Stardust Digger

grabcad

Update in reopened period: A very interesting video of the drum, which was simulated by dd008c74, can be seen here - with smaller balls, the filling ratio is near to 100%: https://youtu.be/DQ-GpTodRec The "STAR DIGGER SIM2" MP4 file is included in the entry. Overall dimensions, material and mass of the drum are as follows: Diameter – 450 mm, Length – 360 mm, Material – duralumin, Mass – 4.47 kg. Inside volume of the drum: Diameter – 356 mm, Length – 352 mm, Volume - little more than 35 liters. The drum is a single welded or soldered construction without moving parts. It has one scoop that can collect regolith along its whole length. The outer helical blades help to scrape and direct regolith to the scoop. Captured regolith distributes further inside the drum's cylinder, forming a helical guide for regolith to go to the sides while the drum collects. In fact, regolith enters a tube folded like a ring. The inlet section is a rectangle with dimensions 116x45mm, and the outlet section (inside the cylinder) is a rectangle with dimensions 348x45mm. This design was found to work after many versions of the geometry – spirals, helices, shields, and so on. Simulations show that such a solution works and meets the requirements. Something notable is that all captured regolith stays inside while digging. There are three simulations with 20 mm balls illustrating the work of the bucket drum and one simulation with 8 mm balls. In first 3 simulations: Speed of drum – 20 rpm, Density of regolith - 1.5 g/cm^3 or 1500 kg/m^3, Moon gravity – 1.62 m/s^2, Diameter of the balls used as particles – 20 mm (density 1.5 g/cm^3). In first simulation of filling and emptying, a surface model of the drum and 20 mm diameter balls were used; a source of balls was defined, which rotates with the drum, and starts "giving birth" of balls when the scoop is at the bottom position. This birth continues ¼ round until the scoop reaches horizontal position. With such a way of filling, it can be seen that the fill ratio for the inside volume is more than 50%. This means that captured regolith will be more than 35/2=17.5 liters. The process of filling takes about 54 s (18 rounds) and emptying – about 33 s (11 rounds). Second simulation shows deep digging; here the fill ratio, as can be expected, is even more than in previous simulation, which means that captured regolith will be more than 17.6 liters (the volume of cylinder is 35 litters). The work of outer helical blades can also be seen – they scrape and direct regolith to the scoop. Third simulation shows the maximum possible filling of the drum with 20 mm balls. In this simulation, the drum is buried in a box full with balls. There is also a fourth simulation with 8 mm balls! With these smaller balls, the fill ratio increases to nearly 100% or it can be said that the drum can collect 35 liters of regolith.