I decided the only way to solve the problem was to monitor the drill speed, detect when it was about to stall and automatically back off until it speeded up again. To this end I started investigating ways to monitor the speed. Off the top of my head I came up with four alternatives :-
- Monitor the current, because it increases as the speed reduces.
- Turn it off occasionally and monitor the generated voltage.
- Measure the frequency of the commutation noise.
- Put a black spot on the chuck and use a reflective opto detector to count shaft revolutions.
So it looks like the drill is ten times more powerful than I thought. The only problem is that it could do with some speed control as it goes a bit fast for plastic when running from 12V.
So now my next task is to tame it with PWM and monitor the speed somehow. I also want to control the vacuum cleaner with software as I am too lazy to switch it on and off.