Introduction: Protopiper: Physically Sketching Room-sized Objects at Actual Scale

About: We believe that computer science and mechanical engineering are about to unite. In the future, users will solve mechanical problems by digitizing the involved objects using 3D scanners, solving the problem in …

Protopiper is a computer aided, hand-held fabrication device that allows users to sketch room-sized objects at actual scale. The key idea behind protopiper is that it forms adhesive tape into tubes as its main building material, rather than extruded plastic or photopolymer lines. Since the resulting tubes are hollow they offer excellent strength-to-weight ratio, thus scale well to large structures.

constructed by: Robert Kovacs, Harshit Agrawal, Udayan Umapathi, Johannes Frohnhofen, Hsiang-Ting Chen, Stefanie Mueller, Patrick Baudisch

official project page: Human Computer Interacion Lab - Hasso Plattner Institute

publication: PDF

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Step 1: Overview

The device creates tubes like a simple assembly line: it pulls the tape off the roll, shapes it into a tube, seals the tube, “brands” the wing connectors into the tube, and finally cuts the finished tube off.

You can access all the design files, schematics, and source code from our dropbox repository. We recommend using the files from the dropbox, they are always up to date!

Step 2: Baseplate

The base of the device is a 6 mm acrylic sheet. This plate holds together all the parts of the device. You can cut it with a laser cutter.

Step 3: Mounting the "c" and "e" Stencils

Mount the "c" and "e" stencils at the right positions using M3 screws (16mm). Take care about the orientation of the stencils.

Step 4: Threaded Rod for Reinforcement

To attach the gear holder on the front side of "e" stencil, and the roller holder on the rear side of the "c" stencil, run a 130 mm long M5 threaded rod through the holes on the middle of the "c" and "e" stencils. Place a nut on on both inner side of the stencils.

Step 5: Placing the Gear and the Roller Holder

Cut M5 thread into the gear holder and the roller holder, and screw them on the end of he rod. Align them with the slit being vertical and tighten them. Start with the front gear holder first!

Step 6: Inserting the Gear and the Roller

1. The axle of the roller wheel is a 16mm M3 screw. Cut a thread into the holes to make it easier to place in.

2. Ont the other side of the rod goes the inner gear. This first needs to be cut to fit inside the slit on the holder, as shown on the picture.

3. Cut a 3mm axle screw to not to have anything sticking out, because this part has to fit inside inside of the tube.

Step 7: Palceing the Extrusion Servo on the "e" Stencil

1. Servo motor used:

2. Glue M2.5 screws with their head in the side holes of the servo using super glue (fig 1).

3. Mount the servo gear using the gear_holder part. Screw a 25mm long M2.5 screw through the gear into the center hole of the servo, then tighten the worm screw on the gear.

4. Place the servo motor in the slits of the "e" stencil and tighten with nuts. Place 2-3 washers underneath that the servo gets a bit more lifted out. The important thing is that the center of the gear is vertically aligned with the center of the bottom gear. You can play around with this to produce straight tubes.

Step 8: Tape Roll Holder and Windback Mechanism

1. Assemble the two laser cut roll holder parts with an M6 screw, like in the first picture. Tighten it with self securing nut.

2. Cut M6 thread onto the other ends of the laser cut parts for the axles for the rolls. Place 70mm M6 screws as axles, and secure it with a nut (fig 3). Make sure that the roll can turn freely.

3. Put the windback_roll and the windback_roll_holder together

4. Place a gummy band into the slit.

5. Mount the windback roll on a screw axle on the same way as the tape roll holder.

6. Place a spring between the two levers to press the two rolls together. They should be firmly coupled, but still easy to roll.

7. Mount the whole assembly on the base plate with M4 screws.

Step 9: Rotary Switch Holder

Mount the rotary_switch_holder with M3x16mm screws on the base plate.

Step 10: Mounting the Handle

Cut M3 threads into the holes on the handle, and mount it to the baseplate using four M3x16mm screws. The Ø16 mm extrusion button is also inserted into the handle.

Step 11: Alphanumeric Display

Place the display in the long slit on the baseplate. If it is too loos, use some tape or glue to fix it.

Step 12: Cutting Mechanism

1. Assemble the parts cutting_cuff_holder, cutting_cuff_left and right using two 64 mm long Ø3 mm axle. Aline the gear teeth that the cuffs meet exactly at the middle.

2. The tube_stabilizer part on the left side needs to be mounted with a spring, which is pushing the stabilizer clapmp inwards. This part should grab and center the tube, before the cutting wires start to cut. Find a little piece of spring and cut and bend like in the picture. Drill small holes into the parts at the right positions for the spring to push the part inwards. The turning force should be rather soft.

3. place the complete assembly into the baseplate using two M3x16mm screws on the sides.

4. Mount the servo motor on the bottom on the plate similarly as the extrusion servo.

Important: Don't tighten the servo against the cuff gears yet, because at the initial position will be find out after you first time turn on the device.

5. stick the hinging square into the holes at the tip of the baseplate.

Step 13: Wiring the Cutting Cuffs

1. Take out the metal screw parts from the screw terminal and place into your 3D printed cuff. To make sure that it fits, use this type (0.5-1.5 mm² with cable protector):

2. Mount the cutting wires (Ø0.25mm 10 Ω/m) in the pattern shown on the picture.

3. Placing the long horizontal wire is tricky, it should be mounted on the sharp tip of a needle, to be able to go into the tube (see pictures 4 and 5). It has to be placed behind the middle vertical wire and in front of the side vertical ones.

4. The wires should be connected in two separate circuit, in order to produce straight and connector cut. One is the two middle vertical wire connected in series. The two top terminals should be connected together, because they might touch each other when the cuffs are closing. One terminal on the bottom should be connected to the + of the battery and the other to the FET transistor on the control board.

5. The rest of the wires should be all connected in series. The order doesn't matter that much, just make your job easier by following some rational order. Here also one side goes to the batt+ and the other to the other FET transistor on the board.

The cutting wires can consume up to 3-4 Amps, therefore use at least 0,75mm2 cables for connecting them.

Step 14: Electronics + Programming

The electronic circuit can be assembled on a perf-board and it should fit in the handle of the device.For the connection diagram see the attached PDF. To power the device use a 3 cell LiPo battery, at least 800mAh (for example this).

Download the code from our bitbucket repository, compile and upload into the Arduino Nano using an USB cable.

Important: the servo motor ID has to be configured. The default ID is 1. You should only connect one servo at a time, and flash and run the setup code for the respective servo (ProtoPiper_extrusionServoSetup and ProtoPiper_cutServoSetup). Wait until the led turns pink and then green, then the setup was succesful.

The default baud rate of the servos is 1Mbps, don't change this.

Step 15: Loading the Tape

1. Use 60 mm wide ORAFOL Oracal 8500 tape. This gave us the best stiffness for prototyping.

2. Cut the end of the tube in a cone shape.

3. Peel off the backing layer.

4. feed the sticky tape through the "c" and "e" stencils with the sticky side upwards.

5. put the end of the backing layer into the slit on the windback roll. It will tighten itself automatically while running.

6. Press the extrusion button and pull the tape carefully until the gear grabs it.

Step 16: Using the Device

The main functions are one push-button that extrudes tubes and another one that cuts tubes. The four digit alphanumeric display tells you the currently chosen function and the length of the extruded tube. Protopiper also offers additional expert functions that simplify precise construction. The tool selection dial offers functions to produce tubes of precise length, such as replicating the exact length of the previously created tube or creating a diagonal strut for a rectangular frame.

The device keeps extruding tube as long as the user hold down the button. By double pressing the extrude button, you can reproduce the previously extruded length, which is stored automatically in one of the three memory slots (A, B, C on the display). By turning the knob you can choose between these memory slots, but also generate the needed diagonals (AA, AB, AC, CD respectively, and also 3D, which is the diagonal of the cuboid with sides A B and C).

The cut button has three functions: 1. Single short press aligns the tube for hinging. 2. Double pressing creates a straight cut. 3. Triple press cuts the tube with the wing connectors. Hint: the tube length shown on the display is always counted from the middle vertical cutting wires. In case of hinging, the tube is extruded to bit to align the exact lengt with the hinging square.

You will also find a maintanance tool for cleaning the wires and ilde function for storing and transportingthe device. You can also recall some stats about the device usage, how many connectors were cut and how long is the tape overall extruded.