Using an Non First Microcontroller with Victor 884 Motor Controller

[jamie_1930]

Hi I am trying to use a Victor 884 motor controller with a non first micro controller. I dont want to use a PWM driver.

Does anyone know any information about the PWM signal used to control the Victors?
Period, Voltage, Current ect...

Thanks

[miker4004]

My understanding is this:
1ms - 2ms pulse width with 1.5ms being center(off) , the 1ms full rev and 2ms being full fwd.
refresh rate or period is 50hz. signal level is a ?. It seem that 5volts was the output but I know that we had issues with some RC type outputs being to weak to drive one.

[Jon Stratis]

There shouldn't be a problem using "something else" to control your motor controllers for testing or non-competition uses. But please check the rules if you're thinking of sticking it on the robot this year!

[Ether]

refresh rate or period is 50hz

this from apalrd:
The current PWM setup in WPIlib (at least in LabVIEW) is a PWM output with a 5s period and a 'period multiplier' of 1,2 or 4. It's enumerated, so 1x, 2x, and 4x correspond to 0,1,2 respectively (I don't think you can add more multipliers if you want).

The Jaguars use a period multiplier of 1, for a 5ms period. The Victors use 2, for a 10ms period. Servos use 4, for a 20ms period, and raw PWM channels can use whatever they want (of the three choices)

[jamie_1930]

I'm using them for the 2013 Robomagellan Competition in San Mateo, CA not a FIRST event so FRC rules don't matter. Thanks for the help, but does anyone know what the minimum and maximum current is for the 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]

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.

[jamie_1930]

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]

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 ?

[Ether]

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]

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]

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]

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]

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]

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]

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]

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]

The Jaguar datasheet says 5.0125 ms minimum period.

Well there ya go :-)

[apalrd]

The Jaguar datasheet says 5.0125 ms minimum period.

I noticed while working with the low-level FPGA interface in LabVIEW that the DIO loop on the FPGA basically cycles every 5.05ms. In this time, it generates a pulse for every PWM that isn't being skipped (because it skips 5.05ms iterations to get 10.1ms or 20.2ms pulse periods) and it shifts out all of the relay outputs at that same interval.

I wondered why it was 5.05 and not 5.00ms, this must be why...

[Ether]

...I wondered why it was 5.05 and not 5.00ms, this must be why...

I'm probably missing something obvious here... why does this explain the 5.05 period?

[apalrd]

The Jaguar spec wants 5.0125ms or greater period, according to Joe.

5ms would be a nice round number of milliseconds to use for timing the DIO loop. It's not 5ms, it's 5.05ms, which is clearly intentional because the timing is determined (in LabVIEW at least) by multiplying/dividing a bunch of things together, one of which is a 5.05 double-precision float constant. Even if it was the nearest round number, since they used a float it would have to round when converting to integer later in the math anyway since the period has to be a whole number of ticks, which itself is a whole number of 40mhz clock cycles.

[Ether]

The Jaguar spec wants 5.0125ms or greater period, according to Joe.

OK. The pronoun "this" was throwing me off. I thought it was referring to something in your preceding paragraph.

Anyway, FWIW I ran a couple of Jags for a couple of days at 5.000 ms period and never noticed a problem.