Re: [CAD_CAM_EDM_DRO] LinuxCNC: if I can choose step/dir or analog on my amps, which should I use?

On 11/07/2012 12:14 PM, Alan wrote:

> I have a few basic questions that I'd thought I'd solicit thoughts on... Before I state these, let me define the project. It is the conversion of a Hurco KMB-1 mill. I will be using the original Electro-Craft brushed servos, LinuxCNC, and Granite Devices servo amps.
>
> Now for the questions:
>
> 1. The Granite Devices amps can work in either step or analog mode. I plan on using a Mesa Electronics FPGA board so a step generator should yield good results. With that in mind, which way is best, analog or step/direction? Encoders will be used in either case; with step/direction the drive will monitor for stall and with analog the encoders will be used for feedback to both the drive and the control.

Well, it depends a bit on how the drives work. A velocity servo with
tach feedback can be very smooth down
to very low feedrates, which can make a difference when orbiting to bore
large holes, for instance.
You can get similar performance with a high resolution encoder to derive
the velocity info.
Do the Granite drives also read the encoder in analog mode? (I'm
guessing they do.)


3. Is there a product *other* than Mesa's that people might recommend, and why.
Well, I'm blowing my own horn here, but you might look at the Pico Systems
Universal Stepper Controller for the step/direction mode, or the PPMC
for analog mode. Both units are 4 axis, the PPMC can be extended by adding
boards, the USC by adding another USC to the same parallel port. These
may initially seem more expensive than Mesa, but they are very much
all in one units with no need to add additional modules, cables and break
out boards, so the price is closer than it seems at first.

Or, if you don't have the Granite amps yet, you might look at our PWM
system, the amps are $125 per axis, good to 20 A and 120 V DC supply.
The USC and Universal PWM Controller are the same board, just different
firmware.

Jon