> From: Thaddeus Waldner [mailto:thadw...@gmail.com]
> Perhaps a more significant advantage of the servo drive described by John
> Dammeyer is that it has a current control loop running
> inside of the LinuxCNC velocity control loop.
> Pretty fancy to do that on an 8-bit microcontroller. That ATTiny has an
> on-chip analog comparator.
>
>
> > On Oct 15, 2020, at 10:03 PM, Jon Elson <el...@pico-systems.com> wrote:
> >
> > On 10/15/2020 09:49 PM, John Dammeyer wrote:
> >> The theory is that if the PWM signal is high the H-Bridge is switched to
> >> say turn the motor clockwise. If the PWM signal is low
> the H-Bridge is switch to turn the motor counter clockwise. Therefore with
> 50% the motor is first asked to turn one way and then
> the other. That results in the motor essentially being locked in place.
> Change the PWM on either side of 50% and the turns in the
> subsequent direction.
> > This is called synchronous antiphase. The advantage is there is no dead
> > zone around zero.
> > The DISadvantage is it causes a triangle-wave current in the motor which
> > can be quite substantial,
> > and causes excessive heating of the motor and power transistors.
> >
> > Jon
And building these isn't as easy as it may appear at first sight. I bought a
couple of UHU boards from a company called embeddedtronics.com (no longer
around now) that didn't work. They had tried to shrink down the design too
much and encoder noised and motor noise caused unreliable motion.
Here's one of the early threads (2004) on the UHU.
https://www.cnczone.com/forums/open-source-controller-boards/14217-cnc-software-forum.html
For high power circuit layout is everything. Especially for EMI suppression.
And servo motors can generate a lot of EMI. I think that's why Gene was
talking about inductors in series etc.
John Dammeyer
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