11.4 - Implementation

Fabrication and Assembly

The primary differences between our prototype and initial final design plan was that the final design were that the final design would be self-supporting and actuated by a servo motor. The linkages and base were laser-cut from acrylic panels and supported with 3D-printed brackets. A screenshot of our initial CAD assembly is shown in Figure 11.4.1 below.

Unfortunately initial testing revealed to us that the servo motor we bought was slower than anticipated, so we modified our design to have a gear train to exchange some torque for extra speed. It took several iterations to get the spacing correct to ensure the belt connecting the gears was adequately tight. Ultimately we were able to find an appropriate spacing and have everything fit snugly together. Figure 11.4.2 shows the final build, with the gears.

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Figure 11.4.2. The final assembly.

Electronics and Circuitry

The servo motor was powered by a 6V-4.5Ah rechargeable battery to ensure it receives enough power to operate at its specified potential. It was controlled by an independently-powered microcontroller board, which dictates its angle and speed based on user input. The Arduino board was connected to 3 potentiometers, 2 buttons, and 2 LEDs, which can be seen in Figure 11.4.3. The potentiometers control the start angle, end angle, and flick speed. The buttons control the state. The LEDs act as indicators of the current mode. See the section on software design below for more details.

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Figure 11.4.3. The circuitry behind the mechanism.

Software Design

Our objective when designing the software for the Arduino board was to enable us to easily tweak the mechanism’s flick parameters without hard-coding in values and reflashing the board. This is the reason the electronics consist of more than a servo, battery, and microcontroller. The mechanism has two modes: setup mode (red LED on) and demo mode (green LED on). The user can change which mode they are in by pressing the red button. Each mode has multiple states, which are cycled through by repeatedly pressing the green button. These modes and states are summarized in Figure 11.4.4, and the video in Figure 11.4.5 showcases us cycling through every mode and state.

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Figure 11.4.4. A diagram of the modes and states of the mechanism.

In setup mode, there are four states: off, min angle set, max angle set, and min-max oscillation. In the off state (the initial state upon powering up), the mechanism does not move. In the angle set states, the servo slowly moves towards the current angle specified by the appropriate potentiometer. The software determines the target angle based on the voltage output of the potentiometer’s middle pin, which changes from 0V to 5V (corresponding to 0 and 180 degrees respectively) as the user twists the potentiometer’s knob. In min-max oscillation mode, the mechanism slowly moves between its start and end angles to showcase its full range of motion.

If the user presses the red button to swap to demo mode, the mechanism enters demo mode. In demo mode, the first state is the prep state, in which the mechanism slowly moves towards the start angle. Once the mechanism reaches its start angle, and not a moment sooner, pressing the green button will swap the state to flick mode, in which the mechanism will move from the start angle to the end angle at a speed determined by the angle of the third potentiometer’s knob. The mechanism will automatically return to the prep state upon completing the flick.

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Figure 11.4.5. A video showing off the each mode and state. It begins in setup mode in the off state, then to the two angle setting states, then to the min-max oscillation state. It then shows demo mode with three flicks of varying speeds based on the speed-setting potentiometer.

Final Bill of Materials

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