stepper motors stalling

[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:

YouTube - CNC stepper motors stalling

YouTube - CNC stepper motors stalling

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

YouTube - 65 ipm

YouTube - 65 ipm

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]

Originally Posted by jalessi 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