How Can I aim at the Vision Target Faster but without overshooting?

[Rick TYler]

Just checking in to give Alan a chance to post his testing results...

[Ianuser]

WAIT! Does that mean all of my pwm values centers are 132 and not 127? That makes thigns very different!

[Alan Anderson]

Yes, I verified a year ago that the "neutral" of a factory-calibrated Victor is rather higher than the theoretical 127. I reverified it last week, finding that the yellow light is on from about 124 to 139. I just now changed a bit of code to put the neutral at 131, and it seemed to be running a wee bit smoother than it did before. (I then totally blew away the tuning parameters in the process of trying something new, so I wasn't able to prove that it worked better.)

[Ianuser]

OK, my camera STOPPED WORKING!! Why? I checked my wires over and over again, I recharged the backup battery. The LEDS on the camera turn on when I turn on the robot and the camera moves to a set location, slightly up and right of the center. But it stays there! There is no light for the camera to track, and just yesterday it was working fine! I added nothing to the code, and this is kinda freaking me out. All I did today was mount the camera to the robot and I rewired some stuff. The sensor board for the camera is mounted upside down, power is on, everything worked yesterday. Any suggestions?

[Ken Streeter]

Originally Posted by Alan Anderson

Wow. I've been going from the official IFI documentation which says the Victor deadband is 117-137. I never gave it a second thought. But that would perfectly explain the asymmetric PID response I wrestled with a week ago.

Add our voice of experience to testify that the "true neutral" we have seen on the Victors is at 132, rather than 127. We repeated this test with many Victors from the last three years and have found all of them to have a true neutral of 132 rather than 127. Similarly, the "deadband" range is actually 125 to 138 (an average of ~132) rather than 117-137 as described by IFI's documentation.

For PID control, the difference in a "center point" of 132 vs. 127 makes a huge difference. We have confirmed this with many victors from the last few years. For software control, we are certain that you do NOT want to run the IFI "calibration" procedure, but instead should simply use a center point of 132, with a "deadband" of 6-7 units.

A past thread from Mike Betts which provides a graph of some detailed tests he ran to confirm this is in this post from 2005.

We don't know whether the source of the error (132 vs 127) is due to the PWM signals being generated that way by the RC, or if the problem is in the Victor itself. We don't have an oscilloscope to track down the source of the issue, but our empirical studies are quite conclusive that 132 is the appropriate center point for PID control loops.

--ken

[Ianuser]

Ok, about encoders. They are physical Things? Or is it just code? I think an encoder would suit me very well since I am usnig a forkilft apparatus and I want to stop the forklift at 4 positions. 3 for the different layers of the SPIDER and one for starting position. I think I could write the code for it, but is an encoder an actual thing that I have to put on the motor? Does it come with the kitofparts?

might be a silly question, but I'm running outta time and i would like to know since my metallic sensor doesn't function.

If all else fails I can use a limit switch (I have two I think) for the bottom and top positions, but I dont think i'd be able to use more for the other 2 positions of the forklift since theres no place to but them...maybe...I think encoder would be easier...right? Thanks

[kaszeta]

Originally Posted by Ianuser

Ok, about encoders. They are physical Things?

Physical things (usually little rotary things that generate pulses as they spin). See http://www.kevin.org/frc/encoder/ for a discussion of encoders and FRC code.