I got 2 dc motors from a broken cheap RC helicopter. How can I Identify what type of motor it is? It has 3 terminals, but only 2 where used. It takes around 2-3 Amps of current at 3.5 V. Each trace in the board is connected to the adjacent one through a capacitor. Here are the pics: enter image description here

enter image description here

  • 2
    \$\begingroup\$ Upload a picture. \$\endgroup\$
    – jippie
    May 2 '12 at 10:48
  • 1
    \$\begingroup\$ To me the pictured motor looks line a pretty standard brushed motor. The capacitors are commonly used to reduce the noise coming out of the motor. One is connected from the + to body, the other from - to body and one to + and -. In helicopters I've seen they were soldered by hand, but since the market is expanding, it's not too strange to see them on a PCB integrated on the motor. \$\endgroup\$
    – AndrejaKo
    May 3 '12 at 8:59

If only two were used and it moved then it must be a brushed motor. Brushed motors only use two terminals for the operation of the motor, brushless use four terminals I believe (three windings plus ground?). The third could be for some sort of feedback or maybe special grounding.

Edit: One caveat - there are some BLDC (Brushless DC) motors that have integrated controllers - these have two power lines and many control lines. Other BLDC motors have integrated commutation sensors (hall effect sensors) - these will have three wires to drive the motor and five for the commutation sensors (three signal plus two power).

Thanks to the picture I can clearly see - that's a basic brushed DC motor. The third connection isn't really a connection - it might be a structural connection (to help keep the PCB attached to the motor) or just grounding to chassis. Does anyone else have a better idea what exactly the third solder blob is used for?

  • \$\begingroup\$ The BLDC motors I know of aren't star-connected but delta-connected and therefore have 3 terminals. \$\endgroup\$
    – AndreKR
    May 2 '12 at 13:20
  • \$\begingroup\$ I think I've seen a 'ground' connection on some. If I remember correctly it's not exactly ground, might be chassis or something. Regardless, if it moved with only two wires hooked up it must be brushed. \$\endgroup\$
    – AngryEE
    May 2 '12 at 14:16
  • 1
    \$\begingroup\$ Brushless motor (Also known as Electrically Commutated Motors (ECM) are very similar to Induction motors. There should only be three wire terminals on it. (no need for ground, typically 2/3 windings are charged when in operation) \$\endgroup\$
    – CyberMen
    May 3 '12 at 13:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.