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Stepper motor squeal with Gen6

Posted by macphyter 
Stepper motor squeal with Gen6
August 31, 2011 04:59PM
I've jumped in and started building a Prusa Mendel. I do electronics for a living, so I started there. I bought a bare GEN6 PCB and parts, and assembled it by hand. I've loaded the bootloader and firmware, and the board is running fine. I was able to connect up a motor, and send GCodes manually from the Arduino serial console to make it spin. I can spin the motor back and forth now. Here's my question:

When the motor is stopped, it makes a high-pitched squeal as its in hold mode. If I configure the firmware to turn of the motor enable when stopped, then the noise goes away, but then I can spin the shaft by hand, and it has no holding power. I was under the impression that the Gen6 electronics are very quiet, but this doesn't seem too quiet to me. I'm wondering if I've done something wrong. Does anyone have the same squeal with the Gen6?
Re: Stepper motor squeal with Gen6
August 31, 2011 05:41PM
This was a problem with batch1 of Gen6, a fix is detailed here:

In short, the squeal happens because the PWM frequency is in the audible range, you can fix it by swapping R36..R43 with 68K resistors.
Re: Stepper motor squeal with Gen6
August 31, 2011 06:25PM
Yes... see here: [forums.reprap.org]
Nophead kindly sent me some 1nF resistors, but I can't find my soldering iron since I moved house. It's in here somewhere...
When motors are on hold, there is current flowing through them, and possible they are at their highest current usage (so I've been told), so I'm not entirely surprised there is some noise. Also, if you turn off the motor, when it restarts it starts at the next full step, ignoring the microstepping point it may have stopped at. Probably not a huge jump, but an inaccuracy none the less.
There is a note on the mendel-parts website here [www.mendel-parts.com] saying "Batch4 is simular to batch3 and 2, but batch4 also has a few new fixes/optimization (in hardware) which we will soon specify." But I won't hold my breath for that information to become available...
Re: Stepper motor squeal with Gen6
August 31, 2011 06:32PM
Andrew Smith Wrote:
> This was a problem with batch1 of Gen6
Are the self-build versions still using the Batch 1 layout? There is still a problem with later versions too, but not quite so extreme.
Re: Stepper motor squeal with Gen6
September 04, 2011 05:40AM
There are two solutions:

1) Switch to Sprinter firmware. Motors are off by default, until printing. Not a true solution, but much less annoying!

2) Change R36-R43 as discussed above. The reason this isn't the default recommendation is due to the side effect of increasing the chopper frequency: increased power dissipation. You'll need to add heatsinks to the driver ICs. But, this will eliminate the noise.
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