servo/motor problem

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  1. - 10th February 2009, 01:04 #1
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    Unhappy servo/motor problem

    hi there im working on a project for science olympiad and i recently got all the electronics done for my robot. what baffles me though is that after about 3 to 4 minutes of controlling the motor (through an h-bridge) and servo all of a sudden both stop working, the motor stops working and the servo makes very jerky movements in one direction. is there anything u can think of that could cause this? i have checked all of my connections which are good, the batteries are still fresh, and i have even swapped out the micro (16f690) all have made no difference.
  2. - 10th February 2009, 04:23 #2
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    What about the voltage regulator? Is it heating up after a bit and dropping out?.

    A schematic might help.
    Dave
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  3. - 10th February 2009, 04:28 #3
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    Quote Originally Posted by mackrackit View Post
    What about the voltage regulator? Is it heating up after a bit and dropping out?.

    A schematic might help.
    I think this is likely, are you running the motor's power through the regulator?
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  4. - 10th February 2009, 15:31 #4
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    the motor does not have a voltage regulator, and i am running everything off of 4 AAA batteries. should i add a voltage reg? how will this affect my battey life?
  5. - 10th February 2009, 16:00 #5
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    Talking Button cells ???

    Quote Originally Posted by griffin View Post
    and i am running everything off of 4 AAA batteries. ?
    No need to see further ...

    Alain
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  6. - 10th February 2009, 16:19 #6
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    Are the batteries rechargeable? The total voltage could be with fully charged cells 4.8 to 6 volts nominal. One could be a bit low if you are running at 10MHz or above and the other is a bit high.

    The 4.8 v will be fine if nothing causes to much of a voltage drop. The batteries may seem fine after everything stops due to rebound. Try a voltmeter when it is running to monitor the voltage to see for your self.

    Solution might be to have a separate set of batteries for the PIC and another for the motors. Share the zero rail.

    If you are not running rechargables then a regulator is recommended for the PIC. Keep the voltage at 5 volts or less here. If you run the PIC at 4 MHZ or so the voltage can be much lower, check the data sheet under electrical characteristics. A low drop out regulator may also be handy. If the batteries are max voltage 4.8 and you run at 4 MHz then you will not need the regulator.

    This "science olympiad ", is this something with a secondary school or university ?
    Dave
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  7. - 10th February 2009, 16:34 #7
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    Talking

    Hi,Dave

    The internal resistance of those batteries is FAR too high to power a servo , so a servo and a Motor ...

    Want some values ??? just to laugh a bit ...

    running the PIC @ 3 v could be a solution ... for the Pic only !!!

    Alain
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  8. - 10th February 2009, 17:28 #8
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    Quote Originally Posted by Acetronics View Post
    The internal resistance of those batteries is FAR too high to power a servo , so a servo and a Motor ...
    eYup, I was not really thinking about the motors, more to the PIC browning out. Good point.
    Dave
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  9. - 10th February 2009, 17:35 #9
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    Quote Originally Posted by griffin View Post
    . . . should i add a voltage reg? how will this affect my battey life?
    No, I thought if you were, then you might be overloading it. Alain is one of this forums R/C and Servo EXPERTS, I would defer to his expertise.
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  10. - 10th February 2009, 19:40 #10
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    I just got done trying to power the pic seperatly from the motor and servo and nothing changed. also i tried some code to just use the servos and that worked fine, any ideas?
  11. - 10th February 2009, 20:07 #11
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    Now is the time to post your code and schematic.
    Dave
    Always wear safety glasses while programming.
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