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Stroller Emergency Braking System

Overview

This project focused on developing a proof-of-concept emergency braking system for a stroller, aimed at preventing accidents when the stroller is left unattended on an incline or begins rolling away. The system was designed as a retrofit module adaptable to many stroller designs.

I was fully responsible for all electronics and software, including system architecture, sensing, signal processing, communication, and motor control. My teammate was responsible for the mechanical braking subsystem, which housed the actuator and physically engaged the brake.

Objectives

The design needed to meet three core goals:

  1. Detect when the guardian is absent.

  2. Detect runaway conditions (incline + rolling).

  3. Automatically engage a brake with minimal false positives.

Electronics and Sensors (My Contribution)

I developed the electronics architecture using two ESP32 microcontrollers communicating via ESP-NOW protocol. Splitting sensing/logic (sender) from actuation (receiver) made the system more modular and fault-tolerant.

  • Guardian detection: Ultrasonic distance sensor mounted on the handlebar. Continuously measured user proximity to confirm supervision.

  • Incline detection: LSM6DS0 IMU (accelerometer + gyroscope) measured stroller pitch and angular velocity. I filtered noisy signals and implemented drift mitigation strategies to produce stable slope data.

  • Speed sensing: Custom reed switch + magnet assembly on a stroller wheel provided wheel speed. I implemented software debouncing to suppress bounce noise and ensure accurate velocity measurement.

This sensor suite enabled redundant detection of runaway conditions by cross-referencing motion, slope, and user presence.

Software and Control (My Contribution)

All embedded code was written in MicroPython, structured around interrupts and timers for responsive, non-blocking performance.

  • Braking Logic: Implemented as a state machine with filtering and delay buffers to avoid false positives. A braking event was triggered only after conditions (guardian absent, stroller moving/tilted) persisted for >1 second.

  • Communication: ESP-NOW protocol provided low-latency, Wi-Fi–independent data transfer between the sender (sensors + logic) and the receiver (actuation).

  • Motor Control: A DC gearmotor with encoder drove the brake actuator. I implemented proportional feedback control with position tolerance bands to prevent oscillation and reduce stalling.

  • Failsafes: Added a buzzer to provide audible feedback when the brake was triggered, alerting the user to system activation.

Mechanical Subsystems (Teammate  Contribution)

The braking hardware was designed by my teammate and consisted of:

  • Actuator Mount: DC motor with integrated gearbox and encoder, packaged in a 3D-printed housing.

  • Brake Linkage: Lever arm attached to motor output, which pulled a friction pad against the wheel.

  • Stroller Integration: Mounts for attaching the housing to the stroller frame.

I collaborated with my teammate by providing actuator torque/speed requirements and verifying that the motor control strategy matched the mechanical system’s limits.

Results

The prototype demonstrated proof-of-concept success:

  • Guardian absence, incline, and rolling were all reliably detected.

  • Braking was actuated consistently under controlled test conditions.

  • System passed basic functional tests for modularity and responsiveness.

Strengths: Robust electronics/software architecture, smooth actuation, modular design.
Limitations: Ultrasonic sensor misreadings, IMU drift, occasional reed switch errors, limited motor torque.

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Future Improvements

  • Capacitive grip sensor instead of ultrasonic for presence detection.

  • Inclinometer instead of IMU for tilt sensing.

  • Hall-effect encoder instead of reed switch for speed measurement.

  • Higher-torque, non-backdrivable actuator for braking hardware.

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