As a follow-up to the rover drops #1 and #2 I spent a day with Assistant Professor Nagatani-san of Tohoku university in Japan (and his students) and Izu-san of EnRoute (a company that specialises in Industrial use multicopters and hobby use RC vehicles here in Japan and China) at Karuizawa's Mt Asama attempting to autonomously drop a 2.5kg rover from a large (4kg+) EnRoute "ZionPro" hexacopter.
The flight was completely autonomous including activating the servo release which held the rover to the hexacopter (we used the camera shutter release). After being released the rover was "lowered" on a 30m wire wound around a brushless motor which was meant to slow it's descent (with mixed results). If you've never heard of this mechanism before, it seems if you connect the bullet connectors of a brushless motor together it resists being turned. If you attach a resistor between the bullet connectors it will resist less strongly. In this way we could somewhat adjust the speed at which the rover descended at.
- the altitude reported by a Ublox GPS (i.e. APM/PX4) vs a hand held GPS can vary by 10m.
- the altitude reported in google maps (and thus the mission planner) can vary by 20m from reality because they only provide the average altitude for the area. I'm not sure how big that area is but we found that google maps altitudes could be high or low from reality depending upon where you were on the slope.
- trying to drop from a wire is tough! we need a more reliable system for the next test. Maybe use a range finder to get the copter closer to the surface without hitting it or perhaps measure the motor output to determine when the dangling rover has reached the ground.
- the hexacopter and battery were more than sufficient to carry the rover the 600m covered in this test. At least twice that distance would have been possible.
- AC3.0.1 is very capable of the accuracy required for this mission. It was a thing of beauty.
There will be one more attempt within the next 2 months which should be pretty much the same except the distance will be further and the dropping mechanism will be improved!
Thanks and all comments, input welcome!