Messages

6901

General Mach Discussion / Re: Sizing my parts

« on: June 21, 2017, 03:40:23 AM »

Hi,
sounds to me like you should recalibrate your 'steps per unit' and the oversize problem should disappear.

Have a look on the Config/Motor Tuning page and have a look at the 'Steps per' in the lower left corner. Your description suggests that it is
0.25% to high. It maybe of course that you cant get it exact, the 'steps per' is an integer.

Craig

6902

General Mach Discussion / Re: add relays to Break out board schematics

« on: June 21, 2017, 03:25:01 AM »

Hi,
the circuit diagram certainly looks like it should work.

Do you have a multimeter or better yet an oscilloscope?

Check for Vcc and Vdd on the board to start with.

Just as a matter of interest how did you make your board?. I note that its double sided and plated thru holes are not an easy proposition
for a hobbyist. Not unreasonable to whip around with your multimeter set on 'continuity' and check any thru holes.

Craig

6903

General Mach Discussion / Re: Question about computer to run Mach 3

« on: June 21, 2017, 12:45:47 AM »

Hi Ussca,
Machs parallel port can be VERY picky about what port control IC is used. Some PCI boards work
ok but others don't.

When you install Machs PP follow the manual, there is a stage at which you MUST reboot the PC or
risk corruption of the software driver/black magic/hocus pocus you've just installed. Therafter the PP should
be seen as a distinct physical device in Windows Device Manager. Now you can test it with Drivertest.exe
in the Mach3 directory.

Craig

6904

General Mach Discussion / Re: Question about computer to run Mach 3

« on: June 20, 2017, 02:49:00 AM »

Hi,
this is very similar to my platform, very modest computing power but it works....
http://www.mini-itx.com/store/~D2550HN

Craig

6905

General Mach Discussion / Re: Question about computer to run Mach 3

« on: June 20, 2017, 02:39:11 AM »

Hi,
there are new computer boards out there with parallel ports built in. I bought an dual core Atom mini-ITX board a few years
ago and used its built in port and added another PCI board for two PPs and ran Mach3 with it for a couple of years no probs.

About six months ago migrated to Mach4 and thought it would be a good idea to try out an external controller. Bought an ESS. Took
a little while to get my head around new ways of doing things but good, very good now! Probably should have got an ESS years ago.

Craig

6906

General Mach Discussion / Re: G31 is sometimes moving the wrong axis.

« on: June 19, 2017, 04:03:39 AM »

Hi,
I can't answer your question but have learnt something that may help you get a handle...

This comes from Mach4 but Mach3 I believe operates identically. When Mach encounters a G31 it interprets it as a G1, ie a linear interpolated
move to the 'end' co-ordinates contained in the G31. Commonly we call G31 and do not wish any movement in X or Y just in the negative Z
direction. When the probe strikes the remainder of the move is aborted and the current position is returned to Mach.

We dot not as a rule specifically mention X or Y in our G31 command but they are implied.
G31 Z-1 F10    is interpreted as
G31 X[current x coord] Y[current y coord] Z-1 F10.

Could it be that the error you describe occurs because the implied X co-ordinate somehow changes?

May I suggest a means of testing this theory would be to re-write your G31 such that the current x co-ordinate is specifically
mentioned, not sure offhand what the pound variable number is for X...

G31 X#nnn  Z-1 F10

Craig

6907

General Mach Discussion / Re: Need Help to Figure out PLASMA CNC

« on: June 19, 2017, 02:33:24 AM »

Hi,
for a low budget plasma table you've spent a few bucks....does the Missus know? Good-on-ya!  Looking forward to see what you do.

Craig

6908

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

« on: June 17, 2017, 05:56:54 PM »

Hi Diego,
yes 5 phase steppers are usually much more expensive than two phase. Firstly there are only half a dozen manufacturers around the world
and they focus on the industrial market not cheap hobby stuff. You get what you pay for. 5 phase drivers are likewise rare beasts and you'll
have to pay if you want one.

The reason I have become familiar with them is that when I was designing my mill I wanted good resolution and given my previous argument,
microstepping was just not going to cut it. Two phase steppers are naturally 200 steps per revolution. Five phase steppers are naturally 500 steps
per revolution. With 10:1 planetary reduction that works out to 5000 steps per rev and with my 5mm lead ballscrews 1um per step.
Note that I don't have to use microstepping or even halfstepping to achieve that. As it turns out 5 phase steppers have smoother motion
characteristics than 2 phase steppers and microstepping for smoothness sakes is not required. All steppers lose torque at speed but 5 phase
steppers hang on a bit better than 2 phase. I have run my steppers at 3000 rpm but find they run cooler and with good authority at 2400 rpm.
A lot of Vexta motors have a gearbox built in. The gearboxes range upwards in price from simple spur gear units with 30 arc min lash to
planetaries of 3arc min lash to harmonic drives of zero lash.

I googled the part number of the harmonic drive you have, nice unit. It is a hollow shaft design which is ideal for robotic arms and are the main
use of such units. Harmonic drives can also be had in a more regular style gearbox with input and output shafts. Vexta have gone one step further
and mated their motor to the gearbox, very handy. Personally I think you'll find such a motor/output shaft combo much easier to incorporate into
you mount.

As to how you control the pulse stream being issued by Mach is going to require you be familiar with Gcode programming. Do some research online
about Gcode. As an example to make a machine drive with co-ordinated axes in a straight line at a given rate:

G1 X20 Y50 F100      will drive from the current point to X=20mm, Y=50mm at a rate of 100mm per minute.

Note that Mach considers X and Y axes as linear and produces pulses. It doesn't know or care if you feed those pulses to a rotational axis or not.
Mach has A,B,C axes as well which it considers as rotational axes and you might find it easier to program using them.

There are other codes for circular interpolation but they are not really going to help you. Circular interpolation is fine if you want to engrave a circle
but it won't track a stellar object. You'll need to calculate the axis movements and then use the likes of G1 codes to shift your scope.

Is there any way to jog while following a path? I would need to adjust position while the machine is moving

Once a Gcode program in operation then you can no longer jog. You can get around this by interrupting your running program every few milliseconds
to see if the operator is fiddling with the jog wheels, execute any jog moves and then return to your running program. I have migrated to Mach4 and
can see how to do this easily but feel pretty sure Mach3 could be pressed into doing the same thing.

How can I run Mach3 without a BOB connected to the computer? I need to simulate stuff...

Mach will run without a motion controller of BoB connected. Are you using the parallel port or an external controller?

Craig

6909

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

« on: June 17, 2017, 06:50:51 AM »

Hi,
you've raised some interesting questions, and a few myths.

The first is that microstepping doesn't increase resolution. Lets say you have 8 microsteps in action. Say at the present time the armature is at
a full step position when a pulse comes along for the armature to rotate by one microstep. What in actual fact happens is that the current in
phase A will reduce to something like 7/8 of normal while phase B will increase to 1/8 of normal. Say your stepper is rated at 50 oz in, then
the torque trying to overcome the load in rotating from the fullstep to the first microstep will be approximately 1/8 of rated, ie 6 oz in. That's
likely not enuf to overcome the load and the armature won't move. Now a second pulse comes along, phase A 6/8 rated, phase B 2/8 rated
for about 12 oz in torque and the armature may well have enuf torque to overcome the load and rotate. If it does it will rotate the equivalent
of two microsteps. Thus whether the armature rotates 1 or more microsteps is highly dependent on the load, nothing like what you could call
resolution.

If memory serves there is quite a good discussion of this on the Geko website.

The reason that microstepping is used so widely is that it is so much smoother than full stepping NOT to increase resolution. Most drives will
enable half stepping and usually both phases are energised with rated current and the torque between a fullstep location and the next halfstep
location is 141% of rated torque. It is usually fair enuf to count on doubling the resolution of a stepper when you implement half stepping,
just that's it incorrect to think that resolution increases by a factor of 8 when using 8 microsteps. For this reason I suggest if you are using a two
phase stepper use it with microstepping for smoothness it will in fact achieve half step resolution ie 0.9 degree. With your harmonic drive
that's about 27 arc sec which is not to shabby.

If you were to use 5 phase steppers with a half step capable driver you would achieve 10.8 arc sec. You can see that 5 phase steppers enjoy a natural
resolution advantage over two phase steppers.

Next myth is your voltage=torque misunderstanding. A stepper has a rated current, the one in the link is 0.75A and it will produce its rated torque
when that current it applied to the windings. The resistance of the windings is likely to be 1 ohm or there abouts. You would need a battery of only
0.75V to drive the current thru the windings, easy. In addition to the resistance of the winding it has inductance and so it will take time for the current
to build up to that level. If you want to make lots of steps quickly using a higher voltage drives the current thru faster. This is what you do for a mill
or router that you want to move around quickly. But you don't need fast...if your tracking an object the scope has to slew 15 degrees per hour,
or 900 halfsteps with your two phase stepper/harmonic drive combo per minute. That's REAL REAL slow for a stepper, you could do that with a 6V battery.

The next myth is the size of the motor. Your 3Nm steppers thru a 120:1 reduction works out to 360Nm! That's V8 torque. You don't need a V8
to drive your scope!!! Losses in the drive will reduce that but more importantly you'll explode the drive before you even get close. You shouldn't
require much more than 1-2Nm for a well balanced scope so with the deep reduction a stepper of 0.01Nm would be adequate, ie it can afford to
be tiny! The deep reduction means that even a very small stepper will work fine. What will improve with a larger motor is the ability to slew your scope
rapidly to a new object.

Steppers are not efficient. They require current even when they're not turning. Usually you can reduce the amount of current when not turning to
just enuf to hold the armature in place. If your talking about 3A as holding current you will flatten batteries quicktime. With the 17 size stepper in the
link I posted I would be trying to get the holding current down to 50mA or so. If the winds that strong that the load on my scope and therefore
the holding current of the steppers goes way up its time for me to go home anyway!

Craig

6910

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

« on: June 17, 2017, 02:13:08 AM »

Hi,
just had a look on Ebay and found this

http://www.ebay.com/itm/Vexta-PH544HG2-NB-Harmonic-Motor-gear-as-photo-4th-Axis-CNC-sn-1521-Promotion-/182582226894?hash=item2a82bfafce:g:FT8AAOSwUKxYftWp

Vexta is a Japanese company and they make a lot of stepper motor systems, a lot of them 5 phase like this example. I have Vexta 23 size steppers with 10:1 planetary
gearboxes for my mill. They are superb. They make really REALLY good stuff. Note that in one of the pics it shows 0.0072 degree/step ie 26 arc sec, if you had a half step
capable drive that is 13 arc sec resolution! That's right up there with pro gear, a man would be proud to show off handmade gear of this capability at a star party!

My drivers, also Vexta, are 230VAC with a DC link voltage of 150VDC. It makes my mill really sing, I run the steppers at 2300 rpm and they NEVER miss a beat.
For a telescope drive you don't need that sort of speed, in fact with the deep reduction you probably won't need anything like the torque that is available at 0.75A
per phase, the rated current. My guess is that you could run these steppers with 12VDC or less and I suspect currents of 100mA would be enuf for anything but
the largest of scopes or one that's well out of balance. I think battery operated is entirely possible, just the thing for star parties in the back of beyond.

Craig