[adamchapman]

Hello all,

I am currently constructing my first machine. My stepper motors appear to stall unless they are at a rather low speed.

I video'ed it at:

[ame="http://www.youtube.com/watch?v=vg1p99FGUXA"]YouTube - CNC stepper motors stalling[/ame]

If anyone can identify a hardware or software problem and solution causing/fixing this; I would really appreciate it.

Thanks
Adam

[LeeWay]

Way too little info given to diagnose this.
You need to give all the info you can regarding the system. Motors specs, driver, PS, screw type and pitch, drive nut type, slide bearing type and design, coupling and main bearing on the screw type etc.

[Mariss Freimanis]

If the motor makes a descending growling sound just before stalling it's mid-band resonance. Otherwise the motor is running out of torque because of a low power supply voltage.

Mariss

[Pplug]

Are you running the motors at full step? if so you might want to try microstepping. I ran into this problem with my machine and it helped.

[jalessi]

Adam,


Even though your power supply voltage may be low, installing balancer's or flywheels to your stepper motors might help alot.

Check this out


[ame="http://www.youtube.com/watch?v=8Am69_F93yA"]YouTube - 65 ipm[/ame]


Jeff...

[rfrenzl]

The flywheel is a nice idea but there is a drawback. With the addition of the extra spinning mass, changing motor direction takes a lot longer as it as to decelerate and then accelerate in the opposite direction. Any increase in speed is offset by this condition and the benefits are even lower if you do a lot of quick direction changes.

Judging from the initial movie, you are just driving the motor too fast and it's unable to keep up. If you want more speed, either up the motor voltage or change the lead screw to something like 10tpi.

Remember, once you start any real work, you don't use high speed motions other than to place the cutter. Being able to move at 100ipm has little effect when you only need to move 12" at the start and another 12" at the end of a 30 minute run.

[jalessi]

rfrenzl,

Your statement is unfounded and total fiction.!!

"The flywheel is a nice idea but there is a drawback. With the addition of the extra spinning mass, changing motor direction takes a lot longer as it as to decelerate and then accelerate in the opposite direction. Any increase in speed is offset by this condition and the benefits are even lower if you do a lot of quick direction changes."

Vexta and many other stepper manufactures provide balancer's or damper to counter act resonance.

http://tinyurl.com/5fkbzd

Jeff...

[ger21]

Jeff, it's not a "flywheel", however, it's a damper. Rfrenzl, it's purpose is to minimize resonance. There's a thread here, but I don't have time to look for it rightnoe. It's called "My take on a stepper damper", I believe.

And Rfrenzl, wood routers frequently cut at 100ipm and well above. When cutting wood, speed is very important, as cutting too slow creates excesive heat and dulls tools quickly.

[jalessi]

Gerry,


Correct me if I am wrong a "balancer" may also be called a "harmonic damper"

Jeff...

[rfrenzl]

Ooookay. Fine! I guess this puts me in my place!

Good luck Adam with your step motor problem. Hope you figure it out.

[LeeWay]

Gerry,


Correct me if I am wrong a "balancer" may also be called a "harmonic damper"

Jeff...

I've never heard it called that on an engine. Always harmonic balancers. They do however dampen vibrations.

A flywheel on an auto trans has almost no weight until you bolt on a torque converter. That get it up around the weight of a standard flywheel. Flywheels typically add mass or gearing to a shaft whereas a damper does just that. Dampens vibrations. It can be large, but isn't necessarily so.
In Jeff's video, I would call that more of a flywheel rather than a damper. I saw nothing there that would dampen resonance. What it does is add weight to the spinning shaft to help it through the resonance stage.
Most typical dampers that I have seen incorporate rubber in some fashion.

It's a wonder that Mariss checked in on this, because with Gecko's, theres not a need for dampers.

[Mariss Freimanis]

They are not flywheels or harmonic dampers. Harmonic dampers are tuned to null a specific, single frequency. Rather, they are rate dampers. They offer resistance proportional to the rate of velocity change only.

A mechanical rate damper (Lancaster Damper) is an oil-filled hollow cylindrical housing containing a vaned, freewheeling rotor. When speed is constant, the freewheeling rotor turns at the same speed as the housing. When speed is changing, the vaned rotor slips and couples a torque load to the housing via the viscous oil filling the housing.

Mathematically this torque is the first derivative of RPM. A derivative is the rate of change and therefore they are called 'rate' dampers.

Mariss

[jalessi]

Marris,

The point that I expressed is in layman's term's

No matter what words you choose to use to describe the solution I presented, the fact is it works!

As usual instead of helping someone with a solution you are correcting my words.

http://www.fluidampr.com/

There are several major company's that use the term harmonic damper by the way.

Typical testosterone induced behavior.

Jeff...

[Mariss Freimanis]

Please don't take it personally. This is not about you nor was I addressing you so please avoid estrogen outbursts:-)

Mariss

[ikram95]

I am a new member and just saying to hey everyone

seeya

Basit

[jalessi]

Marris,

I'll bet several woman have put you in your place, so this instance is nothing out of the ordinary for you.

Sending love and kisses,

Jeff ...

[LeeWay]

Marris,

I'll bet several woman have put you in your place, so this instance is nothing out of the ordinary for you.

Sending love and kisses,

Jeff ...

I hate to put a damper on your sentiments Jeff, but sending love and kisses over the internet is not filling any kind of void. You often seem to resonate BS and could use a little self control at times. Other than your faults though, you are perfect.

[jalessi]

Lee,


You are absolutely correct about my lack of self control.

As for resonating B.S. that also happens frequently however
a little love never hurt anyone.

Thank you for putting me in my place.

Send you some love and kisses too.


Jeff...

[.xXACEXx.]

there have been alot of good suggestions given,such as changing the lead screws to get the motor back down to a more usable speed (i.e. = higher lead ,greater distance between your threads),and maybe the possablity of getting a bigger powersupply,(dont know what you have so youll have to post what all you have got going on with your machine) such as suggested by another poster on the other page...let us know what all you got so the guys can help you much better...

you are using mach3 i belive..chech the settings for acceleration...try droping them so the machine gets to top speed a lil slower

from what i have learned while reading alot of post in CNCZONE ,it may be possable that you are accelerating to quickly can you drop the rate which you accelerate your motors ? the motors sorta "ramp up" to the speed which the are in rapid rate,so it may be that you are trying to reach that speed to quickly.thereby causing the stall,i may be compleatly wrong on this as i dont have a machine...but have been reading alot of post ,hopefully someone more knowledgable than me will help ya out,

while i am no expert ,i did stay in a motel 6 last night..lol sry bad joke


good luck hope ya get 'er running faster to suit you...

[Mariss Freimanis]

Leeway,

I guess I have to be careful to name who I address here.:-) I looked into this thread because it's titled "step motors stalling" and I thought I could help.

I originally studied a Lancaster damper to see if I could generate an analog that would duplicate its function electronically. As it turned it was possible and without the mechanical method's drawback of an added torque load on the motor. It also gave insight into the nature of mid-band resonance which is essentially a phase shift problem. The motor / drive combination develops a 180 degree phase lag when motor speed is high enough to cause torque to begin dropping off. In effect, the motor zigs when it should zag and that pumps an oscillation until the motor stalls.

The cure is to add a phase lead component to the loop and a rate damper does exactly that. It makes no difference if it's a mechanical device like a Lancaster damper or an electronic mid-band compensation circuit; the effect is the same. It reduces the total phase lag to well below -180 degrees and all is right with the world again.:-)

Mariss