Chief Delphi - Limit speed of 4 chassis CIM motors

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- - Limit speed of 4 chassis CIM motors (http://www.chiefdelphi.com/forums/showthread.php?t=135501)

Mr V	06-03-2015 00:15

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by jblay (Post 1454266)

Also, what might help is limiting deceleration. I would make sure my motor controllers are set to coast and not brake, this way you don't decelerate as rapidly so that you have less tipping issues when stopping.

Yes tipping when abruptly getting off the throttle will also likely cause tipping. With 4 motors you can set one on each side to coast and one on each side to brake for a lower braking force. We did that on the rookie team I am working with this year and it has worked good in practice.

Personally I would remove a motor per side if it can be done w/o major disassembly.

GeeTwo

06-03-2015 00:16

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by jblay (Post 1454266)

Absolutely. Deceleration is a form of acceleration, and I included it implicitly. The following line was intended to reduce deceleration, and putting the motor controllers in coast would prevent a sudden unintentional change.

Quote:

Originally Posted by GeeTwo (Post 1454243)

Code:

if (newSpeed < curSpeed - maxSpeedDelta)

     newspeed = curSpeed - maxSpeedDelta;

Ether

06-03-2015 13:53

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by Ether (Post 1454224)

You may want to limit acceleration.

Quote:

Originally Posted by Ether (Post 1454239)

http://www.chiefdelphi.com/forums/sh...69&postcount=8

http://www.chiefdelphi.com/forums/sh...22&postcount=2

The suggestions previously given in the post quoted above can be used to limit acceleration/deceleration without using sensors (no wheel encoders required).

If you have wheel encoders and you want to create smooth accel/decel-controlled pre-planned motion in auto, you might try something like this:

http://www.chiefdelphi.com/media/papers/download/4312

s_forbes

06-03-2015 14:10

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by Ether (Post 1454239)

http://www.chiefdelphi.com/forums/sh...69&postcount=8

http://www.chiefdelphi.com/forums/sh...22&postcount=2

We did a quick implementation of this approach a couple of weeks back. Limiting the rate that the joystick input can increase is an easy fix in code and does the job well. You can set different rate limits for each joystick axis (we have forward/back, strafing, and turning) to match the tipping geometry of the robot too.

IronicDeadBird

06-03-2015 14:13

Re: Limit speed of 4 chassis CIM motors

You using Joysticks or gamepads for control?

s_forbes

06-03-2015 14:29

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by IronicDeadBird (Post 1454475)

You using Joysticks or gamepads for control?

The interface hardware doesn't get rid of the tall-tippy-robot issue; you can still inadvertently send the robot a command of "full speed ahead" whether you use a joystick, a gamepad, or a DDR dance mat.

IronicDeadBird

06-03-2015 14:33

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by s_forbes (Post 1454485)

Going to have to disagree in regards to gamepads or typical console controllers you can gain more control over movement (provided they are bound to the thumb sticks) by increasing the height of the thumbstick you need to accidentally make much larger movements. If you are using a joystick your out of luck though.

microman1934

06-03-2015 21:47

Re: Limit speed of 4 chassis CIM motors

Thank you so much for the help guys, I just ended up doing this:

Code:

double rot = -stick.getX();

double speed = -stick.getY();

myRobot.arcadeDrive(rot*0.5, speed*0.5);

nighterfighter

06-03-2015 21:58

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by microman1934 (Post 1454610)

Thank you so much for the help guys, I just ended up doing this:

Code:

double rot = -stick.getX();

double speed = -stick.getY();

myRobot.arcadeDrive(rot*0.5, speed*0.5);

Glad you found a solution.

I would suggest you throw that in a if-else statement though, making the half-speed your default speed:

Code:

if(stick.getRawButton(1))

{

myRobot.arcadeDrive(-stick.getX(),-stick.getY());

}

else

{

double rot = -stick.getX();

double speed = -stick.getY();

myRobot.arcadeDrive(rot*0.5, speed*0.5);

}

This way, if in the middle of a match, your driver decides that he or she needs full speed, they have the ability to do so.

Just a suggestion. Of course, you may already have it that way in the rest of your code!

microman1934

15-03-2015 21:52

Re: Limit speed of 4 chassis CIM motors

Thanks for the idea, would the throttle work for that as well?

nighterfighter

16-03-2015 01:16

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by microman1934 (Post 1457950)

Thanks for the idea, would the throttle work for that as well?

Yes. You could set the throttle to act as a toggle switch...

I'm on my phone so I can't format this correctly and can only give some pseudo code.

If(stick.getThrottle () > 0)
myRobot.Drive (halfSpeedValues);

else if(stick.getThrottle <= 0)
myRobot.Drive (fullSpeedValues);

Remember the throttle on the joystick ranges from -1 to 1, so 0 will be in the middle.

Knufire

16-03-2015 01:19

Re: Limit speed of 4 chassis CIM motors

Just remember, by implementing that throttle (we refer to it as a software shift), you lose both speed and torque. This shouldn't be an issue driving around on an open field, but things like noodles or carrying large stacks while driving with the throtte enabled could cause very poor drive performance.

JesseK

16-03-2015 09:14

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by microman1934 (Post 1454610)

Thank you so much for the help guys, I just ended up doing this:

Code:

double rot = -stick.getX();

double speed = -stick.getY();

myRobot.arcadeDrive(rot*0.5, speed*0.5);

Depending on your drive train characteristics, you may have trouble turning. This will be especially prevalent in tight spaces or next to a bump. It is just as bad (or worse, perception-wise) as flopping over on your face every match. Could you describe your drive train from a mechanical perspective?

Ozuru

16-03-2015 11:18

Re: Limit speed of 4 chassis CIM motors

Quote:

Originally Posted by microman1934 (Post 1454610)

Thank you so much for the help guys, I just ended up doing this:

Code:

double rot = -stick.getX();

double speed = -stick.getY();

myRobot.arcadeDrive(rot*0.5, speed*0.5);

Why not just square the magnitude? Pseudo code for example.

Code:

double rot = -stick.getX();

double speed = -stick.getRawAxis(drive axis);

myRobot.arcadeDrive(rot, speed * Math.abs(speed));

This allows finer control at lower speeds (when joystick is reading 0.5 you will send 0.25 to the motors) but still allows full speed when the joysticks are at full throttle.

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