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Re: troubleshooting
I'm with Al on this one - the very first thing you should do is look and listen, then apply your knowledge. Generally speaking, we follow these steps:
1. Look at the status lights. Everything has a status light that tells you what it's doing - if the light isn't doing what you think it should, you can start at that light and work backwards.
2. Start with checking the mechanical contraption involved. Check it for binding, odd noises, high friction, anything that could possibly cause your symptoms. If possible, move the contraption through it's motions manually (with the power turned off) - if you can't do this, be able to explain why (for example, the window motor can't be back-driven by hand due to the built in screw gear). Check for any points where something might get stuck. If you can, move it through by hand (or use a drill to run it) at full speed, something might "jump" out at you, as in Al's example.
3. Try manually powering the mechanism. Take a battery and hook it up directly to the motor leads by hand - does it move as you would expect? Can you measure the current being used to perform the motion? Bonus points: Use something like the Anderson PowerPole series to perform all of your power connections, and create a jig with a PowerPole output on one end, and Anderson quick connect for the battery on the other, and a momentary push button to enable power, allowing you to have fine motor control by hand.
4. Move on to the electronics. Starting as close to the mechanical contraption as possible, start working your way back with the multimeter. Check the voltages the motor is getting. Check the voltages the speed controller has for input and output. Check the PWM signal. As soon as you can say "this is correct at this point", checking anything further "upstream" of that pathway drops to the bottom of your list.
5. Move on to programming. At this point, you should be absolutely confident that the expected signal is not being produced by the digital side car, and all the wiring is correct. Check the slot and channel numbers, check the logic, use print statements, create a small test program that simply turns that mechanism "on" or steps through moving it.
These are basic steps to take to localize the problem to the point where specific experience can help guide you. It can certainly be made more specific (for example, exactly where to stick the multimeter to test a PWM cable) A series of lists like Don's could certainly help... but they also involve no critical thinking and as such don't help build up the problem solving skills teams need. Further, due to the amazingly wide range of contraptions people come up with, it's going to be impossible to list out troubleshooting steps for every possible situation.
The one issue i have with Don's example is that it completely discounts any possible mechanical problem - a "motor not working" may be due to excessive friction stalling it, and not be an electrical problem at all.
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