Erwin Smith Animatronics Face

This project creates an animatronic face of Erwin Smith from Attack on Titan that reacts when someone approaches it. An ultrasonic sensor detects the viewer and triggers a pre-recorded speech from Erwin, which plays on a laptop. Two servos move the jaw and eyebrows to somewhat match the dialogue. A third servo operates a mechanical hand that activates when the user places their hand over a photoresistor, adding more interaction. The goal is to practice basic animatronic concepts, such as linkages, sensor-based triggering, and multi-servo control, using an Arduino.

The key moving parts of the face and hand were 3D-printed instead of cut from cardboard. This made them more precise and durable. The lower jaw, eyebrow frame, and hand support were designed in CAD, ensuring their pivots align neatly with the servo horns. This setup enables smoother motion and minimises mechanical play. The jaw features a hinge behind the mouth line and a boss for the servo linkage. The eyebrow is a curved bar with small features for attaching to the eyebrow servo, enabling it to rotate between neutral and “raised.” The hand support is a rigid bracket with mounting holes, positioning the hand servo at the right angle. This setup allows the hand to swing from 0° to 90° without bending the rest of the structure.

For step 2, a popsicle stick bridge was constructed across the cardboard chassis to position the servos at the correct height for the jaw and eyebrow. The bridge serves as a raised beam, allowing each servo horn to align with its corresponding 3D-printed joint without needing heavy supports. Popsicle sticks were taped and glued together to make the bridge sturdy enough to resist twisting when the servos move. The entire bridge assembly was then taped to the cardboard walls to keep it in place while the linkages transferred motion to the jaw and eyebrow.

For the actuators, we utilise three SG90 micro servo motors to generate all the visible motion in the face and hand. One servo drives the lower jaw. A second controls the eyebrow linkage for facial expression. The third rotates the hand between 0° and 90° when the photoresistor is covered. These servos were chosen because they are small, cheap, and easy to control directly from the Arduino with simple position commands.

For the sensors, we used one ultrasonic distance sensor and one photoresistor. The ultrasonic sensor is mounted near the front of the chassis and measures the distance to a person. When someone comes within a set range, it triggers the jaw and eyebrow animation sequence, which is synchronised with the audio. The photoresistor is wired as a voltage divider and placed in a position where the user can cover it with their hand. When the light level drops below a certain point, it activates the hand servo to rotate from 0° to 90°. Together, these sensors allow the project to respond to someone approaching the character and to direct interaction with the hand area.

The Arduino Uno connects to a breadboard that distributes 5 V and ground to all components. Three SG90 servos get their power from a 4×AA battery pack via the breadboard rails. Their signal wires connect to separate digital pins on the Arduino for jaw, eyebrow, and hand control. The HC‑SR04 ultrasonic sensor connects its VCC and GND to the breadboard rails, while its TRIG and ECHO pins connect to two Arduino digital pins for measuring distance. A photoresistor is set up as a voltage divider on the breadboard, with the midpoint connected to an analog input on the Arduino to detect when a hand covers it. All grounds from the battery pack, sensors, servos, and Arduino are linked together to ensure a common reference for reliable operation.

https://github.com/ChethanSrikantappaGaneshbabu/Chethan/blob/main/Project-Final.ino

The final product is a fully assembled Erwin Smith-inspired animatronic that reliably reacts to people and user input. After testing and tuning all three servos, the jaw and eyebrow move smoothly in sync with the audio when the ultrasonic sensor detects someone in front of the figure. The separate hand mechanism responds to the photoresistor, raising and lowering when a user covers the sensor. This adds an extra interactive element. Overall, the system is stable, repeatable, and ready to be showcased as an interactive animatronic demo.

Working on this project taught us how difficult it is to sync servo movements to pre‑recorded audio by hand, and how important it is to leave time for tuning timing and angles instead of assuming it will work on the first try. We also realised how challenging it is to build a sturdy chassis from cardboard with minimal tools, so we had to think carefully about where to place cuts, joints, and supports to prevent the servos from tearing the structure apart. We learned that reliable power and grounding are just as important as code. Once we moved away from a weak 9V battery and shared a solid 5V supply and common ground, the system became much more stable. Overall, this project reinforced the need to prototype each subsystem separately, document everything thoroughly, and anticipate multiple mechanical and electrical iterations before the animatronic behaves as we imagined.