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  #91  
Old Thu 18 January 2018, 06:13
dbinokc
Just call me: DB #118
 
Oklahoma
United States of America
I am very impressed with how you have been using your MM for building aircraft parts. I have used mine for making rib forms and plotting out cut lines on sheet metal. I have never had any success cutting sheet metal directly.

What type of aircraft is being shown in the pictures?
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  #92  
Old Fri 19 January 2018, 13:39
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
<Chuckle> I'll take a swing at that horse, too, as has been done in the past.

The key here is really to think of the entire motion control system. The Acorn is a step/direction interface, which means that closed loop is irrelevant: whether it's an actual stepper motor, or a servo driver which is emulating the behavior of a stepper motor you still have the failure mode that the control system cannot adapt to the feedback that a single axis is running slow and thus the workpiece and possibly the tool are already ruined when you get the feedback.

As Archie points out, if you have a full servo drive system without a step/direction interface in the middle of it, plus a trajectory planner than knows how to use the closed loop feedback it's a different game - as long as you never demand more torque than the servo can provide, which would be the comparable failure mode with the same outcome.

A well designed Step/Direction interface based system will never lose steps, generally by applying more torque than you need at all times. Tech marches on, so now we can construct systems that use single-axis feedback to emulate an open loop stepper using a less complicated/expensive servo motor. That's attractive even without a true closed loop as a drop-in subsystem to provide a certain amount of torque with a Step/Direction interface, which is what Teknic/Clearpath is offering - they've effectively extended the low end of servo technology down to 100W or so in a way they competes with steppers.

Ultimately it comes down to whether the entire system offers sufficient torque for a given demand at a reasonable price, regardless of step/dir/stepper, or step/dir/servo, or closed loop/servo. It appears that for the MechMate, the Acorn/Clearpath combination is in a sweet spot - a similarly priced system gives you the overflow torque advantage of a servo, without the runaway threat of a servo, without the waste heat of a stepper. Sure, it's not a fully closed loop, but if you can never exceed it's torque capacity, who cares? And if you can, well, "you're doing it wrong".
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  #93  
Old Fri 19 January 2018, 14:56
jeep534
Just call me: archie
 
prichard, wv
United States of America
Brad,
Thank you for explaining it in a way even I can understand and much better than I could ever articulate (big word) it

Happy Hunting

archie
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  #94  
Old Mon 05 February 2018, 10:57
WilliamT
Just call me: BillT #111
 
Georgetown, TX
United States of America
dbinock

Thank you for your comments.

Work holding is the key to cutting any material. Thinner material, as with sheet metal, is much more difficult to cut. I don't have vacuum, so I once sandwiched thin material between two pieces of MDF. The cutting process worked and the part looked good, but at what cost!

The aircraft is a two seat, inline full metal fuselage. The engine is a nine cylinder air cooled radial, 450hp. The aircraft will be fitted with fully retractable landing gear to minimize drag.

bradm and jeep534

Thank you guys for your comments too.

I really opened a can of worms here, bringing up the Centroid Acorn. Truth is, there are a large number of Break Out Boards and combination of Stepper motors that work very well for the MechMate application. For software some guys use Mach, some use Linux, and some have adapted Tormach Path Pilot. Parts are parts, are parts. Find a combination that works well for you and learn from the experience.

One guy recently asked me, regarding my comments on professional controllers, "What do I consider Professional Controllers?" You know what, that was an excellent question!!!

My references to professional controllers regards the 'hardware' side only. With better professional equipment you get other features specifically designed for big machines. But these features are not necessarily needed for the MechMate. I was after good hardware only.

In the video that follows, Alan explains why he changed to the Acorn controller. He begins explaining at about 3:20 his hardware failure problems, and the time and the money trying to get it resolved. Same thing happened to me and this is why I moved on to better hardware.

https://www.youtube.com/watch?v=4QqVa2lgU7U
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  #95  
Old Tue 10 April 2018, 06:15
IamDave
Just call me: Davey
 
Ball Ground, GA
United States of America
You guys are way above, my knowledge level of machinery. I just keep reading, and learning little bits. After a while it sinks in, and I have that AHha! moment.
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