Re: New Talon Speed Controller
 

Tom,
I don't remember seeing inductance numbers on most of the motors. Just having a larger motor doesn't mean the inductance is higher. It is more a function of the number of turns of wire in the motor. In the case of the CIM motors, as in most motors, the brush assy actually contacts more than one of the many windings. In the case of the window motor, (trying to remember from several years ago), there are three windings and a three segment commutator. So while running, one of the windings is always shorted out by the brushes. My gut tells me that the window motor has a higher inductance.
Holding the motor shaft on the CIM should not affect linearity but will cause max current all the time. This would be bad for both the motor and the speed controller.
As an explanation, inductance tends to oppose a change in current. So there is a definite length of time for the current to reach maximum when voltage is applied. When the pulse length is short, the current does not have a chance to reach maximum. The designers of the Victor took that into account when they reduced the switching frequency to 150 Hz. The Jag designers on the other hand were looking for fine motor control/linearity and that was accomplished by increasing the switching frequency to 15 kHz. For most of the motor we use, the low throttle values are significantly shorted than the time needed to reach full current. As memory serves, Ether did a simulation a few years back to demonstrate this.

Re: New Talon Speed Controller
 

For what it's worth, we usually linearize our motor controllers based on output velocity and not voltage. This seems to work well.

Re: New Talon Speed Controller
 

Tom, can you elaborate more?

Do you use the encoders in your drivetrain to measure the rate at different PWM outputs, create a polynomial from the resulting values, then use function in between the user input and motor set command?

Do you do it free in the air, or under some type of load?

Re: New Talon Speed Controller
 

Tom,
We use the rotary encoders attached to a shaft in the transmission usually. This helps with autonomous as well.

Re: New Talon Speed Controller
 

Couple comments. The window motor problem seams to only be experienced with positional control under PID. There are 2 parts The locking pins locking and the unit becomes locked up. The other is the heating of the PTC. The window motor test should not experience these problems. We only had problems with the window motor in 2010 while using them for our swerve steering.
Over the years many teams have used a joystick to victor function to change the response. Many times when the drivers get involved the function does not linearize the response. It is set for a " feel" that the drivers like. We have done this with jags too. We Got our Talon last week and will install it tonight for this weekends' competition. Will probably put it on the shooter motor.

Re: New Talon Speed Controller
 

We did it in the air using the encoders. Basically, we wrote an autonomous routine that sets the output PWM from 0 to 1 in steps of 0.01, pausing for a second on each value to achieve steady-state and recording only the last speed measurement.

We then normalized the speeds to [0,1] and plotted the results in Excel (PWM on the Y-axis, measured speed on the X). Playing around with Excel's trendline tool gave us the polynomial that looked the best, and we just took the coefficients and plugged them right back into our code.

Afterwards, we ran through the entire exercise again with the linearization function in place to verify that PWM was now linear with speed.

Re: New Talon Speed Controller
 

Doesn't linearity depend on the load? Running the wheels in the air doesn't give you a realistic scenario. This is a long thread and I did not follow it very closely so I may be missing the point but if the goal is to make joystick drive of the robot more smoothly and more linear with respect to the joystick movement, shouldn't PID control on speed automatically do that? (i.e. the joystick reading specifies the "speed" instead of "power" of the robot).

Re: New Talon Speed Controller
 

To some extent, sure, but the frictional load of the gearboxes and wheels was close enough for our purposes, plus we were too lazy to figure out a way to apply a constant load while keeping the robot stationary. If we needed perfect linearity with the joysticks we would have implemented closed-loop control (as we did with the shooter after first linearizing with this method).

Re: New Talon Speed Controller
 

Neat. Add a file-write to your auton routine, then a file-read on your actual linearization routine and you could do this in a minute or two in the pits and have it load the coefficients automatically when your robot boots up. Labview has a built in polynomial fitting VI that could be used to generate the coefficients.

Did you also attempt to correct for inequalities between the left and right sides of your drivetrain when you did this?

Thanks! I think we'll give that try for Beta.

Re: New Talon Speed Controller
 

This might be of interest:

http://www.chiefdelphi.com/forums/sh...3&postcount=10

Re: New Talon Speed Controller
 

We didn't try; I don't recall that we noticed any significant difference between the sides or the directions of motor rotation, but that would have been a good place to fix it. We just took one set of data and used it for all four side/direction combinations (Tom and I are lazy and like to stop at "good enough", unlike some of the other mentors :)).

Something else I forgot to mention before -- we also tweaked the constant term in the polynomial such that the output is saturated slightly before the input reaches 1, to guarantee that the Victors receive a full-power signal at the extents of the joystick travel even if there's something slightly off mechanically or if there's rounding/precision error in the code.

Did u guys hear that the same people now are making jaguars and victors

Re: New Talon Speed Controller
 

Yes and you would have known that if you had read this thread :)

Re: New Talon Speed Controller
 

Talon, Victor888, Victor884, and Black Jaguar speed vs torque tests at various PWM command levels.

Re: New Talon Speed Controller
 

Nice job on the testing and presenting the data!

Based on these results, the Talon is looking pretty good. Nice linearity, both speed vs. torque for constant demand, and speed vs. demand for constant torque. Like a Jag. Should produce a nice intuitive feel for drivers.