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Defective Motor
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Defective Motor

by JohnGaby on Sun May 22, 2022 6:33 pm

I recently ordered 2 of these motors:

https://www.adafruit.com/product/4416

However, one of the motors appears to be defective. First, it is significantly less powerful than the other motor and the encoder does not function correctly. Attached is a sample of the signals coming from the encoder. Notice that not only is one of the signals missing its pulses, but the two signals are not 90 degrees out of phase.

I am usually quite happy with the quality of the devices I purchase from you, but you appear to have some quality control problems with these motors.
Attachments
SDS00002.png
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Re: Defective Motor

by tepalia02 on Mon May 23, 2022 9:16 am

Really unexpected. Hope you get a proper solution.

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Re: Defective Motor

by adafruit_support_carter on Mon May 23, 2022 1:18 pm

Can you provide more information about how the motors are being used. What are they being connected to for power, control, and encoder feedback?

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Re: Defective Motor

by JohnGaby on Mon May 23, 2022 1:59 pm

The motor power is 7.2v. The encoder is being read via a STM32F103C8T6 using 3.3v.
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Re: Defective Motor

by adafruit_support_carter on Tue May 24, 2022 11:29 am

Is power being applied directly to the motor? There's no h-bridge or other interface for controlling speed / direction?

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Re: Defective Motor

by JohnGaby on Tue May 24, 2022 11:50 am

The power to the motor is delivered via an L298N. However I do not see how this would affect the encoder which is clearly not working.
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Re: Defective Motor

by adafruit_support_carter on Tue May 24, 2022 12:23 pm

Yep, for now, focusing on the power issue:
it is significantly less powerful than the other motor


What if you do power the two motors directly? Is there still a noticeable difference between the two?

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Re: Defective Motor

by JohnGaby on Tue May 24, 2022 3:23 pm

Here is a graph of the motor speeds both with and without a load. In this case I am running the motors at full power (still using a motor controller). For the one with the load the motors are attached to a chassis with wheels. Note that with no load, the motors run at about the same speed, but when driving a chassis, one of the motors runs at close to half the speed of the other. In case you are wondering, I am able to get the speed of the motor with the bad encoder by ignoring the signal that is not working (i.e. I am not running it in quadrature mode).
Attachments
MotorCompare.jpg
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Re: Defective Motor

by adafruit_support_carter on Tue May 24, 2022 3:35 pm

How are you determining the vertical axis (speed) in those plots? Based on what sensor?

For the load scenario, are the motors driving the same load? Not just two copies of the same nominal load (like two different wheels). But they are being attached to the exact same load? i.e. - everything is 100% the same between the two setups with the only difference being the motor itself?

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Re: Defective Motor

by JohnGaby on Tue May 24, 2022 3:40 pm

Are you seriously contending that I don't know what I am doing and there is something that I am doing that is causing the difference. The two motors are driving two different wheels to move a robot. This is the same configuration that I am using with other similar motors and for those motors there is no significant difference in speed. When you look at the graphs, it is clear there is something wrong with one of the motors. When you take into account that that SAME motor has a bad encoder I think it is pretty clear that it is defective.
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Re: Defective Motor

by JohnGaby on Thu May 26, 2022 12:24 pm

I take if from a lack of any further response that this conversation is over. I am saddened to discover that Adafruit is not willing to stand behind the products they sell, but it is good to know for the future.
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Re: Defective Motor

by Franklin97355 on Thu May 26, 2022 2:19 pm

Did you swap the motor on the controller and the problem followed the motor?

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Re: Defective Motor

by JohnGaby on Thu May 26, 2022 2:37 pm

Let's forget about the power problem. The motor is defective based on the problem with the encoder.
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Re: Defective Motor

by adafruit_support_carter on Thu May 26, 2022 3:38 pm

The two motors are driving two different wheels to move a robot.

There could be some difference in the mechanics between the two wheel assemblies maybe? The motors are not being used 100% the same.

OK, let's switch to looking at the encoder issue.

How are you tying in to the encoder signal lines to get the scope trace shown above?

How was the motor run for the signal trace shown?

Did you measure the same signals on the other motor? (just to verify things in terms of being able to get the expected output there)

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Re: Defective Motor

by JohnGaby on Thu May 26, 2022 4:33 pm

I am done here. It is clear you are never going to accept responsibility for the motor's failure and you are wasting my time. Needless to say I won't be buying any more motors from you.
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