Please Help - How to Configure a 5 Axis Head-Head

tommy

I added a photo of the histogram.  Honestly not sure how to interpret this. Let me know what you think. 

So, are the step/dir signals coming to the mesa board through the ethernet cable? Because I don't have a parallel port of my computer, just a vega connector.  


spumco

I added a screenshot of the cad of the 4th/6th axis (kinda works as a 4th axis but will technically be the 6th axis) since it is not assembled yet.  Again, only 5 axis will be moving at any one time and there will be two different configurations.  And a picture of the full machine which you can tell is a head-head I built on your standard gantry style machine. 

Good call on removing power to the driver, I do plan to removing the 4th axis from the table when not in use.  Interesting idea about using a 6 pin connector, I'll def think about that. 

Okay I'll plan on purchasing a 7i96s and 7i85s. Hopefully on Monday.  Lets assume I envy your handwheel and want the vista one and not a amazon one, I assume there would be plenty of I/O for that with the 7i96s and 7i85s?

So it looks like I need a parallel port to run the VFD? As I mentioned above I only have a vega port on my computer (plus usb, ethernet, aux..).  Is there a way to run the VFD off of the Mesa? It looks like there is a way to do it off the usb, I know you just said you don't like usbs but...  I definitely will not be doing rigid tapping with this machine. It would be very cool to get temp and particularly load (I think I am running this machine significantly under its potential power) off the spindle, but honestly, it will just be nice not to have to crawl behind my machine and manually set the rpm like I was doing before this build.  The name of this machine is the "Hackbot" and I consider it a means to an end and also a learning experience.  I plan to make a significantly stiffer, more powerful, more accurate machine in a few years and I want that one to be perfect.  But, if this one is a little janky its okay.  Just to set expectations accordingly. Obviously I still want to be able to machine percise parts..  Let me know what you think. 


I was also poking around on LCNC and I think I can use two sample configurations as the basis for my machine.  The "5axiskins - 5 Axis bridge mill" should work for when I am using the machine in head-head configuration.  Though I will have to flip the y and z axis so that I don't have to change the kinematics (this was a good suggestion by rodw).  This will probably mean that I can never get the A axis to 0 degrees (where zero is in the preconfigured file anyway) though as that would crash the spindle into my A stepper motor.  Will this be a problem?  By the way, does anyone know how to change that machine configuration to TCP control? I would think it is either the 'bridgemill' or 'identity' buttons but is unclear.  I plan to try posting some code and testing that configuration on the laptop soon. 

For the head-table configuration. I think I can use the max5kins or the max5triv to run the machine, it will just be that the home (0) position of what is currently my b axis will have to be 90 degrees off from where 0 is on those configurations,  this moves what I am calling my A table axis to a C axis. Does that make sense? 

The 7I96S has an analog output for a VFD and you can use the isolated digital outputs for FWD and REV. All step/dir signals come from the 7I96S (the 7I85S just buffers these)

PCW 
Gotcha, I just read the mesa 7i96 manual about VFD so thank you. What do you mean by buffers them though? Breaks them out?

Converts the single ended 3.3V signals to high drive 5V differential signals and
breaks them out.

Pendants:

The Vista pendant is USB - it plugs in to your PC's USB port and there are configuration files from Vista which let the pendant communicate with LCNC.  They are solid, and the features on them are really nice.

My only gripe with them, and USB devices in general, is that they aren't 'real time'.  If you jog slowly (turn the handwheel) it's fine.  If you move it faster it's fine...until you reverse directions.  At that point the USB lag or latency becomes painfully obvious as the machine doesn't stop moving immediately.  If you move the handwheel back and forth fast you can quickly get the MPG out of synch with the axis in question.

Some folks have reported intermittent connection issues, possibly related to EMI interference bugging up the USB connection & data.

I've noticed the same latency issue on xbox controllers connected as CNC pendants.

Other USB pendants are, I presume, similar.  Easy to connect, have lots of features, and likley have the same latency issues as the Vista.

Wireless USB pendants are probably in the same situation, only with the additional issue of wireless interference potentially causing problems.

The above may be a non-issue for some users, but my use-case and risk-aversion led me to switch to a hardware MPG.  My Vista has been sitting in a box for a year or so waiting for me to sell it off.

The 'hardware' pendant/MPG I mentioned is simply a 100ppr encoder hooked up directly to a Mesa board's inputs.  In this case, there are no latency issues - it's a direct input.  They require two inputs (one each for A/B signals).

In addition, some method of selecting an axis as well as a jog increment is needed.  The axis selection & increment could be done through an on-screen control, but the typical scheme is to use two multi-position selector switches also connected to a Mesa board.

Oddly enough, the non-USB MPG's on Scamazon are not bad.  I also discovered that the only difference between a "4-axis", "5-axis" and "6-axis" MPG is on the sticker.  They all use the same 12-position selector switches and they all use the same coiled cable.  The extra wires are left un-terminated and the selector switches are set to 4 positions for the 4-axis (cheaper) versions.

I've looked at two different brands, and they're both as I've described above.  Crack it open, solder some wires, set the switches, and print a new legend sticker.  There's probably some that don't follow the scheme I described - but I doubt it.  YMMV.

IO:
There may or may not be 'plenty' of IO on a 7i96s + 7i85s.  There are 11 general-purpose inputs on the 7i96s.  5 or 6 of them are taken up by axis home switches (A-axis is optional but nice).  Should probably have an estop input (from a latching button or safety relay).  Might want to have one connected to the VFD in case it faults.  Maybe another one for a water flow-meter so you don't burn your spindle up... but your VFD might have an input you can use for cooling so no need to use up a Mesa input.  Looks like you've got open-loop steppers, so no drive alarms to worry about.

That leaves you three to five inputs to use. You could:

• Connect a hard-wired MPG encoder to two inputs, and use on-screen controls to do axis selection and jog increments
  • 5 inputs for axis selection (for 6 axes)
  • 2 inputs for jog increment (for 3 increments - 0.1, 0.01, 0.001)
  • You don't have enough inputs to do the above plus everything I mentioned...thus the 'on-screen' selection
• Buy a Mesa daughter-board that has more inputs (connects to 7i96s or 7i85s)
  • A 7i73 has four encoder inputs (8 pins), as well as the ability to use a matrix keypad for up to 64 programmable input buttons for user controls.  Downside is you can't really use it for 12/24v field IO (like homing switches)
  • Other smart-serial boards, like the 7i84, have lots of IO.  Some have 48 inputs and 48 outputs - that's quite a lot.
• Use a USB pendant
  • no IO required and probably has additional controls like a cycle start/stop button, feed-hold, feed/speed overrides.
• OR....skip the pendant for now and just use on-screen jogging controls until you've got your machine moving properly.  Then figure out what you want to do about a pendant.  All of the options I mentioned can be done later with no loss of money or time or brain-investment.

VFD:
If you're going with the 7i96s, there's no reason to bother with modbus right now.  Later on you can still use it to get information from the VFD and display/use it in LCNC - while continuing to use the 7i96s output to control the VFD.

IronManDylan wrote:

So, are the step/dir signals coming to the mesa board through the ethernet cable? Because I don't have a parallel port of my computer, just a vega connector.  

 

Don't worry about a parallel port.  LCNC communicates with the Mesa board (7i96s) through the ethernet port.  PCW will correct me if I'm wrong, but LCNC tells the 7i96s what to do, and the 7i96s generates the step & direction pulses.

That's why it can be so fast - the Mesa board is dedicated to (among other things) producing high-speed, tight-timing signals for the drives.  Whereas your PC has a bunch of other stuff to do, all at the same time, so it can't generate step & direction signals with perfect timing as fast as a Mesa board.

Took me a while to catch on to this as other CNC software (Mach3/4, UCCNC, others) use external boards that are 'motion controllers' and buffer the instructions from Windows.  Windows manages the user interface and gcode-to-instruction conversion, but the motion controller boards do all the heavy lifting.
 

Sounds good, I won't worry about the pendant right now.  Yeah, thats what my Mach4 BoB was doing.

Got the boards ordered! 7I96s and a 7I85s.  Should arrive Friday. Also have a cable coming.  Hopefully everything will play nice with the laptop and hopefully the 5 axis stuff will work!  I'll keep you guys updated.

Don't forget you need a 5v power supply for the 7i96s.

The 7i85s also needs 5v power, but that can be supplied by the 7i96s through the DB25 cable.

Sounds good.  I have a 5v 2 amp supply coming now.  

I did some experimenting on LinuxCNC yesterday.  I was able to get the vismach machine moving around in TCP mode for the bridgemill.  But was unable to do this with the "5kins" table-head machine.  Which had me concerned that I would not be able to use the machine in this configuration.  But then I started thinking..

If the WCS is set at the middle of rotation my "4th axis"  (would technically be the 6th axis of the machine but will be operating as a 4th axis) I shouldn't need any type of TCP control for the 4th axis, correct? I believe that this is how a 4th axis is programmed and doesn't require any kinematics control by the controller. If this is true I can use the head-head in full 5 axis TCP mode and use the 4th axis for indexing or whatever I need it for.  Does anyone have experience machine with a 4th axis and can tell me if my understanding of this is correct? 

I use a 4th axis (A) in continuous and indexing with LCNC and F360.  No TCP.

I set the WCS at the CoR in Y/Z and X wherever is appropriate for the part.  Works like a champ with F360's 'tool orientation' feature.

I suspect you'll want to set WCS at CoR of the table axis and treat each indexing move as a new WCS.  i.e. A0 = G54, A90=G55, etc.

Reason I'm thinking this is how to do it is that F360 will not know when to rotate the table axis vs. the head tilt.  You can set max tilt definition in the F360 machine settings, but it'll be hard to define whether you want 10 degrees of tilt and 45 degrees of table rotation, or 45 degrees of tilt and 10 degrees of table rotation.

Probably a non-issue for head tilt on an axis that doesn't correspond with the table axis, but when they're essentially parallel-but-offset, how does one define which moves when?  Maybe in the post processor... but that's well over my head.

You can also have multiple LCNC configs for the same machine - perhaps one for continuous table axis work, one config for table axis indexing, and one 'non-rotary-table' config.

• The indexing one uses G54/55/56/57 for each 90 degree table axis quadrant, and the head can tilt +/- B90
• The continuous one uses one WCS and rotates the table, but doesn't tilt the B-axis

Just a thought, and perhaps someone with more experience with F360's multi-axis machining extensions can chime in.  In fact, you might ask some questions on the F360 manufacturing sub-forum to get an idea of if/how F360 can deal with tilting-head + rotary table machining strategies.