Figure 6 shows post-test images of a cam of identical geometry, material and surface treatment as the  flight unit cam vibration mechanism. This cam, along with a flight-like bumper was tested in a Mars  ambient environment to approximately 780,000 revolutions, two times the required life of the mechanism.  The test was performed in several segments on a prototype ISAD with similar sample transfer plates and  geometry as the flight ISAD. After each segment, a known mass of dry sample was placed in the rear  chamber. Using the cam vibration mechanism, the material was transferred to the front of the scoop,  where the mass was again measured. After a demonstration of two times the required life, the efficiency  of sample transfer using the cam vibration mechanism did not show any signs of degradation, remaining  at 90% or greater. As shown in Figure 6, there was minimal wear to the surface treatment at the end of  the test, preserving the cycloidal geometry and the ability to produce vibration. The bumper showed  similar minimal signs of wear. During the lifetime test, a witness plate was used to capture the material  worn away by both cam and bumper. Comparing the measured mass of the worn material to the total  calculated mass of the “ramp” portion of the cam, less than 10% of the ramp was worn away. This  combination of material and geometry produced a cam vibration mechanism, which will continue to  generate vibration well past the required operational life.  Before Testing After 1.0 Hour Test After 2.0 Hour Test Cycloidal Cam Geometry Figure 6. Cycloidal Cam Geometry Small Form Factor Braze Joint for High Load Capacity The cutting bit of the ISAD is a modified commercially available tungsten carbide rasp bit typically used in  ceramic tile applications. A consumer rasp bit was selected due to budget and schedule risks associated  with designing and testing custom cutting bits. A variety of bits were tested early in the design process,  and a selection was made which provided the best sample production performance in dry analog material. For assembly purposes, a decision was made to vacuum furnace braze the cutting bit to a  stainless steel shank to allow the use of threaded fasteners as a connection mechanism.  The ISAD cutting bit protrudes from the rear of the scoop when in the rest position. This results in  exposure of the bit to potentially high loads during trench digging operations, and icy surface scraping  operations with the secondary blade. As shown in Figure 4, during digging or scraping operations, the  ISAD is translated in the “X” direction. To reduce the risk of damaging the bit and drivetrain during these  sequences, the Pivot Housing is designed to retract automatically into the scoop if inadvertent loads are  applied to the bit while digging or scraping. During these operations, loading of the ISAD is not limited to  the X-Y plane. The Robotic Arm can impose lateral loads in the ISAD “Z” direction of up to 50 N. There is  no retraction mechanism for the cutting bit to absorb loading in this direction, and although the lateral  loads are small compared to those sustained by the structure in the X-Y plane, they are large enough to  risk damaging the brazed connection of the cutting bit.   The ISAD cutting bit is only 6.35 mm (0.250 in) in diameter, due to limitations in the amount of torque  available, and the desire to run at high speeds to increase sample acquisition productivity. This limited the  selection of braze joint form factors to those that could be fabricated with the amount of material available  on the cutting bit shaft. Due to the high speed nature of the design, minimizing shaft runout was desirable  to reduce imbalance of the mechanism. The exposure to high lateral loads, and the brittle nature of  tungsten carbide added further complexity to the design. A number of distinct features were incorporated  into the braze joint design to minimize stresses in the connection while maintaining shaft runout between  the cutting bit and stainless steel shank. These features can be applied to brazed connections for similar  high speed, small form factor applications.  297