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Thanks for reading my thread. I am new to CNC and have constructed my CNC Mill using plywood. I have researched for a DIY driver circuit for a 6 wire stepper motor without success.Has any one found a system to hook onto the parallel port ?I can etch PCB ( single sided using toner technique)with out too much problem and have a demo version of MACH3 for evaluation. The scene is set can you help with information?
kind regards
Colin300
look at my website.
Hi Colin,
A 'couple' of thoughts. You can use an SGS Thompson IC called an L298 driver in conjunction with an L297 or L297A IC that will save quite a bit of work for each stepper drive cct. ( Google "L298", Download PDF form the Web) This config. only needs a 'step' and 'direction' signal from the parallel port, so you drive a number of steppers from the port. The really nice thing is that the suggested circuit (SGS Thompson application) is a current driven (constant curent source) set up and this will increase the step rate you can achieve remarkably, as a '5 volt' stepper can be happily run from say 36 to 40 VDC, but will only get the set current (no burnout!). The current rise & decay time between steps is reduced in such a configuration and this enables fast phase repetitions (speed!!). The current source is also "switch mode" meaning that power dissipation is neglible, hardly requiring a heat sink for up to 2 Amps drive. Will also drive 4 wire and 6 wire steppers.
In fact you can run a 6 wire as a 4 wire configuration if you like. Neglect the common power wire on each pair and drive the outer ends of each phase pair as 4 wire. (the phase pair windings will be in series!). This will double the operating voltage of the stepper but it works fine, especially with constant current drive!
Of course to begin with, you could drive the steppers from a darlington power transistor connecting the phases to 5V (or appropriate Volts) DC through the common wire, and driving the bases of the power transitors from the logic levels of the port, thru say 1.5K resistors. This will work, but not very well and you will have to code the step logic yourself. (You get this for free with the L297) Again do-able , will get you going... but a touch crude. (yep dunit myself :)
Another thing to be aware of is that when you drive steppers, they like to get smooth speed rates & rate transitions especially around their 'natural resonance'. A program like Mech3 should be taking care of these basics of course; however as back ground you might like to consider the following ideas:
Brain Dump: Skip to end if you are bewildered!
Without going to extensive detail, a normal PC is being interrupted by various functions all the time, especially with any Windows program. This means that 'normally' a Windows type program cannot output stepper phase changes as and when you think it should. The best bet is to run any stepper events from a DOS or a 'Realtime' OS program (Abs. NOT a Dosbox in Windows!) and peferrably output step phase changes in response to either an external timer interrupt, (more work) or even hijack the Dos timer to run at other then 18 interrupts per second time base, say a up to a few Khz. One could then hook the timer interrupt and decide when to output the next step in a controlled (clock timed) fashion. (Mech3 should be doing this kind of thing I imagine). If you have a Windows program doing this there would have to be a "Windows device driver" managing these events, but even then no guarantee is possible regarding smoothness of rates and such because Windows is not a 'realtime' operating system and this limits useful range of step rates. (neither is DOS, but there is a lot less going on under DOS :) ) Failure to attend this kind of detail can result in jittery rates and missed steps. If Mech3 manages this successfully, well and good, but it sometimes pays to be aware of the caveats of a PC based controller at higher step rates and note the mechanical issues at speed ramp rates close to the stepper/system resonance.
(Sorry, a brain dump I know, but there will be good questions as a result I'm sure!)
Steve
hello Colin300,
If your looking to do this on the cheap then you could look at www.oatleyelectronics.com they have a few CNC kit packages under $30 each. From the breakout, stepper driver, and constant current driver. Not real sure if they will do what your looking for but at $30 not a crippling venture.
Boothie
I've tried the Oatley drivers, just be aware they are full step only.
They work as promised but you hafta keep the step rate WAY down.
If you intend serious work, go for a half-step drive at the least.
Better still, a micro stepping drive.
I'm using 3 PMDX 150 at 1/8 step.
I don't own shares, but I've had first class support from Steve and Bob.
http://pmdx.com/
There is a DIY board able to drive a unipolar stepper motor to 8 amps/phase and 80 volts. Micro-step modes: Full, half, 1/4, 1/8, 1/16, 1/5 and 1/10. Look at this thread for more information: http://www.cnczone.com/forums/showthread.php?t=25361 , schematics, gerbers, and firmware are available from Pminmo's site too.
Here is a video with some speed tests: http://www.youtube.com/watch?v=y6BS4B3yT54