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

I would strongly recommend going analog rather than step/dir. First of
all, I think LinuxCNC's PID is easier to set up and probably more
accurate than the PID loop built into the GD drives. Secondly, with
proper encoder feedback, LinuxCNC always knows where the machine is,
even when the drive power is off. This may not sound particularly
important but it encourages safe practice. It is a good idea to estop
the machine when you don't actually need it to move. It makes me cringe
to see people reaching into machines with the drives on, especially if
there is a chance of getting trapped if it moves. With step/dir you can
lose position if the drives are off so you tend not to use estop unless
you really need to. With analog, as you know the machine will not lose
position you are more likely to reach for the estop before doing anything.

For your conversion I would probably recommend a couple of 7I29 dual
drives because they are so easy to wire up. I use one on my lathe and it
works well. My only gripe with these drives is that they don't have much
in the line of output filtering so they generate a fair amount of
electrical noise. A simple common mode choke on the outputs helps a lot.
I have never used Jon's drives but it does look like he has filtering
built in which is nice. His drives will work out quite a bit cheaper
than 7I29s.

If you wanted to use brushless motors I would probably recommend the GD
drives but for this application I don't think they are the best option.

Les

On 07/11/12 18:14, 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.
>
> 2. Question #1 helps drive which Mesa interface board to use, but I thought I'd ask what people have as their favorite Mesa setups, and why.
>
> 3. Is there a product *other* than Mesa's that people might recommend, and why.
>
> Thanks!
>