BernardMarx:
I am more than happy to test the motors to destruction so that my final product works well.
Any pointers as to how to get the most from doing so?
Obviously if you connect (say) 30 volts to a motor and it goes "poof" you don't learn very much so you have to start from the other end - with low voltages.
I think I would write a sketch that puts a steady current through the motor using the L293 - i.e. current flowing but the motor not moving. Since the 3.3v supply seems not to release the smoke I would try that first and see (a) what voltage is across the motor coil (b) what voltage is across the L293 and (c) what current is flowing in the motor coil. It would also be useful to see if the motor is getting hot.
Then I think I would try the same arrangement with 5volts.
The critical information is the voltage across the motor coil and the current in the motor coil.
If the motor is not showing any distress - i.e. getting too hot - I would perhaps increase the voltage to 6v, 7v etc. Power from a bank of AA alkaline or NiMh batteries would be a simple way to increase the voltage in steps.
I don't know whether it applies to those small motors but bigger stepper motors seem to work normally at a temperature which is just about uncomfortable to touch.
I'm interested to learn the results.
...R