Microstepping does do in-between steps, but you lose torque.
The controllers I'm using will (supposedly) allow the motors to be controlled to 0.036 degrees (10000 steps per revolution) from a 1.8 degree motor.
Normally you'd get half, quarter and eighth stepping (0.9, 0.45, 0.225 degree steps).
The perfect current for stepper motor coils would be two sine waves 90 degrees out of phase. Simple drivers approximate to it, pukka drivers try to create it. Intermediate points are a bit springy but rotating a component is a no load situation so tiny changes in angle are possible if your driver is willing and able
For this requirement, where full rotation isnt required, i guess, but accurate partial rotation is, I wonder there would be mileage in a purpose built sinewave phased driver rather than a stepper driver as such? The load is small but not zero.. presumably you'd be rotating the suction head which would have a vacuum tube attached which would give some tangential load.
Originally Posted by Robin Hewitt
"presumably you'd be rotating the suction head which would have a vacuum tube attached"
Correct. And you are also correct that I am thinking in terms of designing my own driver board - mostly from sheer habit, but also because that way I end up with exactly what I want (or alternatively, have only myself to blame if I don't). I'm planning to spend time thinking through this project over Christmas (although I have the wife in bed with 'flu at the moment, and I'm therefore having to do all the running around town that she normally does) and because of family commitments little will actually happen in terms of either hardware or software until Q2 of 2010; but by then I expect to have thought through all the details and be ready to move quickly once I start in the Spring. I'm looking forward to it greatly now, because almost everything I do has a processor and a PCB in it somewhere, and to be able to knock those out quickly and easily will be really useful. I'll post pictures and circuits when I get there.
Look forward to seeing the outcome of your deliberations....:idea:
I am mentally picturing a 'Wallace and Gromit' scenario...
Wallace sitting at his PC designing the board, and ceremoniously pressing a big green button, activatiing a robot arm (complete with shirt sleeve and oversized cartoon hand) which picks up a blank piece of PCB, places it in a CNC PCB router which cuts the board, then the arm picking it up and placing into the SMT placer, and then again into the solder oven, and finally (with singed fingers and a 'boing' sound effect) putting it on Wallace's desk!:heehee:
I'll get back to work now.....
You probably won't believe this but I think I have to mention that you may be making beginner's mistake. I won't be saying, "I told you so", but you can assume that :naughty::rofl:
Originally Posted by saxonhawthorn
Yes, you could gain vast extra control by making a seperate computer to interface Windows to your machine, but you would do well to stick with commercial stepper drivers and PSU.
Given the price of a humble MSD542 it really isn't worth the nightmare of trying to recreate it
Er.... hrrumph! I have to live on a pension now, and our house rule is "If it costs money, we don't do it."
I just checked the price of an MSD542 from Motion Control Products (http://www.motioncontrolproducts.co....roducts_id=3): it's £47.12 presumably plus vat, and presumably I'd need one per motor (you're right that I'm new to CNC).
However I'm not new to electronics, and I have more oscillators, scopes, and logic analysers than I have benchtop real estate to put them on, and for me it's not a nightmare at all. I haven't yet designed or costed up making a multi-channel controller, but my instincts tell me that by the time I've bought four or five MSD542s I could have built many more myself and probably saved quite a few bob into the bargain.
But "He that putteth on his armour ought not to boast as he that putteth it off." I'll do it first, and then boast. :)
Originally Posted by saxonhawthorn
As a hardware designer turned software engineer and one who much prefers to build rather than buy I would dearly love to agree with you. However unless your bits box is very deep you are unlikely to deliver something of the functionality of the MSD542 for the price. I built my stepper drivers based on a very long-toothed design using the L297/L298 chipset and the parts alone for 3 axes came to over £70. While arguably that was cheaper, I could have bought a DIYCNC System 3 for £90 for the same functionality and that doesn't come close to the capabilities of the MDS unit.
So I sadly have to agree with Robin, who I know to be no slouch for going down the "create your own" route (having seen the injection moulding rig he built, and his nearly finished plasma cutter - is that running yet?), that your limited funds are better applied elsewhere.
"They said the thing couldn't be done!
"With a smile, I went right to it.
"I tackled the thing that couldn't be done....
"And I couldn't do it!"
I am, as you know, a complete beginner in CNC. I need to read the spec sheets and think through what's required, and until I have done so I'll defer to your greater experience.
But not the least valuable aspect of DIY is that at the end you know that you know exactly how it all works. I cannot live with bits of engineering in which there is the slightest fuzziness in my mind about how it works. I just have to know, and the only way to know that you know is to do it. (And until you have, you cannot possibly teach anybody else how to do it either, which is something to be considered at the senior end of the age spectrum).
I have an utterly boring meeting to attend all tomorrow morning: but then I'm looking forward to getting stuck into some spec sheets.