A suggestion for the V5 11w rev10 Smart Motor problem

I would like to suggest that Vex publish the wiring schematic for the 11w v5 Smart Motor. Nearly all Vex teams are affected by the faulty Rev10 circuit board. our club had our first match last saturday and 1 team had 3 motors burn out. I understand that there is a band aid solution of limiting the max wattage to 11w but I am skeptical of the long term efficacy of this solution. If Vex published the wiring schematic it is possible that some students or coaches could find the issue faster than just the Vex technical support team. Perhaps a better firmware solution could be found faster. My club is burning motors at an unsustainable rate and new motors are only available via backorder.

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One of the symptoms people have reported and VEX engineering has been able to verify is fast control variations can be a problem.

For example going from full forward to full reverse, with the current flow, the diode can’t manage that. It’s not a video game, these robots have weight and momentum. See Star Trek episodes “Ye cannae change laws of physics, Jim” - spoken by Scotty.

I’d like to forestall a new round of pitchforks / torches / boiling oil of unhappiness towards VEX engineering.

  1. Teach Kyle to have a light touch on the controls.
  2. Write some code that when you go from 100% to -100% that it does it in steps (100-75-50-25-0- (-25) (-50) (-75) (-100) Not hard to program in blocks, Python, Pros, etc. I’ll guess within moments of this post you’ll have examples to use.
  3. Maybe have a strategy / design meeting that you talk about why your strategy needs do to this and why the design won’t support it.

This is not a long term fix, but should limit the number of robots that are injured.


We understand what the issue is, Levi explained that here.

and are testing potential firmware fixes, the short term solution is to keep motor voltage below 11V


Will the firmware update fix motors that are already broken? Or is there a plan to replace them?

No. According to @levipope the damage is physical:

However, it is not clear if the damage is limited to just the diode or other components on the board are damaged too.

My best guess is that Rev 10 has cheaper/underspecced diode and that eventually all those motors will fail as the motor brushes degrade and generate higher voltage transients, short of aggressive firmware update that limits both the max voltage and max current by something like 20-25%.

They will need to replace them with another board revision, that has electronic components specced to survive larger voltage spikes.

As much as I sympathize with OP argument, I just don’t believe vex would open up schematics or let mentors replace diodes with higher specced ones before they fail. If I had any rev10 motors I would RMA them all right now before vex runs out of replacement options.


That’s assuming the replacement would be a non-rev10 motor. There’s a definite possibility for “shuffling deck chairs on the Titanic”


For my own education, using voltage control, what are the max voltages you can send the motor using vexcode blocks, python, robotmesh, c, etc???

12v is the max enforced by vexos/motor firmware. They’re all using basically the same SDK so 12v should be the max achievable across all of them.

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Ok. So if you use speed control, go from 100% forward to 100% reverse, what voltage does the motor see?

“Speed control” is a bit vague. If you mean the motor’s built in Velocity Control, then the user doesn’t directly control the voltage. Instead, the motor’s build in PID loop controls the voltage in order to hit the commanded velocity. How much voltage it uses to do this depends on load and what the commanded velocity actually is. At freespin at full rated velocity, the motor probably won’t be quite at 12v, as in my experience running motors at 12v directly causes them to freespin somewhere between 10% and 20% faster than rated velocity. If you introduce a slight load going both directions, the motor would probably see +12V to -12V though.

In order to set the voltage of the motor more directly, you’ll have to set the motor to a voltage value using the respective functions in your programming environment of choice. For example, in VexCode Python, you would write motor_1.spin(FORWARD, 12.0, VOLT).


Guess my point is that it doesn’t seem to affect those using velocity commands… or did I forget some of the posts in the thread?

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