New Machine Build- Need help with setup

[LaserImage]

I am having some problems getting any kind of reasonable performance out of my cnc router. I built it using 80/20 and trucks similar to the ones on cncrouterparts.com. I used 1/2-10 acme, single start and leadnuts from dumpstercnc. Everything moves very smoothly, no binding and virtually zero backlash. I can move in all three directions with almost no force needed, the trucks work extremely well!

The problem is in the electronics and setup in Mach3. I have Mechatronics 3 axis drive and Keling KL23H276-30-8A steppers and a 24volt 7amp power supply. I have the steppers wired for series connection. I have the vref on the board at 4.2v and the pfd at 2.5v. I have tried full, 1/2, 1/4 and 1/8 resolution on the board, currently it is at 1/8.

The problem is that I am getting a max of 30 velocity and 10 acceleration in Mach3 before I get stalling. Sometimes I can get travel all the way in both directions, sometimes it only goes part way. It's not consistent where it stalls, so I have ruled out binding. I have talked to Keling, he suggested I use 1/8 resolution and it should work fine, if not then there is something wrong with the driver board. I am waiting to hear back from Mechatronics. I have been fighting with this problem for two weeks and really need to get this resolved, it's the last thing I needed to do in order to "finish" my build.

I have read as much as I can find about setup and motor tuning, here is how I got to where I am now:
1. Set board to 1/8 resolution
2. Set acceleration to 1 in Mach3
3. Start at 10 velocity and increase by 5 until stepper stalls then reduce back to where it didn't stall
4. Start acceleration at 1 and increase by 1 until stepper stalls, then reduce back.
This is how I ended up at 30, but it's not working well there either, it just seems that if I go any faster, or slower, then it stalls more often. I have tried this experiment at all resolution settings and none of them made any difference.

Any ideas of what I should do next? Could it be the board? Could it be the power supply? (it's putting out 24v, I checked it with my dvm)

Edit: this is true for all three axes and I have tried switching steppers with the same results

Thanks in advance for any help!

Gary

[Crevice Reamer]

Hi LaserImage. Welcome to the Zone!

Best running voltage= 32 times the square root of inductance. With series wiring, you are running a 95V motor from a 24V PS. AMPs= Torque. Volts = torque at SPEED. So your motors are under volted and don't carry much power into higher rpms.

It doesn't help that you are running the drivers at 1/8 microstepping. Ten X 200 X 8= 16000 steps your motor has to perform just to move the table one inch--OF COURSE your rapids are slow.

If your driver would allow you to wire the motors in Unipolar, (3A at up to 48V) they should perform better. Surely you could lower the microstepping to 2? Can the driver take 36 or 48 Volts? That would help too.

Otherwise you need new Higher voltage/amps drivers along with 48V PS and/or different motors.

CR.

[LaserImage]

Thanks for the reply CR

The board has a max of 32v and recommended 24v, and only supports bipolar series wiring. I can change steps to 2 but I have tried that with no noticable change. I'll try it again when I get home tonight.

It seems that this board/power supply may be too weak for the setup I have. Is the Hobbycnc board a better choice for this price range? Or am I up against the power supply being too low voltage? I would love to use Keling or Gecko but when I figure in the cost for the drive, power supply and bob, I'm at about $300.00 - more than I have in the budget right now.

It's a long story, but I bought what was supposed to be a "complete" system and I have more into rebuilding this than if I had just built it from scratch... I'd rather not have to replace the electronics if I don't have to, not right now anyway.

Thanks,
Gary

[Crevice Reamer]

At 1/8 micro stepping, (16K steps per inch) the motor has to turn 80 revs to move 1 inch. At 1/2 micro stepping, 4K steps per inch) the motor only has to turn 20 revs to move an inch.

CR.

[LaserImage]

CR,
I changed to 1/2 resolution and ended up with the following:
X = 4,000 steps per unit, 34.998 Velocity and 5 acceleration
Y = same
Z = 4,000 steps, 28.002 velocity and 5 acceleration

This is slightly better in the X and Y but slower in Z. Would increasing the voltage of the power supply get me better results? What about increasing the vref? How much could I increase the vref without causing problems?

Gary

[Crevice Reamer]

Your motors, wired in series, are too voltage starved. Series winding current max is 2.1 A. Vref= 2 X desired current. Vref is set as high as it can go for series winding these motors.
CR.

[Crevice Reamer]

Bipolar Parallel wiring would be best for 24V, but your board can't handle the 4.2A that would be needed. I think your best bet with this existing setup is to wire the motors in half winding. Half winding is nearly as good as Bipolar Parallel, but requires less amps.

To do this, connect the Blue and Red wires as the first coil pair. Connect the Brown and Black wires as the second coil pair. Tape the ends of the other wires and don't use them. Now set the Vref at 5 volts. This is 1/2A less than the 3 A the motors will want, but is max for your board and should work. It won't hurt the motor or driver. Try this on one motor and see if things improve.

CR.

[LaserImage]

CR,
I really appreciate the help!

Do you know for sure that this board supports wiring as you mentioned? I only ask because the manual only mentions series wiring. It's funny though, because the board is screened with "Bipolar 3 Axis" and the manual states "Two phases bipolar driver (PWM Technology)".

Also, you said "Blue and Red wires as the first coil pair. Connect the Brown and Black wires as the second coil pair" - are the coil pairs the "A and -A" and "B and -B"? If so, then I would connect blue to A, Red to -A, brown to B and black to -B? And the other wires are not connected, just taped to insulate them?

Thanks again,
Gary

P.S. Just to be clear... When I question something you say it's not because I don't believe or trust you, it's purely because I don't understand and just want to be sure I am reading your advice correctly.

[Crevice Reamer]

Hi Gary! Yes that's the correct way to wire the coils. According to the Data sheet, your drive can be wired for bipolar Parallell, or Bipolar Serial. They do not SHOW the half coil wiring method, but it will work:

http://www.easy-cnc.com/web/download...3Axis(NEW).pdf

Zylotex, on the other hand, with the same type of board, DOES mention the half coil winding:

http://www.xylotex.com/XS3525V202.pdf

Basically, this gives the higher speed of the Bipolar Parallel wiring method, along with the lower amps of the Unipolar method.

CR.

[rfrenzl]

After following this thread for a little while, I just have to chime in. It appears that some of the information it not entirely accurate (but close enough to not hurt anything and simple is a good thing with electronics).

I found some excellent documentation on motor wiring and explains what the different wiring arrangements are, how to calculate current requirements, and many other things. It is on the IMS site. I just happen to have a couple of the drivers so I needed to know the wiring layout and found the motor info as a bonus. Besides wiring options, it also give a little information on why a particular wiring option is better than another (ie. serial vs. parallel in speed and torque requirements).

I hope this helps make things clear for the new CNC person and prevent the inadvertent blow-up of a driver board.

The document is the manual for the IM483 driver and the motor information is on page 28 of the PDF. http://www.imshome.com/Product%20Manual%20PDF/im483.pdf

Good luck,
Ron

[Crevice Reamer]

Hi Ron. Welcome to the Zone!

I THINK what you are saying, is that whether wired in Bipolar Parallel or Half winding, these motors will still require 4.2A either way. This may be true.

Neither way will hurt anything, so maybe best to wire say X Axis in Bipolar Parallel and Y in Half winding, and compare the results. OR, just try both methods on the X Axis.

So to wire these motors in Bipolar Parallel: A+ = Blue & Yellow connected together. A- = Red & Green connected together. B+ = Brown & Orange together. B- = Black & White together. Vref is still set to 5V.

CR.

[Crevice Reamer]

However, I should ALSO state that the motor spec sheet says the motor draws 3A wired in Unipolar mode. Unipolar only USES 1/2 coil at a time--ONE for forward and the OTHER one for reverse. Hence, half coil wiring should have the same amperage as Unipolar wiring. Now it MAY be that different drive electronics see this differently, But I think, in this case, that the half winding method will run faster with more torque at speed than the present series wiring.

CR.