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Understanding Basic Motors

  1. Sep 1, 2015 #1
    This is my first post, so please excuse any mistakes I might make. Sorry in advance.

    First and foremost, if anyone thinks I am being unsafe in any way, please let me know. I like to do things hands-on. I learn best that way, but I want to be safe.

    I am a budding electrical engineering student and I am trying to understand how to salvage basic motors at home. I think I have salvaged a motor from an old RC truck thing that was under my house for years. I'll try to attach a pic later. Now I have looked up the info printed on the motor there and it came up with http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rc_280sa [Broken] data sheet. On the motor that I have salvaged, there is a thick purple wire, a thick pink wire, and a thin brown wire. I think the thin brown wire may be ground, and the two thick ones may be connected? (See point 2 below)

    1. Is it correct to call this a DC motor? Could you know just by looking at it?

    2. I have a 12V 900mA Class A DC transformer that I plan to use to power it. This produces 10.8 Watts, when it draws the full 900mA right?

    3.When I touched the two leads of the power to the two thickest wires, there were small brief sparks and the motor seemed to jerk away. I think I was shorting out the DC voltage briefly. I think I should've tried putting + from power on one of the thick wires, and ground on the thin wire. I will try that later.

    4. What it the cheapest tool I can order to control and/or monitor the speed/torque or just some basic data? Just a potentiometer for control? What about cheap wireless control? I hope to reuse this motor for other RC endeavors.

    Any info is welcome, which is why I posted in a more general engineering forum. Thanks.
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Sep 1, 2015 #2
    You need to research this a little more. If you Google RC-280SA you will find many references. From the data sheet you already have, you should be able to see that a 12V power supply would be inappropriate here. Can you see why?

    You can't necessarily tell if a motor is AC or DC just by looking at it, though there are certain types that are easy to spot. Take a look at "synchronous motors" to see one type that is easily recognisable. In general, however, it is safe to assume that a motor like this, of this size, with just two wires (I don't know what that third wire is but I suspect that it probably is a ground wire - what is it connected to at the motor?) and without any additional components attached is a DC motor. Beware, however, of servo motors of similar size. These will always have more than two wires and can be damaged if you just connect a power source across them!

    The fact that the motor "seemed to jerk away" should suggest to you that you were probably connecting the right leads! Did it just jerk and stop, or did it run continuously? Use the right power supply (see above) and if it runs continuously, fine. If it doesn't then the motor may have seized or be corroded internally.

    You can't really use a potentiometer directly to control a motor of this type - it would need a heavy-duty wire-wound one, and would be very inefficient. The best way is to use a variable voltage power supply. There are other ways, and I suggest you also look at the subject of PWM for more information.
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