failed sending motor x drive level

Submitted by lynch0505@chart... on Mon, 03/08/2021 - 22:20

Forums:

Hello,

I have a two-ThunderBorg robot up and running and I occasionally get these error messages:

Failed reading the drive fault state for motor #1!
Failed reading the drive fault state for motor #2!
Failed sending motor 1 drive level!
Failed sending motor 2 drive level!

They seem to occur after some spirited starts-and-stops as you might find when you are testing a new robot.

The LEDs turn green-then-blue and the robot halts. After a moment, the robot resumes operation.

Any thoughts on where I can look to find the root cause?

Regards,
Brian

piborg's picture

piborg

Thu, 03/11/2021 - 10:29

Based on your description it sounds like the ThunderBorgs may be struggling to get enough current to power the 5V regulators when the motors are working hard. When this happens the voltage on the 5V line drops, causing the on-board logic to reset.

When the boards reset three things happen:

  1. The LED is cycled to show the board is starting
  2. Power to the motor outputs is turned off
  3. While it is starting it does not respond to any commands, causing the error messages.

This usually occurs because the motors are able to draw more current than the batteries can keep up with. When this occurs anything else connected to the batteries struggle to get the current they are trying to draw.

There are several possible solutions:

  1. A battery that can deliver higher bursts of current might be able to handle the motor output and everything else, preventing the problem
  2. Capping the motor output to less than 100% will usually leave some head-room for everything else to draw power (at the expense of some speed) - 95% has worked well for us in the past
  3. Using a higher voltage battery will allow you to reduce the motor output percentage and still get the same power output to the motor
  4. Less desirable - you may be able to switch to less power hungry motors which are within the capability of the battery
  5. The script could be adjusted to reduce sudden jumps in power output - these spikes are usually when the problem will occur

lynch0505@chart...

Sun, 03/14/2021 - 20:08

Thank you for the comments. For my case your suggestion (5) to limit the rate worked the best for me. I have also reduced to a single ThunderBorg for the time being. This will help reduce the surge too, I believe.

Regards,
Brian

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