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Steppers are too slow
« on: November 30, 2011, 04:51:07 AM »
Thanks to all for this great site.

I am currently setting up to build a 1200mm X 900mm router table and have been trying to get some sense out of Mach 3 running 4 stepper motors ("a" axis slaved to "y" axis).

The problem I am having is with the stepper motor speed. I am lucky if they are turning at about 50 RPM. The following describes the setup:

  • The steppers are 380 oz/in being driven by Wantai DQ542MA drivers.
  • The power supply is 24 volts which was supplied with the drivers. I have also tried another power supply with no change.
  • Breakout board is powered by independant 5V supply and have tried 2 other combinations of supply including 2 separate 5V supplies with the jumpers removed from the BOB
  • Have been into the motor tune settings and tried a number of different configurations and calibration settings
  • Tried replacing the parallel cable in case there was a pin out there. No change.
  • I have another combination stepper driver/ breakout board with 3- 180oz/in steppers and they seem to run without any problems at a pretty normal speed
  • Mach 3 driver test is excellent with a very stable trace line at a freq. of 25003 khz.
  • The motors all seem to run smoothly but just too slow. Also it does not make any difference whatsoever where the microstep switches are set. It is like it is running in max microstep all the time.
  • Is it possibly a faulty breakout board or is there a hidden tick box in mach 3 which I haven't found causing my grief.

I find it hard to believe that all 4 drivers are faulty to this extent, but I have pulled what little hair I have out to try and solve this problem.

Any past experiences or knowledge would be much appreciated.

Thanks,

Stuart

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Offline Tweakie.CNC

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Re: Steppers are too slow
« Reply #1 on: November 30, 2011, 05:08:58 AM »
Stuart,

I take it you have set up each of your steppers for optimum Velocity (reduced by some 20% - 30% for reliability) and Acceleration ??

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Steppers are too slow
« Reply #2 on: November 30, 2011, 05:23:09 AM »
Stuart, can I make a plea to you and everyone else that posts similar problems? Without the motor, driver and power supply data sheet/specs and idealy some info about the gearing and drive type of your machine, all anyone can do is guess. By googling "Wantai DQ542MA" and searching the links for a 380oz motor option (the two clues you've given) I could probably spend some time and home in on which motor, driver and PS you might be using but frankly it would be a lot easier to help you if you did that yourself and posted links.

Thanks

Ian
Re: Steppers are too slow
« Reply #3 on: November 30, 2011, 05:43:36 AM »
I'm not an expert in stepper motors; others here have much more experience than I, but I can try to clarify a few things for you.

24V is generally considered to be low for driving steppers - higher voltage will help "punch through" the inductance of the motors (in layman's terms) to allow for higher speeds and better acceleration without stalling. That being said 24V should normally be sufficient to drive them, just not optimal (you will not even come close to the rated torque value). Our lab product that we manufacture uses 24V (actually, it's 28V now, but used to be 24V) and runs just fine, but our CNC machines use 48V for better torque.

Could you provide the motor inductance? That will help in figuring out the problem. My best guess at this point is the 380oz-in motors may be high inductance, limiting the speed. You said your 180oz-in steppers are being driven fine with the same setup - this points to some difference in the motors - must be inductance, I think. Best to check it first, in any case.

Microstepping is always a good thing - higher setting should help increase max velocity and acceleration as it reduces the affects of resonance which reduces the torque of the motor. More steps = smoother current flow = increased torque = increased speed = better motion.

If anything I've posted here is incorrect or incomplete, other more experienced users will likely jump in. In the meantime, please find out what the inductance of those motors are. That would be the best place to start as your other motors seem to be fine in the same setup. 50rpm would definitely be very slow for a stepper.
Re: Steppers are too slow
« Reply #4 on: November 30, 2011, 06:01:32 AM »
Hi Tweakie,
Yes I was setup almost identical to your screenshot. I had 500 steps per mm but otherwise the same. I changed to reflect what you have here but still no change.

Something I omitted to say in my earlier post is that I am not able to get a driver to work when connected to P2 and P3 on the breakout board. It is now connected to P17 & P16 and operates, but slow like the others. For this reason I am a little suspect of the breakout board. Also the motors are only sitting on the bench top, ie. they don't have any load on them. Is this likely to have any effect?

Stuart
Re: Steppers are too slow
« Reply #5 on: November 30, 2011, 06:03:41 AM »
Ian,
The steppers, drivers and power supply were bought ex China at the recommendation of a friend who has the same setup. As you could probably imagine the supporting documentation was minimal (read Nil), but I will source what I can and reply

Stuart
Re: Steppers are too slow
« Reply #6 on: November 30, 2011, 06:09:15 AM »
Hi Sargon,
I will see what I can find out re the inductance and let you know. As mentioned above, the supporting information is pretty minimal. However, this combination is working fine on a friends machine.

Stuart
Re: Steppers are too slow
« Reply #7 on: November 30, 2011, 06:19:04 AM »
Thanks for the prompt replies guys,

This is my first attempt at anything CNC, so I apologize in advance if this turns out to be anything basic.

.xml file attached of current setup.

Stuart
Re: Steppers are too slow
« Reply #8 on: November 30, 2011, 06:27:55 AM »
Sorry,
These motors are actually 425oz as per the details below. The power supply is 24 volt 400 watt

Technical Specifications
Part No.:                           WT57STH115-3004B
Frame Size:                      NEMA23
Step Angle:                      1.8 degree
Voltage:                            6.3VDC
Current:                            3 A/phase
Resistance:                      2.1Ohm/phase
Inductance:                      9mH/phase
Holding torque:                30Kg-cm       425oz-in
Rotor inertia:                    810 g-cm2
Detent torque:                  0.89 kg-cm
Number of wire leads:      4
Weight:                             1.55KG
Length:                             115mm
Shaft Diameter:                8mm
Front Shaft Length:         21mm
 
Stuart

Offline Tweakie.CNC

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Re: Steppers are too slow
« Reply #9 on: November 30, 2011, 07:33:00 AM »
Hi Stuart,

The fact that you cannot use P2,P3 is an indication that something is wrong there.
One difficulty that has cropped up a few times recently is that most newer PC parallel ports have changed from the 5 volt TTL standard to the 3.3 volt TTL standard and some breakout boards will still only reliably work with the 5 volt signals.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.