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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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.

You could use a helicopter instead of a multirotor, and then just auto-rotate on the way down.  Controlled descent rate, full attitude control, zero power consumed.

Did you see this video?

https://www.youtube.com/watch?v=-Db4u8LJE5w

"Interlock" might be just the feature you are looking for...  unless it too disarms the multirotor like emergency stop.

I am flying a 3DR Y6 and do it often while in Stabi-mode: Completely cut the throttle and let it free-fall and recover nicely. It might be the solution: once your auto-mission is complete, you return to Stabi, cut the throttle and let it fall to say 50 Meter and catch it. Mind you though that the copter might disarm if in idle for too long !

Now THIS is intentionally shutting off motors and recovering at the last second :)

https://www.youtube.com/watch?v=RPGUQySBikQ

No proper footage of yesterdays landing yet from geostationary launch, would love to see an onboard view from start to finish!

I didn't see it,and thanks for the link.  As I mentioned, I have modified several of the libraries in APM, so I could modify what the firmware does if I needed to. I try to modify the code as little as possible to avoid unintended consequences, but now and then, I come up with what I think is an improvement. I'm a bit reluctant to send the mods to GitHub, because I don't want anyone else to say that a mod that I made caused a problem for them.

I have been playing with what happens when the motors are spinning in reverse. I have a test setup that runs a motor/prop combination a few inches from my 'test unit'  I spin that up which puts a lot of air by the UUT and spins that one backwards.  I then apply power to the UUT and see what happens.  So far, I have only tried one (cheap no-name) ESC,and the results weren't good (luckily, I have a 20A fuse in the power lead). I'll try a couple others and see what happens.

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