Can't figuring out what's wrong. Please help.

[HeroToXero]

So on our robot we're using the van door motors to lower our bridge and for our launching mechanism. The problem is that when we throw the bridge in reverse it kind of stutters/is really weak/doesn't work at full power. We've switched the motors out and found that it wasn't the van door motor, so something must be happening to the information from the programming to the jaguars. If anyone else has had this problem before please help. Thanks!

[Sean Raia]

"Throw the bridge in reverse"? im sorry but i dont understand what you mean.

If you could give us some more information im sure we could help.

What current is the motor drawing when run?
What mode are you running the jaguars?
Are you connected to the speed controller via CAN or PWM?
Have you tested the motor under no load?

[HeroToXero]

whoops. I meant to throw the bridge arm in reverse (sorry for the typo). We have an arm that pushes the bridge arm down on our side so the robot can get up it, and then the arm comes back up to stand vertical on the bot.

-Its running 12 volts both ways.
-Yep Jags., but i'm not entirely sure what you mean by mode
-PWM
-And yes the motor has been tested under no load

Thanks for your help

[Alan Anderson]

Seeing your code would help us help you figure out what's going on.


I'll guess blindly that you're using two buttons, one to raise the arm and one to lower it. You've got a pair of if/then statements (or case blocks in LabVIEW), one for each button, to decide whether to run the motor or stop it. The problem is that if you press the first button to turn the motor on, the second button's else clause (or false case) turns the motor off again immediately.

Does that hit the mark, or am I totally wrong?

[bf2416]

We had that same problem, and based on your description, it sounds like you are using a case structure. Rather than using a case structure, I would use this as an example. I originally used a case structure and had a similar problem. I hope this helps, but if it doesn't or you aren't using NI Labview, sorry.

You can also use the throttle on one of the joysticks to control the motor, but it can be a little touchy, so I would recommend using the above link.

[Taylor]

Does the arm start (relatively) vertical, lower to horizontal, then lift back to vertical? Perhaps the motor isn't strong enough to lift the arm back up.

[slijin]

Originally Posted by Taylor

Does the arm start (relatively) vertical, lower to horizontal, then lift back to vertical? Perhaps the motor isn't strong enough to lift the arm back up.

To elaborate,

Have you counterbalanced your arm?

Don't forget that when pushing something down, gravity works with the motor, but against you when pulling it back up. The same applies to any mechanism that works with gravity one way, and fights it the other way. Sort of like how going down stairs is easier than going up

If you haven't counterbalanced your arm, then that would produce exactly the type of behavior you describe.

[nitneylion452]

If you are using Java, or a language with similar syntax, you'll want a format like this:

if(condition1)
{
    //perform action 1
}

else if(condition2)
{
    //perform action 2
}

and so on.

What this will do is stop checking if a button was pressed after one of the conditions is true. I.e., when condition 1 is true, the program will not check for condition 2 and not execute its else statement (if you have one). If what Alan said is the issue, this should be a relatively simple fix.


Now for everyone to tell me that I'm completely wrong and that this won't work.

[Jon Stratis]

You say "van door motors" - which motors are you talking about specifically? Most teams would be using either the AndyMark Gear Motor (PN am-091) or dual Window Motors (PN 262100-3040 and 262100-3030). To use a van door motor, you would either have access to previous year's KoP's (several years ago they included a Van Door motor, if I remember correctly), or parts from the ARA donation.

If you're talking about the window motors in the KoP, I recall issues being posted in past years with them and specific speed controllers - when pushing against a load, the frequency of the speed controller would cause issues with running it in that direction.

Try switching the controller out for a Spike relay (if appropriate), or removing the locking pin from the window motor (an allowed modification).

[EricH]

Originally Posted by Jon Stratis

To use a van door motor, you would either have access to previous year's KoP's (several years ago they included a Van Door motor, if I remember correctly), or parts from the ARA donation.

FIRST Choice still had the '08 KOP Van Door motors in Week 6, and they are legal to use if you got them from there. I was thinking those would be perfect for dropping the bridge if you could get your hands on them.

[Sean Raia]

Originally Posted by HeroToXero

whoops. I meant to throw the bridge arm in reverse (sorry for the typo). We have an arm that pushes the bridge arm down on our side so the robot can get up it, and then the arm comes back up to stand vertical on the bot.

-Its running 12 volts both ways.
-Yep Jags., but i'm not entirely sure what you mean by mode
-PWM
-And yes the motor has been tested under no load

Thanks for your help

Ok everything you have told me indicates that it may very well be an issue in the code. Please post the code that interfaces with the manipulator, as Alan said, it really helps us figure out whats going on.

[pyroslev]

If you are using motors that have been sitting on the shelf from an old KOP,
check the inside of the motor itself. That worm gear if it gets bound up can chew up the plastic gear that turns the arm. (First hand breaking experience.)

[Shaun Coon]

you could have a bad jag and are you sure you hooked them up right:/
if they were previously hooked up wrong they will tend to do this

[Brandon_L]

If you stall the van door motor it has a few seconds of pretty much exactly what you described. We had the same problem, check out our arm in this video:

http://www.youtube.com/watch?v=KSUL9_TVooI @ 2:45

[Al Skierkiewicz]

Jaguars do have a failure mode where they work fine in one direction and are intermittant/low power/ or no output in the other direction. Have you tried swapping the Jag?