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What is Railgun?

For more information and videos on railgun visit our railgun page or visit General Atomic's Railgun System 

Background

    A railgun is fired by sending millions of amps of current through the rails and armature which creates a coupled electromagnetic field on the armature, in the longitudinal axis of the rail due to the Lorenz force.  After each shot, the railgun's bore shape is altered; due to wear of rail material and the displacement of oxidized metal from the interaction of the armature, rail, current and air. General Atomics needs a way to map the cross sectional profile of the railgun barrel to check for change in the barrel profile. The two main factors to overcome for this project are the aluminum deposits and the size constraint. After each test of the railgun, the armature that carries the ballistics package undergoes four state changes (solid, liquid, gas, plasma) from the extreme heat and current and creates a large amount of aluminum oxide buildup of the edges of the railgun (Figure 2). This buildup makes it difficult to send an autonomous mapping tool through the bore. Furthermore, the railgun bore is quite small (about 3.2 inches by 2.2 inches) and thus this size constraint must be considered (Figure 3). General Atomics' approach is to use a four wheel driven cart that carries an optics package through the bore. This optics package consist of laser that hits a conical mirror creating an overlaid cross section image of the bore that is captured by a camera for post-processing analysis. However, the cart fails to fully map the inside of the bore due to obstructions, mainly the corner edge sludge.

Objectives

Design, build, and test a new method of mapping the inside of the bore of the railgun in a quick manner and at a low cost. 

Primary Requirements

• The robot must be autonomous

• Traverse 8 m long bore in less than 30 minutes

• Mechanically simple

• Battery powered

• Illuminate bore with a ring beam device

• Capture and store images at 1 mm intervals to be processed afterward

• Image resolution must be better than 1024x1024 

UCSD Design Approach 

Figure 4. ROBO MAT inside the railgun bore

    The design chosen to pursue is the roller cart, shown in Figures 1-3. The roller cart uses the railgun forcing cone to traverse the bore. The amount of sludge on the forcing cone is very minimal and thus is the ideal area of the bore to travel along. The cart has rollers on the top and bottom to do this. The rollers on the top sit on springs to prevent the cart from jamming as it travels over any sludge, while to two bottom rollers are driven by the system shown in Figure 2. Figures 8 and 9 show the roller cart in a test bore and the CAD concept of the cart in the bore. The same optics mapping approach used by General Atomics is utilized in this design with a camera, conical mirror, and laser.  

Figure 5. ROBO MAT CAD model and Components                             Figure 6. ROBO MAT back view inside the bore

Our low cast, simple design can map the inside of the 8 meter long railgun bore within 30 minutes. It uses a high quality video camera to capture the cross-sectional image of the laser beam onto the bore. By driving on the forcing cone of the railgun it avoid the large amount of aluminum oxide buildup of the edges of the railgun, and due to its high power drive-train it can overcome the minimal amount of aluminum oxide buildup on the forcing cone. It is controlled by raspberry pi B+ micro-controller and powered with a 7.4 Volt, 3000 mAh battery. 

For more detail design figures and explanation visit Final Design page