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Motion Controller Design

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sparky961:
A bit of a bump and status update to this thread....

The guys over at the LinuxCNC Forum have been instrumental in helping to get things up and running quickly.  I've been happily surprised by their willingness, patience and thoroughness to help out with what must sometimes be frustrating "noob" questions.

I've attached two pictures below showing the current state of things.  Don't laugh!  Well, ok... go ahead.  Every time I look at my cardboard box control panel I think of the magical adventures that were spawned by the arrival of a new kitchen appliance - or rather, the box it arrived in.

This is a prototyping stage, so it's all good.    I want to keep things neat and tidy enough to work on it without frustration, but without getting too wrapped up in organization, planning, and looks.

Current status is that I have a single axis machine (Rotary "A" axis) with working MPG/pendant.  Just this evening I wired up physical power and e-stop circuits and associated relays.  LinuxCNC is also aware of the status of the latter.

I have a lot more wiring to run for the remaining 3 axes, their limit switches (which I'm impatiently waiting to receive from China), and remaining buttons on the control panel.  After all 4 axes and the control panel works the way I want, I'll be transferring everything to a custom sheet metal enclosure.  I think that would complete what I previously referred to as STAGE 1.

nrml:
How is your project coming along? I see that you have already committed to the MESA route. If you are still wavering, I was going to suggest developing a custom cape to run Linux CNC on a beagle bone black. I am supporting the Necitech kickstarter project. I would love to have a more capable version that supports encoder feedback. There is a little niche in the market there waiting to be filled.

sparky961:
My dealings with Mesa (the company) were less than optimal.  The email communication, though relatively quick, was also very short and not near as thorough as I'd have hoped.  When I did, nevertheless, decide to purchase this setup, the next few weeks were filled with repeatedly checking to see whether the boards were in stock.  As soon as I saw that they were, I placed an order through the web site.

If you aren't completely turned off already, you can rest easy knowing that there's another web site that seems to have much better stocking and (I assume) better service.  MesaUS.com seems to be the way to go.  Avoid MesaNET.org.  Just my $0.00 (due to nearest nickel rounding, my two cents are now worthless).

As for the project itself, it has been going well but stalled for a bit while I wait for one last essential component to arrive from China - the limit switches.  I have been holding off testing the X, Y, and Z axes because I want to make sure the limit switches are in place and working first.  This will avoid damage due to inadvertent runaway of the servos.  It has been very hard to stick to this self-imposed rule but I'd really beat myself up if I threw caution to the wind and did do some considerable damage.

As for the hardware itself, these boards are AMAZINGLY fast - at least compared to anything I've used, which is limited to the PC's parallel port and the latency-prone USB.  Aside from the very steep initial learning curve, I've been having a much better experience with this hardware than any stepper setup I've muddled with in the past.

As for your suggestion on other hardware, you may already know that LinuxCNC doesn't require very powerful hardware to run well.  I'm presently using an older PC, retired from service as my main computer quite a few years back.  It was a solidly built computer in its day and has no problem running LinuxCNC with very reasonable latency.  I have some thoughts of perhaps a single board computer or embedded whatnot in the future, but until I begin packaging things up the host "brain" is doing its job quite well.

sparky961:
A surprising amount of time has been spent thinking about mounting limit switches and wiring management. There's a lot more to go but now that my sensors finally arrived I spent a bit of time designing and building brackets for the Y axis. Attached photos and simple drawing. Sensor is M8 inductive proxy.

While at it I also drilled and tapped holes both for the sensors and "flags" that will actuate the X axis sensors later on.

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