Stepper Motors for CNC control

[rodmcm]

I wish to use picaxe (one master and one for each motor) to control 3 stepper motors for a CNC machine. At full speed rates the clock frequency could be up to 18kHZ. The distance moved is dependent on clock cont. Is there a reliable way to accurately count and stop the PWM output?

 

[inglewoodpete]

PWM is probably not the way you should go if you are trying to accurate position a stepper motor with a PICAXE.

To answer your question, the bottom and top chips in the range can count PWM pulses (08, 08M, 28X2 and 40X2). Have a look at command manual 2 page 137: command "pwm". The command, however, does not give you any control of the frequency.

A recent thread discussed using an external hardware counter and gating control to output a predetermined number of pulses. However, the thread originator's enthusiasm seemed to wane when hardware design became involved.

If you want to control the stepper motors from a PC, have a look at phidgets

 

[Rickharris]

There are lots of not too expensive DIY solutions to CNC work out there PC based as to be realistic you need to interface to a CAD package or it all gets very difficult trying to decode G code.

Cheapest in the UK I have seen is a 3D printer at £700. works though.

 

[rodmcm]

Yes I am aware of parallel output control and the heaps of software to convert G code to parallel out. However, the clock pulses still have to be counted and the frequency of multiple pulses ( 3 off) via parallel ports is iffy. Hence the desire for a serial interface to the PC and use of PWM outputs. the command PWM does not work as the frequency is fixed and hence you cannot control speed. Can you direct me to the other reference on external counters... I cannot find it

 

[BCJKiwi]

Check out http://www.machsupport.com/ and http://www.hobbycnc.com/ sites for proven systems at relatively low cost. No issues whatsoever using parallel ports with these systems.

 

[rodmcm]

Thanks for that. I am aware of both their sites. The advantage of the pic method is that I can run a serial line to the picaxe rather than split out a parallel port plus I can have fun programming and learning

See http://kellyware.com/max_stepper/index.htm

 

[BCJKiwi]

Have you considered why these systems use the parallel port instead of serial - i.e. the speed required?

 

[rodmcm]

Yes There are only three or four variables at any time the x/y/z /(a) posn, usually these are stacked, I think the Kelly unit has 39 memory locations. I must admit that while I am purchasing hardware the use of a picaxe for this control is an intellectual exercise as well, mainly because it has all the elements, controllable pulses, serial in etc. The main item is to count the pulses accurately which I could do on a second pic...maybe I will try this. When you consider that you need 4000 pulses/inch then +/- 1 pulse is proably accurate enough

 

[BCJKiwi]

MadProf has been struggling with this concept as well - see his thread http://www.picaxeforum.co.uk/showthread.php?t=12324 some things in there may be relevant.

 

[rodmcm]

Yes, he is approaching it quite different from me. I want the pic to generate the pulses and count them, which means the PC sends a distance to move and a feed rate. These pulses will go to a stepper controller along with the necessary enables/direction etc which can be set before movement.

http://www.littlediode.com/datasheets/Datasheets-TA/TA8435H.PDF

 

[inglewoodpete]

Refer to post #2: Without additional counter hardware, the PICAXE is probably not the chip for your task.