Solar-powered model planes

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Shaun
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Location: West Yorkshire

Re: Solar-powered model planes

Post by Shaun »

Mike,
Wouldn't using a lower KV motor with a larger prop provide better efficiency at the lower power available from the cells.
Cheers,
Shaun
Ralkbirdy
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Joined: 25 Feb 2018, 13:10

Re: Solar-powered model planes

Post by Ralkbirdy »

Yes, that is why I keep trying, but there are problems. One person uses a low of motor but needs a 70g motor to turn a larger prop. If you use a low kv motor that is lighter, it does not seem to have enough torque to start up, or enough torque to produce enough power. My 8 cell plane had a 2208 1800kv motor but would only consume 2.5A 9W, but this increased to about 4A 12W when I moved to a 2205 2300kv motor, with the benefit of weight loss due to a smaller motor, integrated prop nut so no prop adaptor and a lighter propeller.

The internal resistance of low kv motors means that for a similar size motor the resistance increases as you increase the number of winds of thinner wire, so to get lower resistance you need a larger motor.
Ralkbirdy
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Joined: 25 Feb 2018, 13:10

Re: Solar-powered model planes

Post by Ralkbirdy »

I have not tried how easy it is to use them as 3 separate units, but they could then be used as a 3 cell / 9cell or 4 cell/12 cell plane to give enough volts to operate. Once you get up to 8 cells, they are easy enough to use as complete cells.

The sunpower ones are very robust when soldering, easy to tin and then join up, I use a piece of balsa to hold the tinned connector/ wire and then sweat them together. I have a piece of conti board with strips of 1.5mm ply edges (for holding 3mm Depron while cutting in half to 1.5mm sheets) to align the cells.
Martin
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Location: Warwickshire

Re: Solar-powered model planes

Post by Martin »

My theory about larger heavier more torquey motors is that although they run okay at low average currents, as averaged by a multimeter or wattmeter, they also use very short spikes of higher current - especially when starting and accelerating. The solar cells can't deliver the high current so the voltage briefly collapses and the arduino then reduces the throttle. It's a vicious circle that prevents the system from using all the available power. Maybe a large electrolytic capacitor or some supercaps to provide a small reservoir of stored energy would help.
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Shaun
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Location: West Yorkshire

Re: Solar-powered model planes

Post by Shaun »

http://www.rctimer.com/?product-108.html

I've been using this motor for years on my indoor aerobatic models on 2S with an 8x4 prop (GWS style) Masses of power low current . Any thoughts re suitability?

Shaun
Ralkbirdy
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Joined: 25 Feb 2018, 13:10

Re: Solar-powered model planes

Post by Ralkbirdy »

Worth a try, but the advantage of the Motors that I am using is that the 2204, 2208, 2212, all have the same fixing holes and can swap them around easily. Also all are fixed by the rear holes without a plate on a fuselage that is about 28mm wide n deep so the fixings outside of the motor may need a wide fuselage, larger than needed for internal gubbins. You are working at less than 2s voltage even with 12 cells.
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Phil_G
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Re: Solar-powered model planes

Post by Phil_G »

Thats the kind of motor I was assuming too...
Another question I'd been meaning to ask, whats the significance of the Pololu regulator Mike?
I was thinking an HV receiver, HV servos & a DigiSpark directly off the cells? Maybe simple telemetry?

This is great, there are so many interesting aspects to get your teeth into! I've read up on the suggested 'mppt' controllers on RC Groups (I'm into homebrew campervan solar controllers) and the ones I've seen aren't mppt at all - that needs current as well as voltage measurement, efficient switching controllers, and real-time tracking. They seem to simply adjust the throttle to maintain a fixed cell voltage, but as you'll be aware, many variables move the mppt point, its not fixed - so theres yet another interesting line of experimentation :D , I've plenty of ACS758's :D
Fascinating project, its got me quite intrigued :D
Cheers
Phil
Ralkbirdy
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Joined: 25 Feb 2018, 13:10

Re: Solar-powered model planes

Post by Ralkbirdy »

I have between 12 to 25w of total power, on a normal bec. the Rx and servos were using about 4w of power, on 3.3v the power use fell to 2w, that 2w of power may not seem much but from 12 or 25W it is a significant loss.

Everything is aimed at minimizing the weight, maximize the useful power to the motor. Best aerodynamics. Mine are just my experimentation.
Ralkbirdy
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Joined: 25 Feb 2018, 13:10

Re: Solar-powered model planes

Post by Ralkbirdy »

Telemetry just consumes power for no good benefit.
Ralkbirdy
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Joined: 25 Feb 2018, 13:10

Re: Solar-powered model planes

Post by Ralkbirdy »

I have tested my 12 cell delta, the best motor seems to be a 2212 1450kv motor on either a 7x5 or a Graupner 7.5x4 folding prop. I could get up to 4A 30W with this set up. Moving to a 1000kv motor it did not have enough torque to get going.i will check again another day when there is less cloud.

I measured the resistance across one of the pair of motor wires, this gave 0.2ohm for the motors that work and 0.3ohm for those that do not have enough torque, so this is a simple test to see if a potential motor has much potential.

12 cell - try 2212 1450kv + 7x5 or 2208 1800kv + 6x4
10 cell - try 2208 1800kv + 6x4 or 2204 2300kv + 5x3
8 cell - try 2204 2300kv + 6x4

This seems my best recommendation so far.
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