3 Replies Latest reply on Jun 3, 2020 1:56 PM by dougw

    Looking for a few good motors

    colporteur

      How do you identify the maximum voltage for a motor?

       


      An omission on my part of confirming the specification of a purchase, leaves me with a DC motor that I don't know the operating voltage. I needed an inexpensive motor for some project testing. I purchased the following motor. https://www.banggood.com/Wltoys-P929-K989-128-Rc-Car-Spare-Parts-130-Brushed-Motor-No_K989-06-p-1337823.html?rmmds=myord…

       

      After connecting the motor to 5VDC, the noise from the speed scared the be-jesus out of me. I realized I assumed the voltage. The motor has no rating information. The motor is rated for used in RV cars. I found the specification for one car. It had a battery pack rated at 7.4VDC. I have tried the motor at 3VDC and it is still pretty loud.

       

      It seems I keep making this same mistake in orders. Usually one part I miss a fine detail and end up having to go back and dig up some dirt. If a member has experience with the motor they are willing to share or has a problem resolution method to give it would be appreciated.

        • Re: Looking for a few good motors
          genebren

          Sean,

           

          This tiny little motors can be somewhat frightening and noisy.  Different models spin a different RPM, with some of these running upwards of 30,000 RPM.  This particular motor is listed as 7.4V and 31,000 RPM (although the number is not currently found on the manufacturer's site).  The good news on this motor is that it is built my on of the more reputable manufactures (Mabuchi Motors).  I worked on a small handheld device used for improving skin texture.  A small multi-faceted mirror was spun by own of these motors, in a closed loop manner, so a laser could be fired at several points during it rotation (spreading the laser field out into multiple dots along a line).  We were driving this motor and a few slow speed.  We tried several different motors throughout the development process, attempting to find a very stable and repeatable motor.  In the end we went with of these Mabuchi Motors. (Note: we would have likely been better off with a stepper motor, but we designed ourselves into a corner and a DC motor was our only choice).

           

          Good luck

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          • Re: Looking for a few good motors
            DAB

            Hi Sean,

             

            It is not uncommon to overdrive DC motors for short periods of time.

             

            Mostly you use a PWM circuit to keep the coil form overheating and you can control the speed and the noise.

            PWM allows you to ramp up and ramp down the speed to keep the torque forces down as well.

             

            DAB

            3 of 3 people found this helpful
            • Re: Looking for a few good motors
              dougw

              The size of the internal wire and the brushes dictate how much current can be supplied.

              If you can see the wires coming out to the motor terminals (not the lead wires in the picture), you may be able to deduce their current capacity from the wire diameter.

              Then you need to measure the resistance across a stalled motor to get some idea of the stall current at any voltage.

              Small motors like this can usually take up to 6 V, but there are always exceptions.

              Top speed should be around 4000 RPM.

              If the motor is getting very warm, consider backing off on the supply voltage.

              If you are running in an application where the motor can be stalled, consider implementing a current limit to prevent over heating the wire.

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