Motor issues

The motor that is being used by the Clawbot will sometimes work properly to open and then later in the same program, it will not open fully, even though the program is correct. The students are switching out motors now, but was wondering if anyone else has had something similar happen to them? Any suggestions?

Thanks.

Does the robot do this after you use the it for a long time? If so, low battery power may be causing this issue. Make sure you are constantly switching out your battery once it gets low.

No, it doesn’t happen all of the time. But I did have the students switch out the batteries and this made no difference. During my first class today, the claw motor worked fine and then for the next class it did not. Yesterday, it was just the opposite. It did not work for the first class, but it worked fine for the second class.
Doesn’t make any sense to me.

You should also not run the robots for a long time without breaks. If you are taking breaks, and it’s still happening, I have no idea what the issue is

When you say there should be breaks, do you mean breaks in the programming code, or breaks in time? As in not running the programs continually?

Breaks in driving the robot. Example: drive for 5-10 minutes, take a 5 minute break so the robot has time to cool down. Also, make sure when you’re driving, don’t hold the claw shut using the motor for an extended amount of time. Doing this can make the motor burn out. You only need to use the motor to open and close the claw, not to hold it shut

Does your claw use the 3-wire servo motor or are you operating the claw with a 2-wire 393 motor?

If you click on the tabs on this following page, you can see the difference, and I’m sure you will need to code differently for the different types of motors. You might be stalling the motor (overheating it) if you aren’t coding it properly, and that could cause the intermittent failure problem. http://www.vexrobotics.com/motors.html

4361T - What do you consider to be an extended amount of time to use the motors to hold the claw closed?

If you are running it at full power to hold it closed, an extended period of time could be less than a minute. If you are burning it out (tripping the PTC - a form of circuit breaker) the motor, then the motor will just stopped working until it cools down. As you stated it seems to be an intermittent thing and you have changed batteries. I think we need more information. What have you tried using the claw for? What does your programming look like? Are you opening and closing the jaw with analog or digital controls? The Joysticks on the controller are analog. Buttons are digital. If buttons, how are they programmed? Give us more information, please.

What he said

Ok, thank you. I know the programming is correct, because I have used RobotC for a number of years. And given everything that has been posted, the biggest issue we have been facing is the mass of what we were picking up. This may have been causing the motors to trip. We have been working on autonomous movement using RobotC and I came up with a challenge that had the students picking up small cans of soup and moving them to a particular point. I have switched the cans of soup for empty water bottles. Everything is working much better since switching.