jaguar scaling factors

[MAldridge]

My team (3247) just got our bot driving today and we noticed a big problem. With four motors we are using 2 black jags and 2 grey jags. This seemed fine except for a problem where the scaling is not quite right! When driving foward, one side (black side I think) is way faster. As the programer for the team, I was told to fix it. I was thinking that maybe I should attempt to scale the joysticks. The problem with this is that my team also wants to use arcade drive. We used last years DS for testing but they think it will be easier to control with arcade.

My questions are:

1. How do I make each side move in step so that the bot drives strait using PWM
2. How do I re-scale the joysticks so that most of the range is for slow speeds and it is still possible to get full speed
3. Is there a better solution that does not involve buying more jaguar controllers

Thanks in advance

[markgryzwa]

Same issue for our team. Would love to hear the answer. The black jaguars output about 12.5V in full on, the grey/tan jaguars are about 10.5V. Quite a difference to balance.

[Us3rNam3]

idk if this would help any but you could always try installing encoders onto each side of the drive train then using those output values and then scaling back each motors output.

[Mark McLeod]

Originally Posted by MAldridge

With four motors we are using 2 black jags and 2 grey jags.

By far the simpler solution would be to pair a Black Jaguar with a Gray Jaguar on each side, rather than having all Blacks on one side and all Gray's on the other.

You can certainly scale back the faster side permanently by multiplying the joystick input to just the Black side by a factor or by using encoder feedback and PID.

[MAldridge]

because these are the CIMple gearboxes from andymark, I don't think it would be advisable to mix controllers. I see ground gears for anyone who tries that...

The voltage data is very helpful, does anyone know if the speed is ramped in a linear fashion? If it is linear, then it would be some very simple math to make them even.

[kamocat]

I would suggest using PID with encoders to get a closed-loop control.
There's nothing quite like feedback for repeatability and low-speed handling.

[MAldridge]

Can you suggest any good resources for creating PID algorithms? I am used to text based languages on OS/2 so any resources that are labview based would be nice.

[kamocat]

If you're using LabVIEW, the FRC version does include a PID toolkit. Note that the LabVIEW toolkit uses the Standard form rather than the Ideal form.
http://en.wikipedia.org/wiki/PID_con...ndard_PID_form

Wikipedia has a good article on PID.

[MAldridge]

I read through the article posted and I am trying to make heads or tails of it. I do not understand how exactly a PID loop will allow me to synchronize the movements of the left and rights drivetrains so that the robot drives in a straight line. PID does however seem to be an excellent way of defining the movements during autonomous to place the ubertube.

More questions:

1. How do I use PID to make the system drive in a straight controllable line while not sacrificing response times?
2. Is PID a good choice for autonomous?
3. Is all of this overkill for what I am trying to achieve?

[Vikesrock]

Originally Posted by MAldridge

More questions:

1. How do I use PID to make the system drive in a straight controllable line while not sacrificing response times?
2. Is PID a good choice for autonomous?
3. Is all of this overkill for what I am trying to achieve?

1. If you use the joystick controls to set a velocity that you use a PID loop to maintain instead of setting the Jaguar values directly the robot should maintain equal velocity on both sides and drive in a straight line.

2. Yes, PID control on position is a good way to handle dead reckoning forward/back movements in autonomous. PID control on angle using a gyro is a good way to make dead reckoning turns.

3. Nope, not at all.

[MAldridge]

so do I use one PID VI for each input needed on the drive VI?

In my question about autonomous, would I want to use a setpoint VI.

Lastly, does the PID VI need to be in a loop to work? Sorry for all the questions, but short and simple answers for APPLYING code are few and far between over at NI's site.

[Al Skierkiewicz]

Have you tried calibrating the speed controllers?

[MAldridge]

I have, but there is still a slight variance from straight on.

[kamocat]

Yes, yes, and yes.

I think a global variable would work wonderfully for transferring your setpoint from your autonomous code to your PID loops. Put the PID loops in Periodic Tasks so that they run all the time.

[MAldridge]

Should the PID Loop run with a delay or should it run at full speed?