Vex V5 Smart Motors breaks down

Our team uses V5 Smart motors and for some unknown reasons clamp motor breaks down and we broke down 3 motors and 10 ports trying to figure out whats happening .Motor isn’t warm its cool and motors are kinda working when we plug the cable(btw we tried to different cables) motor resists us and it is shown at devices tab but we can’t control the motor. RPM and revolution things at devices tab is also kinda broken.

So, you’ve broken some ports.
I have three questions.

  1. Have you used the same motor in the clamp, every time?
  2. What do you mean by “breaking down”?
  3. Do the same motors work fine on different brains?

1.We used 3 different motors in the clamp(and all of them broke down).
2.It doesn’t works properly(It resists to movements but it doesn’t do anything else)
3.Nope, they do not.

Okay, I have a few more questions to ask.

  1. How much force is the clamp moving with? I’m looking for an estimate here.
  2. Do the motors move in any way when powered?
  3. What force are you making the motors move with in the code?

A picture of the clamp would also be nice to have.

Sorry for my late reply,
1.It shouldn’t be moing more than 1.6(I’m estimating btw Im not sure about this one)
2What do you mean move in?
3Max %100 torque

V5 motors fail in different failure modes. From what you describe, it looks like a shorted H bridge.
Let me reiterate your symptoms, is this correct?

  • The motor is visible in device info
  • The motor ignores commands
  • It’s hard to turn it extrenally

Further questions:

  • Does the port on the motor light up red? Does it blink red when selected in the device info screen?
  • If you try to control it from the device info, does the motor emit any sound? (clicking, high-pitch noise)
  • Does the device info position/rpm update when you try to rotate it externally?
1 Like

Yes exactly what you said it is visible in device info,the motor ignores everything and its hard to turn externally
1 Yes it does,it slowly blinks red
2 No,there are no sound
3 No it doesn’ updates.

And what do you mean by shorted H bridge?

TL;DR: burnt electronics inside the motor in a specific way, which you can’t fix.

Inside the motor, you could identify several subsystems that, if failed, show different symtoms

  • The RS485 transceiver - translates the signals on the wire to the levels acceptable to the MCU. It’s on the forefront and most exposed to damage by static electricity, issues with long wires etc. If it dies, no communication - motor won’t be visible to the brain. The chip (SN65HVD1782) is made to be in such a harsh environment, it should survive 16kV static discharge as well as 30V overvoltage on data pins.
  • Local power supply - produces low voltage for the MCU. If it fails, everything else would fail in one way or another.
  • The MCU (LPC824 I think) - controls everything. If broken, the motor won’t communicate either.
  • The optical encoder - An LED + 2 photo-transistors that sense the rotation of the internal gears.
  • H-bridge driver - A chip sequencing the control of the H-bridge switches that engage the motor.
  • The H-bridge - a quad of FET transistors that actually apply the voltage to the motor. The arrangement allows to control the direction of the motor motion, braking modes and, using pulse-width modulation from the driver chip, the speed and torque of the motor. If one leg burns through, the motor, even unpowered, would behave as in brake mode. The MCU won’t know if the bridge is burnt and would still try to drive the bridge, where the driver chip would prevent overcurrent flowing through the H-bride. Some cases of this lead to the high-pitched sound.

What is interesting, though, is your observation of no updates from the encoder. The motors with dead H-bridge that I have seen always had working encoder.


Thank you, so it is beyond our control but how can we prevent it?

1.6 of what?