TL;DR: There are a few possible ways to kill a motor but I don’t know which one is the culprit. There are testing methods I’ve come up with but I don’t know if they’re any good. Thank you so much anyway!
Okay so I have listed the possible modes of failure for the continuous servomotor, I have also listed possible ways to test if the modes of failure are likely/actually possible in this case:
1. Stall Torque (therefore stall current) sustained for too long.
During the early stages of design I created a mass budget and did rudimentary motor sizing calculations. I have attached two images (Images 3 and 4) which show my calculations. The mass of the whole photovore is at most 0.8kg (I need to weigh it to get the actual mass still), each motor’s efficiency is assumed to be 50%, the radius of the wheel is 33.4mm (0.0334m), and the rolling resistance coefficient is assumed to be 0.1 (pretty much as velocity is so low).
Now, according to the motor’s specification the stall torque is rated at 3.1kgcm (or 0.304 Nm in proper SI units). My calculations say that a minimum of 0.026 Nm/motor are required to overcome rolling resistance. The stall current is supposedly around 500 mA, 6V with 0.5A gives 3W of heat which could get hot. Have I made some fundamental errors in my calculations or assumptions about motors?
Test: Test the motors without any external loading (i.e. the rolling resistance and inertial loading from the robot). I do have a third motor which is brand new.
2. Bad Motor
I tested both motors with the same sort of setup previously and they worked fine. I don’t recall mistreating the motor in any way between testing it and mounting it onto the photovore. Perhaps the current surge when turning the motor was enough to harm it? But then agian, the second one wasn’t harmed. However, I did use a different breadboard which takes me onto No.3.
Test: Not sure how to test this as it’s “dead” now. Perhaps it’s still miraculously alive…
3. Low-quality breadboard?
So I’m using the same model of breadboard that came with the Arduino Starter Kit (or a very convincing clone). However I have noticed that it is sometimes difficult to insert the electrical components because the power lines in the breadboard aren’t always straight or aligned with the holes. Between the previous tests and the robot build I have switched to another Ganvol breadboard which is apparently the same model as the other one. Perhaps there is a defect in the second one which prevented the second motor from completing its circuit properly.
Test: Create some simple circuits to test the lines (thinking basic LEDs with some resistors).
4. Bad wiring
I’m using a combination of Elegoos and the wires which came with the starter kit, perhaps fatigue failure or previous overheating has caused one of the connections to break (the only one I can think of which would cause such a catastrophic failure is the grounding wire).
Test: Make some circuits with the suspect wires.
5. Bad signal
So just to be clear this is a continuous servo so no end stops (I hope!). But it raises a good question about the quality of my coding abilities. The code is exactly the same as in the previous tests but perhaps the code was somehow overloading the motors? Is there a possibility of that?
Test: Perhaps I could post my code and others could scrutinize it? (does that fall under the scope of this forum?)
On another note: Is there a way to include two common ground wires in parallel? Gives the circuit a bit of redundancy. Also how do I include pictures in the body of text, the insert an image button asks for a URL.
Thanks in advance!