Z axis settings

[ger21]

No, it's not closed loop.

[Ntl]

No, it's not closed loop.

I said “perform like” maybe you skipped past that part? So what is closed loop vs what Centroid did with the Acorn? I never really understood the difference with the Linux system since it’s running on a pc not the control board? I thought it had to do with the pc controlling the motion vs the controller board? Doesn’t the BBG processor handle the actual G code movement vs the windows pc on other controllers? Or does closed vs open have nothing to do with what controls the motion? I honestly haven’t read that much about either other than everyone always is like “you have to have closed loop this or that “ I understand closed vs open on steppers since the encoder keeps absolute position of the motors or spindle. Please explain to me what a closed loop controller is as well as the benefits, also tell us how the Acorn works since apparently I’m incorrect assuming that the BBG on the Acorn handles machine movement and apparently it’s there for some other unknown reason.

Thanks
Dan

[ger21]

Closed loop requires encoders on the motors feeding position info to the control, and the control adjusting position on the fly based on the position provided by the encoders.

Correct, it's not whats controlling the motors, but how they are controlled.

The fact is, that very few hobby users actually run a true closed loop system. Imo, there little to no benefit.
And if you are running servo, the servos themselves are closed loop, with the drive closing the loop.
I'm on my phone right now, and can't elaborate further until my power is restored. Its been 20 hours, and my phone is getting low on juice...

The Acorn is different, though, in that the controller board does the motion calculations, rather than the software.

[Ntl]

No, it's not closed loop.

Also you sure love your one liners with a emoji, but never give any real explanation.

[ger21]

Sorry, im usually in a hurry. That was directed at your "please tell me if im wrong".
And as I mentioned, still in a hurry as my phone is fading. ????

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I guess phone emojis dont work.

[DDgitfiddle]

Also you sure love your one liners with a emoji, but never give any real explanation.

For a system to be "closed loop", the motors need some way of measuring position (rotary encoder, linear encoder LVDT, etc.). The controller will command a position then "watch" the position of the motor and continuously adjust the command until the motor reaches the desired position. Usually closed loop controllers control motor current or voltage. Stepper motors (without encoders) are open loop because they are given a command and then we hope that they reach the desired position. As long as they are not underpowered, they usually do. Stepper motors receive pulses of voltage that cause them to increment. You can have closed loop steppers, but most hobby grade machines don't bother.

The Acorn controller provides step and direction outputs just like most of the other motion controllers used on hobby machines. Steppers work with that and other drives do also. Some other motor/drive combinations may be internally closed loop. In this setup, they see a step and direction input them watch the motor to make sure that each step has been made correctly. ClearPath motors are an example of this. This is not completely closed path because the motion controller doesn't know when the motor actually reaches the desired position. So it keeps sending more commands, regardless of what the motor is doing.

-Robert

[Ntl]

Sorry, im usually in a hurry. That was directed at your "please tell me if im wrong".
And as I mentioned, still in a hurry as my phone is fading. ????

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I guess phone emojis dont work.

As I said I know what a closed loop encoder is and what it does that wasn’t what I was referring to. I was referring to the type of controller Linux systems use and the one that Linux users say is better because “it’s a closed loop controller “. I’ve read multiple people refer to a Linux controller as a closed loop system on forums, maybe they are using the incorrect terminology? If that’s not the correct terminology let me know because I don’t want to add to the confusion. I just know that the Acorn is similar since the controller has its own discrete processor that controls the motion and that windows can’t create any lags on information. I just want people who tell me I’m wrong to go into detail on what is correct. Otherwise I will never learn what is correct, there’s a ton of misinformation on forums given by people who don’t know what they are talking about. I personally don’t want to be one of them and when I’m wrong I want people to straighten me out so I don’t contribute to bad information. Nothing personal I don’t know you and you have never given your qualifications for me to know if you know what you’re talking about or not. For all I know you could be a engineer for HAAS or a accountant that has a cnc hobby. I would suspect that you are somewhere in between, maybe have a cnc retrofit company or sell parts and software or work for a cnc shop as a machine operator. I’m new to owning and building a cnc machine for my small business. I’ve always just outsourced my cnc work when I was a production manager for a large company. I’m just a guy who designs and builds products and has a lot of experience dealing with product development as well as domestic and overseas production on a large scale. That’s why I’m building my own machine because the shops I deal with are to expensive for my current needs. And I don’t know anyone that uses this hobby stuff, all my associates use industrial equipment and can’t help with the low end stuff. They would tell me to just buy a real machine if I asked lol.

[ger21]

I was referring to the type of controller Linux systems use

"Controller" is a word that get's thrown around a lot, and often incorrectly (technically; by myself included). And I guess it could even mean different things to different companies.

With LinucCNC, the software (and PC) is actually the "controller", not the hardware. The loop is controlled in the software. Hardware used with LinuxCNC would more appropriately be called pulse generators (for step/dir use), or analog signal generators (I guess, not sure on the analog ones)

I'm not real familiar with the details of how LinuxCNC works, but basically, it commands the motors to move. The motor's encoders send the position info back to the software, and if the motors aren't where they are supposed to be, the software makes corrections. That's what a closed loop system is. The software (or controller) constantly monitoring the actual position, and making corrections on the fly.

As opposed to open loop, where the software just tells the drives where to move the motors, and never knows if they actually end up where they are supposed to.
The Acorn is an open loop system, and is not similar to LinuxCNC when it's used as a closed loop control.

Closed Loop is often seen as this Holy Grail, but at a hobby level at least, I think it's way over rated. Any decent open loop machine should give the same results as a closed loop machine, unless the machine lost steps/position. And any decent machine should nefver lose position, or it would be a useless machines.

LinuxCNC can also be run in open loop mode, and probably is more often than in actual closed loop mode.

With most hobby level software, LinuxCNC included, the trajectory planner is handled by the software, which then sends low level position "moves" to the hardware pulse generator, which then generates the step/dir signal.
With Mach3, the parallel port can be considered a pulse generator.

Where the Acorn differs (As I understand it), is that the trajectory planner is handled by the onboard processor, rather than the software. This lets it do things that typically can't be done in software, or can be done much faster. Things like more lookahead, and better path smoothing at higher speeds.

They have add on breakout board in production that will support if I remember correctly 7 axis.

Do you have any links to discussions of this product? I've looked around their forum a little, but never found anything.

[Ntl]

"
Do you have any links to discussions of this product? I've looked around their forum a little, but never found anything.

Thanks for some clarification, and you still keep dodging the question about what you do professionally.

And search the forum for any word on the “i/o expansion acorn board”

Dan

[wmgeorge]

Thanks for some clarification, and you still keep dodging the question about what you do professionally.

And search the forum for any word on the “i/o expansion acorn board”

Dan

Well I think Gerry runs a woodworking shop with a CNC router and does some programming also as I purchased a Mach3 screenset from him.

[Ntl]

Well I think Gerry runs a woodworking shop with a CNC router and does some programming also as I purchased a Mach3 screenset from him.

Thanks that’s what I figured that he was selling something and wasn’t a fab guy. Also sorry for getting snippy with you, I’ve had a very rough week.

Thanks,
Dan