The dream of fully powering everything from aircraft to cars on just the power generated from solar panels attached to the machine remains a tempting one, but always seems to require some serious engineering including putting the machine on a crash diet. The quadcopter that [Luke Maximo Bell] tried to fly off just solar power is a good case in point, as the first attempt crashed after three minutes and wrecked its solar panels. Now he’s back with a second attempt that ought to stay airborne for as long as the sun is shining.
Among the flaws with the first prototype were poor support for the very thin and fragile PV panels, requiring much better support on the carbon fiber frame of the drone. To support the very large solar array, the first drone’s arms were made to be very long, but this interfered with maneuvering, so the second version got trimmed down and the array raised above the frame. This saved 70 grams of weight from the shortened tubs, which could then be added to the new panel supports.
After an initial test flight resulted in a crash when the PV output dropped, the need for a small battery buffer was clear, so this was added, along with a reduction of the array to 4×7 panels to get the same 20V as the battery. The array also had to be reinforced, as the thin array was very wobbly in addition to making it impossible to fly with any significant wind.

During the subsequent five hours long test flight it was clear that the resulting PV-powered drone was at the limits of its performance, with even some mild cloud cover forcing the battery to provide backup power.
For the test location a tree-sheltered site far away from windy Cape Town was also selected to provide the best possible shot, as keeping position with this drone was very hard. With the low weight and the big surface area of the solar panel array catching any little bit of wind, the GPS-based position keeping was essential. Unfortunately a few hours into the test this feature failed.
Manual position keeping is definitely possible, but [Luke] had to constantly counteract the drone wanting to drift off somewhere else. Ultimately the test flight ended when it was still very much a sunny South African summer’s day, due to the current provided by the array no longer keeping up with the power demands of the motors.
What this perhaps demonstrates best is that if you want to use PV solar power for your flying drone – especially with a significant payload – it’s probably best to use it for recharging while idle, or to extend the battery life by an appreciable amount. That said, props to [Luke] for persevering and making it work in the end.

I wonder if it’s not possible to build the solar panel as a curved wing-like structure that an be pointed into the wind, taking some lift from the air current.
Yes, a wing-like structure but on in one dimension or… across a single plane. The improved aerodynamics of tilting the propeller to be inline with this plane would thrust it in the direction of air currents which could lift it up. Who knows, maybe someone will take this air and plane idea and do something with it but probably not.
These types of projects are interesting but I’d like to see them explore using model planes and attempting to use the techniques birds use to stay aloft over their incredibly long flights.
It would be so cool to see a plane using an updraft to gain height and mostly gliding while recharging.
Just use a buoyant semi-rigid bag to support the PV array. Basically a drone under a solar blimp.
I am extremely surprised that the top-heavy version did better. I would think that increases the power needed to constantly stay balanced.
My first instinct would have been to have a flat plane of panels with empty cells where you want a rotor.
Or to carry the panels a fair distance below the copter, like a helicopter “sling load”. That way the extra weight is stabilizing.
Put the panels inside the bag! Can they deal with being insulated and getting super hot? If you use a metalized lower half of the envelope, you can also illuminate the backside of the panel, perhaps eking out extra power there too.
I’m impressed that this worked at all.
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