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
and another question i had was what is the max you could push the speed control (either one) without burning out…
our programmer didnt want to push it pass one… but were there anyteams that did that?
is it also possible to hook up speed controllers in series so that you can max out the speeds?
I don’t know the specifics of how far you can push them but I heard stories about teams who had their jaguars at 1+ and they blew up and melted. At some point there were pictures of the aftermath. I think by build season next year we will know a lot more about the control system and be able to know just how far we can push this new technology.
Are team decided to stick with what we knew for this year and used only victors on our robot, next year we may switch or do a mix or not. We shall see next year.
The “behind the scenes” software clamps the values at +1 or -1. Attempting to go 2 is equivalent to a 1.
In series? You would actually reduce your available power, and it is illegal.
In parallel? You would theoretically increase your available current, but it is illegal and dangerous.
Avery,
The internal circuitry of the either the Victor or the Jaguar switches between the positive and negative leads of the battery. The switching is not synchronous (meaning all devices will not go high at the same time, etc.) so it is possible and likely that two controllers in series would allow the series connection to have one wire at +12 volts while the other is at zero. The result would be catastrophic with max battery current (600+ amps) flowing through both controllers and the wiring in between. The same holds true for controllers in parallel. That is why the rules allow one and only one controller per motor. At full throttle on either controller, the output goes to DC (no PWM output except for a short pulse on the Jaguar) and so there should be little difference between the two types of controllers. The Jaguar uses a 0.0005 ohm resistor for current sense but the FETs have a lower “on” resistance than the Victors so it’s pretty much a wash.
ok i see…
just wanted to know that
thanks!
ok and this leads me to my next question
how are you able to bypass the limit it can handle so that you can get the max value
or is it all dependent on the how you make the drive train, the gear ratios, etc…
You’d have to tamper with the “behind the scenes” software, which is a bad idea.
Changing your drivetrain gearing is a much better idea.
ok that answers my main question
ill have to go research a new drive train for next year
1 and -1 mean “every bit of power possible”. Software can not be written to get around this. Please see “This is Spinal Tap” for reference, specifically “ours go to eleven - it is one higher than ten”
is that supposed to be humourous??
haha
i get it tho…
if its not made to go past the limit, it wont go past the limit…
its like
trying to breathe with no air… sorta thing… right?
It’s like, the FETs inside the drive are at 100% duty cycle and are for all intents and purposes very low resistance wires connecting the motor to the battery, sorta thing.
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
Yes, it was a lame attempt at humor.
Q hit it on the head though. It is not physically possible to go past those limits.
I wouldn’t describe it as breathing without air, more of a “Giving 110% effort isn’t possible”. If you could give 110%, then what you used to call 100% was actually only 91%.
“This Is Spinal Tap” is a mockumentary about a rock band. During an interview, they said that they were the loudest band in the business, and asked them their secret. Their response was that their amplifiers went up to 11 - it is one higher. The interviewer responded “Why don’t you just make 10 louder?”. “But it is eleven, it is one higher than ten!”
The [1,-1] scale was arbitrarily chosen to make math easier. We could have easily chosen [2,-2] or [255,0], but all the values would have simply scaled in response.
Changing the “behind the scenes software” would allow you to send signals that are higher or lower than the current bounds, but they wouldn’t mean anything.
One comment, one question.
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).
Eric,
Now that the math has been simplified by making the input control range -1 to 1; how many places of resolution after the decimal point does the Jaguar have? In other words, will sending .2508 be any different than sending .25? I realize this is only a .32% difference, but I am really looking for the limitations that the input has on it, not the actual output. Would anything over 2 places even be read by the Jag?
The resolution is limited by the cRIO Digital outputs before the Jaguar sees the signal in the first place. The outputs have a 6.625 microsecond update rate, so there are only about 150 different pulse widths possible between the 1ms and 2ms limits of a standard servo-type signal.
Eric,
Now that the math has been simplified by making the input control range -1 to 1; how many places of resolution after the decimal point does the Jaguar have? In other words, will sending .2508 be any different than sending .25? I realize this is only a .32% difference, but I am really looking for the limitations that the input has on it, not the actual output. Would anything over 2 places even be read by the Jag?
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).
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
alright i’ll make sure i’ll let you know!
haha:cool:
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).
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.