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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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.
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.
Even if the motors didn't start counter-rotating, a lot of power would be needed to bring it back to a hover. I certainly notice this with my racing quad, If I punch the throttle after a long free-fall, the voltage alarm sounds for a few seconds even only half way into a flight which reveals the heavier than normal current draw on the battery.
I do this with my racing quad. I send it up to around 100 meters, put it into a crazy spin, power off and let it free-fall for about 6 seconds (disarm is set to 10s plus) then power up 10 meters from the ground, it's a lot of fun. I don't know how the larger ones would handle it, I'd be concerned about the props reversing though. I don't know if escs can startup a motor spinning in reverse without overheating something.
Lowering throttle and tilting forward so that the copter slides into a controlled dive, will bring you down much faster. Going straight down fast will always be problematic since you are flying into your own turbulence.
Completely stopping the propellers is problematic because they might start to counter spin, and this might cause the motor controllers to fail (motor sync) when they try to restart.
Dive example: https://vimeo.com/22205147#t=145
Hello, while I am not sure this is the kind of talk our governments is fond of seeing us have, I think about it as a great thing, would enjoy hearing more while your project unfolds!
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