[motomitch1]

Can Gecko 201's be useds as a closed loop system ?

Thanks in advance Mitch

[motomitch1]

yes no maybe

[HomeCNC]

Yes,

A real closed loop system, closes the loop back to the software. You would need to have encoder feedback to tell the "real" position of each axes. This feed back is sent to the software to compair what it thinks the position is and what the real position is. Adjustments are made by the software if needed.

You need to find step and direction controller software that had the closed loop inputs.

[imserv]

If a Servo driver has an onboard microprocessor that controls the loop and the microprocessor has software is it a real closed loop?

A "Real" closed loop, closes the loop in either hardware or software. Any other descriptions are usually marketing buzz from one or the other company that is trying to puff up the value of their system.

Fred Smith - IMService

[HomeCNC]

He is not talking "servo" The G201 is a stepper driver.

Check out "DeskNCRT" it is capable of closed loop.

[motomitch1]

Thanks thats some good info

[kong]

I see Mach2 has inputs available for encoders. Would this be the same thing?

[Mariss Freimanis]

Steppers are usually run open-loop and they give excellent accuracy that way. Servomotors are run closed loop because they simply cannot run open loop.

Closed loop operation doesn't confer super-human powers to a motor. Overload a stepper, it stalls; overload a servo, the drive "faults" and shuts down the motor. In both cases the result is the same: a stopped motor when you wanted a running one.

An encoder on a stepper is at best a stall indicator. Your ears or eyes pretty much do the same.

There are a few, expensive drives that do run steppers in true closed loop mode, meaning the encoder commutates the motor. Driven that way, the stepper effectively becomes a 50-pole brushless DC servo motor. The problem is it is at a disadvantage compared to standard 6-pole brushless motors, that being the effects of inductance and iron losses as a result of the high pole-count.

Mariss

[HomeCNC]

Ah, So it's not good to try to control a stepper in a closed loop software situation.

[motomitch1]

Oh I see I was thanking that if my stepper lost a step here a there it might line it self back up

[Mariss Freimanis]

It's not that it's not good, it's there are better motors suited for that.

Look at it this way. Step motors can be driven with relatively simple drives yet give ecellent accuracy. They are unconditionally stable and there is nothing you can do that will hurt them load-wise.

Their main disadvantages relatively low efficiency (read heat) and low power output relative to servo motors. These disadvantages remain when they are run closed loop. Closed loop operation brings only modest improvements over open loop operation at a considerable increase in cost and complexity.

Moral of the story: It's not worth the effort to dress a sparrow up in peackock's plumage. If you want a peacock, start with one.

Mariss

[bb99]

Or… It’s not worth dressing a snake up in a Gecko’s outfit. If you want a Gecko, start off with a Gecko. (Perhaps this belongs in a different thread ;^)

--bb99

[motomitch1]

I’m not trying to build a peacock, I could also buy a CNC Machine shop with state of the art, climate, dust and humidity control, using precision calibrated 5 axis machining centers to perform ultra precision machining of components. But all I have now is my little HF X=8.250 Y=4.250 Z=8.000 2900 RPM $400.00

Manual mill converted into a cnc with 3 201 Gecko’s 200 oz steppers and Thomson ball screws and nuts that runs great and I have some free encoders that I got from my work off some old burned out fadel 6 brush servos.



I was thanking if all I had to do was run some more wires to the pc to have a closed loop cnc mill would make it a little nicer incase it skipped some steps and I didn’t see or hear it and Im cutting for hours and hours .050 out of location and

I wouldn’t have to tram for location of fixtures or parts if it were to skip witch would be kind of nice.

[turmite]

Motomitch I think what Mariss is trying to say is the steppers will not lose position unless you simply apply too much of a load. If they don't lose or gain steps there is no reason for a closed loop system. I have run an open loop system since 1990 on a Digital Tool machine running full/half step software. The machine has served me well and I have just now updated to Mach2 controller and Gecko 201 micro drives. I wish I had known about all this good stuff back in 90, because I would have built my own machine and saved that $19,000. Repeatability is what I am amazed at with my open loop system. I made thousands of wood parts that fit exactly each time, and that was fitted to metal parts that were made on $250,000 vmc's. I personally think the best way to look at this is to look at your needs first. How accurate do you really need your parts?

turmite