Project development

Unfinished business

System diagram

• One single beam, b x h: 140 x 90 mm.
• General estimate for maximum load capacity.
  2kN/m x 1.5 =3 kN/m
• Symmetrical cantilevers: yes
• Board height: 600 mm.
• Define the shape of the supports. (interim design)
• Define the shape of the individual seats: WildcardWeek: milling with the robotic arm.
• Nine seats will be arranged along the beam.

Seats

• Define the pressure sensors: plattform type 4 x 50 kg per seat
• Calculation of support reactions? Possible
• Shear force diagrams? Option by now
• Determination of spans and stresses at each point? In a later development

Load Cells

Problem-solving steps\

• 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

• I will use 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.

• These values will be sent via WIFI to the microprocessor installed in the LED frame to evaluate the bending moment diagram.

LEDs

• Objective: drawing the bending moment diagram
• Frame dimensions: 1000x500 mm 17 rows and 32 columns. Number of cells: 544.
  Cell dimension: 30x30 mm
• The neutral fiber will be drawn in the center row.The number of rows must be odd.
• The graph must be proportional to the applied forces.

Option for now:

• Maximum load alarm.
• Possibility of significant values information.
• Proportionally draw the presence of loads and support reactions.

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:

Final project progress by week

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.

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. I was also able to prepare a 1:10 scale 3D-printed model of one of the bench supports this week, although its final design will almost certainly change based on feedback from my students.

Week 11

In addition to the assignments scheduled for this week, I worked on the design and fabrication of the frame that will hold the LEDs. I also made significant progress in the development of the code, both on the server and client sides. On the server side, I prepared it to scale up to reading nine load cells. On the client side, I learned how to remap the LED modules in order to define the lighting criteria, including color and intensity, based on the values evaluated by the server.

Week 13

System Diagram

Week 15 & 16

Under Luis’s guidance, I have moved forward with the design of the PCBs for my final project to use them during the System Integration week. I am also preparing the PCBs that will collect the load cell information.

In the beam structure design, I will place a board under the seats. On this board, I will mill the necessary spaces to house the PCBs corresponding to each load cell, create cable pathways, and allocate space for the box that will contain the central control PCB.

Central PCB Bench side

Individual PCBs for HX711
These PCBs will be placed under the seats according to the numbering shown. It will be necessary to manufacture three units of each of them.

Weekend Progress

On Friday, May 9, I decided to make a significant change after simulating the bending moment diagram in Rhinoceros using 50 x 50 mm cells. I found that the resulting representation was too pixelated. To resolve this, I reduced the cell size to 30 x 30 mm. Thanks to the Grasshopper strategy I had prepared, the modification was straightforward. I created a new frame with 3 rows and 3 columns to evaluate its appearance.

At the same time, I designed the covers to be placed on each cell. These covers will be 3D printed. To optimize the printing process, I developed a strategy in Grasshopper, defining the nozzle diameter and layer height as the main geometric control parameters. This approach ensured the perfect execution of the covers.

On Saturday, May 10, exactly one month before the final presentation, I prepared tests to verify the intensity of the colors I will use to represent the bending moment diagram. I used the PCB prepared during week 6 Electronic design and wrote this code to make the LED colors change cyclically with each button press on the PCB.

On Sunday morning, I made the laser cutting machine work hard. Early in the morning, I exported the paths from Grasshopper and imported them into CorelDraw to manufacture the frame for the LEDs. I used a 5 mm thick MDF board, and after performing a couple of tests, I adjusted the cutting speed to 550 mm/min and the power to 95% for linear movement and 85% for curved paths. The cutting process for the bottom board of the frame took a bit more than 1 hour and 40 minutes.

In the afternoon, I dedicated my time to defining the shape of the seats that I will place on the beam. I had been thinking for a while about using a shape similar to the tall stools I have in my kitchen, which I bought at Zara Home. I scanned one with Scaniverse, exported the points in PLY format, and in Rhinoceros, I cleaned and adjusted the points before generating a mesh that I later discretized and adjusted to obtain a symmetrical and smooth piece. Next week, during Wildcard Week, I will use this design to fabricate the seats with the robotic arm.

On Tuesday 13th I left almost finished the assembly of the frame that will hold the LED modules.

BOM

Hardware

Electronics

Schedule for remaining task

Schedule updated 05.10.2025

Files

LED frame color cycler. Arduino IDE .zip
Lid for LED frame. Grasshopper
Lid for LED frame. STL