High Pitch Sound from the PF Motor

[Leviathan008]

Hi, i new with this, and sorry for my english. I´m from Peru, i have a problem with the PF speed remote control, when i.m use my 4 x 4 Crawler, with one L motor and one XL motor, sounds a high pitch sound and both motors run slow with negative power, this no occurs when i use a regular PF remote control,the strange is, that occurs when i replace the batterys, because before i replaced them, it works fine, is this common

thanks for the help

Edited August 18, 2015 by Leviathan008

[dr_spock]

You can get the same whine with the speed control on PF train motors at slow speed or starting off. I think that's due to PWM (pulse width modulation). It's normal behavior.

[bonox]

This bloke (http://www.google.com.au/url?url=http://www.hackvandedam.nl/blog/%3Fpage_id%3D559&rct=j&frm=1&q=&esrc=s&sa=U&ved=0CBQQFjAAahUKEwi57amm-bPHAhVJoZQKHaxvBg8&usg=AFQjCNGFgrGwJgnsWkR6Yfn7mbJ3rXVReA) says that the PWM frequency is 1150Hz.

That's quite audible for people and sounds like a 'high' pitch, but nothing like a top C from a soprano or cornet. The noise is the motor being driven intermittently (rapid start-stop) at that frequency. TLG have done it that way because it's cheap.

You can drive motors at almost any frequency you like, but you need a driver circuit with a frequency above human hearing before it will appear to be 'silent'. It isn't actually silent of course, just inaudible.

As an interesting aside, changing the drive frequency is commonly used to "play tunes" on motors. I believe there's someone who has used an SBrick and a PF motor to play the starwars imperial march.