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This is a plan for a RepStrap made with electronics and motors completely from a Lego NXT set and various other Lego pieces. As of now, this is just a concept, but a promising one for low-resolution prints in hot glue. The extruder concept has been taken from the FTIStrap.



1 Lego NXT Set
1 Glass Plate
1 Hot Glue Gun
1 Piece Picture Frame Glass


As it has been said, this is just a concept for now, but these are the general steps. In addition, the printing idea has been reengineered due to the lack of a fourth motor.

Create the Extruder

Extruder Concept

Follow the steps for the FTIStrap extruder, but modify the mounting to fit with Legos. Mount it as shown in the Extruder Concept picture to the left. Make sure, in addition, to create a holder for several hot glue sticks for the glue gun at a time and a support for the wires.

Create the X/Y Axes

Base Concept

Create the Base Concept shown to the left, and a frame to mount it on. The bottom rectangle will be the printing plate; use the glass as hot glue will not stick strongly to it. The top rectangle should be made of Legos.

The Z Axis

Refer to the next section. No hardware needed.

Mount the Extruder

The extruder should be mounted on the top axis (be it in your view X or Y) so that the motor can drive it to both ends of the glass plate.


Now, the only thing left is to wire the motors to the NXT control brick, which should be conveniently situated nearby.


This should be fairly straightforward in regular old NXT-G, but I recommend LeJOS (Java for Lego MindStorms). Either should work.


By now, you should have noticed how the extruder moves to each X/Y position on the glass plate.

Making the Z Axis

The Lego NXT is limited in that it only has three motors. Therefore, the Z axis could not be made. Instead, the printer is designed to print small sections at a time, and then they have to be manually glued together. Perhaps you could subdivide the glass plate to print every part at once. Yes, it's not the best way, but it's the only way (it is thought).

Alternative Idea: Use a manually-driven z-axis, which is driven by hand after every layer. Likely easier than gluing.

Alternative Idea 2: At the end of each layer, have the extruder 'dock' in the home position (the gears on the extruder mesh with some other gearing). When the extruder runs (in reverse) in this position, it drives the z-axis gearing.

File Format

As of now, I believe that either instructions could be hard coded in, or a voxel style could be used. A computer link would be helpful.

Further reading