Assignment 17

This week is the second to last week before the final projects should be presented. The aim of this assignment is therefore to best prepare the final project, compile a summary and answer some very essential questions. This weeks's assignment were to answer these questions:

• What will it do?
• Who's done what beforehand?
• What will you design?
• What materials and components will be used?
• Where will they come from?
• How much will they cost?
• What parts and systems will be made?
• What processes will be used?
• What questions need to be answered?
• How will it be evaluated?

My final project, as proposed here and completely shown here, will be an experimental setup for my PhD. I would like to investigate the locomotion and the attachment performance of soft bodied animals, e.g. frogs and snails. For this, I need to visualize the contact area of the animal and its surrounding while optionally applying various forces to it.

The former, i.e. the visualization of the contact area, can bew achieved with so called "frustrated total internal reflection" (FTIR). Total internal reflection occurs for example when light is shown into the side of a glass plate. Due to the high refractive index of glass compared to its surrounding (air), the light is internally reflected.

However, if for example a finger touches the glass plate which increases the refractive index of the local surrounding to a similar level than the glass plate, the light is not internally reflected but can escape at this point. Therefore, the contact area oof the finger with the glass plate lights up which can be recorded by a camera.

Working Principle of FTIR (Source)

The second goal was to apply various forces to the animal while recording the contact area. Here, various forces mean different angles varying from a flat landscape (0°) to an overhang environment (180°). This can be achieved, by rotating the glass plate 180° with a known speed.

To summarize, my final project will incorporate a glass plate with an LED strip around it to generate FTIR. Simultaneously, a camera will record the screen. Next, the glass plate should be able to rotate. The user however should have the choice to switch the rotation off ("static mode") or on ("dynamic mode") and in the case of the latter also specify the end angle of the rotation.

Last but not least, an angle sensor should record the current angle of rotation to validate that the rotation happened as intended.

This is a really easy question for me as I got inspired to make this experimental setup from a paper I read. This paper utilized exactly such experimental rig. So in short, the University of Wageningen already did this. However, I have no other information than available in the paper which is mainly an image of the setup as well as the rotational speed of 3.6° per second.

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

I am trying to design and thus make as much myself as possible, rather than buying the things. However, there are various thing that I had designed and still will design, including the mechanical and electrical parts. These include:

• Parts suspended by the frame
• The frame
• The PCB
• Parts integrating wires and attaching them to the mechanical parts
• App/Software for the user to interface the peripherals

Please find the details of what I designed on the final project's page.

Parts Suspended by the Frame

The Frame

The PCB

System Integration

The App/Software

There are several different materials I will be using. First of all, below is a list of materials, I will be using to make parts. The dimensions are the minimum dimensions for sheet material.

• PLA Basic: Black, 500 g
• PLA Generic: Blue, 70 g
• POM Sheet, 3mm thick: 50 cm x 40 cm
• Multiplex Board, 12.55 mm thick: 1.5 m x 1.25 m
• Stainless Steel Shaft: 10 mm diameter, 15cm
• Copper Sheet: FR4, one-sided, 5cm x 8cm
• Aluminum Profile: 20 mm x 20 mm, 220 mm length, 2 mm wall

Used Raw Materials

In addition, I will be buying some parts or use complete components from the lab. In general, these include the following parts:

• Glass Plate: 20cm x 30cm x 8mm
• LED Strip: Bright, cold white, continuous, 150cm length
• Power Supply: 24 V, 1 A
• Stepper Motor: NEMA 17
• Motor Driver: A4988
• Hall Sensor: KY-024 Linear
• Plug for Socket (Connecting to Power Supply)
• Two Phase Cable, 1m
• Pulley, big: 10 mm inner diameter, 60 teeth
• Pulley, small: 8 mm inner diameter, 12 teeth
• Belt: GT2, 6mm width, 300mm length
• 4 Ball Bearings: 10mm inner, 30mm outer diameter, 9mm width
• Raspberry Pi: Model 4B, 4GB RAM
• Camera Module: 12MP HQ-Module
• Camera Lens: 6mm
• Raspberry Pi Power Supply: 5V 3A
• Braided Sleeve: 25 mm diameter, 40 cm length
• Diametric Magnet: 10 mm diameter, 5 mm width
• MicroSD Card: 32 GB

Used Components

However, there are also parts which are used for the PCB of my final project. These are:

• Male Pin Headers
• Female Pin Headers
• MOSFET NCh TO252
• 2 Screw Terminal
• 2 Capacitors 1206 (1uF, 0.1uF)
• Capacitor Motor 100uF
• 2 LED size 1206
• 2 Resistors size 1206 (2x 10 kΩ, 2x 4.7 kΩ, 1x 1000 Ω, 2x 200Ω)
• Button
• Microcontroller ATtiny1614
• Solder
• Female-to-Female Jumpers
• Long Female-to-Female Jumpers
• Ferrules 0.25 mm

Used Electrical Components

Not listed above are screws and bolts. For more details, please refer to the complete bill of materials that is available for download in the bottom.

The sources are sometimes hard to tell as most of my final project was designed to use materials and components that were available in the Lab. However, I ask my instructor for the missing sources. In this case, for the parts that I will make, the sources are the following:

Please not for the materials above, the source is linked for a full sheet even though I have not used the complete sheet.

For the materials above as well for the components below, I have marked whether they came out of the FabLab's Inventory or were bought by me. As you can see for the components below, some of them were from the Inventory, some were bought:

Lastly, for the electrical components, I basically used the FabLab's Inventory. I only highlighted below, where the "more special" components came from:

The costs of the components amount to 281.04 € in total not including nuts and bolts. The main parts of the expenses are caused by the camera which consists of a Raspberry Pi, the glass plate and the LED strip.

As the costs of the single materials were supplied with the link to the source, I compiled a list of costs for them. Please note that the costs listed below are valid for a full sheet, even though I did not need all of it. In total, the costs of the (used) materials amounts to about 81.25 €.

For details on the calculations, please refer to the complete list of materials below.

I have tried to make as many parts as possible myself. Therefore, there is quite an extensive list of parts, I will be making. The parts and the materials used are shown below. The costs for the raw materials are shown above. The costs for the individual parts made with these materials are presented in the complete list of materials below.

Most of the parts that I will make are actually 3D printed. In addition however, I will be using CNC milling, PCB milling and lasercutting as digital manufacturing processes. Only the rotating shaft will be made manually by cutting it with a saw to the right length and sanding it.

At this point of my final project, I am more or less done. I have assembled most of the parts already. From the pure mechanical point of view, I am still missing the attachment of the counterweight mount and the actual counter weight. Here, a question would be

• How large does the counterweight need to be such that the motor is able to turn the shaft?

Next, I am missing most of the system integration week as my 3D printer at home broke down because of a new update that messed with the settings apparently (and I cannot use a different one without excessive work as the parts were designed to be printed on this printer). Therefore, I still need to answer:

• Do the JST connectors work as intended?

Additionally, I need to mention, that I still need to figure out how to transform the readings of the sensor to the actual angle. I will probably need to generate a sine or cosine function for it. Hence, there is the following question that needs to be answered:

• How is the curve fitting done starting with the readings of the angle sensor generating the actual angle data?

Lastly, I have to address the rotation of the shaft. Here, the interface right now starts at a more or less random initial position and rotates it (in case for the dynamic mode). However, the questions that I need to answer for this are:

• How to ensure that the initial position is always at 0°?
• How or when is the platform rotated back to zero after the dynamic measurements are done?

I hope it will be evaluated with a "Pass" obviously. However, this questions targets actually the following questions: "What does it take to be evaluated with a pass?". First of all, there are requirements from the side of FabAcademy. However, I also formulated my own requirements. If all are met, my final project is successful.

In addition to the requirements from FabAcademy, I also formulated my own demand which should be met in order to successfully absolve FabAcademy. These were created in the initial assignment on project development but are also posted on the final project page. These are:

• An LED strip must be placed around the glass plate.
• The glass plate must be connected to a rotating shaft able of rotating 90°.
• A camera must be able to record the surface of the glass plate from below.
• The camera must be able to follow the rotations of the shaft.
• The shaft must be suspended by a frame.
• The rotation is controlled by a motor.
• An angle sensor is used to measure the angle
• A GUI is used as an interface via USB to the microcontroller.
• The microcontroller has a housing.

• Bill of Materials (.xlsx): List of materials and components split into "Making", "Buying" and "Electrical" showing the needed quantity, source, the costs and for materials also the fabrication process