Chief Delphi - Waiting Until Limit Switch Is Pressed

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Wildcats1378

07-02-2014 23:01

Waiting Until Limit Switch Is Pressed

Hello everyone!

So I am the programmer mentor and team lead for the Wildcats #3878 here in Hawaii.

I am writing a piece of code for our shooter that will continue moving a motor until it hits a certain limit switch, and then continues onto the next frame.

I am writing the code in an autonomous program as part of a flat sequence to $@#$@#$@#$@# the catapult to a set area based on limit switch, to determine the power of the shot we want.

How might this be accomplished?

Thanks everyone,
#3878 Head Programmer

wireties

07-02-2014 23:14

Re: Waiting Until Limit Switch Is Pressed

Put it in a loop? I'm not sure how specific to get - depends on what framework you are using. Something like this..

...
while(limit input is not asserted and still in auto mode)
{
set motor speed
}

stop motor
...

virtuald

08-02-2014 00:14

Re: Waiting Until Limit Switch Is Pressed

I would recommend hooking the limit switch up to the Jaguar, so it automatically turns itself off. No code required.

Read the Jaguar's datasheet to determine how the limit switch functionality works and where you need to hook it up to.

Alan Anderson

08-02-2014 00:51

Re: Waiting Until Limit Switch Is Pressed

Quote:

Originally Posted by Wildcats1378 (Post 1339481)

I am writing a piece of code for our shooter that will continue moving a motor until it hits a certain limit switch, and then continues onto the next frame...
How might this be accomplished?

You mentioned a flat sequence, so I assume you're using LabVIEW.

Just put a while loop in the frame, reading the limit switch inside the loop and using the returned value as the termination condition for the loop. It'll keep looping until the switch is activated. Be sure to also put a 10 ms delay (or thereabouts) inside the loop so it doesn't use up all the CPU cycles just waiting for the switch.

Quote:

Originally Posted by virtuald (Post 1339505)

I would recommend hooking the limit switch up to the Jaguar, so it automatically turns itself off. No code required.

In this case, code is definitely required. This is a sequence of events that waits at one step until the switch is hit, so the program needs to be reading the switch.

tcjinaz

08-02-2014 22:05

Re: Waiting Until Limit Switch Is Pressed

Is 10MS good enough to catch one of those switches with the lever arm and roller on the end? I am fretting about catching the signal in time to prevent arms slamming into supports.

I am almost wishing for interrupt driven controls here. Is there a way?

Tim

Whippet

08-02-2014 22:06

Re: Waiting Until Limit Switch Is Pressed

Quote:

Originally Posted by Wildcats1378 (Post 1339481)

...flat sequence to $@#$@#$@#$@# the catapult...

Wow, CD really doesn't like for people to reload their launchers...

wireties

08-02-2014 23:28

Re: Waiting Until Limit Switch Is Pressed

Quote:

Originally Posted by tcjinaz (Post 1339888)

Is 10MS good enough to catch one of those switches with the lever arm and roller on the end? I am fretting about catching the signal in time to prevent arms slamming into supports.

How far will the mechanism travel in 10ms? How quickly will the motor stop? And is that distance dangerous? In FRC, it is hard to imagine 10ms being too long for most any event-driven response but I would do the math.

HTH

Adamz_

09-02-2014 00:42

Re: Waiting Until Limit Switch Is Pressed

i dont know what language your using, but in java it would look something like this

Code:

if(!limitSwitch.get()){

   motor.set(1.0);

 }else if(limitSwitch.get()){

   motor.set(0.0);

}

in englsih all this is doing is saing, if the limit switch if false (not pressed) spin the motor, then in the else if statement, it checks if the limit switch is true (pressed) and if it is, it will stop the motor, if you want it so once its in this state, you press a button to shoot, the code would be this;

Code:

if(!limitSwitch.get()){

   motor.set(1.0);

 }else if(limitSwitch.get()){

   motor.set(0.0);

 }else if(controller.getRawButton(1)){

  motor.set(1.0);

}

Alan Anderson

09-02-2014 00:45

Re: Waiting Until Limit Switch Is Pressed

When we're worried that we might miss a brief switch input between samples, we open the input as a counter instead. Then we watch for the counter to change values, and that tells us the switch was hit.

If something pulses quickly enough to be missed by the FPGA, we've already got some re-engineering to do.

MrRoboSteve

09-02-2014 09:14

Re: Waiting Until Limit Switch Is Pressed

This is as much a question of programming as it is of limit switch positioning.

It's often easier to modify the limit switch position to solve end position problems like this.

Joe Ross

09-02-2014 13:52

Re: Waiting Until Limit Switch Is Pressed

I would be less worried about detecting the limit switch as I would stopping a fast moving part with a lot of inertia. Programming can only minimally impact the latter.

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