# Small PLC with 3 Axis Stepper Control

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#### Curt Wuollet

Hi all

I'm looking for a small, reasonably inexpensive PLC that can do trapezoidal motion on 3 axes of step and direction outputs. Modbus RTU would be great. I know the more recent offerings have been emphasizing motion. Reasonable software cost would help.
I need to run two 3 axis stations, (simple motion, one axis at a time, don't need coordinated motion), and using 6 PLCs doesn't appeal to me.

AB has a micro that will do 3 but the software, CCW, was not ready for prime time last time I tried it.

Regards
Curt Wuollet
Maintenance Team

----------------------------------------------------------
BAYER BUILT WOODWORKS, INC.
Quality Millwork, Unbelievable Service
www.bayerbuilt.com

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#### Curt Wuollet

Hi All

As I said before, I want to control 3 axes of steppers from a PLC. There seems to be a piece missing. Stepper motors and drives are now truly commodity items. I can find all kinds of hardware for doing trapezoidal control directly to motors from a USB or parallel port due to the popularity of DIY CNC. But these are generally small motors. What I haven't been able to find is a module that will accept commands from RS485 and provide 3 direction lines and three step lines to feed the commodity stepper drives. I could design something, but I really don't want to reinvent the wheel. Has anyone seen this type of gadget? I know there are a lot of people doing motion out there.

Regards

Curt Wuollet
Maintenance Team

----------------------------------------------------------
BAYER BUILT WOODWORKS, INC.
Quality Millwork, Unbelievable Service
www.bayerbuilt.com

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#### DonnyM

You might look at Automation Direct. There 4850 Stepper Drives can handle up to 5 amps and there 8100 can handle 10amps. They take serial inputs and use a SCL language. One of our engineers designed a multi axis system just using the serial commands and a simple VB app. I know the drive is not a PLC but it might get you pointed in a good direction.

Donny

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#### Bob Peterson

While I am a fan of most of the AB PLCs, the AB Micrologix 800 family and the CCW software does not impress me in the least.

I seem to recall that the Micrologix 1400 has 3 fast outputs.

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#### Curt Wuollet

Hi Donny

I've been there and considered just that solution. But, I would need either 6 PLCs or a rather expensive Do More system. First I considered 6 DL05s but they only output to 7 kHz. It wouldn't break the bank to put 6 Clicks in a cabinet and I could use the ones with Modbus built in and have a solution, but have no way to assess the reliability of the ascii SCL serial links.

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#### Curt Wuollet

Scary, yet another thing we agree on. Although I think the PLCs might be OK with usable software, I'll re-examine the MicroLogix line.

Regards
cww

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#### Curt Wuollet

After much research and beating my head against the wall, I think I've found a solution that fits. Someone wise once said: "If the problem is insoluble, change the problem". or something like that.
Instead of thinking of this as motion control of 6 steppers, I just changed the problem. All the _automation_ solutions I was finding had serious drawbacks, too expensive, too much hardware, too much........
So, I changed the problem. Really what I need to do isn't much different from a CNC router or even a 3D printer. They obviously don't use a whole cabinet full of PLCs and they cost a lot less these days than the _automation_ solutions I was seeing.

I just called it CNC and followed the maker crowd.

I have a proposed solution that will control 3 axis of stepper drives and motors and will set me back less than $100. Maybe much less. An Arduino UNO is about$16 and the software is free. We see the Arduino mentioned here occasionally. Some folks have written a G code interpreter and motion controller that runs on an Arduino.
It's called Grbl and looks to be a great fit. In fact it's pretty much overkill, but should work fine for what I have to do and it's all pretty much OTS and open source to boot. I'd much rather use two of these tiny SBC's and write in standard G code than spend hundreds and have to learn an(other) oddball proprietary language. So, I think the problem is solved or at least I have a good prospect.

Thanks for the replies

cww

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#### BruceD

The XYZ Da Vinci 3D printer uses the same microcontroller as the Arduino Duo and there is Arduino software available to replace the firmware in the printer - check out Repetier.

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#### Curt Wuollet

The plan right now is simply to use Grbl on a DUO. The ballscrew slides will be coming with 2.8Nm steppers and drives to suit so all i need are the step and direction outputs for 3 axes. Grbl accepts Gcode directly, so I'll just set up a Click to send Gcode. Since the DUO wants USB, i'll either use a converter or, I've got a few arduino clone board blanks that have a serial port. I'd prefer a checksum protocol, but we'll see how it goes. It must be reasonably reliable, it takes a lot of Gcode to print something or even mill something. It's been a while since I've played with Gcode, but what I need to do is very simple. Grbl provides a lot of handy inputs that save PLC IO as well. It's a great fit.

Regards
cww

#### paulb

> I'd prefer a checksum protocol, but we'll see how it goes. It must be reasonably
> reliable, it takes a lot of Gcode to print something or even mill something.

How has this project turned out Curt? In the past six months I've done a little motion control hooking a PC (with 3 Ethernet sockets) up to a Kollmorgen drive.