Maiden Flight of Stephen's Long Endurance Hexa Design

Hi folks,

this is my first post here. I was looking for some UAV for mapping and same as Gerard Toonstra came across Stephen Gienow's great "concept design for a long endurance hexa".

And here it is!

I'll post more details within the next weeks.
Here is a video of the maiden flight(s) of this configuration under windy conditions:

Thanks a lot to Stephen for posting this setup and for his help!

Thorsten

Views: 1566

Comment by Erle Ellis on August 29, 2013 at 9:52am

Wow!  Want one for sure!

Comment by Thorsten on August 29, 2013 at 10:07am

Yes, it should be able to do a 30 min image acquisition mission now. I will test a waypoint mission next week. Concerning endurance the Maxamps 11000 mah packs should be worth testing - either one or two. However I came across this post: http://www.rcgroups.com/forums/showthread.php?t=1761789 But it sounds that for Stephen's design it should work.

Comment by Stephen Gienow on August 29, 2013 at 1:25pm

Interesting link.  I was surprised to find out that those maxamps batteries (I have had my eye on them for a while, they are supposedly the best lipos you can get for RC flight) are only 5C continuous.  That means they are rated for 55 amps of current.  Of course, if you use two in parallel, then the lipos split the current equally and you can pull up to 110 amps!  Those 11000mAh paks are pretty hefty though, I would be worried as to whether this copter has the lifting power for them.  Thorsten perhaps as an experiment at a later date, you could subtract the weight of your lipos from the weight of two maxamps and add that amoun of weight to the copter as ballast, to see if it is physically capable of carrying that much weight.  If so, 22,000mAh would certainly keep us aloft for a good long time!

Comment by Thorsten on September 12, 2013 at 10:15am

After changing the ESCs two times since my last post (now I have some flyduino 20A ones), balancing the props and motors more carefully and some further tuning of the PIDs the hexa is flying again: rock solid - stabilize and loiter! However, there is one problem. The copter yaws CCW when I speed up (throttle). It might be one of the motors. I will record some logs tomorrow if it stops raining... 

Comment by Gerard Toonstra on September 12, 2013 at 9:44pm

Well, can't stay behind in this post. I had to wait out 4 weeks for the motors to arrive, but here's the completed build:

I'm using rctimers 5010-14's and did buy the big maxamps battery, which I plan to use only for actual jobs and the endurance test planned for saturday. AUW is a confirmed 2563g with maxamps battery and 143g camera payload (IXUS-230HS), which theoretically yields 36 minutes of flying time in hover according to my calculations. The hardware is what Stephen spec'd out.

Interesting here is to read the practical achievements from Steve Westerfeld in comparison to my calculations. He squeezed 42mins on an AUW of 2800g with 12000mAh. (the batteries are a lot heavier, yet no payload). My calculations for such a setup however show 35 minutes flying time. Since my hardware is essentially the same, I would be disappointed if I didn't get 41 mins with payload and 46 minutes without. Saturday will make that clear.

This makes one thing clear. Once the frame is chosen correctly for its purpose, the biggest gains are had by choosing the right battery. The lower you go in C-rating, the lighter a battery becomes, but the lower your acceptable AUW becomes as the battery can't deliver the current. The maxamps is claimed as 825g, but I weighed mine at 852 instead. My 4Ah/4S is 418g. So the 4Ah one has 9.57 mAh/g vs. the maxamps at 12.91 mAh/g. If there's an interest in understanding more of the theory behind this, see: http://www.rcgroups.com/forums/showthread.php?t=1880665  . This guy soldered his own Li-Ion batteries together (tricky!), which yields a pack that delivers 13600mAh @ 770g : 17.67 mAh / g.  He doesn't have payload though and those batteries are 2C, so for heavier setups like hexa's they're not suitable, probably only for quads.

I also checked (theoretically!) what happens with 2 maxamps. It doubles the current for each motor, brings AUW to 3460g with flight time approaching 48 minutes, vs. 36 minutes theoretically now. Motor temp, ESC max current and battery delivery are still well within limits though. After 2 batteries there's no more gain in endurance from more batteries. The graph flattens out until the amount of calculated current through the motor exceeds the specs or throttle reaches 80%. With 2 batteries lift-off throttle is calculated at 50%.

Comment by Thorsten on September 13, 2013 at 5:23am

I recorded a log file this morning and posted the results at the DIYDrones forum.

I will make a second endurance test with the new ESCs, PIDs and balanced props later today. Can't wait for Gerard's results!

Comment by Thorsten on September 13, 2013 at 7:40am

OK: so with 13.85 V (log file data; Droidplaner reported 14.2V and 23%) left I have a new flight time of 33 min. At that some failsafe (RTL) was initiated. I have to check... It was pretty windy and I most of the time the hexa was in loiter mode.

Gerard, can you please make a test and enable motor logs? It seems the CCW props are less efficient compared to the CW props...

Comment by Gerard Toonstra on September 13, 2013 at 8:05am

Good idea. I'll turn that on. Where did you get the props from, link?

I've also run a calculation on your build now. I'm getting 28 minutes hover time for yours, again 5 minutes short of actual flight time.

Comment by Thorsten on September 13, 2013 at 8:38am

The props are from RCTimer - same as the motors.

There is another problem with the props as you can see here:

DO you have the same problem?

Comment by Gerard Toonstra on September 13, 2013 at 12:57pm

I mounted mine and don't want to take them off, but the centers of the screws line up pretty well. It's not 100% conclusive, but they seem allright. I have the exact same props, note there are two different models. One is this shape with variable chord, the other is more evenly shaped on the chord.

I had a problem on the motors though. The distance is correct luckily, but the disadvantage is that the screw grips on the side and not evenly distributed around the circumference:

Last question... how did you make the motor graph on diydrones forum post?

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