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#16
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Re: How to get maximum output from a Jag?
My team is actively having the same problem. We are currently using 16" wheels with the standard cim gear box and a 3:1 ratio for the chains instead of the standard 2:1 provided with the KoP. I am glad that we are not the only team having this problem.
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#17
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Re: How to get maximum output from a Jag?
Alright so I'm the Mech in question.
let me clear up some things 1. yes we are using 20in wheels and yes they are staggered 2. the drivetrain is running a 5:1 gear ratio on top of the 4.67:1 of the gearboxes so a total of a 23.35:1 ratio 3. i am 98.9% sure that we are not tripping the 40A breakers 4. we are using a fresh battery so that being said is there any way to keep the jags from triping Thx P.S. thund plz get your facts strait before posting it saves me from wasting my valuable sleeping time. %-l |
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#18
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Re: How to get maximum output from a Jag?
Quote:
Freespeed of CIM = 5310 RPM /60 (min / sec) = 88.5 RPS /23.35 (gear ratio) = 3.79 RPS (rounded) 20" dia * 3.14 = 62.8" circ 62.8" circ * 3.79 RPS = 238.01" / sec /12 (in/ft) = 19.83 ft/ sec. These are theoretical numbers that will never be attained but typically anything over ~16ft/sec in a single speed gearsetup will trip the breakers at startup and while turning (depending on CoF, weight on wheels, wheelbase, etc). Now lets calculate thrust. Stall torque (again for theoretical measurements) of cim = 344 in/oz * 23.35 (gear ratio) = 8032.4 in/oz /20" (distance of torque) = 401.62 oz /12 (in/ft) /16 (oz/LB) = 2.09 LBs thrust * 4 (CIMs) = 8.367 LBf thrust Thats low, but managable (someone check my math ... I'm terrible in the morning )All in all your setup might work, but I'd expect tripping of the breakers when turning and in any sort of pushing match. |
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#19
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Re: How to get maximum output from a Jag?
Quote:
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#20
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Re: How to get maximum output from a Jag?
Alright I uploaded a video of a drive test from a few weeks ago, although I believe the drive train stuff is all the same (aside from a bit of tightening, but it looks the same). Unfortunately we don't attempt to go over the bump in this video, but here it is.
http://www.youtube.com/watch?v=bGlak6ijWPg The robot doesn't start moving until about 1:15(I trimmed it with yt but atm the changes are still being processed -_-) For me the important thing is to find out whether our issue (I know its difficult to discern our exact issue) is one that can be fixed via software/firmware, because I would enjoy people getting off my back so I can program. Last edited by Thundrio : 18-02-2012 at 12:12. |
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#21
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Re: How to get maximum output from a Jag?
You have a high center of gravity and a shorter-than-normal wheelbase (because of the 20" wheels). Even with your present low-torque gearing, you popped a wheelie. What's gonna happen when you go over the bump?
With your high center of gravity and shorter-than-normal wheelbase, you don't need to be geared for 19 feet/sec - it would be very difficult to control at that speed. Change that 5:1 sprocket ratio to 10:1 and you'll cut your amps in half (for a given wheel torque) and still have adequate speed. If you modify the gearing for more torque, you will have to be extremely careful with the throttle. Adding a slew rate limiter to your joystick would limit your acceleration and help mitigate the wheelie-popping. PS - You and Kilo Foxtrot 7 need to take your bickering off this forum. Last edited by Ether : 18-02-2012 at 12:42. |
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#22
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Re: How to get maximum output from a Jag?
I'm not sure how to add that code in.
Code:
change = joystick - limitedJoystick; if (change>limit) change = limit; else (if change<-limit) change = -limit; limitedJoystick += change; Any help would be appreciated, I would like to get the slew rate limiter tested as soon as possible so it either fixes the issue or we need to try something mechanical (Since the mechs won't do anything to fix it if they think it can be fixed through software). |
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#23
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Re: How to get maximum output from a Jag?
Quote:
What is your wheelbase* measurement, exactly? * wheelbase: distance between front and rear axles. |
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#24
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Re: How to get maximum output from a Jag?
Quote:
Code:
Joystick joystick = new Joystick(1);
double lastJoystickValue = 0;
// Limit the Joystick to a change of 1% every iteration of the robot. Basically,
// limit the acceleration of the robot.
final double MAX_CHANGE_PER_ITER = 0.01;
public void teleopPeriodic() {
double currentJoystickValue = joystick.getMagnitude();
double magnitude = limitRate(currentJoystickValue, lastJoysitckValue);
drive(magnitude); // pseudo method
lastJoystickValue = magnitude;
}
/**
* Uses the value from the last iteration to limit how much the Joystick can
* change in one iteration.
* @param goalValue The ideal value that we ultimately want to reach.
* @param lastJoystickValue The value of the joystick from the last iteration.
*/
public double limitRate(double goalValue, double lastJoystickValue) {
double difference = goalValue - lastJoystickValue;
if (difference > MAX_CHANGE_PER_ITER) {
return lastJoystickValue + MAX_CHANGE_PER_ITER;
} else if (difference < -MAX_CHANGE_PER_ITER) {
return lastJoystickValue - MAX_CHANGE_PER_ITER
} else {
return goalValue;
}
}
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#25
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Re: How to get maximum output from a Jag?
The mech lead says the wheelbase is roughly 15 inches (I won't be there for another few hours, I just called him).
Thanks for the pseudo-code ianonavy, I'll give that a try. |
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#26
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Re: How to get maximum output from a Jag?
There is a cimple box at 4.67 to 1
and there is a 5:1 reduction from the cimple output to the wheel (12 tooth sprocket to 60 tooth sprocket) This makes a 23.35 reduction We need help trying to identify if we can change the ramprate on the jags to a level that prevents it from overloading and do some testing. How do we program a different ramprate in the JAG using Java? edit: btw, clarksnack is our mentor that Thundrio was talking about in the original post. Last edited by Kilo Foxtrot 7 : 18-02-2012 at 13:47. |
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#27
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Re: How to get maximum output from a Jag?
Is there a way to set the ramprate of the Jag in the Java code? We tested one of the motors using the BDC COMM software and placed the ramprate at 1000 and just the one motor appeared to have much more torque available without the Jag internal trip "tripping" How can we program the ramprate in the jag using java?
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#28
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Re: How to get maximum output from a Jag?
Quote:
When you say "ramp", are you referring to the barrier or the bridge? And what do you mean by "bottom ones"? The rear wheels? If the wheels are 20" diameter and the wheelbase is 15" diameter, how can the front wheels be "over the ramp" (the barrier) before the "bottom ones" (rear wheels) hit the ramp (barrier)? Unless by "over the ramp" you mean "on top of the ramp" ?? See the attached PDF. |
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#29
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Re: How to get maximum output from a Jag?
Quote:
Quote:
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sorry for the confusion. -_- |
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#30
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Re: How to get maximum output from a Jag?
Quote:
If you are using PWM, you can enable the fixed ramp rate of full reverse to full forward in 1/8 second by placing the limit jumpers parallel to the front of the Jag. See Pages 2-3 of this document. Or you can put the very simple code shown here to limit the rate at which your joystick command is allowed to change. That will limit the rate at which your Jag changes voltage. You can try it, but I do not think ramp rate is your problem. Last edited by Ether : 18-02-2012 at 14:34. Reason: added link to Jag Q&A doc |
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