Polarity of small coreless brushed motors

Hello,

First of all, thank you for taking the time to read this.

I have some questions on polarity of tiny brushed coreless motors. I recently purchased these:

to build a light micro quad. Although the seller mentioned that 2 motors are clockwise and the other 2 are anti- clockwise, I wondered if it makes any difference. I did try running the anti-clockwise motors reversely, they did spun clockwise without any noticeable issue. The voltage drop across these motors that were ran reversely were the same as the ones run according to the specified polarity. However, perhaps due to coincidence, I noticed that after a while, these motors that were not run according to its specified polarity seemed to not work (not spinning anymore when the same voltage was provided).

I read about this online, and I got conflicting answers. Some forums mentioned that polarity does not matter, some said that the performance and the life span of the motor would be affected if it is made to run on reverse. If I am not wrong, I understood that for this kind of DC toy motors: Amazon.com: Topoox 12 Pack DC Motor 1.5-3V 15000RPM Mini Electric Hobby Motor for DIY Toys Science Projects: Toys & Games , the polarity depends on how you wire it, there isn’t any fixed polarity. Would you please provide some basic technical insight on this?

In case you need to know, my motors are connected to a motor driver DC Motor + Stepper FeatherWing Add-on For All Feather Boards : ID 2927 : $19.95 : Adafruit Industries, Unique & fun DIY electronics and kits. I powered the driver with a Lipo (3.7 V, 2000mAh). The voltage drop across the motors were low- about 0.7 to 0.8 V per motor, and the input to the driver measures 3.0V. The lipo was measure to be 3.9 V when not connected to the driver. At this stage, I was only testing the motors.

So in summary, I have a couple questions/ issues here:

  1. I noticed 1 or sometimes 2 motors would stop spinning after a few times of power up, I wonder if this has to do with me wiring the motors to run in reverse directions. The motors that did not spin had about 2 times the voltage drop of the ones that are spinning during powered up.
  2. The voltage drop across the motors seems low, the coreless motors requires about 3.0 to 3.7 V to operate according to spec.
  3. When given the same speed, all motors would spin, however one side of the frame ( the sides with motors connected to M1 and M2) would lift up, but the side with motors connected to M3, M4 would not. The propellers and motors directions are matched accordingly, so I would think this is issue is related to the motors.
  4. I am unsure if the polarity of the motors brushed coreless motor matters. I would like to know if I can just wire these motors in reserve and have them run in the opposite directions? I know they will spin, but I wonder if they would run slower ( I have no way to measure their speed but the voltage drop seems to be no different) or they will burn out sooner.

Thank you for your time and help once again.

Did you see this in the product description?

Option: Clockwise Motor(With Red Blue), Anti-clockwise Motor(With Black White)

Package:
2 pcsCW 8.5x20mm coreless motors
2 pcs
CCW 8.5 mm brushed motors
2 pair 55mm propeller

Apparently, there are 2 different motors with different wire colors for CW and CCW, Is that what you have? You might have a CW propeller on a CCW motor.

No real experience on the subject, but I can see two problems.

  1. Brushes are designed/angled for one direction, and spark/wear out faster if you use them in the other direction.
  2. Oil grooves in sinter bearings are made for one direction, and loose lubrication if you use them in the other direction.
    I could be wrong, but it's never a good idea to go against manufacturers recommendations.
    Leo..

Another reason is timing-advancement.

DC motors, especially those that are designed for high speed, have the brush position advanced so that commutation happens early. This is to allow for the time it takes current to build up when the inductance of the windings is slowing down the change.

Thus there's a forwards direction and a reverse direction. The forwards direction will be more efficient at full speed than reverse, although both will work.

Coreless motors have less inductance, but they do run at very high speed, so I suspect the effect is important.

Thank you for all your helpful answers.

JCA34F- I appreciate our input. Yes, I am aware that the CW and CCW motors are indicated by the colors of the wires. In my previous questions, I was trying to find out if the motors can be used in reverse polarity without any harm done to them. From the response I received here, the answer is no.
As for the propellers. I did make sure that the CW props are mounted to the motors that spin CW, and the CCW are on the CCW motor. I am still puzzled why one side of the frame lifted and the other did not.

MarkT & Wawa- thank you for explaining the working mechanism of the motors to me. If I may ask, how are my tiny motors( brushed, coreless motor) differs from this kind of toy dc motors
Amazon.com: Topoox 6 Pack DC 1.5-3V 15000RPM Mini Electric Motor for DIY Toys, Science Experiments: Toys & Games.
As far as I know, this kind can be made to turn in either direction without hurting the motor.

Thank you!

Most small toy motors are biased, and turn faster one way than the other - the leads are marked +/- or red and black. Most brush systems work better one way than the other, but the difference may not be a show stopper(*)

You can get motors with variable timing where the brush mount is adjustable, and ditto for hall-sensors on a BLDC. For use as a servomotor you’d normally want unbiased, for instance, and for driving a linear actuator or other reciprocating machinery a bias is not wanted.

Many applications use both directions, but not equally (electric screwdriver, winch) - the direction used most or with most torque would be deemed the forward direction for a biased motor.

(*) Big graphite brushes in large motors sit to one side of their guides if the motor always goes one way, then will not sit nicely on the commutator when spun the other way due to slack in the guide-tube (the brush tilts a bit). For a large bidirectional motor the brush guides/mounting has to be better engineered to prevent this I think. Its one of the many issues with brushes that has seen the inexorable rise of brushless DC motors.