Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

Are you asking how quickly the Jag hardware can change from 100% reverse duty cycle to 100% forward duty cycle? If not, please clarify what you are asking.

It can drive its output from 100% duty cycle of reverse supply voltage to 100% duty cycle of forward supply voltage.

The hardware schematic is freely available, is that what you're looking for?


Are you asking what is the resolution of the Jag's output? i.e. What is the smallest step it can take in the range -100% to +100% ?


The output is a Pulse-Width modulation of the supply voltage. The duty cycle (% "on" time) of the pulse can range from 0 to 100%, with either forward or reverse supply voltage. I do not know if there is a firmware limitation on how fast the hardware is allowed to change the duty cycle. Is that what you are asking??

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

No. Not at all. Might be a nice parameter to have measured tough it's not directly what I seek.

If you feed a schematic to PSpice will it give you actual real world measurements on production parts and consider tolerance? No.

Well at least if I knew the resolution of the Jaguar's output...the real resolution considering all the gate drive issues for the N channel FETs and their associated capacitive characteristics...and I knew the upper and lower saturation values with regards to the power supply and of course the upper and lower parameters of the PWM into the gate drive circuit, I could probably make an educated guess at what I want.

No. Frankly I'd be amazed if in the real Jaguar hardware they have the ability to drive the entire 0-100% PWM spectrum into their N channel gate drive and not have issues sooner or later all of which matter to the open loop measurements that will effect what I'm looking for.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

I humbly ask that you re-read your posts. The effectiveness of your communication is impaired by the passion of your posts, and as such I am finding them rather unhelpful. I have great respect for the people who have responded in this thread, and they deserve your patience.

As others have stated, the Jaguar implements a very vanilla PID loop with an internal rate of 1kHz.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

The parameter I'm looking for is described here:

http://www.jashaw.com/pid/tutorial/pid3.html

Look for the part that starts with:
"Units used to set integral or reset"

The only way to get this with a schematic would be simulation that I doubt would be worth the effort once you consider all the spurious issues created by the high gate resistance, the high gate capacitance and a host of other issues you'd have to Monte Carlo to even try to simulate.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

You said reading the code is not your problem. Whose problem is it? David explained it quite well. The PID update is done every millisecond. That is an accurate number.

("run the gambit full range"? I'm not familiar with that phrase. I assume you mean force the output to its maximum -- or minimum -- value.)

It seems to me that the time it takes to go full scale depends on the error and on the gain parameters. The gains are fully under your control, but the error is an arbitrary number.

But the range of control isn't really related to time, is it? Full range is full range, whether it takes one millisecond, or a thousand, to reach it. I suspect there's a mismatch in terminology that's keeping us talking past one another.

I'm not following you. It doesn't "back off" until the error term changes sign. Nothing in the controller can tell you when that will happen.

Of course you can't get it from the code; the error depends on the state of what you are controlling. The "assumptions" you must make are not wild; they are based on the response of what the controller is controlling.

There's clearly some idea which you think is obvious but which you are not succeeding in getting across to us. I still do not understand the distinction you apparently are maintaining between the implementation of the controller and the controller itself.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

There is no disrespect in what I'm writing to these people. This is a complicated subject and I am merely trying to get to the meat of it.

I have not, at any point, clearly disputed that the Jaguar has a software timed iteration of the PID loop at 1ms intervals.

The parameter I seek is clearly defined at the link I presented several times. It is not an instantaneous parameter for a iteration around the Jaguar's loop.

The Jaguar will not continue to integrate forever in 1ms steps.
It can't.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

It looks to me like you're asking for numbers that depend on the gain parameters. They are not an inherent feature of the PID controller implementation.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

And it does not. Empirically, I can physically hold my robot back from hitting its setpoint for several seconds - or even minutes. The moment I release it, it does not runaway an appreciable amount. I think it's fair to ask what kind of integral cap/reset characteristics are implemented in the Jaguar, but you won't see me complain too much. I'm just happy that my robot isn't barrelling through a wall due to wind-up.

I promised my last post would be my last post, but this thread has gotten out of hand.

Regardless. We've gotten the PID working with some limitations. We've worked around them, and have an ADEQUATELY workable closed control loop. I would love to have more, but we are given six weeks for a reason...

and trust me, the best use of those 6 weeks is NOT spent on arguing the specifics of the Jag's I implementation.

Say your piece, then let's all move on.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

It doesn't address my question.

If I told you my computer runs at 1GHz could you tell me how long it would take to crunch the first 20 digits of PI?

No you really couldn't. You couldn't because even if it's a RISC CPU and did one instruction per second, you don't know how many instructions it might take in whatever form the code was written to do the calculation or how long it would take to reach the display device whatever that is.


For me, it means the maximum or minimum value in reality. Which is probably not the maximum or minimum supply voltage or current.

For this measurement, error must start at 0. Input then is pushed up a step which jumps with gain and then goes into integration. There's an image at the section of the link I keep referencing.

Yes and no. The range of possible values at the output (of the Jaguar) obviously can't change instantaneously and depending on how fast each iteration of the code can move the output will depend on how many times it can go around before the PID loop can drive to the limits...but of course...within the minimum and maximum you might not start at the minimum because of the gate drive circuit.

The link I keep providing clearly defines that this test starts with 0 error.
http://www.jashaw.com/pid/tutorial/pid3.html

I don't actually understand why you think I've made that distinction.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

No. The number is not about the gain at all it's about what's above it in that diagram.
This link I provided is quite specific.

The error starts out at 0.
The error is shifted to stimulate a response (which will take some number of 1ms cycles because of the discrete time design of the Jaguar).
The gain is apparent and noted.
The integrator gets started.

There's a measurement in time shown at the bottom, it's the repeat time.
That'll be measured in repeats per minute.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

I accept that disrespect is not your intent, but it is the effect. I only ask that you account for that effect in future posts.

It is not clear to me whether you are speaking of the jaguar in isolation, or the jaguar + motor + mechanics as a total package.

In isolation, the best available model of the jaguar is a 1kHz vanilla PID loop with an output that saturates at +/- 100% of the bus voltage. Further levels of detail are available, but the additional accuracy those details provide would be swamped.

If you require a fancier or different control algorithm, you will need to implement it on the cRIO. If this proves to be too great a burden, I ask that you write a proposal whitepaper for the feature and submit it for the 2012 season.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

The question reduces to "How may times per minute does the I repeat the action of the P?"

I really don't see what the confusion is
:confused:

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

If somehow I've offended someone I apologize. However, I do not feel it's disrespectful to ask questions and the link I'm referencing is not some trivial work in the professional control field. Also I'm hardly unaware of the specifics of PID loops, the calculus that supports them, or for that matter I suspect is neither is the author of the link to which I refer:

http://www.jashaw.com/

I can provide additional links if desired in which the parameters I seek factor predominantly.

http://www.scribd.com/doc/6929817/Ba...Dr-Hung-Nguyen
(search for 'repeats per minute')

http://dexautomation.com/pid.php
(search for 'repeats per minute')

http://www.automation.siemens.com/WW...&Language=e n
(search for 'repeats per minute')

It's possible I'm not communicating in a way that is apparent if you focus down on the intimate loop details but I'm sure what I'm asking is a parameter I can get for virtually every single PID loop that controls motion in my shop full of servos and servo controllers. This includes IAI and Mistubishi.

This parameter can be approximated with just the controller, in this case the Jaguar.

I won't disagree, simulating this parameter would likely be nightmarish. I merely touched on a fraction of the details because before because I was trying to point that out.

This was not about having a fancier algorithm. Obviously, I can see this algorithm and I was aware when we had a special case algorithm in the past, which was why we implemented it in Java when that happened. Runaway conditions can't be so easily controlled with ideal, series or parallel algorithms.

This was about obtaining the parameters to perform tuning such as this:
http://www.learncontrol.com/tutorial/pid6.html

I can provide you a several tuning examples such as this, that will produce tuning that in some cases is pretty close to what you'd get with professional PID tuning software, a very complicated simulation and a major headache.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

Here is what I believe the crux of the issue boils down to.

You are basing your demand for "repeat time" and "derivative time" values on the specific PID implementation described at http://www.jashaw.com/pid/tutorial/pid3.html:

Out = G(e + R+ D )

The Jaguar does not implement that PID form. As David posted:

Output = P*Error + I*Integrator + D*(Error - Previous Error)

They can be transformed into one another if necessary, but you will find that the "repeat time" is essentially determined by the P and I constants, and the "derivative time" is essentially determined by the P and D constants.

I think that if you continue to study the description you are showing us as the basis for your understanding of PID, you will also find that the repeat time and the derivative time are not characteristics of a controller that get measured. They are parameters that must be set in order to tune the controller.

Re: Jaguar Speed Control Only Reaches 50% of Setpoint
 

Alan posted while I was doing research, but here's my explanation

This describes the PI controller as K_p(1 + 1/(T_i*s)). Is T_i the value you are looking for?

The Jaguar implements K_p + K_i/s

The equations are equivalent, if you consider that K_i can be described as K_p/T_i. By controlling K_i and K_p, you can make T_i whatever value you want.

LabVIEW implements the form you are familiar with.