DIY Electronics?

[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.