Project development

Unfinished business

Bending bench

• Define the section of the board. Double board with two beams?
  One single beam: 140 x 90 mm
• General estimate for maximum load capacity.
  2kN/m x 1.5 =3 kN
• Symmetrical cantilevers: yes/no?\
• Board height: Sufficient for sitting comfortably without feet touching the ground.
• Define the shape of the supports.
• Define the shape of the individual seat (scan and 3D print in parts).
• Define the number of board subdivisions; at least two in the cantilever.
  Nine seats
• …

Seats

• Define the pressure sensors: How many per seat? Plattform type: 4 x 50 kg per seat**
• Calculation of support reactions?
• Determination of spans and stresses at each point?
• LED lighting.
• Bending moment diagrams.
  Imperative
• Shear force diagrams? Option by now.

Load Cells

Problem-solving steps
For my final project, I need to learn how to simulate the following situations:

• Figuring out how much load the load cells at the base of each seat can handle.
  200 kg maximum
  I will use scales of 50 kg each, four units are grouped in a Wheatstone bridge and should work at a maximum of 60/70% of their maximum capacity so the estimated load will be:
  1'2 kN per seat

• Collecting the data from each of the load cells. Week 09

• Using this data to calculate the bending stress on the beam. I’ll determine the values at n points for each section.

• Once I have the key values, I’ll map them so they can be displayed on the LED matrix.

• Sending the organized data to the microprocessor, which will visualize the stress diagrams.

LEDs

• Frame dimensions.
  2000x1000 or 1000x500
• Vertical dimension: At least one meter. Neutral fiber at the center.
• Proportionally simulate the presence of loads and support reactions.
• Maximum load alarm.
• Graph proportional to the applied loads.
• Possibility of significant values information?
• …

First parametric design

For the parametric design of a wooden bench for bending tests I have used the Grasshopper software in Rhinoceros to design an algorithm that allows the creation of a parametric model of the bench. I will gradually define in more detail the constructive and formal characteristics of the overall design. The advantages of parametric design is that the proposals can be updated dynamically over time.

I have divided the model into the following parts and for each one I have defined the following parameters:

Suplies

Progress made week by week

In Week 9, I solved the connection issue of multiple load cells using a single CLK signal.
Now, I need to tackle the reading problem for nine groups of four load cells each. Each group will be placed under a seat.
Following Luis’ recommendation, I’ve decided to organize the readings so that I’ll have:

• One PCB collecting data from the three seats on the left.
• Another similar PCB collecting data from the three seats on the right.
• A central PCB with the XIAO ESP32C3 MCU, which will not only gather data from the three middle seats but also consolidate the readings from the other two PCBs.

In Week 10, I resolved the issue of storing the load cell scaling data in the MCU (thanks to Preferences) so that it wouldn’t be lost when disconnecting the PCB or closing the Arduino IDE. Thanks to the power consumption tests of the 50-LED module, I now know that each module will consume a maximum of 0.9 A.

This week, I prepared a new PCB with an external 5V input featuring a protection diode. This setup will allow me to power the LEDs with 5V, while the rest of the components will be powered by the MCU at 3.3V. I also defined the geometry of one of the beam supports for my final project. I will begin its fabrication next week.