Experiential Material Determination Station

This project was developed by me, Wouter Huisman, as part of my master’s thesis at the Faculty of Industrial Design Engineering, TU Delft. The goal? To design a hands-on learning tool for the bachelor course Understanding Product Engineering, a course followed by over 300 students each year.

In a course that size, practical learning is often pushed aside by theory. But when it comes to materials, understanding comes from experience. You can’t really know what stiffness feels like, or how different materials behave, by just reading about it. You need to test it. Touch it. See it move.

That’s where this setup comes in. It’s a two-part system: a structured bending test device for measuring material stiffness, and a set of small intuitive tools for testing properties like hardness, magnetism and conductivity. Together, they give students a way to explore and understand material properties themselves, through trial, error and reasoning.

The idea builds on the concept of experiential learning, as described in the work of Bas Flipsen, Stefan Persaud and others. Their research shows that students learn better when they actively engage with the material, make mistakes, and reflect on what they discover. That’s the philosophy behind this setup, and it’s what this Instructable will help you build.

Overview — What’s next

We’ll start with the structured stiffness device and move through nine steps before touching the intuitive tools:

1. Building all the parts – An overview of all parts that need to be produced.
2. Indenter assembly – Build the mechanical core that carries the indenter and guides the motion.
3. Solder the electronics – Use the circuit schematic above to wire and solder the full circuit.
4. First-time software setup – Flash/configure the software to check that the electronics and motion work.
5. Electronics assembly – Mount the boards, route cables, and plug everything into the device.
6. Final mechanical build – Bring the whole device together and finish the hardware.
7. Calibration – Calibrate the system so measurements are reliable.
8. Finalising the code – Using our calibration efforts to finalise the code.
9. Using the device – A short overview of how the device works.

After that, we’ll dive into the intuitive builds for electrical and thermal conductivity, as well as the water/storage container build.

To build this setup, you’ll need a mix of laser-cut acrylic parts, 3D-printed PLA components, some basic electronics, and a few mechanical parts like bolts and screws. The electronics are simple and widely available, a Seeeduino Xiao, a load cell with amplifier, and a small OLED display.

Everything runs on 5V, so you’ll also need a regular USB-C wall charger to power the device during use. No fancy lab equipment required, just straightforward, accessible parts you can assemble yourself.

A full list of materials for both the Young's modulus test device and the intuitive tools is included above.

To Use the 3 point bend test device, you will also need a set of calipers, as well as polymer samples of around 60x15x2 mm.

For the three-point bending setup you’ll need to make parts P01 through P17. All files are included in the attachments and referenced in the Bill of Materials.

1. Laser-cut (acrylic): P01, P02, P03, P04, P06
2. Cut these from acrylic as specified in the BoM. Keep protective foil on during cutting if possible, and don’t scale the drawings.
3. 3D-print (PLA, any color): P05, P07–P17
4. Print the remaining parts in PLA in a color of your choice. Use the 3MF's as provided (no scaling). Aim for clean dimensional accuracy, solid enough infill for load-bearing parts, and standard layer height is fine unless noted in the file name.

The full assembly file is also included: "3 Point Bend Test.step"

This is the first part of the structured stiffness device. The whole device is split into four chunks: (1) the indenter assembly, (2) the electronics assembly, (3) final assembly where the assembly is finalized and finally, (4) the calibration of the device. In this step we focus only on the indenter side, the mechanical core that carries the tip and guides the motion. Watch the video for the exact assembly order; it shows every move up close.

Recreate the circuit from the schematic above using the Seeeduino Xiao, the OLED display, the load cell amplifier, and the load cell. Route power and ground cleanly and solder everything firmly, no loose joints. Once this is fully built and double-checked for shorts and correct connections, we’ll move to the next step: uploading simple test code to see if it all works.

First, install the libraries the sketch needs (Library Manager → search & install):

1. Adafruit GFX Library
2. Adafruit SSD1306 (it will pull in Adafruit BusIO automatically)
3. HX711 (by Bogdan Necula / bogde)

Set up Arduino IDE for the C-duino/Seeeduino XIAO (SAMD):

1. Boards Manager: Install “Seeed SAMD Boards (32-bits ARM Cortex-M0+)” and select Seeeduino XIAO.
2. Port: Select the XIAO’s COM/tty port (plug it in via USB-C).
3. If upload ever fails, double-tap the reset on the XIAO to enter bootloader (the LED will pulse), then upload again.

Wire check (match the sketch):

1. OLED on I²C (SDA/SCL) at address 0x3C.
2. HX711: DOUT → D3, CLK → D2.
3. Common GND and correct 5V/3V3 per your modules.

Upload & verify:

1. Load the test code from the attachments into Arduino IDE and upload to the XIAO.
2. Open Serial Monitor at 9600 baud.
3. You should see “Raw: <number>” updating, and the OLED should show the same raw value.
4. Press on the load cell: the raw value should change immediately. If it doesn’t, recheck wiring, solder joints, and the OLED address (0x3C).

If the raw value on screen/Serial changes with force: great!

Watch the video to see exactly how everything fits: board mounts, cable routing, and connectors. While assembling, be gentle. Don’t bend headers and avoid pulling on wires; that can crack solder joints or damage the load-cell lines. It’s smart to plug in USB-C to the Seeeduino XIAO a couple of times during the build to confirm the OLED still boots and the raw value updates. If it does, keep going; if not, pause and recheck your wiring and connectors before closing things up.

In the video you’ll see the full sequence of putting the device together: Keep cables tidy, and check that the indenter moves freely without rubbing. Snug the screws (not gorilla-tight), confirm connectors are seated, then do a quick power-on check, OLED boots, raw value updates, motion is smooth. If it all looks good, you’re ready for calibration in the next step.

We’re only finding the scale factor now. Don’t change any code yet.

1. Use the raw test sketch (the one that prints Raw: ...). Open Serial Monitor and let it settle.
2. Record three readings:
3. R0 — no weight (or press tare and treat this as ~0).
4. R1 — hang 1,000 g. Write down the raw value.
5. R9 — hang 9,000 g (near the 10 kg limit). Write down the raw value.
6. Compute the scale factor (counts per gram):
7. Quick method (recommended):
8. Subtract the two heavy readings: R9 − R1.
9. Divide that result by 8000 (because 9000 g − 1000 g = 8000 g).
10. The result is your scale factor.
11. If you used R0 (no weight) and it’s stable, you can double-check by:
12. (R1 − R0) ÷ 1000 and (R9 − R0) ÷ 9000, then average those two numbers.
13. Sign check:
14. If the raw number goes up when you add weight, keep the scale factor positive.
15. If it goes down, make the scale factor negative (you can also flip the sign later in code).

Write the final number down (e.g., 209.96). In the next step we’ll put this value into the main sketch.

1. Open the main sketch from the attachments (the one with the TU Delft start-up screen).
2. At the top of that file there’s a line that defines the scale factor. Change the number to the value you just calculated. (It looks like: “float scaleFactor = …”; you only replace the number.)
3. In the setup section, check that the code applies this value before taring: the line that sets the scale must come before the line that tares the scale.
4. In the loop section there’s a minus sign in front of the measurement (weight = – …). If your readings go down when you add weight, keep the minus. If they already go up correctly, remove the minus.
5. Upload the sketch to the Seeeduino XIAO and check with a known weight to confirm it reads in grams.

That’s all you need to edit: the scale factor number at the top, and (optionally) the minus sign in the loop. The correct sketch is in the attachments.

The Full instructions on how to use the three point bending test device can be found in the attachments of this step.

Laser-cut (acrylic): P19, P21, P24

Cut these plates from acrylic as specified in the BoM. Keep protective foil on during cutting, don’t scale drawings, and clean edges/lightly deburr after.

3D-print (PLA, any color): P18, P20, P22, P23

Print as provided (no scaling). Standard layer height is fine; use enough infill for strength on load-bearing bits. Check holes and press-fits—deburr rather than over-sanding if a fit is tight.

Watch the video for the exact build sequence, test clips, contacts, wiring, and enclosure. Follow the routing shown, keep leads short, and double-check the terminal screws are snug. Make sure usb-c polarity matches the schematic in the attachments. If the LED/beeper/meter responds when you touch the probes together, you’re good to go.

Watch the video for the exact sequence, mounting the PTC element, wiring the leads, and placing the cover. Follow the schematic in the attachments for power and polarity. Keep wires short, crimp or solder firmly, and insulate exposed joints with heat-shrink.

Watch the video for the exact build.

Test 1: Electrical Conductivity

1. Clean the surface of each sample.
2. Place the sample in the LED test circuit.
3. Check if the LED turns on.
4. Note: which materials did you expect to conduct?
5. Compare with the actual result. Any surprises?

Test 2: Scratch Test

1. Use a steel nail and scratch each sample with the same pressure.
2. Observe the depth/visibility of the scratches.
3. Rank the samples from soft to hard.
4. Compare: did this match your expectations?

Test 3: Magnet Test

1. Bring a permanent magnet close to each sample.
2. See whether the sample is attracted.
3. Record which materials are magnetic and which are not.
4. Compare with your expectations. Any surprises?

Test 4: Thermal Conduction

1. Touch each sample and compare how warm or cool it feels.
2. Place the samples on a hot plate for 15 seconds.
3. Touch them again and compare the warmth.
4. Note which materials warmed up fastest.
5. Conclude: which are better conductors, which are better insulators?

Test 5: Density

1. Weigh the sample in air on a digital kitchen scale. Write down the mass in grams (m).
2. Put the water container on the scale, fill it with water and tare (display should read 0 g).
3. Submerge the sample fully, using precision tweezers, without touching the cup or bottom.
4. Read the value on the scale. This equals the mass of displaced water = the volume in cm³ (V).
5. Compute density: ρ = m / V.
6. Compare densities: which materials are heaviest for their size?
7. Note if anything floated—did that change your expectations?

That’s it! You’ve built the structured bending device, calibrated it, and tried the intuitive tests. From here you can tweak and improve!

A few parting tips:

1. If readings drift, re-check wiring, re-seat connectors, and re-run the scale-factor calibration.
2. Keep guiding parts clean and screws snug (not over-tight) for smooth motion.
3. Log your measurements and add photos, others can learn from your setup.

All files (3MFs, laser cut drwaings, schematics, and sketches) are in the attachments and listed in the BoM. If you build this, share a photo and what you discovered. Thanks for following along, have fun experimenting!