Grey Jaguar No Power Out

[Al Skierkiewicz]

Daniel,
The resistor is read the other way indicating it is a 470K (yellow, violet, yellow) while the gold band indicates 5%. In the schematic it is the bias resistor for the current sense amp, R43. This resistor centers the opamp operating voltage so that it varies around a quiescent 3.3v/2. When you try to use your Jag what is the color of the LED telling you?

[dbeckwith]

Originally Posted by Al Skierkiewicz

When you try to use your Jag what is the color of the LED telling you?

The lights read as if the Jag were operating normally: medium flashing green when forward, solid orange when stopped, and medium flashing red when backward.
Actually, while typing that I thought of something! The Jags are supposed to show solid green when fully forward and solid red when fully backward, but even when I push the joystick all the way, it never goes solid. When we tested the voltage coming out of the Jag, we just got negligible voltage and assumed it was nothing, but maybe for some reason the speeds are getting scaled down by 50 or something. I'll try to look into why that would be.
That seems the most likely reason for our trouble now, since I couldn't find anything else wrong with the Jag. The manual said: "To accommodate variation in the timing of the supplied signal, the MDL-BDC has a calibrate feature that sets new values for full-forward, full-reverse, and points in between. Calibration is typically only required in applications where the PWM source has uncertainties due to analog radio links or other variables. Direct digital sources are unlikely to require calibration." This might be one of those "unlikely" times.
So that might be it. Al least it's now the primary suspect, and secondary would be the code.

[jhersh]

Originally Posted by dbeckwith

That seems the most likely reason for our trouble now, since I couldn't find anything else wrong with the Jag. The manual said: "To accommodate variation in the timing of the supplied signal, the MDL-BDC has a calibrate feature that sets new values for full-forward, full-reverse, and points in between. Calibration is typically only required in applications where the PWM source has uncertainties due to analog radio links or other variables. Direct digital sources are unlikely to require calibration." This might be one of those "unlikely" times.
So that might be it. Al least it's now the primary suspect, and secondary would be the code.

If you are using a cRIO with WPILib to control your Jag over PWM, you should not need to calibrate it. They were designed to operate together out of the box. Do make sure that you haven't told WPILib that you are using a Victor instead of a Jaguar, though.

[Al Skierkiewicz]

Daniel,
The lights indicate that you are not going to full throttle in each direction but that is usually the case. If the control fault is not software related, Jag calibration will match your controller to the full output of your joysticks.
If you are only testing the output of the Jag with a voltmeter, remember that the Jag output switching frequency is 15kHz which is way above the frequency limits for many voltmeters. They are also not intended to read PWM, square wave signals. The Victors are 150 Hz which is in the range for most meters but are still not accurate due to the square wave output of motor controllers.

[Ether]

I would think an analog voltmeter on the "DC" setting would do a reasonable job of measuring the effective DC-equivalent voltage of the Jag's PWM output.

Haven't actually tried it though. Anybody got data ?

[Al Skierkiewicz]

Originally Posted by Ether

I would think an analog voltmeter on the "DC" setting would do a reasonable job of measuring the effective DC-equivalent voltage of the Jag's PWM output.

Haven't actually tried it though. Anybody got data ?

You mean a Simpson 360 type meter? At best it might give you average readings for most of the higher throttle values. AT 50% or less, I don't think you could depend on it to give you any meaningful info other than the polarity and presence. The meter movement varies so much from manufacturer to manufacturer that I don't think you can make a blanket statement.

[Ether]

Originally Posted by Al Skierkiewicz

You mean a Simpson 360 type meter?

I mean an analog voltmeter, with coil movement and a needle pointer.

Any cheap $10 one would do, set to read DC.

By "effective DC-equivalent voltage" in this context I mean the following:

- When the Jag is being commanded to output 100% voltage, the meter would read 12V at the Jag's output.

- When the Jag is being commanded to output 50% voltage, the meter would read 6V at the Jag's output.

- When the Jag is being commanded to output 0% voltage, the meter would read 0V at the Jag's output.

- When the Jag is being commanded to output -50% voltage, the meter would read -6V at the Jag's output.

- When the Jag is being commanded to output -100% voltage, the meter would read -12V at the Jag's output.

etc


Haven't actually tried it though. Anybody got data ?

[Mark McLeod]

I tested both an analog and a digital multimeter set to DC and got identical responses in the range of 0-5.5v for zero to full throttle on a jag output.

P.S.
I'm a little slow, but I awoke in the middle of the night to the realization that my measurement mistake was because the battery had been drawn low by the motor load probably coupled with a low battery.
The battery I used was drawn down to 7.5v, so apparently ~2v might get dropped by measuring with these type of multimeters.
I'll check again with a fully charged battery and without a motor load when the real morning comes.

[Ether]

Originally Posted by Mark McLeod

I tested both an analog and a digital multimeter set to DC and got identical responses in the range of 0-5.5v for zero to full throttle on a jag output.

Most interesting. Did you have a motor connected or no ?


Also, at full throttle isn't the Jag's output waveform supposed to be essentially a flat-line 100% 12V ?

[Mark McLeod]

I tested with a stronger battery and it had the same 2v drop through the jag showing on both analog and digital meters.
Jag goes solid green for forward.
I'll put a scope on it later to see what's happening to both the power output and to confirm the PWM input signal is at full.
I took the load off for this second test, so the Jag had nothing connected this time.

The original test was done on a competition robot. I moved the second test to a stand-alone cRIO/Jag (quieter that way...).

[Al Skierkiewicz]

Mark,
I know I am asking a lot, but when you set the test up with motors, can you evaluate with a CIM connected and window motor connected?

[Mark McLeod]

I can add tests with both CIM & window motors.

My scope has a problem so I have to use the one in the robotics lab. I think the one in our lab is a 20MHz model.
I got lazy and brought stuff home where I thought I had a better scope...

Both types (analog/digital) of multimeters do measure Victor full power correctly. I even tested by alternately telling the software it was a Victor/Jaguar just for fun.

[Ether]

Originally Posted by Mark McLeod

Both types (analog/digital) of multimeters do measure Victor full power correctly. I even tested by alternately telling the software it was a Victor/Jaguar just for fun.

Are you saying you don't see the 2V drop with the Victor, but you do still see it with the Jag? If so, could you put the scope on the Jag's PWM input and see what pulse width is being commanded at full throttle ?

[Mark McLeod]

Fixed my scope - broken ground reference wire.

Looks like the PWM signal is correct on both the Victor (smaller range) and Jaguar (larger range) settings.
The solid green/red light on the Jag does indicate full power is being ordered via PWM.

The Jag just reads 2v under at max while the victor reading equals max voltage.

This is all without any load. I created button controls to order full power, in addition to a throttle test.

I'll pick up motors tomorrow for further testing.

[Ether]

Originally Posted by Mark McLeod

Fixed my scope - broken ground wire.

Looks like the PWM signal is correct on both the Victor (smaller range) and Jaguar (larger range) settings.

May I echo back to you what I think I hear you saying, so you can correct any misunderstandings?

- you fixed your scope (yea!)

- you scoped the Jag's input PWM and it had a 2.33ms pulse width at full throttle?

- you scoped the PWM output from the Jag while commanding full throttle and you saw a 100% duty cycle on the output and yet the voltage measured by your meters was 2V lower than the supply???