## Introduction: Cirkinemeter: Arduino-Based Circular Kinematics Platform

Hello! I'm BACK from a LONG hiatus!

In this instructable, I introduce my newest DIY platform that can perform experiments on circular kinematics. It utilizes Arduino to measure centripetal acceleration and angular velocity. Additionally, it allows students to observe and measure the Coriolis force on a classroom scale (instead of planes and hurricanes).

This platform is called the Cirkinemeter (Circular Kinematics Meter). It was built to extend the capacities of its predecessor, the Kinemeter, from linear to circular motion. Like the Kinemeter, the Cirkinemeter is affordable, portable, and moddable, thanks to its open source parts.

The premise of this device is to provide students an affordable, portable, and moddable platform to perform experiments on rotating, non-inertial frames of reference. This is mainly because in physics classrooms, students face lots of confusion when it comes to "real" or "fictitious" forces. This is illustrated in the comic above.

Additionally, the Cirkinemeter serves to provide students a quantitative data on the Coriolis force in the rotating frame. Unfortunately, this concept is often only taught on a qualitative scale in high school lessons. The Cirkinemeter's turn table platform provides a polar grid which students can use to generate polar graphs.

This instructables focuses on how to build the Cirkinemeter from its base parts. A video demonstration of the platform will be provided at a later date.

## Step 1: Housings 1: the Regions

Region 1 (Pic 1 and 2): This region shows parts related to securing the motor in place. The large square base (pic 1) attaches to 4 small walls (pic 2), which provide a housing for the motor to rest in. The small screw mount (top of pic 2) goes on top of the mount and is used to screw the motor in place so that the motor does not jerk.

Region 2 (Pic 3 and 4): This region's parts are for attaching the large spinning disk to the motor. Any experiments to measure centripetal or Coriolis forces are performed on the large spinning disk (pic 4), which is marked with several reference radii.

Region 3 (Pic 5): This region shows parts for holding the IR Receiver. The receiver will detect the transmitter (which will be on the large spinning disk) and record the change in time between detections (this is how we measure RPM).

## Step 2: Housings 2.1: Constructing the Mount and Base

To construct region 1, we do the following:

Pic 1: The side walls are placed into the two parallel rectangular holes of the base. The walls have bottom and top notches which are used to click into the base’s holes. The text “Side Walls B----> F” for BOTH side walls should point towards the front as labeled on the base. The Back Wall is placed behind the side walls with its text facing the Back as labeled on the base.

Pic 2: The top is placed on top of the walls (the three upper notches of each wall correspond to three rectangle holes on the top). The top is placed such that the engraved line faces the front as labeled on the base.

Pic 3: The screw mount is then placed on the engraved rectangle of the top. The two holes on the mount are where screws will be inserted to secure the motor.

Use scraps of plastic for additional support when assembling.

## Step 3: Housings 2.2: Constructing the Sensor Stand

To construct Region 3, we do the following:

Pic 1: Place the Sensor stand through its base and weld them together. To keep it perfectly straight up, gently weld and press scrap pieces of plastic over the hanging ends of the stand (that fill the length of the hole in the base).

## Step 4: Housings 2.3: Modifying the Spinning Disk

We take the IR transmitter holder (the rectangular piece) and weld it to the underside of the large spinning disk, with the text "ceiling" oriented as seen in the image. The holder should be placed around the large, non-centered hole of the disk as seen.

## Step 5: Motor 1: the Parts

The parts seen in the image all come from a company called ServoCity.

These parts enable the connection of the rotating disk to the rest of the platform.

## Step 6: Motor 2: Attaching Disks to the Motor

Next, we take the components, and start assembling them.

Pic 1: The motor is secured to the base and mount through the clamp. The clamp tightens around the motor and its screw holes are secured to the plastic screw piece.

Pic 2: A hub and adapter are screwed onto the motor's spindle. the adapter has eight screw holes parallel to the ceiling of the mount. Four of these holes are threaded (alternate).

Pic 3: The Connector disk is then screwed to the adapter.

Pic 4: A spacing disk is placed on top with the holes aligned. This allows the spinning disk to be screwed on top without any interference from Pic 2's screws.

Pic 5: Finally, the rotating disk is placed on top of the setup and is screwed down with 4-40 screws (1/2 inch long). The screws go through all three plastic disks and are secured by nuts.

This completes the entire turn-table housing for the Cirkinemeter.

## Step 7: Electronics 1: the Two Components and Their Purposes

Now, we look at the parts needed for the electronics. They can be broken into two main categories, the Motherboard and Accelerometer Device

The Motherboard performs several key functions, as listed:

* Measure the angular velocity (radians per second or revolutions per second)

* Control the Motor's RPM and direction (CW or CCW)

* Print the Angular Velocity on a visual display

The Accelerometer device directly measures the acceleration felt on the rotating disk and publishes the data to smartphones.

## Step 8: Electronics 2.1: Parts of the Motherboard

Here, we look at the parts and steps needed to assemble the Motherboard.

Pic 1: The main controller is the Adafruit Feather 32u4. It is a variation of Arduino and is completely open source. This is the chip that handles taking in input and publishing data. Adafruit has a series of similarly sized chips called feathers and wings. They are all interconnectable and perform various tasks. Go here to learn more about it.

Pict 2: The OLED feather wing is a visual display which can be placed directly on top of the feather. It has three buttons labeled A, B, C which connect to the feather pins 5,6, and 9, respectively.

Pic 3: The Joystick acts as the manual controller of the Motherboard. It can move in two axes, X and Y. The X-axis controls the direction of the motor while the Y-axis controls the speed the motor travels at.

Pic 4: The TB66 is an electrical component that belongs to a family of circuits called H-bridges. This provides the motherboard the ability to change the direction of the motor.

Pic 5: The IR Breakbeam sensor is used to measure angular velocity. The transmitter () is placed on the rotating wheel. When it passes the receiver (), the receiver then sends a signal to the feather, which calculates angular velocity.

Pic 6: To make the connections, I made a customized PCB which allows people to directly insert the components into. For those curious about how to make manual connections, a table is given on the next steps.

## Step 9: Electronics 2.2: Assembling the Motherboard

To assemble the motherboard, place the components into the PCB as seen in the image.

For the coding pin connections themselves, see the table below:

Feather pin | TB66 pin

6 | Bin1

9 | Bin2

11 | PWM A and B

Feather pin | Joystick pin

A0 | Xout

A1 | Yout

## Step 10: Electronics 3.1: Parts of the Accelerometer

Pic 1: Like the motherboard, the Accelerometer uses a Feather 32u4 for the main controller.

Pic 2: The LIS3DH chip is what directly measures acceleration in 3 axes (as seen in the image). For instance, the chip, if placed on a table, would measure g m/s/s on the z-axis as a result of gravity pulling it against the table's surface.

Pic 3: The HC-06 is used to publish the data. It utilizes bluetooth and sends the Acceleration measurements to a smartphone.

Pic 4: The PCB has pins available for all of the other three components.

## Step 11: Electronics 3.2: Assembling the Accelerometer

Insert the components into the PCB as seen in the image above.

For the coding pin connections themselves, see the table below:

Feather Pin | LIS3DH Pin

SCL | SCL

SDA | SDA

Feather Pin | HC-06 Pin

10 | TX (Bluetooth Transmit)

## Step 12: The Code

All of the code for the Cirkinemeter is available on Github. See the links below:

Motherboard

Accelerometer

They run on arduino. Go to here for feather library installation and here for the feather OLED library installation.

## Step 13: Finally...

Pic 1: Send the Receiver through the stand and the transmitter through the support on the rotating disk. Make sure they align in height properly

And then Pic 2: YOU HAVE BUILT A CIRKINEMETER!