[Lego NXT Motor Jumping][Pls HELP]

[markyn]

Hello guys,

i'm building a Lego NXT to switch a cd from a cd tray,
and as you guys can see in my video: http://www.youtube.com/watch?v=sHt6SBX4LEs
the robot grabs the cd, and after that the motor starts to jump, and i don't know why it's doing such things and how to fix =/

Do you guys have ever seen something like that ? How to fix this ?

Ty,
Markyn

[gloomyandy]

Did the CD snag on the edge of the computer when you tried to lift it?

Looks to me like you are basically overloading the motor and it is being turned off. This may be being caused by the leJOS stall detection or the motor driver chip. Have you checked to see if the motor is stalling (there is a call to the regulated motor class to check for this), If it is stalling you may be able to raise the stall threshold. However I suspect that you are simply asking too much of that motor. If you raise the threshold you will probably just trigger the hardware protection. The NXT has protection circuits built into the motor driver that will cut of the drive if the current draw is too high.

The main problem is that the arm and grabber is too heavy. You may be able to fix it by using a lower gearing on the arm drive, even better would be to use a worm drive arrangement as this will be self locking and will take a lot of strain off the motor.

Andy

[skoehler]

To be honest, I have bad experience with the worm drive things since it slips along the axis under heavy load.
It's probably best to use gears to lower the torque on the motor axis. Also, driving a motor at such a low rate is simply impossible to be precise. Make sure that the motor can rotate at a convenient speed (like 100-200 degrees per sec) in order for the arm to move smoothly. Currently you use the mid-sized wheel and the big one. Cascade that 2 or 3 times, and you're probably ready to go.

[gloomyandy]

Yes if you are going to use a worm drive you need to mount it to prevent it from slipping along the axil, so you need extra parts on each side of the screw that interlock to prevent movement. I've used these to drive some pretty heavy loads, but you do ned to construct things with the loads in mind...

[markyn]

Hello guys

i'm back, with some news ... i solved the problem of the motor jumping using the setStallTreshold, and some build improvements.
Yesterday i made this vídeo: http://www.youtube.com/watch?v=MEIXqwp9Fbo
i think i can improve him a bit, but there are sometimes that i don't understand what the robot is doing.

First of all i forgot to tell that i'm using the Behavior methodology, and sometimes he starts a behavior that he should get down and release the cd ...
and he just get down and don't release the cd, maybe i'm using the setStallTreshold wrong, if you guys want, later i can post the algorithm here...
but i'm using like this: setStallTreshold(2 , 4) to open the claw and setStallTreshold(3 , 6) to close the claw

Thank you one more time guys!
See ya