This is a project that has been in the works since August. It has been very challenging and is still in the early stages. So I am starting a blog to present my work and provide future updates on progress.
In short, this is a fuel - electric hybrid (series hybrid) UAV/FPV plane.
IC engine ---> Electric motor ---> rectifier/filter ---> ESC ---> Electric flight motor
- Endurance of an IC setup
- battery back-up, adding some redundancy (reliability)
- Turning off generator and flying on batteries allows vibration-free HD filming
- ability to use an IC engine that has just enough power to sustain flight/ mild climb. (endurance bonus)
- ability to take-off under both generator output and battery output (power bonus on demand)
- Weight: This design uses two electric motors (one for generator, one for prop), an IC engine, batteries/esc, bunch of power electronics (large filtering capacitors, rectifier, arduino uno to manage the generator speed (voltage output)).
- complexity: The IC engine is directly coupled to the generator motor (alignment is critical), starting the engine requires an electric starter (custom design required because of space confinements), power electronics have to be up to spec for the projected current draw, cooling has to be adequate, have to program the arduino to manage throttle (tuning a PID), etc, etc, etc... A lot to go wrong here...
Setup: (to be updated)
IC engine: DLE 20
So taking that into consideration, I first had to figure out what scale to make this on. My first attempt actually used an OS 15 fp. belt driving a small BL motor. It was too heavy and anemic to even think about putting in the air.
I had a DLE 20 laying around the house so I decided to go big or go home lol. So the IC engine was/is the DLE-20
Airframe: Slipstream RV-8.
It just so happened that the DLE 20 had spent some time in the front of a slipstream RV-8 (30 cc). It was also the case that the engine fit upside-down and backwards in a manner that made cooling feasable. It turned out that there was also enough space for the generator and they would fit in the right proximity to make direct shaft coupling possible. It also has an 80 inch wingspan and a 14 inch chord - so lots of wing area.
Generator: Turnigy SK3 6354
I needed a low KV motor to get the correct voltage (shooting for 8s) at the operating RPM of the DLE-20 (8-10k rpm). This one was supposed to be 260 Kv and it was cheap. Not knowing if this project would work - I bought two of them. Both for the generator and prop.
Drive Motor: Turnigy SK3 6354 swinging 17X8 - 18X10 prop
Rectifier: 50 amp, 3-phase rectifier from digikey with heat sink
Ripple filter: 14 - series connected, actively balanced, 50-farad supercaps. Max voltage of each cap is 2.7-2.8 vots.
IC engine controller: Arduino uno using a PID library. It monitors the generator output through a rectified/filtered DC signal going to an analog input. It also looks at a 3 pos switch signal from my Rx. On position 1 the arduino sets throttle to idle. Position 2 sets throttle to high idle; if the generator is not running, arduino turns the starter and choke on, after one second - turns the choke off, and after two seconds turns the starter off. It waits another one second and repeats if necessary. Position 3 activates the PID and attempts to hold the generator output at a given setpoint.
Battery Charge system: I currently do not have a way to charge flight batteries. In fact - The first time I fly it with the generator on, I will run the generator in parallel with the batteries. Later I am planning on installing a power-diode in the battery circuit to prevent the generator from directly charging it. Then I would like to have some way of charging through the balance leads. I am not sure how to do this - I have read a lot about simple lipo chargers and will likely make my own PCB with 8 switching mode regulators but I am certainly open to suggestions. I would like to charge each individual cell at 4 amps and keep the total weight under say... 250 grams... Supply voltage for the charger will be 27-32 volts.
Camera: RMRC 480 (non-OSD, with audio which is not hooked up... that will change soon)
VTx: 800 mW 1.3 GHz with CP antennas
OSD: ET, I don't like it - but I need to have all that data during test phase. I am currently getting familiar with APM so down the road...
RC Rx/Tx - TSLRS V6+ with Futaba T8fg (with new firmware so it is a "super"). (actually using 9 channels: Ail, Ele, Thr, Rud, OSD menus, IMU gain, Flaps, Generator modes, Pan.) If you look at my vids in posts 3 and 4, you can see that the cam angle sucks for flight view. I will use my cam switch and have another under the wing - one day... So that would be 10 channels.
In the following posts I will detail some build points and ground/flight testing as well as technical discussion and pictures/videos.
Comments, suggestions, criticism and questions are more than welcome.
I also want to thank the people/organizations for helping make this come together.
FPVLAB - great info about FPV and other technical stuff
RCG - Some of the guys in the IC engine forum helped me develop the starter when I was miserably failing.
Microchip support forum - helped me with programming PIC controllers - really helpful bunch of people.
Pixturethis - FPVLAB/RCG member/personal friend who has mentored me in FPV and has the ability to fly any cobbeled-together POS that I hand him - and get it back on the ground in one piece!