Controlled motor board observation

Recently I played with polulu motors : https://www.pololu.com/product/4846
I Use this motor with a Controlled motor board, a USB board and a jack power input board using a 12V 20 Amps power supply.

Before using this motor I setup the PID using the example code at the end of the controlled motor module documentation. During this configuration period I burned some controlled motor board without obvious reason.

So I run an investigation about it, and here is the investigation step and results.

Initial measurement

Before trying to fix anything I need to understand why those boards burn with this particular motor. So I will need to sacrifice some for the good of the community and try to catch why and when it burn.

As I mention previously I have quite a big power supply in my setup so there is no chance that this small motor puts it KO. To be sure I just try to monitor input voltage of the board and input curent of the motor :

The blue line is current at 2A/div
The yellow line is the input voltage 5V/div and the bottom of this line is 12V.

As you can see, there is a voltage spike around 50V. :dizzy_face:
That’s obviously why some boards die. This big spike is due to the motor back EMF, in other words when the motor break the inertia of the reduction and load off the motor are transformed into curent by the motor. If nothing is able to consume this current fast the voltage raise.

So the solution is to put something consuming this current.

Trying to patch it using thing I have

My solution to consume this current is to use a zener diode, so I need to find a 12V zener diode. I noticed that there is something like a diode on smp2dynamixel :
image
So I plug it between my power supply and the power input of the motor and here is the result of the same measurement with the same movement :


As you can see the voltage input spike is now 40V max.
This is not perfect but it works. If I put a zener diode at the input of the board results could be really better.

trying to patch it using specific component.

I buy some 24V 3W zener to compare. I solder it directly into the board :


And here is my results :

As you can see there is no more big overvoltage. The zener just clamp it to 24V (the max voltage allowed on actual Luos boards).

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I think that the zener diode will not work if your motor can drive for and backward. Did you try it ?
A transils (i’m not sur that this is the right english word) diode will solve this issue.
If you remember well, it was our hypothesis at the very beginning…

Here is the big difference with all the observations we have done together, the actual measurement are made before the H bridge (on the power supply side) and before any voltage modification to control the motor. On this side of the H bridge there is no voltage inversion but the current can be driven through the H bridge and cause potential over-voltage and damages on the power supply side.

This zener diode only clamp the voltage input of the motor driver.

Here is an example of position movement using my big motor who burn the driver with a big load and the zener diode before the driver :

As you can see we can go for and backward without any trouble. I think I can make it work for your motor now.