G'day from Australia - Mesa board selection advice. Please help.

Hi all I have not responded to directly, (Mike/Aciera)

I'm sorry, but I've had a busy day and can't respond to you all as I'd like. Thanks for the information.

I get that there's a lot going on in the network when switches and other gear are used as intermediary devices, and that theoretical speeds are almost never achieved due to the overheads and issues at each layer of the TCP/IP stack. However, I have no idea of the bandwidth required for reliable CNC functionality.. but I recall correctly (It has been a while) Parallel ports had bandwidths of only 2.5Mbit.

That seems a long way short of most 100Mbit connections, although I must confess I'm not entirely sure how fast the ethernet interface is on Mesa boards, Is it only 10Mbit or something? I couldn't find that specification in the 7i76e manual.

Anyway, thanks for the responses from you both.

Kind Regards, and good night!
Hamish.

harmo wrote:

Hi RodW,

While I've read about a few boards, there are always the niggling questions like:

"Is this the best combination of Mesa cards in terms of both cost, and/or performance?"
"Has anyone used this particular combination before? Is it going to be reliable?"
"How sure am I in my interpretation of the facts presented?"

I'll keep you posted,
Hamish.

I think its just that your requirement for 6 axes with stepper motors requires more stepgens than what is supported on most of the boards. Other than that, the performance won't change.
You will have to flash the correct firmware to the board. I had a look at the zip file on the 7i76e page and there is one that will support the 7i78 (plus another 7i76 if you really to go wild!)

It just a matter of using mesaflash to install it and restarting your machine.

You can just plug the mesa card into your router but the store and forward communication model can't be depended on for the real time requirements of Linuxcnc.

Remmber what sets Linuxcnc apart is that it is THE_MOTION_CONTROLLER not some emasculated embedded controller on a smoothstepper et. al. This comes at a cost and that is it requires a real time operating system (PREEMPT_RT) and any external hardware needs to be able to communicate in Real Time. That typically means it has to be on time every time to service the 1 kHz servo thread on Linuxcnc that is the core of the CNC system.

So the inability to use a network router is a restriction of Linuxcnc, not the hardware.

What is good about a parallel port has little to do with bandwidth and more to do with real time. The parallel port is directly accessing memory address bits, and the speed at witch the real time thread can service them is the only limiting factor.

While Mesa's hardware is great, for a simple router a couple of parallel port break out boards should be more than adequate.

Hi Everyone,

Thank you all for the input. I've taken RodW's advice and ordered 7i76e and a 7i78 4 axis step/dir card.

I've been peering through the manuals of each, and I was wondering if anyone has any recommendation for compatible accessories such as home/limit sensors, or recommended MPG/Pendant-like accessories.

If anyone has had any negative experiences with certain gear and this configuration, I'd also like to hear some insight.

As always, any guidance is appreciated. Stay safe everyone!
Hamish.

For something super simple I'm using this with a MESA 7i73 (not absolutely required), hasn't missed a beat and seems pretty robust with not a lot to go wrong.

Thats probably a well priced pendant. It does not need the 7i73. If it has 5 volts MPG, then the 7i76e will support it if the correct mode is loaded in HAL. There is an example for a single axis MPG setup on about page 3-4 of my Spaceship plasma thread. You just need another Mux4 for axis selection.

any simple switch will work fine for limits etc or you can use a PNP prox sensor.

Ocean Controls have a 2 amp Meanwell din rail power supply which is perfect.

For your control box, add an IEC EMF filter for mains power inlet. Jaycar has one or RS components with a fuse built in. I put a house breaker in the control box.

There are no negatives. Its Mesa and Linuxcnc so it works!

I wanted to play with the 7i73 and have some ideas for a remote panel, but Rod is correct the 7i73 isn't required.

I came up with a user comp that handles all the logic in one "blackbox" and has outputs for joint_enable & axis enable. I feel it made the hal file a little cleaner and understandable for myself, Also handle the MUX functions for axis & scale select.