Dropping a Rover from Hexacopter - Part III

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.

3689544037?profile=original3689544065?profile=originalA 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!

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  • Developer

    Hi Euan,

    Yes, sorry.  I haven't forgotten.  I was leaving your friend request there as a reminder to myself.  Soon for sure.

  • HI Randy,

    Just a reminder, I need the arducopter build with the EPM code in? Was hoping to demo my payload system this weekend. Oh, and to accept the friend request ;)

  • Really enjoyed the video. I am assuming that the event at 6:33 was due to the differences in reported altitudes as described earlier in the post. Thanks again for sharing.

  • Developer


         We are using these EC5 connectors.  I originally swapped them out for Deans but with the high voltage of a 6S the arc when I plugged in the battery was just too scary so I went back to the EC5s.


         Sounds like I'm passing the buck but I wasn't responsible for the dropping part except that it had to be triggered automatically from the arducopter.  If it was totally up to me I would probably just carry it on a fixed length of wire and then build some smarts into the arducopter so that it can sense when the weight has hit the ground (because the load on the motors would be reduced a lot).  You'll see in the video below that on the more recent attempt the unwinding wire method it actually worked!

    This is the last flight in the series which went pretty well.

  • That's what I was thinking, A lot lighter. Or even small quad rotor motors and props to lessen the drop speed that. The rover could use that only for decent so there would be lots of battery left over for the mission. The quad; not for lifting or flight could at least offer thrust vectoring in a way offer a precise drop to the drop zone.

    However, that being said, Ray Snipes has the cheapest, simplest and lightest option. {K.I.S.S.}

  • Just curious..... But why use a wire to drop? Wouldnt a parachute be more practical?

  • Hi,

    Your build is similar in size to mine, what connectors are you using on your 6s. I was thinking to use Anderson PowerPoles 45Amp, but I fear they might be too small.

  • I still think mechanical drag is how you control the drop rate on the rover.

  • Developer

    @Hugues, re different landing speeds above and below 10m, I'm afraid AC is hardcoded so that it uses the WP_SPEED_DN when it's above 10m above home and LAND_SPEED when it's below that altitude (or once the sonar detects something below the copter).  We do have a DO_CHANGE_SPEED mission command but that only applies to the horizontal direction.

    There's also a do-set-parameter mission command but it's disabled because it's difficult to use (you need to know the parameter's index in the eeprom) and slightly dangerous.

  • Developer

    @Jared, the first test with the wire was just one day before the actual rover drop so there was no time to completely replace the method.  Certainly something's got to be done to improve the reliability!

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