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Old 05-21-2012, 01:30 AM   #1
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Default Electronic Dividing Head using the Arduino

I've made some strides on my Arduino powered dividing head the past few days. Here's a little background for what I am doing. First, the Arduino micro controller.



Available online for under $30, has 32K memory, numerous analog and digital inputs and outputs, including serial and PWM.

Next, the Sainsmart LCD display and keyboard shield



This board is called a shield because it is pin compatible with and piggybacks right on top of the Arduino board. It has a 2 line x 16 character display and 5 input keys plus a reset. The keys are configured like the cursor keys on a PC having a left, right, up, and down as well as a select. So, with this shield in place, the microcontroller can be used with only a power supply and doesn't have to be tethered to a computer. The keys provide input and the LCD provides the display.

Here is the Sainsmart shield mounted on the Arduino...



The Sainsmart gets its power from the Arduino.

Another picture



The Arduino is programmed by hooking it up to your PC through a USB cable. This also provides power to the Arduino board. A free programming environment is available for the PC and allows you to develop programs in a language that looks almost exactly like C. There are a host of standard libraries for interfacing to LCD's, keyboards, wireless, serial devices, and others. You write the programs and compile them on the PC. The compiler then automatically downloads the program to your Arduino. Once the program is loaded on the Arduino, you can decouple it from the computer and run it off a separate power supply from 9 - 12 volts. The program will stay in the Arduino memory even when the power is switched off.



So this is the basis for controlling my electronic dividing head. The up and down arrow keys will be used to set the number of divisions I want, then the left and right arrow keys will be used to step forward or backward one division at a time. The program I have written will calculate the number of stepper steps need for each division and keep track of the position I'm on. The display shows the number of divisions and the current dividing head position.

I have purchased a stepper driver board that is about the size of a postage stamp and will power a stepper of up to 2 amps, 35 volts. I still have to select the stepper motor I want to use and build the mechanical part of the dividing head. Still have a few challenges ahead of me.

Chuck


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Old 05-21-2012, 01:42 AM   #2
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Default Re: Electronic Dividing Head using the Arduino

That is a great idea Chuck! I wonder if you could just send step and direction pulses to a Gecko drive. They can source 7 amp. Not so much for the driving force but for the holding power.

Anyway, awesome project.


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Old 05-21-2012, 12:50 PM   #3
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Default Re: Electronic Dividing Head using the Arduino

Chuck, or in fact anyone else who is going along the electronic RT route. here are a couple of links on to how I did things to mount the stepper to the RT.

You don't need to follow religiously, but they will give you an idea of what is required to get a backlash free with smooth movement RT, and to keep the swarf out. Once assembled, the slot in the tube is covered over with tape.

Vertex type

http://madmodder.net/index.php?topic...44911#msg44911

Arc Euro type

http://madmodder.net/index.php?topic=4730.msg52166#top

Hope it helps someone


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Old 05-21-2012, 01:36 PM   #4
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Default Re: Electronic Dividing Head using the Arduino

Looks really nice so far Chuck.
The stepper board you're looking at sounds like a Pololu driver. Is that the case? The A4988 version is quite good (certainly good enough for a dividing head), and really difficult to kill. By which I mean the short protection actually works. I tried it.

I'm not sure too much holding torque will be needed, because of the worm drive. The one thing you will need to be careful of is that the pololu driver will get extremely hot if you don't give it a good heat sink, and even then will roast if you feed the motor more than about 1.25A. I have some heat sinks that work marvelously on the pololu drivers (if those are what you are using), and would be happy to send one your way.

Best of luck.
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Old 05-21-2012, 03:10 PM   #5
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Default Re: Electronic Dividing Head using the Arduino

Quote:
Originally Posted by stevehuckss396
That is a great idea Chuck! I wonder if you could just send step and direction pulses to a Gecko drive. They can source 7 amp. Not so much for the driving force but for the holding power.

Anyway, awesome project.
Thanks, Steve. I don't see why this wouldn't work with pretty much any stepper driver, incluing the Gecko. There are two outputs from the Arduino... direction and step start/stop.

Quote:
Originally Posted by Bogstandard
Chuck, or in fact anyone else who is going along the electronic RT route. here are a couple of links on to how I did things to mount the stepper to the RT.

You don't need to follow religiously, but they will give you an idea of what is required to get a backlash free with smooth movement RT, and to keep the swarf out. Once assembled, the slot in the tube is covered over with tape.

Vertex type

http://madmodder.net/index.php?topic...44911#msg44911

Arc Euro type

http://madmodder.net/index.php?topic=4730.msg52166#top

Hope it helps someone


John
John, I'll have a look at your thread. I'm sure there are number of issues you have thought of that I will miss otherwise.

Quote:
Originally Posted by Jeremy_BP
Looks really nice so far Chuck.
The stepper board you're looking at sounds like a Pololu driver. Is that the case? The A4988 version is quite good (certainly good enough for a dividing head), and really difficult to kill. By which I mean the short protection actually works. I tried it.

I'm not sure too much holding torque will be needed, because of the worm drive. The one thing you will need to be careful of is that the pololu driver will get extremely hot if you don't give it a good heat sink, and even then will roast if you feed the motor more than about 1.25A. I have some heat sinks that work marvelously on the pololu drivers (if those are what you are using), and would be happy to send one your way.

Best of luck.
Yes, it is the pololu driver. I've sent you a private message regarding the heat sink. I haven't selected a stepper motor yet, but with a 30:1 worm reducer and no real load on the dividing head, I'm guessing it won't take much of a stepper.

Chuck
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Old 05-21-2012, 06:42 PM   #6
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Default Re: Electronic Dividing Head using the Arduino

Chuck,

I don't know what sized RT you have, but both I have converted (a 6" and a 4"), plus my dividing head when I get around to it, all or will use the recommended 180N steppers, which are rated at 2.5amps.

OK, go small if you only want to move the table, but if you are going to use it for machining, even the 2.5 amp one that I use is a little underpowered, and I have to be careful on my depths of cut and feed speeds to stop them stalling.

I would have preferred something around 4.5 to 5 amps to work really comfortably, but my unit just won't give that amount out.

John


Sorry, should have shown location of stepper motors

http://www.arceurotrade.co.uk/Catalo...Stepper-Motors

2nd or 3rd one down. They work out to approx 18kg/cm holding power.
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Old 05-21-2012, 09:39 PM   #7
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Default Re: Electronic Dividing Head using the Arduino

I've used these motors before, and they're really quite nice. http://www.phidgets.com/products.php...duct_id=3302_0

Bogs brings up a good point about torque, and these will probably be inadequate for machining. I would recommend a NEMA 23 sized motor with some more "oomph", maybe this one, which has more torque at a lower current. http://www.phidgets.com/products.php...duct_id=3308_0
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Old 05-22-2012, 03:57 AM   #8
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Default Re: Electronic Dividing Head using the Arduino

I have two candidate steppers in my surplus stepper motor box. Both are bipolar and smaller than the NEMA 23, but I think either would suffice for my needs. This will strictly be a dividing head, not a rotary table and will be used just for positioning, not for machining.

One motor is a 7.5 degree, 48 step motor with 16 oz in holding power. It requires 12 volts and the resistance per phase is approximately 28 ohms which works out to little less than half an amp. The other motor wants 5.2 volts at 0.9 amps and the resistance per phase is about 6.2 ohms. This second motor is a 1.8 degree and has a holding power of 30.2 oz in.

At the moment, I'm leaning toward the first motor because I think 48 steps per rev is more than adequate for a dividing head geared down 30 : 1. This gives me an overall resolution of 1440 : 1. I'm also thinking that the Pololu driver I have will easily handle half an amp with no problem. And, finally, both the Arduino and the motor will operate off 12 volts which means I only need one power supply. Anybody see a flaw in my thinking?

Thx...
Chuck



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Old 05-24-2012, 02:09 AM   #9
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Default Re: Electronic Dividing Head using the Arduino

I'd go for the motor with more steps/rev and more torque. You'll get smoother, (and more importantly) faster motion.
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Old 05-24-2012, 10:52 PM   #10
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Default Re: Electronic Dividing Head using the Arduino

Quote:
Originally Posted by Jeremy_BP
I'd go for the motor with more steps/rev and more torque.

You need the high torque to hold position while you do your work. More torque the better


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