Continuous Servo (HSR 1425-CR) overheat and failure

Hi all,

So, I just tried to power on my “photovore” for the first time. Unfortunately one of two servomotors on board overheated and now it does not work (it’s the bottom one in Image 1 attached, along H21,22, and 23 on the Ganvol Breadboard.

I previously tried the circuit setup (see Image 2 attached) and it worked fine.

However, today’s attempt (Image 1) has not been successful.

The Arduino Uno is powered with a 9V AA Alkaline source,right hand side of Image 1, red and black wires (not ideal, but I figured that the AAs would reduce down to 7.2V over time and so could work with the 5V regulator on the Arduino as I hear that the Arduino’s supply stutters between 6 and 7V). The two motors are powered by a 6V Vapex NiMH rechargeable battery, see on the right hand side (black and white).

Additionally, the resistors are 10kOhm each to create voltage dividers for each photoresistor.

A common ground has been provided between the two batteries (at least I hope I did it correctly). I searched the forums for other ways to fry a motor (or rather to avoid doing so!) and I’m convinced I had them covered, but apparently not. Perhaps I have inadvertently wired the circuit differently to how I previously did it. One thing to note is that I have used a different breadboard (same model).

Losing a motor is always a frustrating experience but I would like to learn from this failure so I don’t make this mistake in future.

Many thanks for your help!

Let me know if you require any more information.

Alex

The wiring appears to be correct. You possibly had a bad servomotor. What kind of load did you have on the motors? Another possibility is that the Arduino sent it a signal which caused it to hit an endstop and burn out.

Here’s OP’s pix…

2986fcc97e080485a820646811e48f51013e10d8.gif

d76d4981de438631a6ef1e0854ed6da3997d89c0.gif

Isaac96: The wiring appears to be correct. You possibly had a bad servomotor. What kind of load did you have on the motors? Another possibility is that the Arduino sent it a signal which caused it to hit an endstop and burn out.

An endstop on a continuous rotation servo?

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!
Alex

Also how do I include pictures in the body of text, the insert an image button asks for a URL.

https://forum.arduino.cc/index.php?topic=364156.0