RE: [CAD_CAM_EDM_DRO] reprap build started

I agree that there is no point using servos for filament feed (nor, for that matter, for table motion).
Your comment about filament slippage instantly gave me an image of a second wheel measuring filament motion for the servo feedback. Now it has occurred to me that the pinch roller (which pinches the filament against the drive shaft) could be given markings that an optical encoder could read, thus giving the servo feedback.

But back to reality. Servos probably aren't worth the trouble.

It should be pointed out that, unlike on the axis drives, the occasional missed step on the filament feed is generally not a problem because each step represents so little volume of plastic, and it is not necessary to move the same number of steps in reverse and return to the starting point.

Before going around replacing axis steppers with servos, a better approach would be to put the acceleration smarts into the gcode interpreter/stepper drivers, and make it possible to adjust these tuning parameters without having to build and load new firmware. Properly-tuned steppers could go a long way in curing (perceived or real) stepper performance problems.

-Kevin Martin
the Papertrail Handmade Paper & Book Arts
New Dundee, Ontario
518-884-7123
www.papertrail.ca

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Mike Payson
Sent: Sunday, October 09, 2011 8:58 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] reprap build started

On Sun, Oct 9, 2011 at 3:27 PM, Kevin Martin <kpmartin@...> wrote:

> DC extruders as implemented so far are obsolete, but nothing prevents
> someone from using a servo-controlled DC motor which would be just as
> reliable (if not more so) than the stepper feeders.

Actually, there is one thing preventing it... Why bother?[...]

People regularly suggest servos as a way to improve the performance of a
reprap (mostly for the XY, not usually for E, though it has been discussed),
but I have yet to hear anyone say why it would be a better solution to what
we have now. If we need more torque or speed (and for the extruder we really
don't), the obvious solution would be to go up to NEMA 23 steppers, not
servos. Servos make perfect sense for a router or a mill, but a 3d printer
has very different requirements. Is there some reason that they would be
better that I am failing to see?