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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

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    \$\begingroup\$ Upload a picture. \$\endgroup\$ – jippie May 2 '12 at 10:48
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    \$\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
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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?

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  • \$\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
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    \$\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

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