Victor Vs Jaguar

[kapolavery]

Kapolavery,

I've noticed you around CD a lot lately. You ask a lot of really good questions. Although some of these could actually be answered by doing a search, the honesty in which you ask and the detail you give in what you are looking for is quite refreshing. KEEP IT UP!!! (Aloha, and welcome to CD).

thanks Mr Bill
well i am still on spring break (which is why i have all this time to post) and one of my assignments/ side project for my senior project is to improve the robot we entered this year..(which is why im asking all these questions)
since i didnt get to work in the electrical/rogramming team, i thought it would be good to learn the things i didnt overthe build season.
ill do better research next time though XD

but yea thats why i started this thread.. b/c we have spare victors from our 08 bot, and for our 09 bot we wanted to put a conveyor lift to pick up balls since currently our robot is manually loaded.
so i was wondering which speed controller would be better for the conveyor belt mech, and perhaps which motor should be used for which speed controller.


our season is over (for now) so my teacher wants us to sharpen up by

[kapolavery]

Originally Posted by Qbranch

Going past the limit would mean a >100% duty cycle, which is impossible. A direct analogy would be working 25 hours a day.

If you do manage to figure this out though, please let me know. You'll have singlehandedly solved the world's energy crisis.

-q

alright i'll make sure i'll let you know!
haha

[billbo911]

Originally Posted by EricVanWyk

Bill -

Alan's post is only half correct. It is true that the outputs have a 6.625uS update rate, which does equate to 150 signals over the standard window.

However, this is slightly higher resolution than the Victors can respond to. Additionally, the Jaguar does not use the standard 1ms - 2ms window by default (it can be set to do so). It uses a wider window in order to get more resolution. This is why you must use the Jaguar or Victor specific API calls - they will scale the pulse width accordingly.

I don't have access to the exact numbers right now - I've managed to get out of the office this weekend. Hopefully someone with better knowledge of the specifics will jump in.

I'm 30% confident that internally, the Jaguars represent the Duty cycle with a 16 bit number (even though they are using a 32 bit processor). I'd be surprised if we are getting more than 8bits over the PWM channel, so this extra resolution isn't used (this year).

Honestly, having a ~150 Hz update rate has no relevance to the answer I am looking for, but in regard to the OP's question, it might. I understand the Vic and the Jag have different update rates and their responses to the signals are significantly different. For instance, the Jag has a much more linear response than does the Vic. All this aside, what I was really looking for was:

While doing the math to generate the values used to send to the Jag, how many decimal places are really necessary? Would sending .38 have any noticeably different output than sending it .3835?

If in fact the Jag is using a 16 bit word to represent the duty cycle, that would translate to more than 65K possible values. That would indicate that 4 places would in fact work, though I highly doubt that you would really need more than 2 places after the decimal.

All this may be limited by the cRIO at this point in time. While sending a PWM signal generated by these values, the cRIO may only be looking at the first two digits and ignoring the rest. This is just a guess on my part. When we move to CAN Bus, this whole discussion will be somewhat different, but that is for the future.

[EricVanWyk]

Originally Posted by billbo911

Honestly, having a ~150 Hz update rate has no relevance to the answer I am looking for, but in regard to the OP's question, it might. I understand the Vic and the Jag have different update rates and their responses to the signals are significantly different. For instance, the Jag has a much more linear response than does the Vic. All this aside, what I was really looking for was:

While doing the math to generate the values used to send to the Jag, how many decimal places are really necessary? Would sending .38 have any noticeably different output than sending it .3835?

If in fact the Jag is using a 16 bit word to represent the duty cycle, that would translate to more than 65K possible values. That would indicate that 4 places would in fact work, though I highly doubt that you would really need more than 2 places after the decimal.

All this may be limited by the cRIO at this point in time. While sending a PWM signal generated by these values, the cRIO may only be looking at the first two digits and ignoring the rest. This is just a guess on my part. When we move to CAN Bus, this whole discussion will be somewhat different, but that is for the future.

Sorry, bit of a misunderstanding. It isn't a 150Hz update signal - it is a signal with 150 possible distinct values, which is about 2.2 digits. The Jaguar would have about 2.4 digits (if I recall the numbers correctly.

The Victor's resolution is limited by itself. The Jaguar's resolution is limited by the cRIO's PWM output (for now).

[MikeE]

Originally Posted by kapolavery

in what scenario would you use the victor speed control and in what scenario would you use the Jaguar

this year our team used all the kit jaguars for our turret, shooter, and drive

It's been a fascinating discussion on the second question you asked in the OP, but I'll restrict my answer the first question.

We used the following simple approach to deciding which speed controller to use:

Q) Do we intend to use closed loop control for the motor?
Yes -> Jaguar (more linear response);
No -> Either

Q) Do we have limited space/footprint?
Yes -> Victor (smaller);
No -> Either;

Q) Do we think we might damage the speed controller in development?
Yes -> Jaguar (less expensive);
No -> Either;

This lead to us using 6 Jaguars for our drive system, and 2 Victors for our lifter/shooter.

[kapolavery]

ok so overall then..
which speed controller is better?

or is it just by preference..

[gburlison]

We had some problems with 3 Victors on the same digital sidecar. It seems that the Victors draw more current from the PWM line. We did not have time to prove this definitively. We just moved one of the Victors to a second sidecar. Has anyone had a problem running more than 2 Victors on one sidecar?

[AustinSchuh]

Originally Posted by gburlison

Has anyone had a problem running more than 2 Victors on one sidecar?

We (254) have 8 victors on one side car, and they seem to be working. We (971) have 6 victors on one side car, and they seem to be working just fine too.

[Qbranch]

Originally Posted by gburlison

It seems that the Victors draw more current from the PWM line.

Truth.

All of IFI's motor drives are opto-isolated on the signal input to protect your controller board from the slings and arrows of brushed motor noise (i.e. reverse polarity voltage spikes on brush contact release, generator effect during duty cycle off time).

The current draw comes from the opto-isolators, which put an air gap between you and anything that could come in contact with the motor. The current you input on the PWM signal line runs an LED, which is pointed at a photo diode (think teeny weenie little solar cell) or photo transistor(more popular, transistor with base driven by photon input).

The photo diode or photo transistor's output signal matches the input signal, but with near infinite impedance (for our intents and voltage ranges) back to the signal source thanks to the air gap (between the LED and sensor) acting as a high value resistor between the signal source and the speed controller's circuitry.

If you've ever jammed a drive motor or other large motor coupled to a lot of inertia from 254 to 0 in one 25.4ms update period, you probably have these little guys to thank for saving the life of your RC.

-q

[EricVanWyk]

Originally Posted by gburlison

We had some problems with 3 Victors on the same digital sidecar. It seems that the Victors draw more current from the PWM line. We did not have time to prove this definitively. We just moved one of the Victors to a second sidecar. Has anyone had a problem running more than 2 Victors on one sidecar?

I was going to write a lengthy response, but Qbranch is right on the money.

A few more details:

The Jaguar's optoisolator has a logic level converter in it. This allows it to work with about a quarter of the signal current on the outside world side. This means it can use a larger balancing resistor, which in turn implies that it shares signal current better.

The DSC should definitely be able to drive three victors, provided they aren't all on the same port. It will only support controlling up to 2 Victors per port using a Y-cable.


Lastly, what problems did you have? We should probably move this discussion to personal messages to avoid clogging the thread.

[Al Skierkiewicz]

Avery,
All things being equal, the output of the controllers coupled to a motor are controlling current within the motor. Current translates to speed. So the things that limit this current is the "on" time of the controller and all series resistances between the battery and the motor. Assuming the controller is at full throttle then the battery is effectively connected directly to the motor through the controller. The series resistances are the wiring (.0005 ohm/ft for #6, .001 ohm/ft for #10, .002 ohm/ft for #12) the series resistance of the connections (usually much less than .0005 ohms total for 5-10 connections) the .0005 ohm resistor in the Jaguar, and the series resistance of the FETs. Remember that the FETs are in groups of three in parallel and there are two groups in series at any one time. For the Victor this is 12 mohm per FET or 4mohm per group or 8mohm (.008 ohms) per Victor. The Jaguar is 5.2mohm per device or 1.8mohm per group for 3.5 mohm per controller + 0.5 mohm for the current sense resistor=4mohm or 0.004 ohms Jaguar. However, the Jaguar must add a short pulse to battery common at regular intervals to charge up the internal capacitor for driving the FETs. So the controller output is not at full throttle one hundred percent of the time but is very close.

[BT987]

well we have gone through about 5 jaguars, and no victors and we have about the same amount of the two on our bot....