[DoubleM]

Hey Guys,

I have decided to build a CNC machine. I got a few parts from scanners and printers and such. Before you start thinking up your comment, this is a FIRST attempt, and I'm not looking for great results.

I enjoy making things, and this has been on the to do list for a while now. I don't want to spend heaps of money.

From one printer I procured 24 NPN transistors. If it helps I can pull out the data sheet. These transistors are "hammer drive', and I don't know what this means.

The H bridge I have built is very basic; http://legolab.daimi.au.dk/DigitalCo.../H-bridge4.gif

Transistor 1 and 3 are base tied, as are 2 and 4.

I know this thing works, I can make a regular motor hooked up to one H bridge rotate in either direction. But keeping the base high does not make for continuous rotation. I think that has something to do with the "hammer drive". By tapping the base, I can make the motor turn in either direction. This seems silly to me.

The problem is, nothing happens when I wire up the stepper. I think this is the hammer drive yet again.

I live in New Zealand, and finding components can be hard and expensive, so I would like to stick with these transistors.

I have access to PICAXE chips, and am experienced in using them. I have previous experience with PICs, but I didn't manage to get any kind of reliability with my home made JDM2 programmer.

I don't expect to get the ultimate answer first post, so please feel free to ask questions. I'm keen to get myself a working CNC machine.

This isn't the only aspect of the machine I will need help with, I see there is topics on more than just stepper drivers... There are computer interfaces, controllers... You know what I mean =).


Cheers,

MM

[samco]

This is full of good info.

http://www.cs.uiowa.edu/~jones/step/

off the bat - just tying the bases togather isn't going to work correctly. the upper transistors bases need to be aprox .6v higher than the collector for them to turn on. probably why you see the pulsing. As you turn them on - the motor starts out at 0 volts allowing the top transistors to turn on. but as the voltage across the motor rises - the to transistors are going to turn off.


sam

[DoubleM]

I have ordered 3 of these beasties, hopefully they do a good job.

I now have 24 10A NPN transistors. I am pleased with that outcome =).

Before I start guessing what forums I need to post in, can somebody detail a simple CNC machine?

I want it to be wired into a parallel port, (Mach3 looks good), and have X, Y, and Z axes. I will add the various input sensors as necessary.

To achieve this, what do I need? All I know so far is I'll need a table, 3 stepper drivers, and the parallel port cable.


Thanks Guys!

MM