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The PC Turn 55 that I converted used 5 wire steppers that looked like NEMA 23 motors but in reality the bolt pattern was slightly different and the shaft size was a little bit smaller. I managed to modify the mounting plates and ream out the pulleys to fit new motors without too much trouble. Jason states that his machine actually has NEMA 23 motor so he won't have to deal with any mods other than drilling a hole in the motor shaft to pin the pulley.

I chose the Keling Inc motors because they can be wired in bipolar parallel for very low inductance which is desireable for driving from the original 24V supply. I kept the original supply because I needed 24V for the tool turret. Without that requirement I would have chosen a higher voltage to insure high speeds. As it turns out, the steppers operate well on 24 v.

It is also important to keep in mind that while 185 oz motors might seem small, I am pretty sure they are substantially stronger than the original motors and there is no reason to push things much further and risk damaging other components such as the lead screws.

So I went through the stepper board. There are 3 slots for driver cards, two of which are filled (for the X and Z axes).

Of the 16 connections, there are 6 pairs of inputs (2 pairs per axis) that are each differenced, amplified, and sent to the 3 motor cards slots. So persumably these are direction and step.

That leaves 4 connections.

One wire that is directly connected to the same pin on each of the cards--zero ohms. It does not appear to be connected to the power supply. The 3 other lines appear to be buffered outputs, one from each motor card.

Does anyone have a guess about what these 3 outputs and one shared connection would be for?

enable and fault would be my guess (with one of the two commoned)
(this assumes these signals use a common signal VCC or gnd)

another possibility is that there is just an enable in or fault out per drive
and its isolated, so the signal common is brought out to connect to gnd or +5 or some such

Andy-
Why do you advocate using the Mesa board rather than parallel ports? One parallel port come for free, and extras can be had for about $25, while the Mesa pair 5i25 7i76 cost $200. I suppose that doesn't take care of the VFD control.

Probably the same reason I like and use the 5i25 7i76 combo for a stepper system for anything beyond an etch a sketch or a low powered hobby machine with no I/O. I have ran my plasma on the parallel port and it might make sense to start there depending on the machine and other considerations. As soon as I started adding things like limit and home switches and probe inputs and.... I quickly ran out of I/O. Just as a note I did not run directly from the parallel port but used a BOB from CNC4PC to safeguard my parallel port and then I needed to add some relays but in the end I was still limited by software step generation speeds limits. So in hind sight I would have been better off to skip step one if only the 5i25 was out then...

John

jrkeat wrote:
A parallel port is $25 and a 5i25 is $80. Considering that the 5i25 gives you 2 x 25 pin parallel-port equivalents and also has hardware step generation then I think it is a better investment than a second parallel port.
Hardware step generation is not just about higher maximum step rates, you also gain from a much lower granularity at high step rates. This ought to mean that the peak step rate can be higher. (the worst case with software stepping is when you switch from 1 pulse every 2 base threads to one pulse every thread. That demands an instantaneous doubling of motor speed, which clearly won't happen in the real world.

Add to that the fact that the 5i25 is rated at 25mA per pin whereas a plug-in parallel port might be 3.3V and 3mA source / 15mA sink (if you are unlucky).

The 7i76 is optional, but many people do add a BoB to their parallel port system. These typically cost $50. Again, the Mesa 7i76 is about 3x as expensive. But it does give you a lot more IO pins (48), and those are able to switch 32V @ 300mA, so can drive proper big relays and contactors directly.
As already noted, the 7i76 has a built-in fwd-rev and analogue voltage for VFD control.

I agree that it often makes sense to use just the parport, and it can also make sense to buy a BoB for that parport. But I am less convinced that it makes sense to buy a second Parport and BoB because by that stage you are likely to be working on a more serious machine and are likely to see the advantages of a more capbable IO system such as the Pico PPM or Mesa cards/

I am aware that I sound like a Mesa salesman half the time though.