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Crystal Clear action run.png

Release status: experimental

License GPL
Author jonnycowboy
Based-on Robot arm
Categories Polar
CAD Models [1]
External Link LJD2 Website

Arm setup.png

The RepRocker V1 is an in-developement Repstrap by jonnycowboy ( It is a 2DOF (y-axis, z-axis) robot arm mounted on two or three 8mm linear rails (x-axis) or linear bearings (rollers). It is very similar to the Robot Arm created by galaxyman7. The main difference is that it uses a "frog leg" quad-parallelogram flipped 90 degrees to work vertically (patented by Brooks in 1984 - Brooks Leapfrog). The build platform remains stationary at all times. The effector will remain as light as possible by using a Bowden Extruder. In addition, the top parallelogram will be counter-weighted to reduce the load on the servo.

RepRocker arm movement is detailed in the attached PDF: Media:Reparm.pdf.

The goal of this robot is to drastically reduce the build time and cost. It uses two servos at the 'base' of the arm driving each of the two parallelograms (via worm & gear or threaded rod) and a NEMA-17 driving a belt for the x-axis. This means the x-axis size is determined only by the length of the rods and belt. Currently the joints and support structure are planned to be printed and the arms to be prototyped in Microrax 10mm aluminium extrusion (Microrax Website, Microrax Wiki). Eventually the arms will also be printed once the design is capable.

In order to compete for the Gada prize, the complete 3D printed version will be able to be clamped to any surface (picnic table, for example), and use a pane glass as a build surface. Sub-60watt power consumption should be able to be generated by a small solar panel in rural villages.

The electronics and extruder will be sourced from other reprap projects. The bowden extruder motor will eventually probably not be a stepper but a simple brushed or brushless RC motor in order to reduce costs.

V2 of the RepRocker will be designed with a moving conveyor belt (300mm wide) and a more stable (stationary) arm implementation.


Brief specification

  • 300x400x100mm build vollume
  • Heated (V1) or non-heated (V1-Gada, V2) build surface
  • Bowden fed extruder for 2-3mm filament


  • Read the forums at and Robot Arm, got inspired. Markus' work at,70221 are very useful as well. I think the Gada interim prize can only be won with a non-heated bed, robot arm. In order to reduce costs, the stepper motors and drivers could be replaced by simple servos modified for continuous rotation. The goal is to make this for less than 200$, complete (cost price). 150$ for the electronics, steppers & hot end and 50$ for the materials (rods, bearings, plastic for printed parts).

Bill of Materials

Printed Parts [currently a placeholder from Huxley]

Quantity Description Type Comments Diagram
2 coupling RP Ehux coupling.png
1 x-idler-bracket RP Ehux-x-idler-bracket.png
1 x-motor-bracket RP Ehux-x-motor-bracket.png
1 x-carriage RP Ehux-x-carriage.jpg
1 nozzle-mount RP Ehux-nozzle-mount.jpg
1 idler-cover RP Ehux-idler-cover.jpg
1 y-motor-bracket RP Ehux-y-motor-bracket.jpg
1 y-idler-bracket RP Ehux-y-idler-bracket.jpg
2 frame-vertex RP Ehux-frame-vertex.jpg
4 frame-vertex-foot RP Ehux-frame-vertex-foot.jpg
2 z-motor-mount RP Ehux-z-motor-mount.jpg
8 bar-clamp RP Ehux-bar-clamp.jpg
2 belt-clamp RP Ehux-belt-clamp.png
1 z-endstop-holder RP Ehux-z-endstop-holder.jpg
1 spring-anchor-single RP Ehux-spring-anchor-single.jpg
1 spring-anchor-double RP Ehux-spring-anchor-double.jpg
4 bearing-holder RP Ehux-bearing-holder.jpg
1 M6-extruder-block RP Ehux-M6-extruder-block.png
1 idler RP Ehux-idler.png
1 small-gear RP Ehux-small-gear.png
1 large-gear RP Ehux-large-gear.png

Non-Printed Parts ("vitamins")

2x 10kg-cm servo motor, (X, Y-axis drivers) (servos 20$ each)
1x Nema 17 bipolar stepper motor (Z axis driver) (motor 10$, driver 15$)
1x Nema 17 bipolar stepper motor or small RC motor (Extruder driver) (motor 10$, driver 15$)
2x 8mm LM8UU Linear bearings (1$ each)
32x MF63ZZ 3x6x2.5mm flanged bearings (1$ each) (yes, that's 32 bearings!!!).  These would eventually be replaced by telfon or delrin bushings.  There are four (4) for each double-joint and 2 for each single-joint.
1x build surface, copper for now (from Printrbot, later from something cheaper and larger)
2x T2.5 16 tooth Aluminium timing pulleys (for x-axis, cost?)
1x T2.5 timing belt (for x-axis, cost?)
2x 623 bearings (for x-axis, cost?)
2x 626 bearings (for x-axis, cost?)
4x 200mm Microrax
4x 250mm Microrax
2x worm gearbox or threaded rod
10x 3x20mm stainless steel clevis (50 cents each)
1x Extruder: TBD
1x Sanguinololu. (how much$?)

Printing the Parts

2x vertical stand footplate
1x arm base including stepper mounts
2x intermediate joiners
1x end-effector mount and z-spacer (to mount the extruder lower)

Buy the printed parts

Coming soon to LJD2 Webstore

Test Videos