BEND_it : Don't Stress Out Just "BEND_it" Out

INTRODUCTION

BEND_it is a small scale quick testing machine. It's pretty good at bending and breaking things. It could also be useful at times. It could help one retrieve information like:

1. Horizontal thrust force due to arching action.
2. Change in Bending stress due to change in geometry.
3. Material Stiffness

The Project was done by Anand Shah and Ryan Daley as a part of the Seminar Course: Computational Design and Digital Fabrication at the ITECH program, University of Stuttgart, Germany.

The project was conceived during the challenging COVID-19 times and therefore could be completely done at home without the need for using Laser-cut parts/ 3D Printed parts or other workshop based tools.

System for Mechanism

• 1 X 900mm x 600mm Paper-Board Sheet
• 1 X 900mm x 600mm Polysterol Sheet
• Some waste Cardboard from packaging boxes
• Plastic Gears and Racks (Amazon)

Main Electronics

• 1 X Arduino Uno R3 (Starter Kit - ebay)
• 15 X Jumper Wires (Included in Starter Kit)
• 1 X Breadboard (Included in Starter Kit)
• 1 X 5V Power Adapter (Amazon)

Tools

• 1 X Super Glue (1g)
• 1 X White Glue (200g)
• 1 X Insulating Tape
• 1 X Electronics Cable Cutter
• 1 X Soldering Rod
• Regular Stationary (Scissors, Paper-Cutter, Cutting Mat, Pen, Pencil, Eraser, Ruler)

Motors and Sensors

• 1 X Stepper Motor : 28BYJ-48, 5V, DC (Included in Starter Kit)
• 1 X ULN2003 APG Driver (Included in Starter Kit)
• 1 X 1 kg Load cell with HX711 weighing sensor (Amazon)
• 1 X ADXL345, 3 - Axis Accelerometer (Amazon)

THEORY

Stepper Motor

The 28BYJ-48 is a 5-wire uni-polar stepper motor that moves 32 steps per rotation internally but has a gearing system that moves the shaft by a factor of 64. The result is a motor that spins at 2048 steps per rotation. In order to control the motor and let it run smoothly we would a ULM 2003 Darlington Transister Array. For more detailed information, the mentioned website is a great resource:

Stepper Motors with Arduino – Getting Started with Stepper Motors

Load Cell

For the project we are using a 1 kg Load cell with a HX711 weighing sensor. Load cells are metal parts which has strain gauges attached to it. Strain gauges are sensitive resisters , whose resistance varies as they undergo deformation. The HX711 microchip amplifies this resistance and transfers it to Arduino Board. The Load cell needs to be calibrated initially with know weights. here in our case the gauge is calibrated in kg and then the serial value is multiplied by 9.8 to get force in Newtons. To get more information you can check out this video:

Electronic Basics #33: Strain Gauge/Load Cell and how to use them to measure weight

Accelerometer

Accelerometers are sensing devices which are useful for measuring static and dynamic forces. They measure difference between linear acceleration in Accelerometer's reference fame and earth gravitational field vector. here in this experiment we use Pitch as an output from Accelerometer. Pitch is an angle value in degrees which would provide the orientation of the bent plate with respect to y-axis of the Accelerometer. The below image can used used as a reference to understand pitch value.

For more detailed information you can visit this website:

How To Track Orientation with Arduino and ADXL345 Accelerometer

PRINCIPAL

Bend_It machine laterally actuates a material with a stepper motor, then measures the material’s response using Load cell and Accelerometer. The load cell measures the lateral force that the material is resisting with. The Accelerometer are means of measuring the geometric deformation in the material. The collected data is sent as a data stream to an Excel spreadsheet where it can all be compared on a scatter plot. This allows the designer to see how much force it took for the material to reach a plastic deformation. The lateral load is reduced once the material has reached a threshold of actuation, and we can see that the material does not return, in an elastic manner, to its original shape. This testing method is a quick and easy means of analyzing custom materials that are perhaps too small to be tested using full scale crushing machines.

Supplies Needed: Paper-Board Sheet, Waste Cardboard, Plastic Gears, Racks, Super Glue, White Glue, Reqular Stationary items, Arduino Uno R3, Jumper Wires, Breadboard, 5V Power Adapter, Stepper Motor (28BYJ-48) ULN2003 Transistor.

Supplies Needed in addition to Step 1: Polysterol Sheet, Insulating Tape, Electronic Cable Cutter, Soldering Rod, 1 kg Load cell with HX711 weighing sensor

Supplies Needed in addition to Step 2: ADXL345 - 3 - Axis Accelerometer and Jumper Wires

The Machine is finally assembled and packed inside the paper-board base box.

Please use this link to get access to the code:

Bend_it.ino