Re: Replace timing belts with FireLine
October 04, 2018 04:09AM
Quote
the_digital_dentist
The magnetic fields acting against the rotor in the motor act like a spring with a mass (the rotor) hanging from it. The mass of the extruder carriage and/or Y axis or bed assembly adds to the moving masses that have to be accelerated. The whole system is a spring (the motor) coupled to a moving mass (the printer mechanism) by another spring (the belt). You can't eliminate ringing just by playing with the belt. It is a much more complex problem than that.

I put together a spreadsheet to estimate the effects of belt elasticity and motor elasticity on Cartesian printers. It's at [www.dropbox.com]. For CoreXY printers there are probably some factors of 2 or sqrt(2) to be included somewhere.

Edited 1 time(s). Last edit at 10/04/2018 04:10AM by dc42.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Replace timing belts with FireLine
October 04, 2018 07:20AM
Motor to carriage belt length varies depending on carriage position. What numbers are you looking for there?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Replace timing belts with FireLine
October 04, 2018 12:26PM
Quote
the_digital_dentist
Motor to carriage belt length varies depending on carriage position. What numbers are you looking for there?

The predominant resonant frequencies will change with belt length too. You could use the spreadsheet to get some idea of the likely spread.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Replace timing belts with FireLine
October 04, 2018 04:35PM
Thanks for the handy spreadsheet DC42!

For the belt section, while textbook correct for a two spring + mass arrangement, I think in practice you can only use the belt doing the pulling to determine resonance frequency. Reasoning being our 3d printers have belts that have very little tension to the point of having slack, so when one belt applies force in the opposite direction of travel the belt stretches until traveling in the force direction, then resonates by relaxing and stretching until the energy is dissipated. I think the relaxing portion doesn't stretch the other slack belt to the point of it's spring being meaningful. I could be wrong, just got me thinking.

Moral of the exercise though: use highest belt tension (to use more of the second belt spring), along with lowest moving mass, shortest belt, and slowest accelerations.

Edited 1 time(s). Last edit at 10/04/2018 04:39PM by gmedlicott.
Re: Replace timing belts with FireLine
October 05, 2018 06:10AM
Quote
gmedlicott
...Reasoning being our 3d printers have belts that have very little tension to the point of having slack, so when one belt applies force in the opposite direction of travel the belt stretches until traveling in the force direction, then resonates by relaxing and stretching until the energy is dissipated. I think the relaxing portion doesn't stretch the other slack belt to the point of it's spring being meaningful. I could be wrong, just got me thinking.

Moral of the exercise though: use highest belt tension (to use more of the second belt spring), along with lowest moving mass, shortest belt, and slowest accelerations.

Poorly made machine have their belt not tensioned enough ! Acrylic frame, extrusion not beefy enough, flimsy 3D printed parts etc... My 6mm GT2 are tensioned to 26N, no slack at all.
Note a flexible built is what allowed most to function without binding smiling smiley

One has also to account for the dampening effect of bushings when made with Igus or similar material.


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Replace timing belts with FireLine
October 06, 2018 02:23AM
Quote

Poorly made machine have their belt not tensioned enough ! Acrylic frame, extrusion not beefy enough, flimsy 3D printed parts etc...

Agreed.
That's why I prefer guiding the belt ( or cable ) through the slots: there are no sideloads on the extrusion...no matter how tight.
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