[Parameter]

Hi, I recently got great bipolar drives (4wires) and upgraded my fixed gantry router with 100oz-in unipolars motors (from 90oz-in unipolars) ran as bipolars serial and to 40v power supply (from 18v).

Now I reach rapids above 96IPM (from 36IPM) (on a MDF machine with roller blade bearings!) using ACME 1/2"-10 at quite nice accelerations. Repeatability with no load seems limit (+- 0.005) at this speed but I know that this is too fast for the actual motors. Just a max speed test. It must drop some steps here and there, but impact is limited since those are microsteps drives (10:1) so a step there is not much...

If I start engraving a picture at 60IPM, the table vibrate so much I had to lower my start speed and acceleration all around... down to 25IPM! At this speed, the engraving (0 degrees angle toolpath) does not go sideway. If I go above 30IPM, the picture left top corner end-up being between 5 and 30 degress to the left when starting at the lower left corner... So the top left corner end up at around y-0.25 or so after a few inches of X travel when engraving at 0.02 inch per line.

Now, I use a Pentium75 with TurboCNC on there. I don't seem to have a step problem but when running at hight speed, the motors are set with this config:
ACCEL: 22000
START SPEED: 2000
MAX SPEED: 24000
runing at 0.0005" per step.

Which may be WAY above what the PC can deliver and would cause the missed step problems when trying to move all axis to these speeds... I do understand you can jog 1 motor at 25khz but when all 3 try to go at 20khz this seems a bit too much for the pc... Or something's wrong?

I really need to make those 4 hours jobs faster, what are your tought on this?

I may have some stepper coupler slip because of the acceleration. Rubber hoses are fine but not on twisted shafts... To this end, I'll have to make bushings to slip and lock on the motor shafts THEN use the rubber hose. Diameter of the shaft is probably too small to handle the forces involved as well (a bit less than 1/4).

I understand a couple things there. My motors being plugged as bipolar serial are set at half amps on the drives to deal with inductance. The power supply should go to 70v pretty soon, as soon as I can find the appropriate transfo.

The motors are probably too weak OR I'm just driving em past their torque curve available at 40v OR I have coupler slip OR all of this...

Comments?

Note that I would'nt be there at all was'nt it for this board. Thanks guys...


Para

[ESjaavik]

The motors are probably too weak OR I'm just driving em past their torque curve available at 40v OR I have coupler slip OR all of this...

You're right. But those are easy to debug. Add to that the possibility that the step signals have jitter on them, getting worse at higher speeds. Alas not so easy to debug even with a good oscilloscope. So eliminate the easy ones first.

From what you write, it seems you just pushed hoses on as flexible couplings? That means trouble. At least fit them with Locktite and secure with hose clamps. Steppers run very rough. Add to that the vibrations you mention and slip is very likely.

If you don't mention it to anyone, I'll tell you I run with one of my couplings being an armoured rubber hose (50mm coolant hose) fitted with clamp rings. I did it as an intermediate solution, but I have never caught it slipping a step so it's not high on the todo list. And this is with a 10Nm stepper.

[Parameter]

Indeed, the more I fix, the more I find... Of course the plastic hose are secured with clamps and are braided. The thing is I go from 1/4 to 1/2... no hose really fit so it's an assembly of a hose over a hose... it's clamped tight all right but it just does'nt cut it for higher speeds...

The problem is with the twist-gear shafts as they are not really 1/4 (0.245) and this make it incompatible with some couplers. Plus when it get latteral load, it want to twist and screw... I'll have to get the lathe running and make some poly couplers... seems easy once you got lathe, but it's in a rebuild and lagging...

The main concern I have is the settings in turbocnc? Can the system handle this high a frequency, all mechanical items being excluded?

Para

[jeffs555]

I understand a couple things there. My motors being plugged as bipolar serial are set at half amps on the drives to deal with inductance. The power supply should go to 70v pretty soon, as soon as I can find the appropriate transfo.

The reason for dropping the current when you change from unipolar to bipolar serial is power dissipation(ie heat) and not inductance. Power is equal to resistance times the square of the current. When you go from unipolar to bipolar serial you double the resistance, so you must drop the current to keep from overheating the motors. However, because power is a function of the square of the current, you usually only have to drop the current to .707 times the unipolar current( ie 1/sqrt of 2). This will give you 1.414 times the unipolar torque. Most motors will handle the increased flux, and many motors spec both unipolar and bipolar torque ratings with the bipolar torque being about 1.414 times the unipolar torque.

[pminmo]

Paramater,
Pulse width on the step pulse, and timing from direction to step, maybe an issue.

[ger21]

WHen you say the whole machine vibrates, is it from starting and stopping very quickly at every line of g-code? If it is, you need a control with Constant Velociy mode, like Mach3. If not, disregard this.

[Parameter]

Hey Phil, the pulse are set at 10ms on the mistery drives (x and y) and 20 on the 3977. Seems good, maybe too much?

I think I may have power set too low for the motors. if .7 x 1.4 amp/phase is about 1 amp, it is quite different from the .75A I have for now...

GER: About the vibrations, it seems that what you refer to is the answer to the question I could'nt formulate. I love turbocnc but for engravings it is over it's head. Here is the breaking point I waited for. That "in between moves" stops are what really kill me. Thanks ger, now I can make a more educated buy knowing that mach3 will fix this peculiar issue, and also handle joystick :wee: .

I really consider buying mach3 but being in canada, there will be customs and change fees almos anywhere so was considering bundles from all over the world. With meshcam if I rememember, cnctoolkit, v-carve, etc...

Are the other soft bundled with mach any better in some areas than my actual bobcad/bobart combo? V-carve is quite interesting. Of course I dream of visual mill or onecnc xr but pricing is out of my league and does'nt do v-carving.

this forum is priceless...

Para

[ger21]

Mach3 is developed in Canada. You can downoad it and run it in Demo mode, limited to 1000 lines of g-code. www.artofcnc.ca

[MrWild]

The reason for dropping the current when you change from unipolar to bipolar serial is power dissipation(ie heat) and not inductance. Power is equal to resistance times the square of the current. When you go from unipolar to bipolar serial you double the resistance, so you must drop the current to keep from overheating the motors. However, because power is a function of the square of the current, you usually only have to drop the current to .707 times the unipolar current( ie 1/sqrt of 2). This will give you 1.414 times the unipolar torque. Most motors will handle the increased flux, and many motors spec both unipolar and bipolar torque ratings with the bipolar torque being about 1.414 times the unipolar torque.

If I understand this correctly, the 4.6 amp unipolar motors I have would only need ~ 3.25 amps when run biploar. The 300oz/in of torque they are rated at for unipolar operation would then become ~425 oz/in. As the largest hobby driver you build is the picstep at 3amp rating, I'd have less than the full affect of a 3.25 amp drive, but still more than the 300 oz/in unipolar rating.

Is this right? I've read this relationship (.707-1.414) a number of times, but this just hit me. Somehow it doesn't seem right. Imaginary numbers in math didn't seem right either, but I just accepted them under the FM principal of science. Maybe this will be the same thing. Don't make sense, but works.

[jeffs555]

You understand it correctly. If you have 6-wire unipolar motors, you can run them with a bipolar driver and get 1.414 times more static torque, using .707 times the current. You need to make sure you use the end wires, and leave the center tap wires unconnected. Connecting it this way will have more inductance, so the torque will drop off more rapidly with speed, than it would with the unipolar connection.

[H500]

Running 6 wire motors with the center tap unconnected is one of the few crimes where capital punishment is applauded by human rights groups worldwide.

Althought the holding torque would increase, the speed would be atrocious.

For 6 wire motors, bipolar half winding is the only bipolar way to go. The current and performance will be exactly the same as with a unipolar driver.

[Parameter]

Ok, a 733 has been XPzed and MACH3 installed, i'm delighted, seduced and reassured.

There is a difference in looking at the program, and looking at it at work... That pause in between moves is gone and the flow of movements is awesome. Gotta get a key and fast... I cannot go back to TCNC now...

Para

[ger21]

Ok, a 733 has been XPzed and MACH3 installed, i'm delighted, seduced and reassured.

There is a difference in looking at the program, and looking at it at work... That pause in between moves is gone and the flow of movements is awesome. Gotta get a key and fast... I cannot go back to TCNC now...

Para

The problem with TurboCNC, is the painfully slow development. Constant Velocity, which would have fixed your problem, has supposedly been in the works for 2-3 years. Features get added to Mach3 sometimes weekly. Bug fixes are repaired overnight.... A lot of people are making the switch, and everyone seems to share your enthusiasm. Glad it's working good for you.

[jeffs555]

Running 6 wire motors with the center tap unconnected is one of the few crimes where capital punishment is applauded by human rights groups worldwide.

Althought the holding torque would increase, the speed would be atrocious.

For 6 wire motors, bipolar half winding is the only bipolar way to go. The current and performance will be exactly the same as with a unipolar driver.

It all depends on what you consider atrocious. The inductance of the full winding connection is typically about 4 times the inductance of half winding or unipolar. However, it only takes half the current to generate the same torque, so theoretically, using the same power supply and driver, the maximum speed of the full winding connection would be half the speed of the half winding connection. If your drives will handle it, you can get back this speed by doubling the supply voltage.

For many hobby machines, all out speed is not the most important consideration. Many of the homebuilt hobby machines discussed on this board are built on a shoestring budget, and being able to use cheaper lower current drives is a big advantage to the full winding connection. There are all kind of tradeoffs to be made in designing and building a machine, and I would not dismiss the full winding connection without examining all the goals for a given machine.

Jeff

[Parameter]

GER: I'm in love, whiiiiiiiiiiiiiiiiiiiz, whiiiiiiiiiiiiiiiz, that joystick jogging, I'll never tire of it.... whiiiiiiiiiiz, whiiiiiiiiiiiiiiz....

Got a license, should arrive anytime soon. Just love the dynamism of the project too as I did realize those update came fast and appreciate it very much.

As well, the motors twisted shaft have been fitted with aluminum bushings, pressfit + red locktite to make em 1/2". Now the hose is pressfit on both ends (motor and screw) with the usual hose clamps. The plastic hose I use is too stiff and has been kept wound too long, it induce some wobling in the leadscrew. Gotta get real rubber hoses but it works okay up to 36IPM as of now.

Oh, and once the drive settings have been changed some torque is now back. Not much but at this power level, all I can get make a difference.

Can't wait to engrave a picture with all these enhancements and mach3... More to come!

Para

[Parameter]

Well, it's here That kind of support is never seen with the corporate kings...

Thanks Art

Para

[Parameter]

Well, consider this thread closed. After some tests the conclusions are obvious.

No more sideways, slip or lost steps due to better coupling, enough torque to get a good cut depth at decent speeds and most of all, SPEEEED
.
To anyone considering how cruelly slow it is to engrave pictures with TurboCNC, there is a solution. Mach!

Got a small engraving that took 58 minutes in TurboCNC and now take less than 14 minutes! Gotta go much more often to check the job now... spindle relay on it's way...

Para

[Parameter]

Yah! First real part done. Looks great and took only 47 minutes for 2 passes. I'm in love...

[pminmo]

Nice,
What was your software process from the image?

[Parameter]

That's BobArt v19. It a nice software once you learn to do everything as art then bring it in BobArt. I mean borders are hard to add to the cad so I just do all in the graphic editor.

For editing and format conversions I use The Gimp which is free and Inkscape which is free too. Both are linux softwares ported to windows and quite well loaded.

Inkscape can handle svg files and then save as PostScript. Then there is a script in Inkscape (ps2dxf.sh) that permit one to convert the postscript to a dxf file.

To run this script under windows, one must install Cygwin and ensure to install ghostview, python and pstoedit. That's it. The script is in share/extensions and is launched this way: ps2dxf.sh MY_FILE.ps > MY_DXF_FILE.dxf

This is the only way I found to convert those SVG files to dxf. If someone has a script please I would love to have it.

I might set up a quick how-to about this...

Para