Three-Axial Helmholtz Coil Design and Validation for Aerospace Applications

This paper presents the detailed design, construction, and validation of a three-axis square Helmholtz coil. It also describes the methodology used to drive each pair of coils as well as the setup to operate it in a closed-loop system using a digital PID controller. The coil will be mainly used for aerospace applications, especially to aid the development and testing of attitude determination and control systems that use the earth's magnetic field as a reference vector. Most of the system was built using commercial components, reducing cost, and complexity compared to similar commercial systems. The assembled Helmholtz coil has approximately one cubic meter and can generate magnetic fields up to 2 G/ axis, keeping a uniformity of 0.04% around 11 cm of the center, in each axis. A custom-designed voltage-controlled current source, based on the Howland current pump, was employed, requiring no complex electronic circuits. The coil was designed to be part of a hardware-in-the-loop (HiL) system, which is controlled by a dSPACE modular simulation hardware and uses a commercial fluxgate magnetometer as the reference. This setup reduces the complexity of the proposed system when compared to similar ones. This paper presents two distinct results: first, there is the validation and results of the uniformity regarding the generated field around the system's center; second, results of the setup with the closed-loop HiL simulation are shown, which includes tests of the coil when generating a dynamic magnetic field.