Introduction: Paper Plane Folder

Everyone has already made a paper plane at least once in their lifetime. Imagine now an automatic device that would do this for you. That's where the idea of the paper plane folder came from. Additionally a shooting mechanism could be added.

This project is a part of the Mechatronics course given at the Vrije Universiteit Brussel and Université Libre de Bruxelles.

Course titularis: Bram Vanderborght

Assistent: Albert De Beir

Team members: Aly Diane, Amin Ibrahimi, Anass Jabbour, Raphael Netels, Philippe Phalempin

Step 1: Conceptual Design

To tackle this problem the idea of the "Paper plane folder" was born. This is basically a fully automatic robot that folds A5 papers into a paper plane. To get to this result different steps are made.

During the whole process, the paper will be pushed through a long tray with the same width as the paper. Throughout this tray, the paper will pass the different steps.

The pushing of the papers will be done by different rolls. These rolls are made up of PVC tubes. To make sure the rolls won't slip on the paper, a grip is placed around the PVC tubes. For this "Yonex" overgrips for rackets are used. To ensure a correct fold, double rolls are integrated in the design.

One motor will be used to power the folding of the paper. The transmission of power between the different steps is realised using gears and timing belts. The motor is chosen accordingly to the needs. Extra pulleys are placed to ensure the correct tension of the belts.

The first step is the detection of the paper. The robot has to detect if there is any paper that needs to be folded. To realise this a photo resistor in combination with a light source was used. When paper passes through, the light is blocked and the resistance changes. When a variation is detected by the Arduino, the motor starts rotating.

After this is done the first fold can be made. It consists of folding the corners. It is realised using two metal sticks which uplift the corners while a central piece holds the paper down. The flattening of the fold will be realised by the following double rolls.

During the third step, the second fold is performed. It is realised using three thin circular plates, made of mdf-wood, that are placed in consecutive order from small to big.

A last, additional step was also included in the design. The shooting of the paper is done by using two vertically placed rolls that are powered by an extra motor. The motor is placed next to the shooting mechanism and the transmission is done using gears.

Step 2: Used Materials

For the assembly of the final product, different components were used. An overview of the parts and prices are listed below.

Mechanical parts:

First the basic structure is built out of wood and plexiglass. The prices are shown per plate but only a fraction is used. So this gives a total price of 5.36 euro of used materials. The precise dimensions can be found in the CAD.

  • MDF 3 mm (4.99 euro/ plate)
  • Birch 6 mm (14,50 euro/ plate)
  • Plexiglas 3 mm (39.90 euro/ plate)

For the rolls a PVC tube of 32 mm outer diameter is used with badminton grips fixed around it. These are connected with plugs on bearings to the motor pulley. For the calculation of the 3D printed parts, a charge of 2 euro/h is used. The total price of these components is 161.4 euro.

  • PVC tube (1.59 euro)
  • 3D printed parts (~100 euro)
  • Bearings (52 euro)
  • Grips (7.50 euro)

All the rolls are mounted on steel rods of 8 mm, again the price is given for a lot of 14 m but only 2 meters are used. The belts are standard T5, the total sum is equal to 19.77 euro.

  • Steel rods 14 m (25.87 euro)
  • Belt T5 285 mm (2.87 euro)
  • Belt T5 375 mm (5.40 euro)
  • Belt T5 410 mm (7.80 euro)

Electronic parts:

A micro controller runs the whole system. To deliver the needed power to the DC-motors it is connected to a motor shield. The motor used was oversized to ensure the working of the system but a smaller motor can be bought for future projects. The total price of these parts is 43.48 euro.

  • Arduino (3.50 euro)
  • Arduino motor shield L298N (1.34 euro)
  • DC motor (38.64 euro)

The final components needed are the sensors, the LED's, a Protoboard and a power supply of 9V to power the whole system. Total price of this is 15.95 euro.

  • Photo resistor (7.74 euro)
  • LED (2.62 euro)
  • Protoboard (2.93 euro)
  • Power supply 9 V (2.66 euro)

The total price is thus 245.96 euro.

Step 3: Utility of the Components

Arduino Uno

The Arduino is used as a micro controller to control the whole electronic circuit.


Drives the rolls which push the paper through the device.

Arduino motor shield L298N (H-bridge)

Allow control of the speed and direction of the DC-motor.

Photo resistor

The photo resistor is used as a sensor to detect if there is paper in the device or not. It is used in combination with the LED's. The brightness of the LED's is used to keep a constant resistance across the photo resistor. This is done so that the measurement of the resistor is not affected by the light of the room. Once the paper passes above the photo resistor, it won't see the light of the LEDs anymore and the resistance will drop. Once the resistance has dropped under a certain value, the motor starts to drive the rolls which push the paper through the device.


The LEDs are used to keep a constant brightness above the photo resistor.


Used to facilitate the connection between the different components.

Belts, gears and pulleys

These components ensure the right transmission between the different steps. The number of teeth of the gears and the belt are computed in Autodesk Inventor. This is done based on the length between the parts that are connected.

Step 4: Protoyping

The most difficult part of this whole project is the finetuning of all the steps. This needs to be done to ensure the correct folding of the paper. A lot of prototypes have been made before getting conclusive results. Each time a prototype was made and tested it revealed certain problems. These problems are discussed with their respective solutions.

Overall design

Initially plates of 6mm birch were used and assembled using a casing system (see figure 1), however this system was not very rigid and stable. Additionally, there was a lack of space for the motor or electronics. Therefore, the middle plate was raised to leave some space for these parts (figure 2). This led to a final design consisting of plates of MDF 3mm for the walls connected to each other using nuts and bolt (figure 3). With the middle plate out of 6mm birch. This design is very rigid and stable, with respect to the previous ones.

Fold 1

The first design was made from 6mm Birch to ensure solidity of the construction, but this is costly and not efficient. The design was changed with plates of 3mm MDF using nuts and bolts.

For the paper to pass smoothly through the device, the tray width should be slightly larger than of the paper. In the first design this extra spacing was 1mm (figure 4). This spacing was not enough as the paper got stuck between the walls quite often. For this reason, an additional spacing of 2mm was added to make sure the paper would not rub on the walls.

Another aspect that was changed during the conception process are the rolls. As can be seen on the figure 5, there was only 1 roll used in the first prototype. Later two rolls placed on top of each other were used. This was changed due to the large friction of the roll on the wood.

The walls were at the beginning 10cm high while the rolls and shafts were placed close to the bottom plate, so a lot of material was unused. This was reduced in the next prototypes and final product to have a more efficient use of the material.

The threaded rods were replaced by shaft for aesthetics and to be able to use bearings. The finetuning of the fold was done by changing the angle and the placement of the rolls. The results were noted (see excel on figure 11) for different combinations, until one satisfactory combination was obtained. The following video shows how this was done.

Fold 2

To test the second fold, a separate prototype was made to test the influence of the distance between the rolls and the diameter of the middle discs. First 1 threaded shaft with a disc in the middle, which was held on each side by 2 bolts, was used (figure 7). A hole in the middle of the bottom plate was made in order to fold the paper in the middle. Holes on the side plate were also made to adjust the height of the shaft.

The drawbacks of this design were:

· The transition of the paper into the hole was not smooth.

· The discs did not make contact with the paper once this last one was deeper into the hole.

To solve this problem, 3 shafts with discs of different diameters were used in a second prototype (figure 8). The difference in diameter was made to have a smooth transition of the paper into the hole. A second reason for this is to allow the discs to make contact with the paper once the paper passes through the device. On the second prototype, PVC tubes were added to the side of the last disc to pull the paper through the tray.

The drawbacks of this prototype were:

· The distances between the discs were to big

· The diameters of the discs were to small

A compromise had to be made between the distance between the discs and the diameter of the discs. Increasing the diameter of the discs will reduce the distance between them. Also, because there is limited space for the discs, the decrease of distance has as a consequence that the diameter cannot be increased as much.

For the last prototype (figure 9), a combination of these two solutions had to be made. A horizontal hole was made along the side plates to be able to move the shafts and reduce the distance between them. The diameters of the shafts were increased in order to make contact with the paper. PVC tubes were added to the 2 first shafts to pull the paper through the tray


For the additional shooting mechanism. The first prototype was also used in the final design. Once this mechanism was implemented in the final product, the paper got stuck in the gears. Due to lack of time and complexity it was opted to remove this mechanism.


Initially there was only one bearing used in the plugs. But because they were connected to belts and gears the plugs were skewed. To avoid this an additional bearing was placed in the plug to hold it horizontal. The teeth were made bigger so that the timing belts had a good connection to the plugs and to ensure no slip. The placement of the motor was changed by 3mm to the left to have a good tension in the belt. To have the tension right in the other timing belts, rolls were added (figure 10).

During the development of the project the plugs were made more compact so they could be printed more easily and quicker.

Step 5: ​Mechanical Design

For the design, Autodesk Inventor has been used. The assembly has been designed in such a way that the whole design is robust. This is done by using bolts and nuts which allow to easily assemble the different parts together or to disassemble them afterwards. An IPT-file of the whole design can be found below.

The dimensions for the shafts and PVC-tubes can be found in the Final assembly of the CAD-file at the end of the section.


Laser cut:

  • 3 mm MDF: Vertical plate 1 and 2, 2 x horizontal small plates, 2 x horizontal support, vertical support
  • 6 mm MDF: Large horizontal plate
  • Plexiglas or MDF 3 mm: Vertical plate

All the DXF-files can be found in the zip-file below. The DXF-files can be used in combination with a laser cutter.



  • 4 x Left plug
  • 4 x Right plug

The rolls are PVC-tubes which are cut at a certain length. To ensure the connection of the PVC tube to the plugs some notches are made into them. The grips are then put onto the tube. Do this as tight as possible, for a uniform surface.

To make sure that the rolls have free angular movement with respect to the shaft, bearings have to be placed. The bearings are placed in the plug by press-fitting . The press fitting was done by making the hole for the bearing 0.1 mm smaller than the outer radius of the bearing. The bearing is then being pushed into the plug.

Fold 1


  • Fold mechanism: Head, body, 2 x feet, mount fold 1
  • Middle holder: Middle holder, mount middle holder, square middle holder

First, the folding mechanism must be built. The head, body and feet of the mechanism must be assembled using bolts and nuts with a diameter of 2.5 mm. This is then placed on the mount using a threaded rod of 6 mm with corresponding bolts. This is fixed on the vertical plates of the paper plane folder.

Next, the device to hold the middle of the paper must be assembled. This is done using press-fitting and a bolt and nut of 4 mm.

Fold 2


  • 3 x left plug
  • 6 x middle plugs
  • Right plug for the 3 rolls

Laser cut:

  • The 3 central circles for the rolls

The plugs, PVC-tubes, shaft and grips are assembled using the same method as in fold 1. The central circles are fixed with the notches of the middle plugs. Once more, bearings must be used to ensure free angular movement.



  • Small and large pulley
  • Motor pulley

The small and large pulley are placed on shafts, which are then placed in the corresponding holes. The motor pulley is directly placed on the motor.



  • Fastener

Fasteners are used to fix all parts that can have longitudinal movements on the shafts. These are placed on the ends of the shaft, next to the vertical plates.



  • Mount

The LED's are fixed to the board with glue.



  • 2 x shaft holders
  • 1 x plug connected to the motor.
  • 1 x plug not connected to motor
  • 1 x motor pulley

Mount the sockets of the launching mechanism on the desired place under the gliding board this is done using regular 2.5 mm screws. The shaft is then pressed into these sockets and the launching plugs are put into place on these shafts. There should be paid attention to the fact that the motor and the two plugs should be aligned perfectly to assure good transmission.

Step 6: Files

In the file named "PaperPlaneSteps_STL+DXF", all the parts that must be lasercutted or 3D-printed can be found for each step. The other file contains the CAD file of the final design.

Step 7: Electronics

The electronics of the paper plane folder consists of two parts, the first one being for the detection of the paper and the second one for the spinning of the motor.

For the detection of the paper, a photo resistor is used which is connected to the +5 V and GND pins of the Arduino. A resistor of 4.7k ohm is used to have an adequate range for the resistance of the photo resistor. The value of the photo resistor is then read through the analog pin 5.

For the spinning of the motor, an H-bridge is used in order to control the direction and speed. This last one is fed through the VCC terminal by a power supply and takes voltages between 5 V – 35 V (for this project, a voltage of 9 V will be used).

The motor is connected to the H-bridge through the terminals for motor A (the terminals for motor B can be used to drive a second motor). To control the speed of the motor, the ENA (Enable A) pin is used which is connected to the PWM pin 6 of the Arduino. The IN1 (input 1) and IN2 (input 2) are used to control the rotation of the motor. The motor spins forward if IN1 and IN2 are respectively HIGH and LOW and spins backward if IN1 and IN2 are respectively LOW and HIGH. When both IN1 and IN2 are LOW or HIGH, the motor stops spinning.

For rigidity and support, the cables were soldered to the Arduino and the photo resistor and resistor were soldered onto a Protoboard. Screw connectors are being used to avoid flying wires. Two mounts were used to fix the Arduino and H-bridge to the bottom of the gliding plate.

Step 8: Coding


The flowchart consists out of two-parts. The first one being the detection of paper and the second one the spinning of the rolls

The detection of the paper

As stated in the previous part, the photo resistor detects if there is paper or not by comparing the resistance with a threshold value. If there is paper the motor starts to spin which spins the rolls.

The spinning of the rolls

If the motor is spinning for less than 20 seconds (time needed to push the paper through the device), it keeps spinning otherwise it stops spinning.


Pin declaration:

In this part, the global variables are defined.

Void setup:

This part is used to initialise the defined pin in the previous part as INPUT or OUTPUT pins.

Void loop:

This part is used for the code that controls the motor. One if-else loop is used to turn the motor ON or OFF based on the value of the photo resistor.

<p>//-----------------------PIN DECLARATION-----------------------<br>#define lightSensor A5 //resistance value of the photoresistor
//Pins 6,9 and 7 will be used
int enA = 6;                
int in1 = 9; 
int in2 = 7; </p><p>int threshold = 1000; // threshold value for the photoresistor</p><p>void setup() {
  //Declare which pin should be used for which output
  pinMode(lightSensor, INPUT); 
  pinMode(enA, OUTPUT);
  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
}</p><p>void loop() {
  int lightLevel = analogRead(lightSensor); // read the value of the photoresistor
  int lightLevel2 = lightLevel*2; //increase range (decrease the sensitivity)
  if(lightLevel2 <= threshold ){  
      digitalWrite(in1, HIGH);
      digitalWrite(in2, LOW);
      delay(20000); // time needed for the paper to go through the device
   else{ // turn the motor off 
      digitalWrite(in1, LOW); 
      digitalWrite(in2, LOW);

Step 9: Experimental Results

As can be seen in the video, the first fold acts as expected. Once the paper is placed above the sensor the motor starts running for 20 seconds. It is then pulled forward with the double rolls and flattened with the second rolls.

The next fold is ensured by the rolls with different diameters. To have the same speed at the contact point with the paper, the plugs have adapted ratios. This is why the timing belts were not used. But as a consequence the belt slipped when the torque was needed. This can also be seen on the video.

Also we had some issues with the launching of the paper. Due to a lack of space, when sliding through, the paper gets stuck in the gears of the launching mechanism. As the launching was additional and the rest was already cut and printed, doing radical changes was a lot of risk, so it was opted to drop the launching of the paper.

Step 10: Conclusion

This project has learned us a lot of skills for the development of a real Mechatronics project. From simple aspects like building a stable MDF frame to working with 3D-printers, many different obstacles have come up. We answered them gradually to get our final result, but some problems still remain. An efficient way to not lose too much time is to ensure that the CAD-files are complete before starting the construction.

The main problems we have left, are the slipping of the last two rolls and the launching of the paper. A simple solution for the slipping would be to use timing belts for the connection. For the launching, more space should be created under the gliding board. This to ensure enough place for the transmission and the paper to slide through.

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