Previously I tried to make an RC plane that purely fly using solar energy with battery to power its control surface this plane was able to fly if weather conditions are good. This plane was having the peak power output of 24 watts in ideal condition.
For more details please refer the link:
Article on the Previous version of the plane
This plane will be having hybrid power. The solar panel will continuously charge the battery as well as gives the power to plane. At the time of peak load requirement (take off) battery also provide power along with solar cell. We will also try to keep its weight below 150g.
Complete details are there in the video I prepared: https://www.youtube.com/watch?v=AE89vQiu-IU
Structure of the plane:
This plane is relatively smaller than the previous version. It is having flying weight of 160grams and wingspan of 78cm. It is powered battery and solar cell combined. It is having 3channel control. Making of the structure is straight forward and can be prepared using the plan as attached.
Preparing solar cells:
To power our motor we meed 3.7 volts, and battery highest voltage is 4.2 volt. So we need to provide a continuous supply of 5 volts. The cell we are using (SunPower c60) gives the voltage of 0.5V with 6A peak supply. However, for the size, we are aiming 10 cells cannot be accommodated. So we will cut these cells into half and use it. In this case, each cell gives the voltage of 0.5 V but current will be halved at 3A. We will connect 10 of these half cells in series which will give 5 volt supply and 3amp peak current.
As these cells are very brittle cutting it is difficult. Once you cut them a copper wire can be soldered to each of these such that all of the there cells are in series. You need to be careful of the polarity of half cell as sometimes it gets confusing. Than solar panel can be stuck to the wing. I have used hot glue for so. Use a good amount of hot glue such that there is not any gape in between wind and solar cell.
Now to protect the solar cell I have covered it with transparent tape. This is actually a bad idea to do so, but to protect it from dust and other contamination it is necessary. You can also use other better techniques for encapsulation. Now open circuit voltage and short circuit current need to be measured.
Once everything is ok you are good to move to the next steps. And of voltage shown is lower than 5.5-6 v than you might have made mistake in soldering -the mistake is soldering correct polarity to make a series.
The plan can be downloaded from http://diy-india.org/wp-content/uploads/2019/02/Usolar_dwg.pdf
Electrical system:
As explained earlier, this plane has hybrid power. Battery and solar panel connected in series. This comes with the problem. we are getting an open circuit voltage of 6 volts and the battery having the highest voltage of 4.2. so the battery can be easily failed due to overcharging which is bad.
I am going to use a battery that is having inbuilt battery power management circuit (kind of...). this circuit does not let is overcharge or even protect it from deep discharge. Typically all LiPo used on toy quadcopter or airplane comes with this type of inbuilt circuit. however, any Hobby grade battery does not have such a circuit. so you need to take care while selecting the battery and if the battery does not has such a circuit it can be purchased separately and used with the plane.
While in operation high current needs are taken care off by the battery while the continuous supply of 1-2.5 Amp is provided by solar cell which can be directly consumed by plane or can be stored in battery depending on throttle setting.
I have used receiver brick for all controls, It costs around 10-15 USD and contains 2 servo motor, Brush ESC and receiver that can be used with flysky Tx. And all of this at just weight of 7 grams!!!
This plane makes use of the geared coreless motor. This motor is extracted from old toy quadcopter and provide around 40 grams of thrust.
Tests:
Here I have carried out two tests on the plane to check overall performance of solar charging.
Video of power system testing: https://www.youtube.com/watch?v=oxRIcwgHkGA
1. Continuous run till battery run out:
The throttle was set to 100% and the voltage across the battery is monitored until battery empties. In the attached video, you can check out where I placed a plane with 100% battery with 100% throttle and the battery lasted for around 22 mins. this was 10 AM of time and as it was winter solar angle was around 50 degree (maximum). so this performance will be further improved in other days of the season as this was the time for minimum solar energy available. And while flying plane does not require 100% of throttle every time. So to know the exact contribution of battery and solar cell I conducted the next test.
2. Monitoring current from Battery and Solar cell:
One Amp meter is connected to the solar cell to monitor current input and voltage from the solar cell while another Ammeter is used to measure the current consumption of airplane. I have captured around 3 min video of it at full throttle. At full throttle, it takes around 1.3-1.5 amp of current out of which 1.2 amp is provided by the solar cell.
There is a single video which starts with test 2 and then with test 1.
Flying...
So the plane is ready to fly. but it needs some final touch to make it happen. CG of the plane need to be adjusted to a typical 25% of the wing as a starting point and can be tuned by doing some glide trials.
As this plane is having very low thrust it will gain height slowly and as this plane is having very low wing loading it is a bit difficult to fly in windy days.
You must need to be very careful while flying to do not let it crash. as it can damage the solar cells of the plane. and it is very difficult to repair it. Video of flying can be seen in the previously attached video.
This plane needs to be further improved for better payload capacity and some surplus power to run other stuff (like FPV cam).
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