MechMate CNC Router Forum

Go Back   MechMate CNC Router Forum > Common Assemblies & Parts > Motors & their mountings
Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Reply
 
Thread Tools
  #1  
Old Tue 27 February 2007, 16:26
Thomas M. Rybczyk
Just call me:
 
For those of your interested in attempting a closed loop system, this board from Rogers Machine
http://www.rogersmachine.net/encoderinterface.html works with Mach3.

Brian, one of the moderators of the Mach3 forum demo this on his machine at a recent trade show.

Of course you also need double shafted motors to attach these encoders to. http://www.usdigital.com/products/e4p/

I might attempt this with my next build.

Since I prep very expensive pre-finished solid wood cabinet doors for glass for a local kitchen company.

Tom
Reply With Quote
  #2  
Old Wed 28 February 2007, 18:38
Jay Waters
Just call me:
 
Thomas, Gerald, anyone, Is there a motor that is equivalent to the Oriental Motors PK296A1A-SG7.2 that would have a double shaft so we could use this board, and that would also fit directly onto the Mechmate without any mods? Could this be wishful thinking or a hopeful reality? I would really like to incorporate a closed loop system into my machine when I build it.

Jay
Reply With Quote
  #3  
Old Wed 28 February 2007, 20:08
Mike Richards
Just call me:
 
Oriental Motors PK296B1A-SG7.2. The "B" is the identifier for the rear shaft.
Reply With Quote
  #4  
Old Thu 01 March 2007, 05:46
Jay Waters
Just call me:
 
Thanks Mike. When it comes to the electronic side of things, I have to defer to others' expertise. I believe this will be the first thing I attempt to do since it will be the most difficult for me. Thanks again.
Reply With Quote
  #5  
Old Thu 01 March 2007, 06:12
Thomas M. Rybczyk
Just call me:
 
Jay,

The biggest problem I have found so far is finding a larger stepper motor (Nema 34) that has a 1/4 inch top shaft to accommodate the above mentioned encoders. Most are 1/2 inch top and bottom.

Brian recommended the Keling model KL23H286-20-8B http://www.kelinginc.net/SMotorstock.html but this smaller motor will not work with my current rack and pinion system.

Let me know what you or anyone else finds.

Tom
Reply With Quote
  #6  
Old Thu 01 March 2007, 06:32
Jay Waters
Just call me:
 
Tom,

Once again, I learn something new everyday. I didn't know about the shaft sizes. If I find something that will work, I will definitely let you know. Now, on to the encoders....Is there an encoder that would fit a 1/2 inch shaft we could use? Maybe could go that route, who knows? Is your rack and pinion system the same as in the Mechmate's plans?
Reply With Quote
  #7  
Old Thu 01 March 2007, 06:43
Gerald_D
Just call me:
 
Adding an encoder to a stepper motor, and then running it in a "closed loop", does not help with Reza's issue. Maybe my response to him has misled you all.....

It is fine for each axis to have its own little closed loop, but there still is no bigger "inter-axis" loop. One axis might slow down to prevent stalling, but it won't slow the other axes - your part is already ruined while this single axis is doing a quiet little catch up.

I mention a "quiet" catch up because noise is a factor. People love telling you that a stepper motor driven CNC has the danger of losing steps and that you must get either a servo-motor system or an encoder-based closed loop system. This danger of lost steps is waved before you like the plague that quietly creeps up on you. Nothing of the sort - it doesn't creep, it bangs!

When you lose a step, the system makes a horrible banging noise as if the pinion gear is jumping out of the rack. And it only happens when you are pushing the system way too hard. So you get a solid warning that you have pushed it too hard. With a encoder and closed loop on each motor, each of those motors can quietly do their own thing - they can float in and out of sync with the other motors and you are none the wiser till you look at the finished part.

Gecko is looking at a way of sync'ing all the axes in unison (Mariss calls it the "unstallable stepper" project) but he is not there yet. As far as I know, no-one else has beaten him to it either.
Reply With Quote
  #8  
Old Thu 01 March 2007, 06:45
Gerald_D
Just call me:
 
Jay, the other thing is that some stepper motors have shafts that float a bit in the axial direction - they could smash the glass disc of the encoder into its reading head...
Reply With Quote
  #9  
Old Thu 01 March 2007, 06:50
Gerald_D
Just call me:
 
Reza asked in the Gecko thread:
How do you know when a Gecko has a fault. I was running the system and something happened the Gecko is displaying a green and red LED. Mach continues to run as if everything is Ok but the motor is not running and Gecko has faulted.
1. How do you get to know if that's happened. Geck is inside the control box and you don't see when it has faults
2. Does Mach not know about this to stop the program. If this Gecko is on one X-axis, that motor stops but everything else is running.



I replied:
You make an extremely important point. The whole MACH/Gecko approach is very much open-loop with one axis not knowing about a problem on another axis. The guys have been talking of closing the loop, but nothing is available yet....

Reply With Quote
  #10  
Old Thu 01 March 2007, 08:51
Mike Richards
Just call me:
 
Gerald makes some very valid points about why you should NOT use an encoder. Last year I bought several Oriental Motor steppers that had rear shafts so that I could use an encoder, but I haven't found it necessary. IF an WHEN the G100 project is finished so that the "unstallable stepper" becomes a reality, I'll probably try it out.

BUT, if you need encoders that fit 1/2-inch shafts, visit the U.S. Digital site. The E6 series is popular.
Reply With Quote
  #11  
Old Thu 01 March 2007, 09:43
Gerald_D
Just call me:
 
I am not "anti-encoder" - I am simply pointing out that encoders probably will not solve the problems that some think that they are going to get. Either the anticipated problems are probably not going to happen at all, or are going to be different to what you thought. Meanwhile, you would have doubled the level of complexity (and wiring joints) bringing in potential for problems of their own.
Reply With Quote
  #12  
Old Thu 01 March 2007, 10:55
Jay Waters
Just call me:
 
Well, I've decided to stay with the "tried and true" open loop system. I definitely don't want to bring more complexity into the situation. I guess I get caught in the trap of well.....if I do this it would be better!!! Just gotta keep reminding myself to stick with the plans and what is working now!! Gotta say thanks again to you all for keeping my feet on the ground.......
Reply With Quote
Reply

Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 19:17.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.