Messages

6911

VB and the development of wizards / Re: Computer guided telescope mount using Mach3

« on: June 16, 2017, 07:19:54 PM »

Hi,
amongst my other interests is Astronomy. I have a 10 inch Dobsonian and have given some thought to making it a goto mount.

Mach will easily produce the pulse signals required to drive steppers/servos. Further with Machs programming capability makes things
like Alt Az DROs easy and numerical calculations necessary to convert to RA Decl easy as well. Interfacing with another astronomy program
I think is probably doable if the manufacturer of the program is prepared to publish the format of its output data.

A more immediate challenge is how to drive the scope. Two phase steppers have a full step of 1.8 degrees and half step of 0.9 degrees.
Microstepping might give you the impression that greater resolution can be obtained but as many a CNCer has found that increased resolution
is fictitious. Clearly any direct drive from a stepper to the scope would not have the resolution to do the job.

I have seen designs where the stepper shaft acts as a small diameter pinion on a much larger diameter wheel attached to the scope in fact
part of the existing Dob mount. A reduction of 100:1 is probably achieveable. Note that this is not a gear, any gears will have lash which will
like as not render the goto mount useless. The design relies on friction contact between the nominal 'pinion/crownwheel' and has no lash.
Such a setup with half step resolution at the stepper would get 0.54 arc min or 32 arc sec resolution at the scope.

A lot of servos out there have 2500 line encoders for 10,000 count per revolution. A direct drive would result in a resolution of only 2.16 arc min.

I have low backlash planetary gearboxes for my 5 phase steppers for my mill (0.72 degree/step, 0.36 dergree/halfstep) but despite being  expensive they
have a guaranteed backlash of less than 3 arc min. So while at half step with 10:1 reduction I can get 2.16 arc min resolution the potential
backlash is 3 arc min. I might point out that I cant measure any backlash with my units I'm sure it must be there.

A top class worm drive with a large diameter worm wheel is the usual approach to telescope drives. They are VERY expensive, so much so
that really they go beyond any cost saving attempt to make your own drive/stepper/servo system.

Another alternative is harmonic drives. Really groovy idea to produce reductions of 50:1 ,100:1 etc with NO backlash. That's correct, NO
backlash. The manufacturers do allow 'lost motion', which is actually flexure rather than lash but has the same general meaning as backlash.
Typical 'lost motion' specs are 8-12 sec arc. Practical resolutions of 15-20 arc sec could be had. Unfortunately they're not cheap, I followed
them on Ebay for $300-$500 with a stepper or servo built in. Worth having a look. Doing some reading on Harmonic drives is also fascinating.

Craig

6912

Mach4 General Discussion / Re: EtherCat Pulgin...co-operative venture?

« on: June 14, 2017, 02:46:18 PM »

Hi,
yes, sorry I was meaning Windows when I actually said PC.

I am impressed that Linux is realtime capable.

Craig

6913

General Mach Discussion / Re: CNC 8060Z

« on: June 14, 2017, 02:35:40 PM »

Hi,
the Diagnostics tab page of Mach3.

Craig

6914

Mach4 General Discussion / Re: EtherCat Pulgin...co-operative venture?

« on: June 14, 2017, 03:34:43 AM »

Hi,
I read it somewhat differently, if you wish to sell devices they are supposed to comply, you can either test it yourself or pay
someone else to certify it. Unless your customer demands compliance you do not have to do so.

EtherCat Master is a realtime system, PCs are unsuitable as is and the solutions to achieve realtime determinism are just to expensive
for me to get into as a hobby project.

Craig

6915

General Mach Discussion / Re: Kinda lost on servo setup- how can I control?

« on: June 14, 2017, 02:58:24 AM »

Hi,
I don't know much about Fanuc, its way too expensive for me. Those servos look like genuine AC servos, in which case your going to
need some AC servo drives. The Gekos are DC and won't work and probably to small anyway.

Fanuc servo drives are probably the best way to go but expect to pay hundreds if not thousands. Another alternative is to replace the servos and
drives, Taiwanese Delta 750W servos and drives maybe $750-$1000 each. There are cheaper servos but increasingly 'cheap and nasty'. Or bargain
hunt Ebay.

You might get satisfactory performance from lower power servos, you might for instance get some with plenty of torque but only 1500 rpm or so.
Will mean your lathe has plenty of grunt but slower rapids, probably perfectly OK for hobby use.

Time to do some research online. If you can save the Fanuc servos do so, they're really really good. Cost may dictate that you have to swap them but
to get even comparable performance is not going to be cheap.

Craig

6916

Mach4 General Discussion / Re: subroutines?

« on: June 13, 2017, 02:48:52 PM »

Hi,
I thought a subroutine O********* was actually part of the running Gcode program. If Mach had to go 'find' it wouldn't
you have to provide a path and filename?

Those Gcode jobs I have that do use subroutines  are included/part of the Gcode file and they run fine.

Craig

6917

General Mach Discussion / Re: CNC 8060Z

« on: June 13, 2017, 02:37:22 PM »

Hi,
on the Input Signals page you have Estop port=1 pin=3 and Probe port=1 pin=4. That doesn't sound right to me.

When you manually trigger either input by taking input voltage high (or low) do the diagnostic LEDs operate? With these port
and pin numbers I suspect not.

Craig

6918

General Mach Discussion / Re: HELP a newbie, so stress and depress...

« on: June 11, 2017, 02:24:51 AM »

Hi,
do you have a multimeter?  Disconnect all wires from your BoB except the power supply wires.

Suggest: Config/Ports and Pins/Input Signals  scan down to Estop, check Enable, Port=1, Pin=10, click Apply.

On Mach3 Diagnostics Tab is the Estop LED active or not? With your multimeter measure the voltage of pin 10 of your BoB
relative to 0V. If the voltage is high, 5V for a 5V BoB then your BoB has a pull-up resistor. In Machs default configuration, Estop
is active high, then I would expect the diagnostic Estop LED to be ON. If the voltage is low, 0V, then your BoB has a pull-down
resistor and I would expect the diagnostic Estop LED to be OFF.

Now: Config/Ports and Pins/Input Signals/Estop Enable=checked Port=1 Pin=10 Active Low=checked, Click Apply, I would expect with pin 10
voltage high then diagnostic Estop LED to be OFF. With Estop OFF you should be able to Reset Mach and have the Reset button go green and
be continuously light. If however pin 10 voltage is low, ie pull-down resistor, the diagnostic Estop LED should be ON. With Estop LED ON
no matter how hard you try you will not be able to Reset Mach, nor will you until you clear the emergency fault and get the Estop LED
to turn OFF.

If you now take a small wire from pin 10 to 0V, or alternately to 5V you should see the diagnostic Estop LED change state.

If you can follow this and get the Estop to work you've learnt about you BoB, that is, a pull-up or pull-down resistor and you've established
that your BoB can communicate over the parallel port. Thats good progress.

Let us know how you get on.

Craig

6919

General Mach Discussion / Re: CNC 8060Z

« on: June 10, 2017, 11:18:09 PM »

Hi,
one thing which I have not really addressed in my recommendations to you regards external controllers to replace the existing one
is spindle speed control.

The real question is what spindle control you actually need. Your pics show a VFD and guess that you have a high speed spindle, maybe
24,000 rpm and 2kW output or thereabouts. Further I assume you will be doing routing with this machine. If you want to do metal milling,
and by metal I mean steel or tougher, then not only does the spindle lack the torque but the machine lacks the rigidity to contain the
cutting forces ie not suitable for it.

When I built my mill, and it is a mill, very small but rigid for metal cutting I bought a high speed spindle, 24,000 rpm 750W which I thought
would be plenty. I have used it extensively for routing, circuit boards in particular, but as a metal cutting spindle it sucks! It just doesn't have
the torque to spin reasonable diameter tools at modest speeds. So for my spindle I find that when I use it I just set it to max rpm and leave it,
after all the ONLY use it gets is routing with micro-endmills or engraving bits. Niether do I require clockwise/counter clockwise direction control,
do you have any LH cutting tools or drills or whatever? All I require is on/off.

I, like many other spent a lot of time shagging around trying to get spindle control just so, accurate speed and direction, accel and deccel etc.
In the event I was wasting my time, with the spindle I have and the work I do with it all I require is On/Off. If I want to spin a particular tool
more slowly I can manually adjust it and 99 times out of 100 leave it like that for the entire job.

My recommendation is, at least to start with, is just on/off control, the PMDX 416 for instance has a relay on board for just this purpose.

I have recently built a spindle for my mill, 3500 rpm, 1.8kW and 6.5Nm, for milling steel. Works a treat but find that I don't actually need much speed
control with it either. Unless I'm putting a large diameter facing tool or flycutter or similar I usually set it at max speed and leave it. Again without having
LH tools or drills not worried about direction control either. This spindle motor is an AC servo so I have quite a rich selection of speed control including
indexing for threading available by virtue of the servo drive but in actual use don't need any of them.

Until you get plenty of hours of actual use under your belt don't go overboard in terms of time of expense with spindle control. You may find as I did that
you don't really need all that refinement or what you really need is something entirely different.

Craig

6920

Mach4 General Discussion / Re: EtherCat Pulgin...co-operative venture?

« on: June 09, 2017, 06:08:30 PM »

Hi smurph,
thanks for that clarification, its great to get a seasoned viewpoint from someone who has no vested interest.

My first exposure to a distributed motion control system was Panasonics RS485 system. They publish enuf hard facts about
the communication protocol that I could in theory make my own. This was on a large plasma table belonging to a customer thru
work. While it uses Panasonic servos it uses Logosol drives and these particular drives support RS485 comms exclusively.
I was trying to make the case to the owner to change to Mach4 but would need to fit genuine Panasonic drives at the same
time because they can accept step/dir type input. That unfortunately pushed the price up that he declined to change.

Thats when I became interested in distributed motion control in general. EtherCat appealed on the basis of flexibility and very
favourable licencing arrangements. What I did not twig to at the time was that EtherCat Master must be realtime effective.
I have looked at a couple of software solutions that use one or more CPU cores to run a genuine realtime system while reserving
one core to run Windows. Unfortunately they are expensive.

As to Why? I can see that EtherCat or some other bus system would be great in a factory with large numbers of servos, valves,
sensors etc. For a CNC machine even with co-ordinated slaved multiaxes more than 8-10 servos would be rare. Ehtercat would be
convenient to reduce wiring and so on but not necessary on a single machine. I imagine years ago when analogue servos were the
norm and pulse (step/dir) input was the new kid on the block lots of people asked Why? As you say time will tell whether distributed
control will take over and what protocols and standards evolve if it does.

My motivation is more personal, I would like a software project that would stretch my skills and make some useful contribution to
the community. Even were I to achieve a useful plugin would there be any uptake, even if free, if it required a multi-thousand dollar
investment in a realtime OS to run it?

If memory serves the PC running the plasma table was not running a realtime OS. The servodrives had a PVT table of 64, I think, entries
which allowed a buffer of moves. Depending on the granularity of the moves co-ordinated motion is possible. The difference between
that and realtime passed over my head at the time!

Craig