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Crystal Clear action run.png

Release status: concept

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CAD Models
External Link

This will inevitably be known as the 'BAT'Rap since it's easier to type.


This machine uses Block and tackles driven by stepper motors in order to move the hanging extruder platform.

if you are having trouble imagining it before i post some mockups, imagine the Aricebo telescope, with it's hanging sensor platform. BATrap.png
To be clear, the threaded rod isn't meant to be driven by a motor. it's just used to fine tune the balance of the platform assembly. by applying force at the center of gravity, we can minimize swaying.

benefits of this design

  • Much larger percentage of the machine can be repraped.
  • nearly limitless build area. (just use longer wires/string). (B&TRap can be a kind of MegaRap).


-probably prints slowly
-triangular build area
-long cables.
-requires significant electronics rework? maybe just a software change?
-balance of hanging platform will be key. if swinging and swaying can't be controlled then this idea won't work. i see feeding filament into the hot end as problematic, pulling the platform this way and that. maybe if the extruder motor is at the center of gravity? (Double-up the blocks and tackles to control two points on the vertical beam?)
-certain speeds or movements might resonate in the cables and cause shaking. ideally such speeds would be avoided out by control software

What's needed

-experimentation with printing block and tackles; maybe try replacing the lead screws in the Mendel with a hoist-based system using printed block and tackle.
-probably need a winding mechanism, like level wind screw used in baitcasting fishing reels.
-pulley ratios. -etc.


-I'm imagining a large robot that can assemble a cinder block wall. it would extrude mortar, then pick up the blocks and put them in place. the block and tackles could be attached to cherry pickers or telescoping poles like in a news van for it's satellite feed.
-There are lots of way to actively compensate for sway or vibration. Adapting those techniques will allow for faster printing. but complexity needs to be kept low so that novices can still source and assemble it.

Further reading

Not sure where to put this idea. I came along the Polargraph Machine for 2D printing. Polargraph.co.uk and I was very impressed by the video Big Bear. After some thinking, the question came up, when using 3 instead of 2 cords with an extruder etc in the middle it should be possible to have a very simple and small 3D printer. Based on the accuracy of the pen plot there is a good chance that a lightweight printer head (as started in the RepRap II models) could allow high accuracy, too. When the print model is lightweighted, it also possible to have a fixed printhead and move the model around.