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 Developed here is a computerized method of motor testing. This is a follow on from the NiCad tester that I covered on this site. I learned so much computer programming that I felt able to develop a method of testing motors by computer.

Reading up on motor testing I would need to measure amps' volts rpm and torque. The first two were comparatively easy, I had already done these on the NiCad tester. rpm and torque was a little more difficult.

I wanted the testing to be fully automatic, letting the computer run the motor up to a predetermined speed, amps or volts.

If you have already read my previous article on NiCad testing you will have realized I use the BBC computer, now getting on in years but still able to out perform the PC in adaptability in respect of input and output ports.

One of the ports is the Analogue to Digital converter. This takes a voltage of between 0 to 1.8 volts and converts it to a digital signal that can be processed by the computer program.

To measure volts in excess of 1.8 volts I used a potential divider. By using resistors across the motor a percentage of the total voltage is fed to the computer input. To measure amps you use a low value resistor and measure the volt drop across this.

To measure rpm I converted and old rpm meter that I built some years previously. This had an output of 0 to 1 volt for an input of 0 to 20,000 rpm.

Torque proved to be the hardest problem to solve. This needed a mechanical method to measure the rotational force. After much discussion we hit upon the idea of supporting the motor by a motor plate held by three bearing arranged around the motor mount, this allows the motor to rotate freely. It would rotate but it is stopped by connecting the motor mount to a strain gauge. This stain gauge is connected to some more electronics which in turn are fed into the computer.

One other problems was getting the computer interfaced to a speed control, After finding some programs from some computer magazines I had a program which would work. I started using a electric flight type speed control and getting the computer to mimic the receiver pulses. But I found that is was tricky to control and needed a lot of programming code. So I used a different method. I found that the computer will generate a steam of pulses at any frequency you require, when set this frequency does not change until told to. These pulses are then converted to a voltage fed into a linear op-to isolator then into four F.E.T’s.

I used this method to set the motor at a certain speed measure the amps, volts, rpm and torque then increase the speed of the motor then take the measurements again. I can do this in about 50 steps.

We now have our amps, volts, rpm and toque, all we do now is collect the data and correlate it. Using volts, amps and torque a measure of the motors efficiency can be made. With all this data pretty graphs can be drawn.

On this chart the rpm is ramped up to a preset voltage limit or a preset rpm limit to protect the motor. The load motor has a static load by using a fixed resistor across the motor terminals..

On this chart the voltage is preset to start with then the motor load is increased by changing a variable resistance across the load motor terminals