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Feb 23 2011

Hexakopter Suspended Payload Tests–Results

The results of our Hexakopter payload tests were better than expected!

You can see a few clips from the test flights here: http://www.youtube.com/watch?v=OZlamfvl3VU

Basically, we suspended a 1.5lb weight from a metal cable, dangling about 12 feet below the Hexakopter.  We tested take-off, landing, auto-controlled hover with GPS and altitude lock and waypoint flying.

We found that the onboard computer can fly the unit with payload better than I can and that it performs very well at staying balanced despite a pendulum effect from the payload.  The unit appears to dampen this effect after a few seconds and in periods of calm wind the whole rig appeared virtually motionless.  In an auto-hover test, the unit lasted about 12 minutes before reaching the battery limit, it is expected that this time would be a bit less in a real flight.

Overall, a successful experiment and a great day to be out in the field!

Feb 17 2011

Hexakopter Suspended Payload Tests

How well will a Hexakopter work at carrying an instrument payload suspended several meters below?

That is the question we will be trying to answer in the next few days as we get ready for some work for the Forest Service. The goal is to suspend an instrument payload several meters below the Hexakopter on a light-weight metal cable. The payload will weigh about 1.25 lb (0.56 kg) and needs to be far enough away from the Hexa to avoid the effects of downward prop wash. The payload and Hexa will be flying through smoke and we want the instruments to be unaffected by the Hexa itself.

I purchased some 1/16" (~1.6 mm) braided metal cable, some ferrules and some clips from the local hardware store to build the suspension system. I am going to use a 'calibrated' water bottle in place of the instrument payload for weight.

I am going to test:

1) At what distance below the Hexakopter will the effects of prop wash be non-existent / negligible? This will be done in the field by flying a Hexa above a pole with flagging tape on it. This distance will be referred to as X meters.

2) Can the Hexakopter fly in manual and auto mode with a 1.25 lb payload suspended at X meters from a 1/16” metal cable? This will be tested by performing take-off, manual flying, auto-hold, auto-waypoint flying, and landing with the payload attached. Results will suggest total success or a range of flight performance. It is expected that wind will play a significant factor.

3) How long can the Hexakopter fly with the payload attached? This will be tested by first getting the Hexa to altitude with payload and letting it to hover until the battery is at the minimum safe capacity. Then, with a fresh battery installed, it will be tested by flying a simple ‘back and forth’ route over the flight area to simulate increase battery demand.  It is expected that there is a great potential for pendulum affects to occur during flight.

Stay tuned for some results!

UPDATE: I forgot, one of the main Hexakopter videos shows Holger doing his insane Hexa flying witha 1kg soda bottle suspended from below.

http://www.youtube.com/watch?v=gvH2f-AewX8&t=8m0s

Oct 22 2010

Weekly Flight Progress (Week of 10/17/10)

This past week I got in 3 good flights at UMBC and New Jersey and learned a lot more about how to get things working well.

The first flight was at the pine barrens site in Pemberton, NJ.  I arrived at the site on Saturday to scout things out.  I met the local forest researcher Ken Clark and he showed me around the plot where I would be flying and we checked out the forest from atop a modular tower used for making meteorological measurements; I was not crazy about climbing the tower, but Ken had no problem.  I was up at 6am Sunday and at the site by 7:30.  By about 8am I had inflated all of my new huge 3' diameter balloons and set out to place these new aerial markers in the field.  This ended up working pretty well, although I think I put a tiny hole in one balloon and several balloons popped between the time I set them up and when I went to retrieve them.  It was gusting to about 13mph (according to the local met data, thanks Ken!) and the balloons blew around and into the trees throughout the morning.  Overall the flight went well, but I think that because of the gusty winds, the Hexa got blown of course several times and we may have issues with image overlap during the 3D reconstruction. Site prep took about 3 hours as it was more challenging to place the balloons in the field than when I am just using buckets on the ground.

The next flights were both on Thursday at the UMBC Herbert Run location.  I had everything set up by about 11am and then commenced with flight testing.  I think it is a good idea to use a spare battery for testing out the flying conditions on site prior to the actual image collection mission.  I found that the GPS and altitude were holding well, but that it was still quite windy.  At this site I use buckets instead of balloons as they are more stable and there are more open areas to place the buckets.  Things went well on the first flight, but the Xbee inexplicably cut out quite often.  I thought it was odd that the Xbee cut out so frequently because there was almost no data connection problem at the New Jersey site earlier in the week.  Also, it was apparent from the Garmin Astro track that the route was being affected by the wind.  I landed the unit after the flight and swapped in a new lipo, new camera battery and new camera memory card and proceeded with another flight at an altitude 40m above the first flight and along the same route.  The track of this flight showed a similar pattern as the previous one.  I posted more about the flight paths and looking at the tracks in an earlier post this week, here.  In all I got in two full flights in under an hour, by myself, with about one hour site prep. 

 

In summary, I had three good flights this week that I setup and flew on my own.  It looks like at each flight winds above 13 mph may have caused the Hexa to deviate from the flight path, hopefully not to the detriment of image overlap.  I think the procedure for preparing gear and setting up the site is finally getting honed down to a smooth operation.  And thank goodness for my station wagon!