My Final Project

I am a researcher currently starting my PhD about soft robotics bio-inspired by soft-bodied animals. To make the most of my limited time, I want to use my final project for my PhD, i.e. to produce an experimental setup that allows me to visualize the contact of a small animal with its surroundings. More specifically, I want to make the contact area between the animal and a glass plate visible by "frustrated total internal reflection" (FTIR) under different environmental conditions, such as a normal horizontal plate, a wall or even an overhang environment to also assess its attachment performance.

This experimental setup already exists, made by a research group at the University Wageningen in the Netherlands. However, setups like these are self-made and cannot be bought off-the-shelf. Therefore, I have to build one myself during FabAcademy 2024.

From: Langowski, J. K. A., Rummenie, A., Pieters, R. P. M., Kovalev, A., Gorb, S. N., & van Leeuwen, J. L. (2019). Estimating the maximum attachment performance of tree frogs on rough substrates. Bioinspiration & Biomimetics, 14(2), 025001. https://doi.org/10.1088/1748-3190/aafc37

Already in the first week of FabAcademy, project management is an essential task. This includes defining requirements, sketching the idea, time management, creating a bill of materials and a fabrication plan.

I started project management with formulating some demands and wishes what the final project should implement.

Below, you can see the sketches of the experimental setup how I imagined it. You can see, it does not really differ from the image shown in the description. However, sketching emphasizes concepts and important aspects and is therefore an important task.

Sketch of Components Suspended by the Frame

Sketch of Frame and Enclosure

Laster, as you an see here, I neglected the shading box and instead focussed on the frame which can also be enclosed by attaching sheets of material on its sides.

In addition to the demands and sketching the idea, time management is an essential task. I addressed this also in the documentation for the first week. However, in contrast to it, I will keep the Gantt Chart below updated on this page. You can see in which week I contributed to a task as these weeks are marked with an "X". The weeks in which I plan to accomplish them are marked in orange and buffer time is marked with yellow.

Gantt Chart (Last Edit: 4th of April 2024)

As previously sketched, the general setup consists of mainly two groups of mechanical parts, namely the parts that are suspended by the frame and the frame itself. Therefore, these components, the design of the parts, manufacturing and assembly is described separately below. In the end, the mechanical components are all put together.

The mechanical parts suspended by the frame are:

• Glass Plate: Dimensions 300 x 200 x 8 mm (w x d x h)
• 3D Printed Profile: Positioning of LED strip, fixing glass to more rigid structure
• Lasercut Frame: Two sheets sandwiching the 3D printed profile
• Rotating Shaft: Diameter 10 mm
• Shaft Mount: Mounting shaft to lasercut frame
• Camera Mount Mount: Mounting camera to lasercut frame

These parts were firstly designed using CAD, then manufactured with different manufacturing processes and lastly assembled.

Designing the individual parts suspended by the frame was achieved using the 3D CAD software Autodesk Fusion 360. I started with it already in the second week of FabAcademy. Later, I finalized the designed so that they can be manufactured and assembled properly.

In the second week of FabAcademy, I started with the preliminary CAD design of the parts suspended by the frame using Fusion 360. Please refer to this section for more details on the design.

The parametric design is centered around a glass plate with the dimensions of 200 x 300 mm. From the side, 3D printed profiles can be slid onto the glass plate to hold the LED strip in place, one profile per side. These can be connected by finger joints in the corners and furthermore secured in place by screws traversing though the overlapping parts.

The 3D Printed Profiles

Profiles Assembled Around the Glass Plate

In addition, the profiles are sandwiched by two lasercut frames from the top and bottom, respectively. They are secured in place with the same screws that joins the four profiles at the corners.

Lasercut Frames Sandwiching the Profiles

As you can see in the image above, the lasercut frames protrude from the profiles at both sides creating a slot where a mount for the rotating shaft can be attached with additional screws. As this shaft mount is designed to consist of two halves with a cylindrical slot, tightening the screws compresses the mounts onto the shaft between them. The created friction should prevent any rotation of the shaft in the shaft mounts.

Below, you can see a video showing the complete assembly and an animation of the rotation.

Shaft Mounting Halves Inserted in the Lasercut Frame

adjusted led width parameter to 2mm, measured however 1.8 with a bit of force

Deepening the Slot for an Offset in the Assembly

Offset in the Assembly allows for LED Strip to Enter the Profiles

In addition to the parts that are suspended by the frame, the frame itself must be designed, manufactured and assembled. In contrast to the other mechanical parts, these steps were completed for a single assignment, namely for computer-conntrolled machining. Please refer to its documentation for more details as below only a summary of the steps is described.

The design of the frame was also done in Fusion 360. It consists of many parts that are all joined by finger joints and press fits. The two sides are connected in the top by a straight crossbar and in the back by an X-shaped crossbar. This structure is mounted onto a baseplate. At about half the height, the two sides of the frame have a cylindrical hole where the bearings for the rotating shaft can be inserted. To make the suspension of the rotating frame more stable, two bearings on either side of the frame are used. Therefore, a second layer of the material is used to thicken these parts.

On one side however, the motor must be mounted. Therefore, the second layer of the material is placed in an offset and elongated. On its top, a stepper motor (NEMA 17) can be fixed such that its shaft protrudes into the space between the two layers of material. This creates also space to run a belt from the motor shaft in the top to the rotating shaft connected to the glass plate in the bottom.

Complete Assembly

Panel for Mounting the Second Bearing on the Left Side

Panel for Mounting the Second Bearing and Motor on the Right Side

After the design was completed, the manufacturing must be prepared with computer-aided machining (CAM) which is also done in Fusion 360. For this, nesting must be accomplished, i.e. arranging all parts on a single sheet of material with the aim of minimizing the waste of material. This is done by placing the parts on the same plane in the correct orientation and moving them such that only the milling tool fits between them.

Then, the toolpaths can be generated. Here, certain milling techniques like "2D Pocket" or "2D Contour" are selected for the according feature. After having selected all necessary aspects, the toolpaths can be exported as machine code with the according post-processor.

Finished CAM: Cut Stock (Green) with Toolpaths

The machine code obtained by CAM can then be opened in the software for the machine. After fixing the material and setting up the machine and software, the milling job was started.

Done Milling Job

Once the milling job is done, the parts need to be post-processed with a bit of sanding, tab removal and so on. Then, I started with the assembly using a mallet and a sacrificial piece of wood to hammer the press fit joints together. The tolerances were quite low which is why I also had to further sand some joints. But after a while, the assembly was complete. I am really happy about how this turned out.

Assembled Parts from the Left

Assembled Parts from the Right

In addition to the mechanical parts, electrical components are needed. These include a printed circuit board (PCB), some output devices, i.e. a motor and an LED strip, and input devices, i.e. an angular sensor and a camera.

In the eighth week about electronics design, I made use of the assignment to make a PCB for my final project. Below, only a summary is shown. Please refer to its documentation for further details.

Before starting the design and consecutively the manufacturing, I had to consider what other electrical components are necessary and how they are connected to my PCB. For the stepper motor, a motor driver is needed, the LED strip requires a MOSFET for controlling the brightness and, to measure the angle of the rotating shaft, a Hall sensor is needed. Lastly, to power the motor and the LED strip, connections to an potential external power supply must be an implemented.

The design of firstly the schematics with its logics and secondly the physical layout of the PCB was done in KiCAD. In the image you can see the outcome of the design phase. From KiCAD, Gerber files are exported.

Completed PCB Layout

The Gerber files can then be imported into the software LPKF CircuitPro for the PCB milling machine, the LPKF ProtoMat 1S04. This software is really handy as it also includes the CAM processing. This includes e.g. selecting a tool and defining the starting point of the milling job.

After the CAM processing was completed, the milling can start which is guided with a Wizard in the software for the machine. This really comes in handy as the user basically cannot miss a step with these steps being very well automated, e.g. setting the height of the tool.

Milled PCB

After the milling, the board can be stuffed with the components by soldering. This includes the microcontroller, capacitors, resistors, LEDs, buttons, pin headers, the MOSFET and other comonents.

Lastly, a bit of testing is completed with a multimeter to ensure the functionality of the PCB. The board I made is shown in the images below.

Finished PCB

Angled View on Finished PCB

The output devices for my final project are a stepper motor and an LED strip. To explore how to control then, I used the assignment on output devices. Once, I had finished the PCB for my final project, it was very easy to control the output devices as most of the wiring is already implemented on the PCB. For more details than shown below, please refer to the documentation on output devices.

For controlling the stepper motor, I mounted the driver onto the female pin headers on the PCB in the correct orientation, connected the motor to it and attached a bench power supply with 24 V and a load-depended current to it. Then, I attached a programmer board to the PCB via the 1x3 pin header for UPDI, including VCC, ground and the UPDI pin. Then, I wrote an Arduino sketch shown here and uploaded it to the microcontroller. This made the motor spin back and forth with a small pause between it.

For more details, please refer to this documentation.

For the LED strip, I controlled the brightness with a MOSFET which is basically a voltage-driven gate. By opening and closing it via pulse width modulation (PWM) with different duty cycles, the "subjective" brightness can be adjusted. This is "subjective" as the brightness actually does not vary but just the "On" time vs "Off" time such that it is only perceived as a changed brightness.

For wiring the components, I firstly connected the LED strip and a bench power supply with 24 V and a load-depended current to the according screw terminals. Then, I also connected a programmer board via the UPDI pin header and uploaded the Arduino sketch shown in this section to it. This turned the brightness of the LED strip up and then down again, over and over again.

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