Back to the concept of a foldable RepRap using a scissor-like mechanism for the Z axis.
The main advantage is that this time the folding mechanism is part of the movement, and don't require any preparation for the machine to function... it will unfold as much as the part to print is tall. And makes for an even more lazy foldable RepRap : open the case, plug, print.
- tensioning the z-belt should be done in the upward direction, in order to tension against gravity
- change the aluminium flight case (not cheap) for a regular wooden flight case (easier to use and customize)
- move the linear rail 5mm closer to the pivot, in order for the end rail (printed part) to play its role of mechanical stop
- if the aluminium plate were made with a CNC instead of a laser-cutter, we could include the tapping of the holes (would save lot of time)
- the complete upper plate weight enough to move the gearbox of the z-motor (if motor off) : caution when using M84, or use a higher gearbox ratio, a worm drive, a nema 23 ?
- fine tune E step value (837 for a start)
- test print even without an adapted firmware
- creating a RepRap Firmware for the scissor Z axis, probably using a mathematic similar of a linear delta : solving a square triangle equation (will need help here)
- add LED lights
- add Duet enclosure
- 18teeh and 14-1 reduction.jpg
32 teeth pulley being bigger, leave not enough belt length to position the motor, so the new combination is 18 teeth pulley but with the 14:1 gear ratio motor, and it works !
- Plan B.jpg
And/or, if it is not the belt skipping but the motor having not enough torque, I will use the same form factor but with a greater gearing ratio (from 5:1 to 14:1), or change it completely, from planetary to worm drive (with the advantage of can't being moved by the upper plate, the mechanical conversion being only motor->worm and not the other way)
- 2020 progress.jpg
Almost one year after... faulty blade-fuse changed, Duet2 works, and it moves ! But with the full weight multiplied by the scissors at the lowest height, the belt skip some tooth on the classic 18 teeth pulley. My guess is that not enough teeth are in contact to transfer the torque. Next try will be with a 32 teeth pulley.
once assembled there is more rigidity than what I feared to have, thanks to alternating the orientation of the scissors (good intuition here) the material works mostly in its horizontal plane, so even plastics seems fine (except that a scissor broke for pushing to far) - [video of a test move]
was imagined during the initial concept of the "FoldaRap2" mid-2012, then named "Mondrian" when it was not pursued at the time