Motor help

Thread Starter

SeanV123

Joined Nov 12, 2020
46
Hello, I need help understanding these motors. I dont know what type they are and I would like some info. I took apart an old RC car I had and salvaged a few motors. However they have 3 cables, as shown in the pictures. I tested one motor in my breadboard, the one with the yellow, green and black cable. I want to know what each cable is for. I connected the yellow cable to my supply and the green to ground and the motor worked. But, my confusion lies in the function of each wire. I thought the black wire may be for ground but the motor works fine when I have the green to ground and yellow to supply. Can anyone guide me as to what the function for each wire is and what type of motor it is?
Thank you.
 

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MaxHeadRoom

Joined Jul 18, 2013
22,022
Looks like a simple DC brushed motor, measure the resistance between all three , the black look like it might just be a ground?
Also spin it and see which of the conductors show a voltage.
Max.
 

LesJones

Joined Jan 8, 2017
2,839
They are permanent magnet DC motors. The black wire is only to ground the casing to reduce interference to the R/C receiver. The capacitors connected to the brushes also reduce interference. (They play no part in the function of the motor. ) These motors can be reversed by reversing the polarity of the supply to them.

Les.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
46
Looks like a simple DC brushed motor, measure the resistance between all three , the black look like it might just be a ground?
Also spin it and see which of the conductors show a voltage.
Max.
Thank you sir, I'm still confused as to the function of the black wire as when I mentioned that the motor worked when the green wire went to ground. I will do some research on DC brushed motors. Funnily enough we have just started looking at DC brushed motors in my power electronics class in college so I may ask my professor.
Once again,
Thank you.
Sean.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
46
They are permanent magnet DC motors. The black wire is only to ground the casing to reduce interference to the R/C receiver. The capacitors connected to the brushes also reduce interference. (They play no part in the function of the motor. ) These motors can be reversed by reversing the polarity of the supply to them.

Les.
Thanks Les for your reply, can you elaborate on your point about the black wire and how it is only ground to the casing and to reduce interference.
Thank you sir,
Sean.
 

MaxHeadRoom

Joined Jul 18, 2013
22,022
The black wire should be connected to any earth GND that is available, it is only used for suppression and not needed for motor operation.
If you connect a meter to the two other leads and spin the motor, you should see a generated DC voltage, if it is a simple DC brushed motor.
Also, if you short the two conductors and attempt to spin the motor, you should see the dynamic braking effect.
Max.
 

Thread Starter

SeanV123

Joined Nov 12, 2020
46
The black wire should be connected to any earth GND that is available, it is only used for suppression and not needed for motor operation.
If you connect a meter to the two other leads and spin the motor, you should see a generated DC voltage, if it is a simple DC brushed motor.
Also, if you short the two conductors and attempt to spin the motor, you should see the dynamic braking effect.
Max.
I see, go raibh míle maith agat
 

LesJones

Joined Jan 8, 2017
2,839
If the casing is not grounded the fast transients caused by sparking on the brushes will be coupled via stray capacitance between the windings and the casing. The casing would act as antenna and radiate the RF energy. The capacitors will have a low reactance at high frequencies so they bypass the RF to ground so it is not radiated from the supply wires. (NOTE this does not totally eliminate RF interference.)

Les.
 

Tonyr1084

Joined Sep 24, 2015
5,549
Something I'm noticing in the comments - or actually something I'm NOT seeing: The mention of "Ground". It's often a confused word, misapplied in many instances. Since you're discussing motors from an RC car - nothing about it is grounded to - um - "the ground we walk upon". There are potentially three states; "Common" which is a form of a ground, but not necessarily the negative end of the power supply (batteries). Common can also be a point of reference somewhere between Positive and Negative, such as one will commonly see in an amplifier where the chip requires a positive and negative rail with a common which may sometimes mistakenly be called ground. It's possible the black motor wire is connected to the most negative end of the batteries. If that's the "common" point then all other potential voltages will be above that point. Since this is from an RC car, it's likely that the negative most point is NOT the common point as radio signals will need to be amplified.

The black wire is directly soldered to the case of the motors, so it only acts to keep any electrical noise generated by the motor brushes arcing on the commutator shielded from influencing any other electrical signals the RC car may see. The other two wires - colors be damned - are only to power the motor in one direction or the other. Those capacitors are also implemented to reduce unwanted electromagnetic radiation (noise) from interfering with the radio receiver.

I mentioned there were three states: Positive potential, Negative potential and Common (sometimes called ground). In an RC car you will find all three of these potentials, and yes, common is also a potential.

As far as the word "Ground" goes - there are many different terms or types of ground. But there are three basic "Ground"s. Earth ground is exactly what it infers - Earth (or the ground). It's symbolized by three parallel bars growing smaller toward one end with the connecting wire to the longest. Then there is the common ground, which is symbolized by a triangle which replaces the three bars. Then there is "Chassis Ground". It is similar to the first ground symbol in that it has the wire intersecting with a perpendicular bar but with three rake like lines on an angle. Refer to the attached symbology. And remember, there are far more than these few symbols.
1608049519839.png
First is chassis ground, second is common ground and third is earth ground. Again I want to point out that these are relative terms and often are misused and incorrectly referenced. There ARE others.
 

MaxHeadRoom

Joined Jul 18, 2013
22,022
First is chassis ground, second is common ground and third is earth ground. Again I want to point out that these are relative terms and often are misused and incorrectly referenced. There ARE others.
I have said this many times probably ad-nauseaum.
I always preferred the UK usage where the difference was distinct.
You always ran a EARTH wire.!
Dr Bruce Archambeault once had a good video on it!
Max.
 

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