FIXED (Was VEX IQ Motor Timing Bug and Temporary Fix)


Synopsis: Inconsistent motor travel/timing affecting “spin”, “spin to”, “drive” and “turn”  blocks

Details:  Version 1.6.2 VEX IQ motor firmware  has a bug that affects the “spin” and “spin to” blocks:

These blocks will move a certain number of degrees either relative to the current position or absolutely from the motor’s zero position.  Each of these blocks will not continue to the next block beneath it until the motor reaches its position and notifies the VEX IQ brain that it is done.  


The bug in version 1.6.2 of the motor firmware will unreliably report when it is done causing the Modkit code in the brain to wait until a “timeout” is reached to move to the next block.  The timeout defaults to two seconds but can be set by the user.  There is a related bug in version 1.6.2 of the motor firmware that causes the motor not to reach its desired position or to take considerable time to get there under load.

Symptoms:  This bug manifests as inconsistent timing between two motors programmed in different tabs but with similar commands such as:

While this is not a recommended approach to coordinating motors (since there is actually no coordination between the above two motors) many users still program drivetrains in this way.  The bug causes these motors to seemingly behave randomly since either motor may not report that it is done and cause a timeout before the next block is executed.  When this happens in one motor and not the next there will be a two second delay between the next motor move on the first motor compared to the second.


This bug also manifests as unexpected waits between drivetrain moves (using the Modkit for VEX Drivetrain tab) and the related bug manifests as incomplete or “skipped” moves.


Workaround/Fix:  VEX is aware of this issue and will update the official firmware in the near future.  In the meantime we are making available a pre-release of this firmware for affected users.  Please follow the following steps:

  1. Download the pre-release motor firmware: 228-2560-656-REV1_6_2.txt 

  2. If you haven’t done so already please download the VEX IQ Firmware update tool here:

  3. Launch the VEX IQ Firmware update tool

  4. Plug in the Brain with the affected motors (make sure Brain is powered)

  5. Click “Update from File -> All Motors”

  6. Chose the file downloaded in step 1.
Updated 27 months ago