VICTOR RESPONSE DELAY? - AGAIN

[yoyodyne]

There are a lot of posts on this topic but I have not found a good measurement of the time from when a new PWM value is set in the USER processor until the VICTOR output reflects that change. The closest post I have seen was from Mike Bortfeldt in 2006 that it takes about 50ms for the VICTOR to respond for PWM outputs 1-12. We are using outputs 1 and 2 right now for the right and left CIM drive motors and it seems like it takes over 200ms for the actual motors to respond to a user processor PWM change. We only have indirect evidence in the form of the plots attached which show our failed attempt to get the robot to rotate to a new heading. There are control system enhancements that need to be made to the P and D gains and probably also to remove the clipping at a PWM magnitude of 50 but it also looks like from a system perspective the motors don't actually respond to the control system changes for about 250ms.

The attached plots show the PWM left and right outputs (before the left side is inverted) and the Gyro reading. This is for our two wheel drive practice bot on a tile floor so the as expected it takes a while to stop it after it gets going and we can fix the code in that area but it also looks after the motor rotation is reversed to slow/stop the robot rotation the angular rate does not even start to change for about 250ms. I would think that the angular rate would start to change very quickly after the motor voltage changes and that makes me think that a lot of the 250ms delay is in the control system. Either in communications between the user and master processor or between the PWM output and the VICTOR output. All I have is this system level data and will not have access to the practice bot until our next Fix-It-Window next Tues. The VICTORS are in coast mode but now that I think of it I'm not sure if they are 883 or 884 - this platform has been around for a few years.

I think the first thing we will try is to move the drive motors to PWM 15 and 16 (camera is on 13 and 14) and we are using the new timer3 PWM code so the outputs should be solid.

From your experiences would you say that this delay is really due to the control system or just physics?

Thanks,

Greg