[ktkg]

Is there any info somewhere on building your own electronics for a cnc machine?

I am an electrical engineering student and would like to make my own motor controllers, etc, for a cnc machine I plan to build in the future but I would prefer to have some sort of guide to help me. I plan on eventually converting a SX3.

Thanks!

[Al_The_Man]

MicroChip site.
AN1307 - Stepper Motor Control with dsPIC DSCs - Application Notes - Details
Al.

[wizard]

For example there are many approaches to stepper comtrol on the net, you just need to do the required searches. Likewise chip manufactures have prints, guides and even complete development systems. Your solution can be as simple or complex as you want though if you are a beginner at design the obvious approach is to go for a simpler solution for controller #1.

[kensbey]

hey ktkg

I am a recently graduated mechatronics engineer, and i gave thought to doing the same thing. As others have said, the solution is as complex as you want it to be, depending on how much you want to do yourself.

what i will say is this; be aware that you are VERY unlikely to end up with a better end product than somthing you buy off the shelf. Marketed motor drivers have large amount of post-design testing done to account for wide ranges of operating conditions etc.

Dont take this as discouragement, as i am a HUGE fan of DIY, and i do a lot of it myself. If you are doing it as a learning experience, or for the satisfaction of completing it yourself, then i say go for it. But if you just want to end up with a good driver, it will be cheaper/more relaible to just buy something.

Ok warnings aside, there are alot of motor driver chips avaliable, some are just control ones, designed to be used with transistors or FETs. Others are total intergrated solutions capable of directly driving motors. I would suggest working out what size motors you need to drive first.

Also think about microstepping. this is a little more difficult to implement, but is required for any decent level of accuracy/smoothness on a mill. All the gecko drives use 10x microstepping and then jump up to 1/2 stepping at higher speed. This works pretty well.

Basically, just do as much reading as possible on the subject before you start anything.

[cameraguy]

what i will say is this; be aware that you are VERY unlikely to end up with a better end product than somthing you buy off the shelf. Marketed motor drivers have large amount of post-design testing done to account for wide ranges of operating conditions etc.

seconded.

not to say i am against tinkering. In fact, I have a couple of homemade driver boxes on the bench i am tinkering with, and one i have even used reliably for years. i did, however, build them before modern commercial drivers were available for home cnc users.
so, i have built drivers myself, and they worked. nowadays though, i just buy something off the shelf. they are going to be far and away superior to whatever it is you plan on building yourself - and by quite a bit - unless you intend to spend one hell of a long time refining their development.
so, if you have an eye toward competing in the market for drivers and plan to manufacture what you develop for sale, it would justify the development time at that point. if you just want to save some money on drivers for personal use, you are best served buying them off-the-shelf. they are not only better, they are cheaper at this point than the parts to build your own.

[dogsop]

There is a good deal of information about building your own electronics at PMinMO.com. I built one of his controllers and breakout board and have been happy with the results.

He sells bare boards or if you choose you can start from a schematic and completely roll your own.

[ktkg]

Thanks for the advice guys, very helpful. Since I wanted to do some sort of electrical project anyways, I will probably still try to build my own. Its a shame that I will have to sacrifice performance though, especially if I'm not going to be saving money.. As long as I can get it to be accurate enough I wont mind.

In my mind, as long as it supports microstepping, and it steps when the computer tells it to, and has enough torque to not miss a step, it will be good. Are there more variables than just that? Because that doesn't seem too hard. I don't care that much about speed as long as it get to the right place.

I will probably be driving nema 23 or 34 or both.

There is a good deal of information about building your own electronics at PMinMO.com. I built one of his controllers and breakout board and have been happy with the results.

What kind of motors are you using with them?

[dogsop]

What kind of motors are you using with them?

I had already purchased NEMA 23 bipolar steppers so I used his L297-298 controllers. I used his unpopulated boards but he has the images out there for someone who wants to do their own PCB's.

I'm running my steppers at 24V & 2A which works although I'm certainly not going to set any speed records that way.

He has designed for both bipolar and unipolar steppers so you can design a system using either type.

[ktkg]

@ dogsop
Cool, when I get a chance I'll look into that as well as the link Al_The_Man posted.

Do you guys think nema 23's would be sufficient for a BF20 conversion with a 4th axis? Or should I go with 34's?

[kensbey]

Do you guys think nema 23's would be sufficient for a BF20 conversion with a 4th axis? Or should I go with 34's?

remember to look at more than just holding torque. you probably know that stepper torque drops dramatically as speed increases, but what you may not know is that the rate is very different for different steppers.

A smaller stepper sized correctly may enb up having more torque at the speeds you most commonly move at than a larger one.

look at torque/speed curves more than rated torque during stepper selection. also take note of the voltage used for rated torques

[ktkg]

Good advice, thanks. Also, it looks like while micro stepping, the holding torque per micro step goes down substantially depending on how many microsteps per full steps your using.

I suppose the question is - whats the minimum amount of microstepping I should do for best accuracy? And what is the minimum torque/microstep I would want while cutting something like stainless?

Here's a chart:

Microsteps/full step Holding Torque/Microstep

1 100.00%
2 70.71%
4 38.27%
8 19.51%
16 9.80%
32 4.91%
64 2.45%
128 1.23%
256 0.61%

MICROMO - Microstepping: Myths and Realities

[SCzEngrgGroup]

You are significantly misunderstanding what that page says - pay particular attention to the use of the word "incremental".

10X microstepping is pretty much the point of diminishing returns. Beyond that, it's bragging rights, with little or no practical value in the real world.

You really should study this site until you FULLY understand all of it:

Jones on Stepping Motors

Regards,
Ray L.

[ktkg]

Ill probably just go with these.

High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Automation Technology Inc

Since it is what Hoss recommends for the BF20 build and the torque curve looks pretty solid from 100 - 450 rpm.


Thanks Himy for making me aware of my mistake, I'll definitely check out that link! I admit I don't know much about stepper motors right now but definitely want to learn

[kensbey]

This is where you need to start thinking from a systems point of view. Will you be using ballscrews? and what pitch?

if you assume a 5mm pitch (pretty standard) (i am aussi so i work metric) then 1 step = 5/200 = 0.025mm

4 microstepping then would be 0.00625mm. I highly doubt that you are going to need more accuracy than this, as you are going to get many times this error in column flex etc anyways.

geckodrives really only to to 10x microstepping for smoothness i think.

[ktkg]

I read up on stepper motors and micro stepping..

The way I understand it, with regards to torque, is that since multiple rotor teeth are energized in order to orient the rotor in a position between the two steps, the magnetic field holding the rotor in place is not as strong, and hence you get a lot less torque per microstep then you would per step. This doesn't mean that you will miss a step though, because the torque on the rotor increases after successive microsteps and eventually the rotor will be able to turn to catch up to the current position.

Ideally I suppose you would want your motor to be powerful enough, or at least operate for the majority of the time in a region that supplies enough torque so that at say 1/4 or 1/8 microstepping, (or higher) you will not normally miss a microstep. This will give you the greatest accuracy and anything else past that will only aid in reducing the noise, resonance problems, etc. But will actually give you less accuracy since at times, in the software the motor will be moving when in reality it hasn't moved yet.

Another potential drawback of microstepping is that the motor cannot hold its position accurately against a load, but I don't know if that would come into play. Most stepper drivers probably implement some sort of fix for this.

Also, a high holding torque could actualy hinder microstepping abilities since it would likely take more torque to turn it, making you miss more microsteps.

Feel free to correct me if I'm wrong about anything btw. lol

I wish I actually had a mill right now, then I might be able to somewhat accurately determine how much torque I would actually need for the speeds I want, and to get the most out of microstepping. For instance, if I knew how much everything weighed, and approx how much friction loss there would be, I could caluclate how much torque I would need at a certain acceleration or speed for milling a certain material, and make sure it could do atleast 1/4 microstepping without missing any microsteps. Then I could get the most efficient motor and ballscrew combination. Thats what a real engineer would do

[george4657]

You won't find a better resource than Mariss for stepper design.

[george4657]

Sorry posted before finished typing . check out these two topics by Mariss

http://www.cnczone.com/forums/steppe...ng_have-5.html

http://www.cnczone.com/forums/genera...torial-26.html

[KOC62]

I started to learn stepper controller concepts with this old thread.

http://www.cnczone.com/forums/steppe...epping-42.html

From there I bought a G540 lol.

[Iron-Man]

Is there any info somewhere on building your own electronics for a cnc machine?

I am an electrical engineering student and would like to make my own motor controllers, etc, for a cnc machine I plan to build in the future but I would prefer to have some sort of guide to help me. I plan on eventually converting a SX3.

Thanks!

Most of my work is here:
http://www.cnczone.com/forums/bencht...red_candy.html

I derived it from Glaister Consulting Services
dspic - servo

Hope this helps,

Iron-Man

[ktkg]

Great links guys thanks! I think everything Mariss has ever said should be compiled together and stickied lol, he's a genius when it comes to stepper motors.

Anyways, there is definitely more to this than i had initially anticipated. I might have to reconsider whether or not I want to go the DIY route. If time wasn't an issue I would totally go for it. I should have started this a month or two a go.