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.
A couple of things that we learned from this test in case you try something similar:
- 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!
Comments
Very cool. I loved the machine vanishing into the mist (onward, brave little traveler!) and the reappearing at the target.
Why wire? Why not some strong synthetic?
How do you program a landing with a first descend speed until altx and then another descend speed until toich down ?
Randy, here's another suggestion: Maybe the rover-release function could be allocated to the rover, which would release itself from the line when an on-board sonar sensor determines it is close enough to ground surface. The quad/hexacopter could have an attached spool of a known length of fishing line (with the copter end securely fastened), and a loop of line at the other end that slips over the shaft of a small solenoid on the rover. When the copter is in the desired location, it slowly descends until the rover's sonar triggers the solenoid, releasing the line and allowing the rover to drop to a surface. This approach could minimize the risk of damage to the rover, and maybe less risk of it tumbling down a slope.
several blogs ago there was a airplane that looks allot like a military drone, cannot recall the name, the four motors can rotate for forward flight or vertical flight.
hey Arthur, the copter that transitions into an airplane, is that custom code?
i am surprised after the first wire break you guys did not immediately scrap the wire and use a different material like fishing line which is far far stronger
How about a very small fishing reel? They usually have adjustable drag.
Perhaps it is better to give the rover a simple and weak multicoptersetup as well (quad/tricopter). I just think of weak and light motors and a simple flightcontrol. Just enough to level it and brake the fall to an sustainable impactspeed. Just a crazy idea..
Can we not use any of the free topographic mapping data available from various sources? Wouldn't this be much more accurate than the GE data? I have topographic maps available for my area, and I think it's much much finer than a 90m grid.
The google maps DEM (Digital Elevation Model), is collected for most of the world at 3arc/sec, that means 90x90m grid and the data between the grids is interpolated to provide a smooth result. The interpolation seems to be really well done (I did compare google Dem data with an survey D-GPS on an wide hilly terrain) and in most of the sample points the deviation was between +-1.5m. For some country you can have access to 1arc/sec data, that means 30x30m grid, to see if your country is covered check on NASA website.
Said all that, the drone I use to do magneto metric surveys use a laser altimeter to asses the altitude from the terrain, none of the D-GPS RTK + DEM data did work that well.
I will suggest you to buy a sonar or if you budget is not tight a laser altimeter.
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