My Prop's slow degradation and death
tosjduenfs
Posts: 37
I've been working on a program that will have a telescope track an object. I breadboarded a prop had one of the motors and encoders hooked up an adc and accelerometer all hooked up and working well and tracking. I installed the second motor and edited the code for the second motor. I tried running both motors at once, I had all of the PID, pwm motor speed, and encoder values being sent to the serial terminal and some of them were showing strange values like I had used an integer in a floating point calculation but the motors were running and trying to track but could not because of the bizarre numbers. I switched back to running just one motor and the single motor code. It worked but the prop would occasionally crash and stop sending values to serial terminal and stop controlling the motor. The more I reset the prop and reloaded the code the more it crashed eventually it did not work at all, I tried reloading other known working programs and nothing. Hello World works but I can't get any of my other programs working. Supply voltage is a steady 3.3v. Any idea what happened here? I checked all my connections and I can't see anything wrong. The only thing I changed that started this was installing the second motor and I checked the connections about 10 times when I started having issues. The motor controller works fine and the motor works fine as well.
Thanks
Mike
Thanks
Mike
Comments
It's like being back in the 1920s when you could sidle up and listen to the "wireless" but you couldn't see anything, or click on anything to find out more, you just had to imagine the scene in your head. Nowadays there is this interweb thingy I heard people are using, I believe it's fairly easy to post code and diagrams and even include a photo or two. Imagine that, being able to see it instead of imagining it!
However two things caught my attention despite the lack of real information, "BREADBOARD" and "MOTORS". All too often the Prop is connected without all it's grounds grounded and all too often the motor ground current runs through the Prop's grounds. This makes the Prop very sick, almost to the point of dying, in fact I thought the thread title was a death notice for the Prop itself as a product, not as your breadboard. Analysis of common failures show that this grounding problem with high currents can zap the Prop's PLL. You can confirm this by running without the PLL or just using RC fast if possible, at least for a blinky program. The other thing that was brought up are "spikes" on the supply line but then I can only imagine at this point how it's hooked up.
loose connection, software bug....
Never share high current ground or power wires with logic circuitry, logic chips need clean supplies, and clean means free of glitches (which
a multimeter has no hope whatsoever of detecting). Decoupling is essential for all logic chips.
I use an H11L1M optoisolator :
Turn on and turn off speeds around 1 microsecond
Schmitt trigger output with open collector .16 V withstand and 16 mA drive
Emitter required input current only 1.6 mA
-Phil
I'm doing PWM on a motor with a FET. I'm thinking about separate power supplies. Is there anything else I should add besides connecting grounds like filter capacitors or something?
Things are working ok off the same supply now.
-Phil
If you think about it adding capacitor across the FET source/drain leads to large current spikes when it turns on and the cap dumps its
charge through the FET. A cap here can be useful as part of a snubber network I think, but I wouldn't add one without careful consideration
of what value is appropriate for the FET and supply voltage.