I have been doing some testing (outside the US) that involve very high altitudes - 1800 meters or more. The climb takes no more power than coming down. Even though going up takes more power per minute, coming down is slower, so the total power consumed when coming down is easily equal to the power going up.
I was thinking that it would be more energy-efficient to shut off the motors at the highest point, and letting the quad free-fall and then turning the motors on again at 30 meters or so to right itself and slow down for landing. Has anyone tried this? I have been told that dji can do this.
I'm using APM and PixHawk controllers.
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If you are going for an altitude record, does it need to land? I mean, can you just go up as high as possible until batteries fail and then let it come crashing down? I'm not necessarily suggesting that, as it involves some potential dangers. But in an unpopulated area, like some remote parts of Nevada, it might be alright. Of course, it would cost you the cost of your aircraft, but to break a record may be worth it.
I would think that at record breaking heights, a parachute, even if deployed at lower altitudes would still be high enough to potentially, and likely, drift in the winds. Since there is a very good chance it would be lost, might as well not add the weight of the shoot and let it come crashing down. Again, not actually recommending it, I'm just bringing it up for discussion.
When the Model Rocketry clubs come to the Dry Lake Beds here in Nevada, they get special permission from the FAA to do record height flights with their high power rockets. That would be a perfect time to hook-up with such a club and go for a legitimate altitude record!
That was my plan, once I figured out the best way to do things. I have some tricks up my sleeve to go really high.
BTW: Long ago, I used to be a member of a Rocket club in Iowa. We built our own rockets and motors and used GALCIT58 (asphalt and oxidizer) for fuel. Check out Rocket Manual for Amateurs by Capt. Bertrand Brinley.
Love the Rocket Days! My wife was really into building and flying rockets.
This is my beast that will climb at 30'/s or 1800'/m. Imagine the altitude possibilities with a 35 - 40min flight time. And that's enough time to go up and come down under control.
http://www.rcgroups.com/forums/showthread.php?t=2274072
Skip to 1:06 to see the actual hex.
Nice build. I am a 'junkie' and have around 10 quads and 1 hex. The one that I sent up to 1610M was just a little quad. It also climbs at 1800'/min. Current draw when going up is approx 50A, coming down, approx 20A. 4 cell battery, 6600 mAH.
If you are bragging about flight times, I should pull out my quad with 18" props, 510KV motors, 4 Cell. Homebuilt CF frame that weighs 660g (bare). Over 60 mins airtime. It won't climb as fast, though.
Depending on your quad size it may be possible but when stabilization is turned back on it will stress the hell out of the quad. A lot of variables here to say it will be safe, unless its a strong acro quad with carbon fiber or composite props I wouldn't even think about it..
With the latest generation of ESC's with active freewheeling enabled, "right side up" descents are very fast, much, much faster than without it enabled. You may even be putting power back into your battery with active freewheeling. Simonk has it and so does blheli.
Like other have said, doing a controlled dive is much safer but since you are flying beyond visual sometimes you may dive the wrong direction. Depending on your setup, even a dive may cause failure. Been there, done that! Good luck
What mode were you flying in? You mentioned that you wanted to go straight up and straight down, if you were in Loiter or Alt Hold, you are limited by your max vertical speed parameter. When I'm in stabilize mode, I descend like a rock at minium (not zero) throttle. I have never ascended to 1800m, but from 120m I would estimate 5-7 sec to the ground. It really sounds like your descent is being limited.
I was flying in AUTO mode the entire time. The max descent (in Mission Planner) is 500cm/sec. I set mine to 450 and it wobbles quite a bit on the way down.
The wobble can be reduced by forward movement. In auto mode, I would create a descending spline circle. However, to increase your speed coming down, you will need a different mode. Before thinking of turning off motors, I would try descending in stabilize, using telemetry like an instrument flight. Be wary, coming down fast you may need more than 30m to slow down.
I've done that with my tiny $98 plastic quad, it recovers quickly, It'd probably take a larger, heavier copter longer to recover and you may want to make sure your battery is well secured or the copter my throw it out when you throttle back up, and it may put undue stress on the copter's arms, but it might work.
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