Solar-powered model planes
Posted: 28 Jun 2018, 20:56
Not really retro so it's in the general chitchat section. I suppose there are some vintage designs that might lend themselves to solar conversion: that would be no worse than converting an old i.c. design to electric battery operation - something that most of us accept nowadays.
Mike (Ralkbirdy) came up with this present design - prototypes really - but they fly really well.
I assisted with the on-board power controller. This is just an Arduino that takes the motor output from the receiver and passes it on to the speed controller.
The Arduino monitors the available voltage from the solar cells and throttles the motor back quickly if the voltage begins to fall below the ideal level. So if you do a loop and the solar cells are facing down, or the sun suddenly disappears behind a cloud, then the motor is automatically slowed down, or even stopped, so as to always keep enough power back to run the radio and servos. You can hold the plane upside down a few inches off the ground when it's cloudy - and there is still enough power to operate the radio and servos, so there's no need to worry about losing radio control.
The solar cells used are about five inches square. Each one makes about 0.6 volts, so with ten in series you have 6 volts to work with. The no load voltage varies hardly at all from cloudy to full sun, but the brighter the light falling on the cells, the more current can be drawn from them - up to about 4 amps in direct sunshine. Maximum power occurs when you draw enough current to pull the voltage down to about 85% of the no load value - so about 5.1 volts with a ten-cell setup. If you shop around you can get the cells for about a pound each if you're prepared to buy about thirty of them. AliExpress is one source. The Sunpower C60 cells are nice and a little more rugged than some other cells (slightly bendable but still eggshell thin and fragile). If you're buying, look for cells that are advertised as 'tough' or similar.
Mike is now working on a twelve cell design and I'm sure he'll be happy to share the details if anyone is interested in building a similar model.
Mike (Ralkbirdy) came up with this present design - prototypes really - but they fly really well.
I assisted with the on-board power controller. This is just an Arduino that takes the motor output from the receiver and passes it on to the speed controller.
The Arduino monitors the available voltage from the solar cells and throttles the motor back quickly if the voltage begins to fall below the ideal level. So if you do a loop and the solar cells are facing down, or the sun suddenly disappears behind a cloud, then the motor is automatically slowed down, or even stopped, so as to always keep enough power back to run the radio and servos. You can hold the plane upside down a few inches off the ground when it's cloudy - and there is still enough power to operate the radio and servos, so there's no need to worry about losing radio control.
The solar cells used are about five inches square. Each one makes about 0.6 volts, so with ten in series you have 6 volts to work with. The no load voltage varies hardly at all from cloudy to full sun, but the brighter the light falling on the cells, the more current can be drawn from them - up to about 4 amps in direct sunshine. Maximum power occurs when you draw enough current to pull the voltage down to about 85% of the no load value - so about 5.1 volts with a ten-cell setup. If you shop around you can get the cells for about a pound each if you're prepared to buy about thirty of them. AliExpress is one source. The Sunpower C60 cells are nice and a little more rugged than some other cells (slightly bendable but still eggshell thin and fragile). If you're buying, look for cells that are advertised as 'tough' or similar.
Mike is now working on a twelve cell design and I'm sure he'll be happy to share the details if anyone is interested in building a similar model.