Self-Replicating Cardboard Pen Plotter

Ever wondered what to do with these cardboard leftover from notepads? Or maybe looking for a pen plotter design that requires no advanced tool? Either way, you are at the right place!

The nice thing about this dense cardboard from notepads (or that you could get from an art store from a pretty cheap price) is that it is strong enough but also easily cut using a simple cutter knife, and one can also cut it only half way to ease its folding. Plus it does not make dust so you can really build this plotter in a student dorm without trouble!

In this design, I tried to minimize the number of pieces and to favor folds over cuts so that strength is based on entanglement. As a consequence, you can use as imprecise ties as brads because they are just here to lock the pieces, not to resist mechanical constraints.

The nice bonus of this approach is that you end up with a self replicating plotter that can trace its own blueprint on other sheets of cardboard! The surface of operation is larger than the biggest part because it is defined by the length of the rods.

• 6 sheets of dense cardboard like typically found bellow notepads (A4 sheets)
• 25-30 brads (you get 100 for $3 at Staples)
• 4 half meter 8 mm rods ($2 each at my local DIY retail store)
• 8 linear bearings, to go with the rods ($10 on Amazon)
• 2 stepper motors, to move the plotter's head (around $10-$15 each)
• 1 extra motor to lift the pen, a servo is enough, I used a stepper only because I had an unused stepper
• A CNC kit, to drive the motors from a computer: $18 on keyestudio.com (Keyestudio CNC shield v4 + 3pcs A4988 driver + Nano CH340 for Arduino CNC)
• A kit of 3+ meters of timing belt and 3+ matching pulleys: $10 on Amazon
• 4 toothless pulleys, to route the timing belt, or if you opt for the French touch, just 4 nails and 2 wine corks do the trick pretty well!
• A 12V power supply, like an old computer power block.

The blueprint is parametric in the dimensions of the motors so you can easily adapt it to your needs.

Tools

• A cutter knife.
• A surface that you don't mind using a cutter on.
• A pencil
• A ruler

That's it!

I like to check the electronic first, but feel free to start by cutting out cardboard if you haven't received all the supplies yet! ;)

Assemble the CNC kit

• The Arduino Nano (medium board) also has its dedicated slot (take core
  of putting it in the same orientation as in the attached photo).

• The little pololu controllers must be plugged on the corresponding slots for axes X and Y on the shield (the largest board of the shield). Do not forget to glue the radiator on the pololu's chip because it will handle power sent to the motors and hence tends to heat.

• Plug the 4 wire connectors of the stepper motors next to each pololu.

Setup software things

• We are using a pretty standard Arduino (nano) based, so you need to install the tiny Arduino IDE.

• Then get the last release of Grbl. This is the program that will run on the plotter's Arduino to translate G-code instructions sent from a computer to instructions for the motor's drivers.

• Plug the Arduino Nano board to you computer, make sure the Arduino IDE finds it following Keyestudio's wiki page for the CNC shield we are using.

• Compile Grbl and upload it onto your Arduino using this Grbl's wiki page.

Check that it works

• Open the Serial Monitor and set it to 115200 baud

• Type in for instance G0 X5 Y-5

Both motors plugged in axis X and Y should turn, in opposite directions!

Both ends of the first axis are the very same piece. Each hold one of the steppers and an end of the first two rods.

You can either use the reference blueprint attached here or generate your own depending on your steppers' dimensions using this GeoGebra sheet: https://www.geogebra.org/m/m7qakfsn

1. Print or trace the blueprint, use thin lines as construction guides.
2. Cut along thick solid lines
3. Half-cut along dotted lines so that you can fold them by 90°
4. Once all folds are marked, place the stepper inside and lock the piece using 6 brads.

All folds are in the same direction so you do all half-cuts on the same side of the sheet.

Before locking make sure to plug the stepper's wire

Hint Areas that share the same color in the blueprint are meant to be parallel to each others once folded!

Remark The green part may seem useless but is actually important to ensure non deformability, which is important to care about when building out of cardboard.

The carriage holds both axes together and routes the timing belt. Maybe it's time to talk about this routing of the timing belt by the way!

You may have noticed that only a single belt is used for both axes. This is a pretty standard differential routing, meaning that the direction of a move is given by the difference between both motors: if they turn in the same direction, it moves along the first axis, and if they turn in opposite directions, it moves along the other one.

The good thing about this design is that we don't need to move any of the engine, which is reduces the mechanical stress on our pieces!

You can notice from the design sketches that there are 4 pulleys inside the carriage. Although we could buy actual pulleys, it turns out that it is not critical to have perfect pulleys here. This is why I came up with this quick hack of building pulleys using just a nail and slice of a cork.

Remark If you do not have corks, find something else, but something that has at least the same radius (the bigger the radius the less important the quality of the pulley)

Let's now build the carriage itself. It is important for this piece to be strong in order to maintain the planarity of the axes, but again the design ensures that cardboard is enough to build a correct one.

The instructions are basically the same as for Step 2 (the first axis ends).

You can once again either use the attached images or adapt the blueprint to your dimensions using this GeoGebra sheet: https://www.geogebra.org/m/w38crp6q

Remark 1 Currently the GeoGebra sheet is a incomplete.

Remark 2 The pictures of my actual plotter show an older (and less strong) design for the carriage, don't worry if you get something different.

The second axis has two ends that are quite different. One only consists in routing the belt, and the other one contains the head (next step). When moving this axis, the belt pulls one the ends, so the design ensures that the pieces do not deform under this kind of traction.

This piece is simple enough, but don't forget to add the extra slice for better strength (see last picture).

Remark I just used a nail as the axis of rotation for the teeth pulley, it is enough!

This last piece takes care of:

• locking the timing belt
• holding the pen (or any other drawing thing)
• lifting it up
• pressing it softly onto the drawing surface

My very design is a bit tailored for the stepper I had at hand (got it from an old ink printer) so you may have to adapt it to whatever engine you use. A servo would be a better choice for instance, being not as heavy as the stepper.

From there, you may use any tool compatible with Grbl, there are plenty of them! For instance you can use GCodeTools for Inkscape (it's installed by default with Inkscape). For the first tests, I just manually entered G-code into Arduino's Serial Monitor.

Enjoy then! And if you have any suggestion for improvement feel free to contact me on twitter @exppad. I already have a few ideas for a v2, and still need to finish creating GeoGebra sheets for this one.