Question about Limits

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chambrot
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Joined: Mon Sep 30, 2013 2:55 pm
Location: Miami, FL
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Question about Limits

Post by chambrot » Wed Mar 26, 2014 3:49 am

First a little background....

I have had my custom built 1000mm x 1000mm shapeoko for about 6-7 months now, at first I had a bunch of ideas that I wanted to use it for...but so far all i have been doing is tweeking it getting it to run right and all has been fine. Ran a few little projects, mostly just to test and learn about the CAD / CAM side of things.

I started with a TinyG running TGFX 2, and at first i was happy with it but I feel like it lacks support not many updates to the software. So I am switching to the basic GRBL / Arduino system just like the stock Shapeoko, so I went ahead and ordered that. (I also bought a TB6560, but that has proven to be a huge challenge and I set that to the side for now)

My machine has all the homing and limit switches. I tell the machine to go home and it does just fine...if i run too far and it hits a limit switch it shuts down the motors...all perfect!

A few months ago I bought a small 3D printer (printrbot Simple) and I love it, its kinda taken my attention from my Shapeoko. Now I think its time to get back into my Shapeoko, but I have noticed something in my little 3D printer which I am now wondering if my shapeoko should be behaving the same way. My 3D printer homes itself, then knows how far it can travel in all directions...no need for the limit switches, only the homing switches.

So here is my question...

Is there a way to do this with Shapeoko? Is there a setting where I can tell the software what the limits of the machine are so that there are no need for limit switches on the far ends of travel.

Thanks in advance.

J
Custom ShapeOko using original design, 1000mm MakerSlide X Axis, Double 1000mm MakerSlide Y Axis, Nema 23 on all, upgraded Z Axis, Dremel 300, controlled by TinyG

edwardrford
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Re: Question about Limits

Post by edwardrford » Wed Mar 26, 2014 4:45 am

What you are referring to is typically called a 'soft' limit. As in, it's a limit dictated by software. For the major hobby control packages like Mach3 and LinuxCNC, that a feature that is built in and set during the initial config. It's a nice feature to have.

For grbl, that is a feature that is not implemented yet. However, I believe it's set to be part of the much anticipated v0.9 release. If you're the type that lives on the edge, you can download v0.9 from the grbl github repo here.

Be sure to read through the v0.9 release notes, and to be aware that it's the edge branch, and the bugs still exist.

-Edward
Shapeoko 1 #0 - a couple of upgrades.
Shapeoko 2 #0 - a couple of upgrades.
Shapeoko 3 #2 - Stock

danimal
Posts: 332
Joined: Wed Mar 13, 2013 5:53 pm
Location: Colorado

Re: Question about Limits

Post by danimal » Wed Mar 26, 2014 8:06 pm

Generally soft limits work well with servo driven or position aware machines. LinuxCNC has soft limits and they work great, but with steppers there is no positional feedback so it is a good idea to have limit switches in addition to soft limits.
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

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