just about time

[gun_mike]

Over the past 10 months I've been building a benchtop cnc machine from an old taig lathe, a crosslide table and some metal stock. The mechanical aspects of the machine are nearly finished. I was lucky enough to recieve 3 vexta nema 23 2.8a 4.2v 1.8dps bipolar (4 wire) steppers from a friends father who is an electrical engineer for a large industrial printer company. I have these motors mounted to my machine, they turn 1/2" 20tpi leadscrews with preloaded bearings. The led screwnuts are made from acetal and are adjustable for backlash. Now that I have the machine built, Im starting to think about the electronics. I have researched a few different motor controllers. In the begining I was considering stepperworld or hobbycnc boards, but now that I have bipolar steppers this is not an option. Later on I was looking into a xylotex board, the only concern I have with that is how delicate the thing is, you pretty much cant breath on it with out possibly damaging the driver chips. This is a concern for me because I have limited knowledge of electronics (the steppers have a wire diagram). Idealy I would like a motor controller with some form of protection. If I happen to make a minor mistake with the set up I would rather not have to buy another board. I'm willing to spend up to about $600 Canadian. I wouldnt mind paying more if I knew for sure I would never have to buy another whether its a controller board or chopper drives.
I dont need a plug and play. I would rather save a bit of money and assemble the parts myself. So my question is what kind of control system would you guys recomend?
I briefly took a look at gecko 203v drives, they are very appealing.

Mike

[project5k]

I've heard good things about the gecko's, but i've never playd with them... i decided to just build my own... 4 amps per phase, 48 v max supply, full or half stepping, chopping bipolar... spins my 500oz-in motors with some real zest... cost me about $120USD for 3 axis.... thats laying out the boards, etching them myself, ordering the parts from digikey, and so forth...

just another option...

[gun_mike]

thats also an option. how difficult do you think it would be for a person with limited eletronics knowledge to build it? I have built a 36v power supply for my spindle motor so im not completly in the dark.
thanks Mike

[dertsap]

if you ve got the money to spend i d say gecko all the way ,their support is second to none

[project5k]

oh i dont think it would be that hard for ya.. have you ever etched a board? the process is fairly simple.. and you have choices, but it can get rather involved... you can get most everything that you need from radioshack, including the copperclad board and the etchant solution.. get yourself a rubbermade container that you will dedicate to this process, as the chemical will render it unuseable for anything else... personally i just use thoes disposable glad containers.. thier cheap, and if one gets messed up, i can toss it.. plus they have lids, so i can save my chemical and re-use it a time or 2..

the board layout is the hardest part, getting the 2 sides lined up.. there are a couple ways to do it, toner transfer, spray masking, photo etching and so forth.. i prefer the spray masking and photo transfer, but i have used the toner transfer method...

theres lots of information out there, and a user group on yahoo...
http://tech.groups.yahoo.com/group/Homebrew_PCBs/
thats a good source of info... i'm not at home right now, so i cant share the other links that i have.. but there is free software out there that you can use... basically you just need a good working schematic, this free software, a laser printer, a clothes iron(to transfer the toner) and a few other odds and ends, from there its your time... thats why i did my own.. time i got, money i dont...

one tip, allways remember this.. whatever method that you use to get the "image" ie the trace layout on the board, before you etch the board, you can use a sharpie to help the traces.. add lines, fill in opens and so forth, the ink in a sharpie is resistant to the chemical... so just for example, if you do the toner transfer, and you see some breaks in your traces, or holes, or forgot a line or something, you can fill it in with the sharpie...

if you really wanna discuss this in detail, pm me and i'll give you my email addy, that way i can share some of my files and stuff with ya...

[gun_mike]

heres a few picture of the mill as of this morning. I made a bearing support arm to make the headstock move up and down with out binding. The binding was a big problem and this has seemed to fix it quiet well. Theres also some hommade flex couplers I made. from some alum and a sheet of bendy plastic. It works well and I havent noticed any buckling in the plastic yet.
As for the electronics I have decided to go with the gecko 203v drivers as they seem to be one of the best out there.

[Bajaman]

I like your flex coupler design, it looks very simple to make.
I made solid couplers and they wobbled real bad.
Its looking real good,keep up the good work!

[gun_mike]

they took more figuring out that machining. took about 30 min to machine them both and assemble them. I had a problem with run out in one of them but I've seem to fixed that by offsetting the the holes in that bendy plastic. I'm able to turn the coupler, lead screw and stepper motors with my fingers smoothly. This could mean two things:
1) the runnout error in the couplers closly matches the error in parrallelism between the stepper shaft and lead screw
2) the couplers work well :P
anyways is there anybody out there that have made there own couplers?

MIke

[Stepper Monkey]

I have to point this out; You are thinking about building your own board from scratch but are afraid of hooking up a Xylotex? I think that all of the smoked board posts on here from people who can't RTFM are really giving people new to this a bad vibe about driver boards! Don't let them scare you off!

Really, a Xylotex setup is this easy, I have one in front of me now; Using clearly marked screw terminals you mount the 2 wires from the power supply into a 2 terminal block clearly labeled and separated from the motor terminal blocks in case you still didn't get the picture, then you mount the four wires out to each motor, also clearly marked and broken down by axis each axis with thier own 4 terminal screw block. Thats it. The parallel port connector is a computer ribbon cable like hard drives use, goes into a keyed socket so you can't even plug it in wrong. If you can use a voltmeter and a screwdriver, you can set the current adjustment in seconds.

I **** you not, it's that easy. If people can't get it right they shouldn't be playing with power tools or sharp objects.

I think one of the main reasons that they blow up so frequently is that they unfortunately left the current adjustment up to the customer, a bunch of guys famous for being of testosterone-crazed power junkies used to pushing or overclocking things. The instructions say not to run them over certain Amperages, but then they made a big misjudgement of thier customers and gave the engineering specs for the power ratings, which means no overhead (wiggle room) was included. The rated Max is the rated Max. Exceed it and flames come out, period, and obviously Continous duty is lower. You can imagine what the ratings actually get set to in practice, and the few Budweiser-fueled Bubba's of our hobby who can't grasp that are of course the loudest and most abrasive screaming about how crap the boards are after they smoke them, usually trying to overdrive motors stupidly oversized for the board in the first place. That isn't even taking into account the fact many are run with the wrong or shoddy power supplies in the first place, because although Xylotex does clearly recommend 24V, they also unfortunately gave engineering specs for the max allowed voltage (which includes spikes and feedback!) before flames shoot out (which is 35v). Bad idea. Guess what people try to feed it?

I have had several, with stable 24v power supplies and motors well-matched to the board, and strangely never had a problem. Go figure.
So have most of us on here. They really are reliable and trouble-free in practice. Don't worry about it.

[gun_mike]

In that case I may take a second look at the Xylotex board. The one part that really scares me is adjusting the current. By the way you put it, it sounds very simple. My motors are rated for 2.8 amps per phase. So I need to adjust the current on the board to >2.5 amps per phase and it'll be okay? I was reading on the Xylotex websight and I noticed their motors have a current rating of 2.8 amps per phase aswell. Xylotex offers a 24v power supply and a 24v fan. Do you use a fan on your set ups?
thanks
MIke

[Kipper]

Originally Posted by Stepper Monkey I **** you not, it's that easy. If people can't get it right they shouldn't be playing with power tools or sharp objects.

Well said!

[Stepper Monkey]

They are very reliable and cost-effective, but the one limitation of the Xylotex is the power output - you can't get 2.8 amps out of them. 2.5 is the max they rated for, and I would run them back from that a bit.
I have 2.8 amp rated steppers on my Taig, and I run them at 2.2 amps from a Xylotex. This only gives about 80% of the steppers max rated power, but this is still well more than adequate for a small to medium machine.
If you need or want to run them at a full 2.8 amps, there are a number of drivers out there that will deliver rated currents of 3.5 amps or better. They are a lot more expensive, however, and for smaller machines it often doesn't pay to double the cost of the drivers for an incremental performance boost.

If you really do need the power, Geckos easily become the best choice. They also run at a higher voltage which helps immensely if you are pushing the limits of speed. From the size of your machine I would say entirely unnecessary, however.

Oh, and yes, I always run a fan, whether it requires it or not. Fans are cheap, and even if a component doesn't require it to safely run, less heat = longer component life. It almost always pays to use a fan!