Which Mesa board?

Hi All, A few years ago I built a 4 axis mill, converted a Chinese drill mill. It works surprisingly well. I went from Mach 3 to Mach 4. Im not overly satisfied with the performance and feel it could be a better.
I want to switch the whole show over to Linuxcnc.

XYZ are brushed DC servos coupled to step and direction drives with encoder feedback. The 4th axis uses a Leadshine drive with hybrid stepper again with encoder feedback.

The set up uses mach 4 with Ethernet smooth stepper connected to a classic breakout board. My early research suggests I can switch to Linux cnc and replace the Ethernet smooth stepper with a Ethernet Mesa board which would connect to my existing breakout board via a ribbon cable.

Am I on track? If yes can any one can suggest a Mesa board that will do the trick, perhaps the MESA 7i92M

Paul

It might be a bit more work to migrate to Linuxcnc from your BOB this way but its hard to go past the Mesa 7i76e ethernet card. 5 step generators, spindle interface with encoder input, 2 MPG inputs, 16 outputs and 32 inputs and a few other features. Plus almost unlimited expandability.

I've not used one, but I think the 7i92 will let you use an existing BOB, but the 7i76e is vastly superior. You just need about a 2 amp 24 volt power supply, and maybe some 24 V relays.

The 7i76eD is designed for active low switching which might suit your existing wiring and sensors better.

Thanks Rod,

Im new to linux CNC. But Im sold on it.
I have also have a Kasuga mill with Heidenhain 355 control to retro fit next so cutting my teeth on this small drill mill first as all the hardware is done and working.

I was expecting the PC via Ethernet would couple to the economic 7i92M and then the 7i92M on to the existing BOB via the 25 pin interface, I think that would work. The MPG may be an issue. (Currently don't have one)

So yes I started looking at the 7i76E which looks even better I like the idea of connecting the MPG directly the the 7i76E. The existing BOB would stay in play save me on rewiring.

I think if I was going to keep the BOB, I'd save my money and go with the 7i92.

But you do leave a fair bit on the table that way I think. I've never used Mach or BOB. I have a mate who lives a few doors down who knows Mach backwards which would have been handy if I chose Mach when I started but everything I saw said Linuxcnc was superior in every respect.

One of the positives I saw was that the Mesa cards would allow a more robust industrial 24 volt logic system that was significantly more impervious to noise than lower voltage systems. It needs a lot of noise to invert a signal at 24V!

The other alternative would be to spend nothing, turf the smooth stepper and spin up your BOB via a parallel port.

Rod, yes I'll order the board soon. One last question, if I go with the 7i92 is a wired MPG going to give me much grief to set up?

palmac wrote:

Rod, yes I'll order the board soon. One last question, if I go with the 7i92 is a wired MPG going to give me much grief to set up?

Probably but I'm not sure! Most people seem to struggle as its not in pncconf to my knowledge

There is a full walk through of setting up a 7i76e MPG for a single axis on my build thread starting on this post
forum.linuxcnc.org/show-your-stuff/32029...build?start=20#85279

You can use the same method I used for Axis select as I showed for MPG scale. That way you only need a single MPG
Whilst the 7i76e supports 2 MPG's, I think you can use any inputs via the encoder component (eg. for 7i92)
linuxcnc.org/docs/2.8/html/man/man9/encoder.9.html

One of the positives I saw was that the Mesa cards would allow a more robust industrial 24 volt logic system that was significantly more impervious to noise than lower voltage systems. It needs a lot of noise to invert a signal at 24V!

I believe that the 7i92 only has 5V system and no opto's on it although you can connected to drives as they have opto's but you have to be careful re the inputs without using a BOB I have used one converting a Novamill but used a Chinese bob on one of the ports

Clive, ok getting there,.,.so it seems the 5v system is much more prone to noise than the 24v that makes sense and believe me I had a hell of a time with noise when building this machine. component location and filtration became a real issue. Its s till a little flakey today.

The BOB I have is 5volt. So regardless of what Mesa I choose if that BOB is still in play would I be right in saying the noise susceptibility likewise remains regardless of what Mesa I choose as the 5v BOB remains the weak link?

So it looks to me like the 7i76e does not require a BOB as it has its own opto couplers to cover the required I/O. So the 5V BOB can be discarded altogether for the 7i76e.
The 7i76e also has MPG capability.

If I'm right on all this I think it has to be the 7i76e.

palmac wrote:

Clive, ok getting there,.,.so it seems the 5v system is much more prone to noise than the 24v that makes sense and believe me I had a hell of a time with noise when building this machine. component location and filtration became a real issue. Its s till a little flakey today.

The BOB I have is 5volt. So regardless of what Mesa I choose if that BOB is still in play would I be right in saying the noise susceptibility likewise remains regardless of what Mesa I choose as the 5v BOB remains the weak link?

So it looks to me like the 7i76e does not require a BOB as it has its own opto couplers to cover the required I/O. So the 5V BOB can be discarded altogether for the 7i76e.
The 7i76e also has MPG capability.

If I'm right on all this I think it has to be the 7i76e.

I have never used DC brushed servos so cannot comment on what they need. A lot of drives use 5V to control the step/dir but using differential signalling that the 7i76e and 7i96 etc has, is much more immune to noise. They can also cope with 24V stuff for the switches and other controls.

The 7i76e has 0-10v spindle control also with a high speed encoder on it. The 7i96 has the high speed encoder but not the 0-10V but it dose have SSR's for the outputs that can handle about 2A each .

Personally I would go with the 7i76e I believe there are two versions (sinking or sourcing outputs) www.mesanet.com/pdf/parallel/7i76eman.pdf