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DC Motor Sync
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Author:  LinK [ Wed Jan 08, 2014 1:08 am ]
Post subject:  DC Motor Sync

My team is using two motors to move an arm and they are noticing that it does not always move smoothly. I think the motors are getting out of sync with each other. I have not been able to find a way to programmatically sync two DC motors.
If we plug both motors into the same controller port, will that help them stay in sync?
I have also seen some suggestions to use encoders. Has anyone done this? I am thinking we would check the encoder values each time the arm stopped and set on of the motor to be the same as the other motor.
Thanks

Author:  MHTS [ Wed Jan 08, 2014 4:27 am ]
Post subject:  Re: DC Motor Sync

Are they Tetrix motors? How do you tie the two motors together mechanically? We also have an arm design using two Tetrix motors. They are tied together by a chain and sprockets. So we have three sprockets, one on each motor and one on the arm. The chain ties all three sprockets in a loop. You don't need to explicitly sync motors in this configuration because the chain will make sure the two motors will run at the same speed. So tell us your configuration and see if you need to worry about it.
BTW, do not connect two motors to the same motor terminals on the motor controller. You will fry it. I am pretty sure it is illegal and the robot inspector will call you on that if they pay attention.

Author:  BurningLights [ Wed Jan 08, 2014 11:48 am ]
Post subject:  Re: DC Motor Sync

MHTS wrote:
BTW, do not connect two motors to the same motor terminals on the motor controller. You will fry it. I am pretty sure it is illegal and the robot inspector will call you on that if they pay attention.


This is not true. My team ran an entire season last year with six motors running off of three ports on motor controllers. This year, we're doing it again. It passes hardware inspection without any problem and works fantastic! Now, it's true that three motors in one port has been banned by a Q&A post, but two motors is allowed.

Author:  BurningLights [ Wed Jan 08, 2014 12:49 pm ]
Post subject:  Re: DC Motor Sync

By the way, see http://ftcforum.usfirst.org/showthread.php?1921-Robot-Electronics-and-Power-Answer-Thread&p=7575&viewfull=1#post7575 for reference.

Author:  LinK [ Wed Jan 08, 2014 12:57 pm ]
Post subject:  Re: DC Motor Sync

Yes, they are tetrix motors. We have two long channels connected to a basket that the need to lift. There is a tetrix motor on each channel. When they start it almost lifts too fast and then it slows down to the point where it can barely lift.
Thanks

Author:  LinK [ Wed Jan 08, 2014 12:57 pm ]
Post subject:  Re: DC Motor Sync

Yes, they are tetrix motors. We have two long channels connected to a basket that the need to lift. There is a tetrix motor on each channel. When they start it almost lifts too fast and then it slows down to the point where it can barely lift.
Thanks

Author:  BurningLights [ Thu Jan 09, 2014 5:37 pm ]
Post subject:  Re: DC Motor Sync

LinK wrote:
Yes, they are tetrix motors. We have two long channels connected to a basket that the need to lift. There is a tetrix motor on each channel. When they start it almost lifts too fast and then it slows down to the point where it can barely lift.
Thanks


Hmm, it seems like you might need to use some gearing. It sounds like your two motors might not have enough power to lift the arm when it gets close to the horizontal position (where the effects of gravity on it are the strongest).

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