Rollers

The rollers were the point of the contact between the cart and the railgun bore forcing cone and thus had to be fabricated with precision. The rollers exactly matched the curvature of the railgun forcing cone. In doing so they allowed the cart to effectively travel along the forcing cone with high center alignment capabilities. Furthermore, the roller wheel was chosen for its ability to avoid the main sludge locations in the bore as well as its ability to prevent tipping of the entire ROBO MAT assembly. 

       Fig 1.Size Comparison of Top and Bottom Roller

The top-guiding rollers kept the cart aligned in the bore as it traveled over any sludge. As the bottom rollers were driven, a high level of traction was desired between the bottom rollers and the bottom forcing cone. Thus, the bottom rollers were fabricated with grooves so that o-rings could be easily put on them; increasing the coefficient of friction between the bottom rollers and the bottom forcing cone. In order to get all of the o-rings on to the bottom rollers, they had to be 3D printed in two separate halves (Figure 34). As mentioned, both top and bottom roller sets utilized set screws to secure the rollers to their drive shafts. Since the bottom roller was two different parts, a set screw was required for each roller halve (Figure 35). The top roller on the other hand only required one set screw since as it was one solid piece. 

The suspension system of the top-guiding rollers (Figure 36) was an essential element of the ROBO MAT design. As discussed, the top rollers were vital for cart alignment in the bore as the cart traveled over any residual sludge on the forcing cone. To guarantee that the cart would not jam, the top rollers needed to be spring suspended. As the cart would travel over sludge it would experience translation in the vertical direction. Without the springs this vertical translation would cause the cart to jam. However, with the springs the top rollers would be pushed down, while remaining in contact with the top forcing cone. The top roller’s ability to allow the cart to travel over sludge, while remaining in firm contact with the top forcing cone ensured center alignment. Each top roller suspension system features two rod ends with bearings to hold the top roller rotary shaft. Furthermore, each rod end had a threaded set screw hole (Figure 36) so that said rod end would not be pushed out of the chassis by the spring. The ideal spring constant for the top roller suspension system was determined from a Workingmodel simulation (Section 4)

        Fig. 2  Top Roller Assembly Outside Chassis                                                  Fig 3. Top Roller Assembly Inside Chassis