PDA

View Full Version : Speed Controller Data


viewtyjoe
01-30-2006, 03:09 PM
In order to control/limit the acceleration on our drivetrain, as well as seeing if we'll need some sort of PID control on our shooter, we took data samples to see what sort of voltage the Victors would give at each input value. What I'm posting here is the raw output of our data, duplicates removed. If I ever get around to it, I'll try and get a graph up showing the curves for the output voltages.
All data was gathered using the '06 Victors and a CIM motor under load attached to a gearbox (3 meshes).

Hope someone can use this data for their own purposes.

Danny Diaz
01-30-2006, 04:45 PM
If I ever get around to it, I'll try and get a graph up showing the curves for the output voltages. Attached is the same Excel spreadsheet with the voltage plotted (plot attached as well, in case you don't have Excel - y-axis centered at PWM value 127) - using the chart wizard it takes about 24 seconds... :D Awesome work, though! We had always heard the voltage was non-linear, just never set out to prove it...

-Danny

Joe Ross
01-30-2006, 08:13 PM
The following thread goes into a lot about why the graph looks like that. http://www.chiefdelphi.com/forums/showthread.php?t=31903&highlight=victor+non-linear

The following graph shows the response of the speed controller when connected to a purely resistive load (and is linked towards the end of the above thread). http://www.saratogarobotics.com/php-nuke/modules.php?name=Content&pa=showpage&pid=1

viewtyjoe
02-02-2006, 03:54 PM
A couple of nights ago, we were discussing why the output comes out like that, and the only conclusion we've come up with that makes sense is that if we graphed the power, it would be linear. Has anyone taken a look at it that way? I didn't see it in the discussion, so I'm throwing it out to see what everyone else thinks.

Al Skierkiewicz
02-02-2006, 04:05 PM
The data you logged is representative of the DC value of the output but not representative of the power delivered to the motor. The output of the speed controller is itself a PWM signal and only is a steady state battery voltage at PWM values of 0 or 255 when the speed controller is calibrated. All other times it is a pulsed DC output of varying width. The small voltage variations you see just outside the deadband are due to the very short pulses interacting with the complex impedance of the motor. The graphs linked by Joe Ross show current delivered to the motor which is more representative of the actual response of the motor.