Getting started with Servoes

[Chris Albertson]

Hi,

I happened upon a few servo motors and thanks to people on this list I
know how to measure their performance in a simple but good enough way.
They are DC brushed motors with TTL compatible optical encoders that
send quadrature and index pulses. They are about right for use on a
small to medium machine tool.

So far I've run them off a bench power supply and looked at the
encoder output on a scope and frequency counter.

Question is how are people connecting these to Machine Kit. I'm
inclined to use a simple dual H-Bridge using four MOSFETS. EMC2/MK
would send PWM and direction and read the quadrature A and B channels.
I don't see a use for Index as I'd be controlling X, Y, Z on a small
mill.

Are there other or better ways to connect the motor? I notice Gecko
makes a controller that accepts step and direction inputs and makes
the servo look like a stepper. This has the advantage that it turns
it into something I've used before

--

Chris Albertson
Redondo Beach, California

[Claudio Lorini]

...well, if you're willing to do some electronic DIY, there are some interesting servo dc driver projects around:

http://www.uhu-servo.de/

https://sites.google.com/site/marcosinatti/elettronica/downloads (sorry, in Italian)

both have step/dir inputs and can be seen as a stepper (but have closed loop control with encoder!)

C.

 

[Chris Albertson]

Step/Direction controllers close the servo loop inside the controller.
I wonder if it is better to do that inside the EMC2/MK HAL file?

The specific step/direction controller linked to below is a closed
source project. I hate to build things when I can't see how they
work.

On Wed, Mar 15, 2017 at 10:17 AM, Claudio Lorini <claudio...@iit.it> wrote:
> ...well, if you're willing to do some electronic DIY, there are some
> interesting servo dc driver projects around:
>
> http://www.uhu-servo.de/
> https://sites.google.com/site/marcosinatti/elettronica/downloads (sorry, in
> Italian)
>

[Eric Keller]

On Wed, Mar 15, 2017 at 1:51 PM, Chris Albertson
<alberts...@gmail.com> wrote:
> Step/Direction controllers close the servo loop inside the controller.
> I wonder if it is better to do that inside the EMC2/MK HAL file?

step/dir to analog converters seem to come and go, it seems like it's
probably better to avoid that conversion if possible. The BBB seems
well suited to control a dc servo.

[Marius Alksnys]

I offer you the Furaday cape for BeagleBone which can take encoder
signals and output PWM (or analog 0..10V) signals. I integrated a number
of them, closing servo loop in machinekit HAL successfully, including
using standard AC motors + VFDs + encoders.
Here is the link, where you can also find template machinekit configs:
http://www.robotise.lt/hardware-for-beaglebone/8-furaday-cape-1-2.html