cs.ROSep 28, 2026

MagNav: A Dual-Core Magnetic Track Guidance Framework for Lighting-Invariant Navigation in Two-Wheeled Robots

Authors: Arpita Kumari, Anupam Chatterjee, Richa Srivastava

Organizations: Department of Electronics and Communication Engineering Krishna Institute of Engineering & Technology (KIET), Ghaziabad, Delhi-NCR, Uttar Pradesh, India.

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Abstract

Two-Wheeled Inverted Pendulum (TWIP) robots are useful for studying how to control systems that are naturally unstable and have fewer actuators than degrees of freedom. Adding autonomous line-following to these robots is challenging because steering and balancing are closely linked. Most existing systems use infrared sensors, which can be affected by changes in lighting, such as sunlight or shadows, making them reliable only indoors. This paper presents a self-balancing robot that can follow a line using a magnetic track guidance system. By using a five-channel analog Hall-effect sensor array, the robot is not affected by optical interference. The control system uses a cascaded PID structure: the inner loop keeps the robot balanced using data from an inertial measurement unit with a complementary filter, while the outer loop adjusts steering based on the magnetic sensor readings. Stepper motors provide precise torque control without needing extra rotary encoders. For comparison, an optical sensor module was also included. Tests show that the magnetic guidance system keeps accurate tracking even in very bright lighting, over 10,000 Lux, while the optical system loses accuracy and sometimes fails. This design provides a reliable, lighting-independent solution for autonomous navigation in places like factories, warehouses, and outdoor paths.

Figures & tables

Fig. 1: Conceptual comparison of navigation modalities for the Two-Wheeled Self-Balancing Robot. (a) A traditional 2-channel digital IR proximity sensor configuration tracking a black line, which is highly susceptible to ambient lighting interference. (b) The proposed lighting-invariant approach using a custom 5-channel analog Honeywell SS49E Hall-effect sensor array tracking a magnetic strip.
Fig. 2: Physical arrangement of the TWIP platform. The upper deck houses the power source, a 12 V, 5000 mAh battery. The lower deck contains the custom-built PCB, which integrates the ESP32 development board, an LM2596 buck converter, and A4988 stepper motor drivers. The bottom view shows the main drive assembly, comprising NEMA 17 stepper motors, an MPU6050 6-DOF IMU for pitch measurement, and two sensor arrays: digital IR and analog Hall-effect sensors.
Fig. 3: (a) Side CAD view of the physical platform. (b) Free-body diagram of the wheeled inverted pendulum, defining the pitch state ( θ\theta ), the horizontal translation ( xx ), the wheel radius ( rr ), and the distance to the centre of mass ( ll ).
Fig. 5: Mathematical conversion of raw analog voltage from the five-channel magnetic sensor array into a high-resolution lateral distance error.
Fig. 6: Schematic of the standardised benchmarking track (15 mm track width). The identical geometry was utilised for both optical and magnetic testing phases. An artificial high-intensity interference zone ( >> 10,000 Lux) was positioned at the 90-degree vertex to evaluate sensor robustness under extreme ambient lighting.
Fig. 7: Sensor Mounting & Clearance Schematic. Both sensor arrays are mounted with a 7.0 mm floor clearance. The 2.0 mm thickness of the magnetic strip results in an effective 5.0 mm sensing air gap for the Hall-effect array, optimising magnetic flux reception while ensuring mechanical safety.
Fig. 9: Baseline evaluation: Optical (IR) System Failure. (Top) Physical sequence demonstrating complete path loss upon entering the 10,000 Lux interference zone. (Bottom) Internal telemetry data plotting the Discrete Error State against Distance Travelled, demonstrating the erratic bang-bang control limit cycle and total track loss at 789 mm.
Fig. 10: Proposed solution: Magnetic System Success. (At the top) A physical sequence that shows perfect tracking through the >> 10,000 Lux interference area and along the following continuous curve. (At the bottom) Extended telemetry data illustrating complete immunity to optical interference, together with slight, damped overshoots and accurate baseline tracking over a distance of 2742 mm.
Performance MetricIR Optical (Control)Magnetic (Proposed)
Max Error: Straightaway±1.8\pm 1.8 mm±0.6\pm 0.6 mm
Max Error: 90 ∘ Turn16.016.0 mm8.08.0 mm
Max Error: Light ZoneTrack Lost (Failed)8.28.2 mm
Steady-State Curve ErrorN/A (Failed prior)1.51.5 mm
Overall RMSEN/A (Incomplete run)2.142.14 mm
Overall IAEN/A (Incomplete run)30.930.9 mm ⋅\cdot s
TABLE I: Comparative Performance Metrics

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