javeharron / magnetaralpha

Current build

Magnetar

Magnetar is a distance-ranging coil gun platform.

Description

This system is designed to utilize commercially available LiDAR modules for distance-based energy correction. As a projectile from a coil gun flies through the air energy is lost through drag. The goal of this project was to create a model to correct for this loss so projectiles impact with consistent energy.

This system utilizes a simple revolving design to house multiple projectiles for subsequent firing. These projectiles are standard-length Nerf darts combined with a ferromagnetic insert (M4x12mm Bolt with bolt head against inner tip of dart). The coil used is 215 turns of 18 AWG enameled copper magnet wire. This is wrapped along a 45mm 3D-printed PLA shaft. To calculate the corrected velocity necessary to overcome drag energy losses an iterative equation is used. Essentially, out to a set amount of resolution drag losses are added to the projectile's target impact velocity. The target velocity is found using the kinetic energy formula or:

$E_k = \frac{1}{2}mv^2$

From this target velocity drag is added over set time intervals modeled by the equation:

$ V_i = V_t + \frac{\frac{1}{2}{\rho}V_t^2AC_d}{M}R$

In this equation, $V_i$ is the initial velocity after a set time interval of inverse drag. $V_t$ is the initial/target velocity of the projectile and R is the resolution of the time interval (e.g. 0.001 for millisecond intervals). Per loop $V_i$ becomes the next $V_t$. This is continuously run until:

$V_it = d$

Finally, the voltage necessary to achieve this velocity is calculated using the formula of:

$V = \sqrt{\frac{\frac{1}{2}V_i^2}{C\frac{1}{2}E_c}}$

where $E_c$ is the efficiency constant of the coil (e.g. 2.25% or 0.0225) for how much potential energy of the capacitors is converted to the kinetic energy of the projectile.

Items

The Magnetar project files include the following:

• Fully modular and customizable software.
• A modular data logging program and corresponding visual studio project files to intercept serial port communication for dumping into .XLSX formats.
• All 3D files in .STL format for additive manufacturing.
• Data from testing the system at various 1-meter distances.
• Full circuit schematic of the design.
• Flow charts for all code present.
• Sample BOM for at-home fabrication.

Configurable features

Currently, the firmware allows for the configuration of:

• Pins for circuit control and HID.
• Capacitance of system.
• Efficiency constant of the coil.
• Mass of dart projectile.
• Cross-sectional area of the projectile.
• Density of environment.
• Maximum voltage for capacitors.
• Table output.
• Switching between full and auto-ranging power.
• Target energy.