measuring load on a motor

[martinn]

If I wanted to measure how much force was being used by a drill going into a piece of wood, assuming a known force on the drill (e.g., a 1 kg weight) and a known drill bit diameter, fluting, a fully charged battery, etc, would it be possible/feasible to measure the current load on the motor several times a second and record the data using a PicAxe?

Martin

 

[atharvai]

figure out some way of measuring the current supplied to the drill. this should be inversly proportional to the load. look up on magnetism and eddycurrents on a uni website or somewhere there's a formula for the voltage/ current applied and torque

 

[moxhamj]

As a rough estimate, force is going to be propoertional to watts going into the motor, which is amps times volts. Measuring volts is easy using a voltage divider. Measuring amps is a bit more tricky - take a low value known resistance (eg 0.1 ohms) and measure the volts across it using an op amp differential amplifier.

In practice you can use any old bit of wire as the current sense resistor - just need a power supply capable of producing varying volts for the calibration. Run (say) 10V into a 10 ohm resistor, then through a DMM on the 10A range, then through the current sense wire. Set it all up for 1A exactly. Then measure the volts on the sense wire. Or even better, measure the volts after going through the differential amplifier. Now it is calibrated for 1A.

Both volts and amps should go through low pass filters of maybe 0.1Hz time constant to smooth out any fluctuations.