Using an Non First Microcontroller with Victor 884 Motor Controller

[McGurky]

Maximum: 40 Amps Continuous, No minimum current.

More information can be found here (which to my understanding is the only place 884's are being sold!): http://www.robotmarketplace.com/products/IFI-V884.html

[Ether]

Originally Posted by McGurky

No minimum current.

Where did you get that info from ?

[engunneer]

Since you can turn them on and run them with no load, this implies no minimum current. Keep input voltage around 12. The pwm signal should be pretty low current. Any standard microcontroller output should provide enough.

Thanks for the 5 and 10ms info. I find that quite helpful.

[Ether]

Originally Posted by engunneer

Since you can turn them on and run them with no load, this implies no minimum current.

Ever look at a graph of output current vs input command for an 884 ?

[jamie_1930]

Originally Posted by McGurky

Maximum: 40 Amps Continuous, No minimum current.

More information can be found here (which to my understanding is the only place 884's are being sold!): http://www.robotmarketplace.com/products/IFI-V884.html

When I say max and minimum current I mean for the controlling signal going in to the Victor (the pwm).

[Ether]

Originally Posted by jamie_1930

When I say max and minimum current I mean for the controlling signal going in to the Victor (the pwm).

Yes, there is a minimum current required to operate the opto-isolator in the Vic's input. Don't know off-hand what it is.

There's also a max current above which the opto-isolator can be damaged.

[electroken]

Our test box is using a Microchip PIC12F675 to generate a PWM signal for the motor controller. The box drives Victor 883s, Victor 884s, and Talons well. Our black Jaguars pretend it doesn't exist. The timing we use is 1mS on equals full reverse, 1.5mS on equals neutral, 2mS on equals full forward, with a rep rate of 244 Hz. We have a 270 ohm resistor in series with the PIC output pin to allow it to survive inadvertent shorts to ground.

The Talon manual states an input frequency of 333 Hz, but it seems quite satisfied with 244 Hz, and allowed me to be lazy with the code in the PIC.

[Al Skierkiewicz]

Originally Posted by electroken

Our test box is using a Microchip PIC12F675 to generate a PWM signal for the motor controller. The box drives Victor 883s, Victor 884s, and Talons well. Our black Jaguars pretend it doesn't exist.

The Jaguars use a slightly different PWM scheme than the standard hobby servo. You have to modify the PWM for the Jaguars to react.

[Ether]

Originally Posted by electroken

Our black Jaguars pretend it doesn't exist. ... We have a 270 ohm resistor in series with the PIC output pin to allow it to survive inadvertent shorts to ground.

How much current can that PIC source thru that 270 ohm resistor?

There's a minimum threshold current required to trip the detection circuitry in the motor controller.

The Talon manual states an input frequency of 333 Hz, but it seems quite satisfied with 244 Hz

I believe all three motor controllers will accept periods from 5 ms up to 20 ms. Some will accept periods outside that range. The period does not affect the motor controller's interpretation of the input PWM signal. It is reading the pulse width, not the duty cycle.

Your period of 4 ms (244Hz) is overkill. The fastest period used in the WPILib drivers is 5 ms.

[electroken]

Originally Posted by Ether

How much current can that PIC source thru that 270 ohm resistor?

There's a minimum threshold current required to trip the detection circuitry in the motor controller.

The PIC output is sourcing 10mA to the one Victor 883 I measured. That's a reasonable input current for the optoisolators I'm used to. I'm pretty sure (but not certain) that the 883, 884, and Talon have optoisolators at the PWM input.

[Ether]

Originally Posted by electroken

The PIC output is sourcing 10mA to the one Victor 883 I measured. That's a reasonable input current for the optoisolators I'm used to. I'm pretty sure (but not certain) that the 883, 884, and Talon have optoisolators at the PWM input.

10 ma should be more than adequate. How did you measure that?

Your circuit should work with the Jag. You may not get full output (see Al's post) because the Jags want a wider range on the pulse width, but it should work... Unless, perhaps, the Jag's don't like the 4 ms period. If had a Jag here I'd test it at 4ms.

[electroken]

Originally Posted by Ether

10 ma should be more than adequate. How did you measure that?

Your circuit should work with the Jag. You may not get full output (see Al's post) because the Jags want a wider range on the pulse width, but it should work... Unless, perhaps, the Jag's don't like the 4 ms period. If had a Jag here I'd test it at 4ms.

The input current was derived from the voltage across the 270 ohm resistor, measured with a o'scope.

In all honesty, I didn't spend too much time troubleshooting the Jag. We have plenty of non-legal 883s for our test boxes.

[Ether]

Originally Posted by electroken

The input current was derived from the voltage across the 270 ohm resistor, measured with a o'scope.

That's pretty definitive :-)

Since I don't have a scope, I set the pulse width equal to the period and measure it with a cheap digital multimeter.

[Joe Ross]

Originally Posted by Ether

Your circuit should work with the Jag. You may not get full output (see Al's post) because the Jags want a wider range on the pulse width, but it should work... Unless, perhaps, the Jag's don't like the 4 ms period. If had a Jag here I'd test it at 4ms.

The Jaguar datasheet says 5.0125 ms minimum period.

[Ether]

Originally Posted by Joe Ross

The Jaguar datasheet says 5.0125 ms minimum period.

Well there ya go :-)