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Mach Discussion => General Mach Discussion => Topic started by: kencor1 on June 20, 2011, 08:41:17 PM

Title: Micro stepping confusion
Post by: kencor1 on June 20, 2011, 08:41:17 PM
I am trying to get my homebuilt 24X36 Aluminum CNC to run without losing steps but I can't seem to get a handle on it.  I am using Keling drivers KL-9082 (http://www.kelinginc.net/KL-9082.pdf) with keling NEMA 34 1200 oz-in Steppper Motors, 72V power supply, PMDX126 BOB and a smoothstepper.

 I can get my motors tuned to run great when I am jogging, however when I try and run a 2 1/2 D  file the motors stall at different times. If run a program that does the carving along the x axis and the steps over in Y lots of stalling, if I have the program run on a 45 degree angle where both X and Y are both turning it runs 100% better.

When I look at all of the different setting for the micro stepping I don't know what is the best one. What would give me the best reliable performance.   I am trying to get my max cutting speed to be around 100 IPM my motors jog at 300 IPM no problem. Am I just expecting to much? I have been working on this for a year now and still can't get the performance that I want. I have tried so many different settings I am lost.

I have attached a photo of the router if that helps.

Thanks for any help

Tom

Title: Re: Micro stepping confusion
Post by: Tweakie.CNC on June 21, 2011, 03:15:37 AM
Nice looking machine you have there Tom.

I would be inclined to opt for 2000 steps per revolution as I am not convinced of any real benefit from going higher.

Tweakie.
Title: Re: Micro stepping confusion
Post by: RICH on June 21, 2011, 06:45:37 AM
Quote
different setting for the micro stepping I don't know what is the best one. What would give me the best reliable performance.

Anything past 10 will not give you any better resolution because of the  stepping resolution / positional accuracy of the motor.
For most reliable preformance you should use a kernal speed of 25K. You  can try higher kernel speeds but run the driver test.

RICH
Title: Re: Micro stepping confusion
Post by: olf20 on June 21, 2011, 06:58:01 AM
Another suggestion;
Try to reduce the acceleration on all axis by a
large amount. Check to see if everything runs
correctly. If so then increase the acceleration
in small steps till the machine has a problem.
Back the settings down 10% (fudge factor).
Sometimes what we think / want our machines
to do is different that what they will do.
Repeatability is the key.
olf20 / Bob
Title: Re: Micro stepping confusion
Post by: kencor1 on June 21, 2011, 10:54:07 AM
Thanks for the replys. I have set the Micro Stepping to 2000 re tuned the motors. I have the kernal speed at 35K The drive test ran good.  What are the best settings to have my smooth stepper at?  Also I ran the same test programs, if I run the toolpath on a 45 degree angle having the x and y move the machine runs great but if I run with the x axis running back and forth and the Y just doing the step over I get a lot of stalling of the x motor I just don't under stand why that would be happining.

Thanks Again,
Tom
Title: Re: Micro stepping confusion
Post by: rrc1962 on June 21, 2011, 01:31:01 PM
Have you tried running it on the parallel port rather than the SS?  On a screw driven machine that light running 1200oz/in motors, acceleration shouldn't be an issue at all.  My last router had a 400 pound gantry, was acme screw driven with 1200oz/in motors and I was running acceleration at around 80...and it would go way higher than that without stalling.

Also make sure your power supply is adequate. If it's not providing enough current, you will get stalling when two or more motors start running at the same time.
Title: Re: Micro stepping confusion
Post by: kencor1 on June 22, 2011, 10:50:09 AM
I have not tried the parallel port, from all of the posts that I have read the smoothstepper give better reliability.  My power supply is 72V but I will check what the output is when all of the axis are running, that might be part of the issue.

Thanks,
Tom
Title: Re: Micro stepping confusion
Post by: rrc1962 on June 22, 2011, 02:41:43 PM
The USB interface is much more susceptible to noise than the PP.  We had nothing but trouble with the SmoothStepper, but that was on plasma machines.  It worked great when it worked, but it wasn't as reliable as the PP.  Even on our routers, it would lose connection now and then during a program run.
Title: Solved Problem I think
Post by: kencor1 on June 22, 2011, 05:25:42 PM
I switched over to the Parallel Port and ran the same setup, same troubles.  But I think I have solved the problem. ;D  I lowered the amp output on my driver to the lowest setting to 2.8 Peak amps and the machine is running with no problems I can push the speeds way beyond what I could before.  My question is why with the lower amp setting is it working?  I thought that the more amps I push to the motor the more power I would have, but I must have been off in my thinking. Hopefully someone can shed some light on this for me.

Thanks,
Tom
Title: Re: Micro stepping confusion
Post by: olf20 on June 22, 2011, 08:25:18 PM
It would suggest that your power supply is under
sized. Not enough current capacity.
olf20 / Bob
Title: Re: Micro stepping confusion
Post by: ger21 on June 22, 2011, 08:28:25 PM
What is the pitch of your screws, and are the motors wired bipolar parallel or bipolar series?
It sounds to me like a very poorly matched system of screws and motors.

You probably have 3 times more motor than you need. A G540 package with 380 oz motors is capable of much higher performance than you're looking for with the right leadscrews.
Title: Re: Micro stepping confusion
Post by: rrc1962 on June 22, 2011, 08:43:15 PM
IMy question is why with the lower amp setting is it working?  I thought that the more amps I push to the motor the more power I would have, but I must have been off in my thinking.

Probably because the power supply can't supply the rated current to the motors.  All you did is reduce the current going to the motors, which reduces power, but the power supply can now keep up.  In your case, the motors are so oversized that the reduction in power is not staling them. 

I agree with the comment above.  A G540 and some 380oz/in motors are more than enough for your setup.
Title: Re: Micro stepping confusion
Post by: kencor1 on June 22, 2011, 10:33:31 PM
The max that my drivers are rated for is 80v. Would it make that much difference to go from 72V to 80V ?

Tom
Title: Re: Micro stepping confusion
Post by: rrc1962 on June 23, 2011, 12:25:00 AM
Your problem is not voltage, it's current.  What's the current rating (amps) of your power supply?  What is the current rating of all of your motors? 
Title: Re: Micro stepping confusion
Post by: kencor1 on June 23, 2011, 09:56:32 AM
Here are the specs for my power supply.  Unregulated Power Supply 1440W, 72VDC/20A ,120VAC or
230VAC, here is a link to my motor specs  http://www.kelinginc.net/KL34H2120-60-4A.pdf

Thanks for the Help on this.

Tom
Title: Re: Micro stepping confusion
Post by: ger21 on June 23, 2011, 11:47:13 AM
I'll ask again:
What is the pitch of your screws, and are the motors wired bipolar parallel or bipolar series?
Title: Re: Micro stepping confusion
Post by: Tweakie.CNC on June 23, 2011, 12:04:27 PM
Gerry,

Looks like the motors just have the one set of bipolar windings at  6 Amps per phase.

Tweakie.
Title: Re: Micro stepping confusion
Post by: kencor1 on June 23, 2011, 03:43:16 PM
My screws are 16mm 5 lead import ball screws, at least that's what I think I remember they are.
I guess my thinking may have been wrong. I wanted alot of power so I thought that the bigger motors would be better. If I want to get a bigger power supply does anyone have a suggestion on what size and where I could buy one?.   I really don't want to have to buy all new motors.
 So what application would warrent the larger 1200oz nema 34 motors?

Thanks, for all of the advice, I am a woodworker by trade and the electronics stuff is really not my strong suit.

Tom
Title: Re: Micro stepping confusion
Post by: ger21 on June 23, 2011, 04:58:42 PM
The bigger the motors, the slower their maximum speed tends to be. You're screws are basically 5 turns/inch, so you need 500 rpm to go 100 ipm.

Depending on inductance, most steppers have a maximum usable rpm of about 1000. Although smaller, low inductance motors can be good for up to 1500rpm, or even higher.

I've seen torque curves of similar size motors that only have 150-200 oz-in of torque over 300rpm.

You'd be a lot better off with screws with a 10mm lead, or even 25mm lead. Those would give you 2 or 5 times more speed, while keeping the steppers moving slower where they have more torque.
Your 5mm lead gives you a large mechanical advantage at the expense of speed. At very slow speeds, you're probably getting several hundred pounds of force. But at high speeds, you have none.

Going from 72V to 80V probably wouldn't make a noticeable difference. And likewise, while changing motors would give you better performance, those screws are still hampering your performance.

To answer your question, big motors and 5mm pitch screws are best used on big, heavy machines that need lots of force, but not higher speeds.

Title: Re: Micro stepping confusion
Post by: kencor1 on June 23, 2011, 05:58:57 PM
Thank you Gerry for explaining for me. I think I will look into getting the bigger pitch screws sometime in the future, for now I at least have a better idea of what is happening.  Do you know of somewhere that I can start looking for the screws, that wont cost an arm and a leg.

Again I would like to thank everyone that has replied to me, this forum is truly a wonderful font of information.

Tom