Hello,
I am new in the Forum and first of all sorry for my bad english.
For my control engineering project I bought a Gearmotor 4.4 :1 25Dx63L HP 6V with encoder. The first tests with the motor showed, that i need 4.5V that the motor starts spinning. When i supply the motor with a lower voltage, the motor doesnt start spinning, the rotor only makes a small movement. It seems as if there is a magnetic resistance, that prevents the motor from spinning. Is this a normal behaviour of the motor?
I have now demounted the encoder cap und tried to rotate the rotor of the motor by rotating the magnetic disc ( like shown in this video (min 1:46) https://www.youtube.com/watch?v=M0JbMNluIfw ) A free, continuously spinning of the disc is not possible. I can spin it but only into like defined, magnetic positions. For one full rotation, the rotor “locks” in 6 positions.
Hopefully you can understand my problem and I am looking forward for your answers!
Kind regards, Johannes
Hello.
It sounds like you might just be observing the motor’s cogging torque, which is normal behavior for small brushed DC motors that use permanent magnet stators like ours. This Wikipedia article gives a decent overview. However, while we have not characterized this in detail, it seems odd that you need 4.5V for the motor to start spinning. In a quick tests here, I found the motor with no load attached usually starts spinning around 1V.
Can you post more details about how you are using the motor (including what power supply you are using) along with some pictures of your setup that show all of your connections?
- Patrick
Hey Patrick,
thanks for your answer. I will reply you within the next days and give you some more information about my setup. I’m on the road and don’t have time right now.
Johannes
In this video, you see the motor being supplied with 3,5V. It doesnt start spinning, but the rotor moves a little bit.
This video shows the motor with no connection to the power supply. I need to apply some torque to being able to even rotate the rotor but when i let go it snaps into place as you can see in the video. There are 6 such places where the rotor snaps in related to one full rotation.
Hello.
The behavior in your latest video with the unpowered motor is definitely from the cogging torque, so I don’t think there is anything to worry about there. Keep in mind that these particular motors (the 25D HP 6V motors) use especially strong magnets for the size of the motor to help get the most possible power out of them, and that makes their cogging torque higher compared to other similar motors.
As for the setup where you are trying to power the motor, my immediate concern is that the power from your supply has to go through several different wires and connections, including a breadboard (which is not suitable for the kind of current this motor draws), so the resistance from those might be accumulating into a non-trivial sum compared to the motor’s resistance (around 1Ω). Another possibility is the power supply is not behaving as expected when you connect the load.
Can you try measuring the voltage as close the motor terminals as possible when the system is powered such as at the soldered connections to the motor terminals visible on the encoder boards? Can you also try connecting your motor to your supply as directly as possible to the motor, avoiding going through the breadboard or extra wires?
- Patrick