Motors whine when under PWM control

[Christopher X. Candreva]

After months of being sidetracked, I just tested out my PWM motor contoler.

Everything works great, except if the motor is running at anything under
full speed, there is a high-pitched whine comming from them.

Is this normal, or bad ? Is there anything that can be done to stop it ?

I've done some searching, but mostly found references to treadmills, with one
page on using your motor as a speaker to give warnings to the user.

PWM controller is an LMD18200 on the Magnevation board, motors are the
DeWirt mototrs mentioned on the Lazlo site (www.theonespot.com)

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Chris Candreva -- ch...@westnet.com -- (914) 967-7816
WestNet Internet Services of Westchester
http://www.westnet.com/

[Dennis Clark]

Christopher X. Candreva <ch...@westnet.westnet.com> wrote:

This is common when the PWM signal is in the audible range, and most of
them are. Don't worry about it, its fine. If the motor and geartrain
weren't making so much noise you'd hear the wine while the motor is turning.

have fun,
DLC

: After months of being sidetracked, I just tested out my PWM motor contoler.

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* Dennis Clark Aristocrat at heart d...@verinet.com www.verinet.com/~dlc *
* Be well, do good work, and stay in touch -- Garrison Keillor *
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[Christopher X. Candreva]

From: Dennis Clark (d...@io.frii.com)

> This is common when the PWM signal is in the audible range, and most of
>them are. Don't worry about it, its fine. If the motor and geartrain
>weren't making so much noise you'd hear the wine while the motor is turning.

Actually, I do hear it when the mototrs are running. They are fairly quiet
motors.

Thanks ! I was concerned when I couldn't find mention of this in either the
MIT or Gordon's book, and my net searches were comming up empty.

After reading your answers and knowing what to look for now, I did find this
discussion from 1995:
http://www.cs.uwa.edu.au/~mafm/robot/PWM.html

It includes this formula for picking a frequency:

To ensure that current flows relativly steadily, we want:

2 * pi * f L >> R

where:

f = switching frequency

L = armature inductance

R = armature resistance

>> means much greater then, lets say 10 or more

[Simon Wakley]

Hi,

Yeah, they do whine and with a motor under constant load it can be a
little annoying - we have used Inductors with low impedance motors to
reduce this and also a choke to remove some high frequency noise. The
switching frequency of the PWM is the central issue. The ones I use
have a 20Khz frequency and you can hear that and a lower harmonic (I
think - I'm not a sound engineer :-0)

If you reduce the tuning parameters, then the whining reduces, but so
does the motor response. I am not really up on this, but it's not
unusual. The only problem is when the motor's inductance is too low and
then the motor will overheat even at rest.

In article <a36m7e$jrm$1...@mycroft.westnet.com>, Christopher X. Candreva
<ch...@westnet.westnet.com> writes

>From: Dennis Clark (d...@io.frii.com)
>
>> This is common when the PWM signal is in the audible range, and most of
>>them are. Don't worry about it, its fine. If the motor and geartrain
>>weren't making so much noise you'd hear the wine while the motor is turning.
>
>Actually, I do hear it when the mototrs are running. They are fairly quiet
>motors.
>
>Thanks ! I was concerned when I couldn't find mention of this in either the
>MIT or Gordon's book, and my net searches were comming up empty.
>
>After reading your answers and knowing what to look for now, I did find this
>discussion from 1995:
>http://www.cs.uwa.edu.au/~mafm/robot/PWM.html
>
>It includes this formula for picking a frequency:
>
> To ensure that current flows relativly steadily, we want:
>
> 2 * pi * f L >> R
>
> where:
>
> f = switching frequency
>
> L = armature inductance
>
> R = armature resistance
>
> >> means much greater then, lets say 10 or more
>
>
>

--
Simon Wakley
Visit our web site at <<www.cameracontrol.com>>

[Ms. Robot Hello]

We ran into this same thing as well. We ended up switching our power supply out and it stopped the high pitched sound. good to know chokes can help. going to play around with some ferrite blocks next time we run into it.

-Ms Robot
https://www.msrobot.com

[Sebastian Fahrner]

Have you tried changing the PWM frequency

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