After seeing Thorsten's post I was quite jealous about the flight times he was getting, so I was really excited when we got in a 53 minute flight yesterday with a new modified copter design here in Panama.
I am down in Panama on a post-doc with the Smithsonian Tropical Research Institute (STRI) to use copters, Ecosynth, and other remote sensing and computer vision technologies to improve our understanding of tropical forest canopies. My stay here is supported by a STRI grant that emerged directly from my work here last year.
I came here geared up to build two Ecosynth-style (aka Gienow-style) Mikrokopter / Arducopter -hybrid copters in an Octocopter configuration. My build consists of MK frames and 3DR / Pixhawk electronics along with MaxAmps 22000 mAh 14.8V lipos, with which we were getting solid 34 minute missions with about 9 minutes of battery life to spare before the alarm started buzzing at 3.3V per cell. This was enough time for us to carry out a round trip 12.5 km mission while at the same time traveling up to 330m altitude and back (ceiling here is ~600 m) carrying a standard Ecosynth payload of Canon ELPH 520HS, Canon WP-DC340L Waterproof case (no longer in stock in the Universe :( ), and Garmin Astro DC50 dog tracker - total weight about 600g. Assembled copter pics here and here.
And we were getting in some great missions over 'The Island' up until I moved the DC50 GPS antenna to try to improve signal which I think resulted in a modified electrical field around the 3DR compass, resulting in a wicked crash, so sad. Fortunately it was the improved signal of the DC50 that allowed us to recover the copter over 1km away in jungle. 1500 hectares of forest and trees and it lands in a creek! We lost 7 of 8 arms, all the props, both center plates, a battery buzzer, and a landing leg, however I plunged all the electronics into tubs of dry rice for 3 days (camera included) and it appears that all of that is working ok.
This leads us to the new long flight times. I lost 7 arms and only had 6 new spares (it was all the stock in the store at the time of my purchases). Struggling to find a solution for the rebuild, I thought, "Why not a Quad?" These motors should produce enough lift for our standard payloads and taking off four arms (motors, escs, arms and props) saved 800 grams total. The existing Gryphon PDB made the new config easy. After a total reconfig of the parameters (Pixhawk firmware, accelerometer, compass, compassmot, PID Autotune, which by the way are all getting super easy, thanks Ardu community!) we were up and flying. We strapped on a 22000 mAh lip and carried out our 12.5 km test mission over our test area (18 700m length laps).
The new quad (Mediaocho "half of eight") performed well, especially considering the high winds (about 12 km/hr). It completed the main mission in about 34 minutes, just like the Octo (same WP_NAV speed, 7 m/s) and then just before landing in RTL mode I switched to Loiter and just waited. And waited. 43 minutes passed (our max flight time with the Octo on the same battery and same mission) and it was still flying. It kept going until the buzzer started going off at about 52:50, and by the time I brought it down to a stop and zero throttle, the timer was at 53 minutes.
We are thinking that this will allow us at least 15km missions, including up and down 300m of elevation. It might even have slightly more flight time considering Translational Lift, which Stephen tells me could make it more efficient for the copter to fly long straight lines than to hover in one place. In addition, the copter makes 74 turns in our test mission, each one costing about 5 seconds were the copter has to slow down to about 2 m/s to get through the turn, whcih is about 5 times more turns than we make in a normal mission and which might be costing us another 5 minutes! Does this mean we have a potential maximum of one hour flight time? I can't wait to find out.
Here is our parts list for the Mediaocho Quad:
Base Weight: 1400 g
Flight Weight (+lipo, no payload): 3120 g
Total flight weight with standard payload (camera, case, tracker): ~3700 g
Granted, I am sure there are places to reduce weight and cost, but this config appears to be working great. We start photo mission tests next week. Stay tuned!