Ground Station, rover ver 6, clearance, solar power harvesting surface.
Last week was spent in redesign of a rover and ground station. It was done by three main reasons – a) ground station needs to be build and 3D models for 3D printer has to be finalized. b) clearance of a rover needs to be increased. c) needs to increase solar power harvesting surface. In old design on frame was mounts for flexible solar panels (cells). each cell has size 25.4 x 63.5 mm = 16 square centimeters. length (long side )of the frame was 600mm, that gives a place for 23 panels with total surface of 0.037m^2 two frames allows to use 4 times more - total 92 cells, or total .14 m^2 with efficiency of 0.09(9%) and power of a sun per square meter = 1000Wt surface can give 13.35 watt total. Top side of a rover can harvest some energy, but at the same time bottom did not, it is in shadow – outcome power probably is half == 6 watts. Solar panels mounted on frame with 45 degree angle. Problem (b) frame is not flexible, in can stuck on terrain - as a result needs to increase clearance. Second problem (c) - needs to increase harvesting power surface. (6 watt capable source with 40% efficiency of a 10 watt transmitter, means that transfer of data can be done only in 1 minutes with another 3 minutes 20 seconds waits to harvest the energy. Flexible solar panel side is 63.5 mm. Assuming it is hypotenuse - that geometrically gives in prime triangle with 45 degree angle, side sizes 45+45mm – which is bigger that original 63mm. Sizes of each cell will be smaller (like 25.4 mm x 44.9 mm) but on same frame now it is 46 cells with 0.052 m^2. On 2 frames can be placed 4 groups of 46 cells, calculating same efficiency and same Sun’s power, that surface allows to harvest total 18.8 watt. Same top-bottom and max outcome power is 9 watt. That is better, than previous design, and it mean == 1 minutes to transmit + 2 minutes to harvest. Placing additional 2 stand (length 0.5m) which can hold 19x4 = 76 small size panels outcome additional 0.17m^2 with total power 15wt (and half of tit is 7wt). Gives the grand total is 34wt from all surfaces, and halfing gives max s 17 watt power. Which is not bad – on top of each minute to transmit it will require 35 seconds to harvest. Now the question where to place that two stands. Plus needs to balance weight- i.e - 350grams for each 4 stepper motor, but gear motors can be reduced to have less torque. That can save around 50-100 grams on a motors in favor for stands. Reducing clearance makes smaller dimensions and also saves weight. Total amount solar cell (sizes 45x25mm) to accommodate on rover today is 168. With weight limit of 400 grams for all system it is 2.3 grams per flexible cell including weights of holders and mounts. Plus needs to account that after 3 week flight cells will lost 1/2 of it power capability. Realistically it will be 8 watt of power at best. That is a theory – up today Ground station's 3D models probably ready to be ordered, but rover's energy harvesting mounts not finalized yet.