Drone Efficiency

[redpoint5]

I bought a Xiaomi Mi 4k drone recently and have been wondering how I might extend the signal range. There are parabolic antenna boosters for the Phantom drones that don't quite fit right, but at $3 I decided to see if they could be modified, and to see if it made any difference in range.



After carving the holes for the antenna out, I slipped the parabolic reflectors on and launched the drone. It has a max speed around 35 MPH, but I headed East at 20 MPH. Flying over farm fields, my plan was to go until I lost signal (drone automatically returns when signal is lost), or until the battery hit 60%. At 60% battery, I was at a distance of 10,600 ft, but decided to keep going for 11,000 ft. Finally at 3.8 miles away and 56% battery remaining, I turned around and headed for home. The drone must have been fighting a headwind as the battery wore down faster on the return. At 2 miles out, I got a low battery warning. At 1.25 miles out the drone started fighting the controls to automatically land with 15% battery remaining. Finally, realizing that there was no way to make it home, I positioned the drone over a flat empty patch of grass and let it auto-land, touching down at an indicated 0% battery remaining and 30 minutes elapsed flight time.

I only had to go 0.8 miles to retrieve the drone, but it got me wondering what the most efficient speed would be to cover distance. It takes a certain relatively constant amount of power just to maintain altitude, but then it takes extra power to overcome drag. Anyone have a guess as to what the most efficient speed to cover distance is? The drone travels at 19 MPH when automatically returning home, so I just figured this is close to the most efficient speed.

As to the $3 antenna booster; it worked incredibly well, doubling the stock range. Great proof of concept that a directional antenna can massively boost the range of a 5 GHz (or any frequency) signal.

[freebeard]

I'm not surprised. When i was doing tech support and people would ask about range and direction to wifi hotspots, I'd suggest they get the lid from a wok and hold it in a circle around the antenna all the while pointing in toward it. When the signal spikes, the wok lid is pointing past the antenna toward the signal source.

Anyone have a guess as to what the most efficient speed to cover distance is?

As your experience with the headwind showed, they would be psychic or AI.

Are you going to use that thing for a chase plane for tuft testing?

[Stubby79]

I would think moving as fast as it can relative to the draw on the battery...the battery can probably only put out so many amps before the effective capacity starts dropping off. And maintaining altitude without moving (or moving slowly) is like having your car idle...a waste of fuel.

If you want to test it, you could use a watt-meter to track how many watt-hours it takes to charge it back up. You don't have to completely drain the battery in the process, as long as the distance flown and the conditions are the same each time. Chart it out in 5mph increments or however fine of an increment you are up for doing.

Your other option is to simply run it until the battery dies, at different speeds, to do the same without a watt meter. Meter would be quicker, since you don't have to go as far and don't have to go chase after where it lands when it dies.

Anything else is guessing...

[redpoint5]

Originally Posted by freebeard

Are you going to use that thing for a chase plane for tuft testing?

Many ideas. Recently there has been a cougar spotted around the apt complex. I've been asked to call 911 if I see it, but my idea is to surveil it from the sky.

My buddy has a band that is pretty good, and they make music videos from time to time. Thinking I might take some footage of iconic places in the area to include in future videos.

I like the tuft testing idea, although I tend to buy vehicles with an efficient design to begin with and don't intend to build a boattail.

https://www.youtube.com/watch?v=hZLFWogW5eg

https://www.youtube.com/watch?v=l-apT0Sxg5c

Originally Posted by Stubby79

If you want to test it, you could use a watt-meter to track how many watt-hours it takes to charge it back up. You don't have to completely drain the battery in the process, as long as the distance flown and the conditions are the same each time. Chart it out in 5mph increments or however fine of an increment you are up for doing.

That's my plan now, to simply test it for myself in 5 MPH increments. I'll test by flying at a known altitude to the same distance and returning, noting the ending battery percentage. I'll also measure energy used to charge the battery back up. This should give a pretty good idea of the sweet spot.

Then it's on to a new distance record! JK, but seriously. Wish there were a way to improve aero on a drone.

[Hersbird]

Don't electric motors have the most efficiency at higher rpm? I was looking at building a mid drive Ebike and most people say downshift a few gears once you get up to speed as it runs the motor faster and you get a few more miles on the range. That may be also because your faster (although easier) peddling may be adding more power as well. I suppose you would have to look into propeller efficiency. I know with water propellers there is a point where enough low pressure forms to "boil" the water releasing gas and letting it slip. Air is aleady a gas so maybe fast as possible is fine.

[freebeard]

Then it's on to a new distance record! JK, but seriously. Wish there were a way to improve aero on a drone.

I'm sure there is*, what do you have to work with?

I think the best use for tuft testing would be to put the car on a standard 100ft circle and hover the drone at the center in object tracking mode, zoomed to fill the frame. That way you get cross-wind performance on a short time scale.

For testing, it can orbit a waypoint, can it not? Put it on a 1000ft circle and count laps.

Hersbird — Motors (at least polyphase VFD) have a power curve that rises to a point where it flatlines due to back-EMF. Gears are only necessary so you can downsize the cabling for high-power low-RPMs situations.

edit: convert the props to a Prandtl-D airfoil.

[redpoint5]

Originally Posted by freebeard

I'm sure there is*, what do you have to work with?

A flying brick.

[jamesqf]

My guess is that the energy used in keeping the thing aloft far outweighs any considerations of air resistance or motor efficiency, so the best efficiency is going to be to fly as fast as possible.

[freebeard]

Extend two opposite prop shafts. New props with larger overlapping disks and a Prandtl-D profile — deep pitch at the hubs that washes out at the tips. This eliminates air rolling over the tips and thus the efficiency. With the washout the props are less likely to interfere.

https://duckduckgo.com/?t=palemoon&q...-D+wing&ia=web

[oldtamiyaphile]

Originally Posted by jamesqf

My guess is that the energy used in keeping the thing aloft far outweighs any considerations of air resistance or motor efficiency, so the best efficiency is going to be to fly as fast as possible.

That would be my thought as well.