Nasa RASSOR bucket challenge entry

grabcad

• Dimensions o Drum length = 358.8mm (excluding gearing) o Drum diameter = 450mm • How it works (assembly shown in animation "v2.avi") o Each drum consists of 3 barrels, each 120mm deep and with a ~120mm scoop that bites into the regolith followed by a single curved wall to prevent material from falling out. The center of each barrel is a reservoir with a rotating hexagonal rod turning a paddle that lifts regolith higher into the bin with each scoop, allowing a void to form that new regolith fills into. Without the paddle, friction in the barrel becomes too great for the loose regolith, causing the scoop to become blocked and pushing regolith out of its path instead of letting it flow into the barrel. The central hexagonal axle is what the drum pivots on and what holds each drum to the arms, as well as what moves the paddles. While the drum rotates one way, the hexagonal axle rotates in the opposite direction through a series of 3 gears. The outside gear drives the rotation of the drum, the central gear is driven by a motor that powers the entire system, and the interior gear turns the hexagonal axle to drive the paddles.• Material --> using these materials, a full-size prototype could weigh under 5 kilograms o Aluminum  The teeth on each drum, axle, paddle, gear, and where the axle interfaces with the barrel side walls would be made of aluminum. o Composite  The sides of the drums would be made of carbon fiber 6K harness satin weave to provide a smooth and durable surface. o Fasteners  Assembly would be mostly completed with solid rivets to minimize weight and minimize the area for a rock to get stuck on. • Testing --> video shows test 3 o Model built at 1/5 scale o Test 1  Collected 40.5mL  49.7% of drum capacity was achieved o Test 2  Collected 41 mL  50.35% of drum capacity was achieved o Test 3  Collected 41.75 mL  51.27% of drum capacity was achieved o Results  Average test result: 50.4% filling of drum capacity  At full size, the drum should have a capacity of roughly 18.7L• Design improvement (based on test article) o Material  All parts were printed out of PLA • Walls needed to be a certain thickness to work; thinner materials could work better than PLA • Gears were printed and hand filed for proper meshing; machined gearing would minimize friction.  Gear sizes • Printed gears had minimum size limitations, but metal gear trains could stay the same size as current gear sizes even when scaled up to full size, allowing them to fit inside the arm and be sealed from regolith entry. o Gearing ratio  The current gearing ratio has the paddle moving at a different speed than the drum; a different ratio could have the drum and paddles move at the same rate, allowing the paddle to always be in optimal position while using the scoop. o Central axle  A circular axle with paddles welded on it would provide a better bearing surface.  The hexagonal axle was printed for rapid iteration and minimal gluing during development.