Hi
I have Arduino Uno + motorshield. External adjustable power supply 9-12V 3A (board without a jumper).
The problem is that the fan makes a high-pitched sound when it is not at full speed.
When it is connected directly to the power supply, changing the voltage changes the speed without making a sound.
In addition, I noticed that the output is ~ 6V by default, so I had to set the SimHub output tuning option to 200%.
Please help what to check?
Hi ! This is inherent to the technology of the shield (based on pwm or "pulses") You can tune the frequency quite easily at upload : 
For fans you can go easily as low as 200-300hz, which will strongly reduce the "humming" noise.
Nicolas
Thanks for help with 200 is definitely better, the sound is but only at the beginning of acceleration.
I am currently using speed with curving, it is a lot of fun
Low force 35km / h
High force 100%
Curving sensibility 82
Changed tuning gain to 100%
I increased the voltage to 12.7
Fans from the old HP server, loud but blowing very hard 🙂
Thanks !
Type in Google "aliexpres 9-24 3a" im using something like that - power adapter with LCD that can be regulated
Hi, I am using a MotoMonster board and have the same issue. Is it possible to adjust the PWM on this board?