Arducopter Flies Gas Powered Helicopter

Now we're cooking with gas!

I have just completed a project to build a helicopter with a gasoline engine, controlled by Arducopter (of course!) This helicopter serves as a test bed for future gas heli development work for a client of mine. The goal was to prove out that it could be done. Gas engines pose a unique challenge for Arducopter due to the heavy vibration they produce. But they also present a lot of promise for UAV applications as it can allow heavy payloads, long duration flight, and high speeds.

The heli is based on a Helix Heli conversion of a Trex 700. However I stretched it to 800, used many aftermarket upgrades such as from KDE, and machined a number of custom parts myself. The machine required quite a bit of customization in order to increase frame stiffness which is important for vibration reduction. The engine is a Zenoah G29RC engine with pull start. This is an increased displacement 23cc engine, which makes more power but creates more vibration than the G23. I could have purchased an aftermarket balanced engine, but I wanted to use COTS parts and also prove the Pixhawk can survive with a worst-case engine.

Last night I performed the first check flights of the new machine and began PID tuning. This is one segment of that flight where I was working on the PIDs.

Today I finished the PID tuning, and it is flying very well indeed. After increasing rotor speed to ~1600rpm and tracking in the blades, the vibrations on the Pixhawk are quite good, better than both of my quads:

I flew it around a bit in Stabilize, and hit 30 m/s without really trying. It should easily be capable of 40 m/s flight speeds. I'm hoping for a 10 kg payload capacity. Flight time is currently better than 20 minutes with plenty of reserve on a 630cc tank. I will probably begin development on a larger fuel tank system on the order of about 2L which should allow for 1 hour of flight time with payload. Currently the 2S 4400mAH avionics battery lasts for at least an hour, but will be supplemented with an on-board generator.

Later today, I will start working on auto missions and will shoot another video.

The success of this project opens up an entirely new world of possibilities for affordable UAVs. It will be possible to perform realistic crop spraying. Aerial imaging with the best quality cameras available. And extended flight ranges in a large aircraft with VTOL capability for usage in areas without a prepared landing strip. Obviously this is not the type machine that would be used anywhere near people. But remote areas, or secured industrial lands would be suitable operational areas.

I have to report that unfortunately this helicopter crashed on Saturday afternoon. After about 1 hour of total air time, it departed from controlled flight and crashed from about 10m altitude. Accident investigation has determined root cause was that the memory backup battery in the GPS vibrated loose from the solder tabs. This in and of itself should not have caused a crash, but what happened next is unclear. The logging data shows a loss of GPS and Magnetometer data, concurrent with a reduction in the datalogging rate about 3.9 seconds before the end of the log. The reduction in data logging rate might indicate the entire Arducopter process slowed. IMU logging dropped from 50Hz to 15Hz, credit to Jonathan Challinger for picking up on that obscure detail. At the same time, recorded vibrations increased dramatically, but I do not believe it was "real" and might have been errors in the data. After that, the Pixhawk may have blacked out before impact as the Baro log ends before getting close to zero.

At this point, I suspect that the loose battery made contact with some of the traces on the GPS carrier board. It may have shorted the power lines, causing the Vcc to drop momentarily. Or it might have shorted the I2C or UART comms lines, causing many possible problems in the code. Hopefully we can figure out exactly what happened and make the code more robust to that type of failure in the future.

In the meantime, and regardless of future code improvements, I will be gluing that battery to the carrier board of all my units. There is also a battery in the Pixhawk that should probably receive the same treatment. I would encourage 3DR to glue these in the factory in the future. The early failure of this unit was largely due to the extreme vibrations caused by the gas engine, but it's probably just a matter of time until it happens to other units subject to lower vibrations.

Damage to the helicopter was not as bad as I expected, but anytime you crash something like this it is going to be expensive (the blades alone are $200). I will most certainly rebuild it and keep going. This type of failure is always going to happen when you do something new and difficult. I will take measures to protect the GPS from vibration on the rebuild.

I would like to point out that, due to safe flight practices, nobody was at risk in the crash. I was using a local RC aircraft club field at a time when few people were there for these initial test flights, and the helicopter was more than 300 feet away from me when it happened.

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Comments

Rob_Lefebvre September 22, 2014 at 12:49pm

Rob, I use the Pixhawk gyro. It works perfectly fine. The external gyro functionality is something else that I am not sure about the status on. Does not get used much.
Josh Potter September 22, 2014 at 12:46pm

Sorry to hear about the crash, but you took away some good information that will make things better for everyone in the future.
Rob Dunbar September 22, 2014 at 12:39pm

@Rob_Lefebvre, sorry to read about your crash. However, thanks for the after event report on your crash investigation. I'm heating up the hot melt glue gun right now to hold in those batteries. I too prefer to test at my local airfield when no one else is flying.

Another question I had is do you run a separate gyro for yaw or are you satisfied with the PIxhawk built in gyro?

I have a Bergen Observer and an Intrepid I want to get flying again after watching your videos.
Tipu September 22, 2014 at 11:08am

Ooh Very Sad.

But dont give up Dear.
Tipu September 22, 2014 at 10:57am

Great Job.

I wished someone do that , so I can mount APM on my Gasser.

waiting for more videos
UAS_Pilot September 22, 2014 at 10:49am

Sorry Rob. I look forward to the rebuild and continued testing of the gas powered system,

Thanks
Moderator

Gary Mortimer September 22, 2014 at 10:49am

Sorry to hear about the incident, but being at the bleeding edge of this stuff brings trouble.
MR60

Hugues September 22, 2014 at 10:45am

@Rob, sorry to hear about your crash. Rebuild and go on ! Crashes are the path to learning as we have all experienced...(unfortunately)
Todd Urban September 22, 2014 at 10:43am

ouch I have had one fall off before I always glue them with hot glue since then that sucks a$$
Rob_Lefebvre September 22, 2014 at 10:37am

I have to report that unfortunately this helicopter crashed on Saturday afternoon. After about 1 hour of total air time, it departed from controlled flight and crashed from about 10m altitude. Accident investigation has determined root cause was that the memory backup battery in the GPS vibrated loose from the solder tabs. This in and of itself should not have caused a crash, but what happened next is unclear. The logging data shows a loss of GPS and Magnetometer data, concurrent with a reduction in the datalogging rate about 3.9 seconds before the end of the log. The reduction in data logging rate might indicate the entire Arducopter process slowed. IMU logging dropped from 50Hz to 15Hz, credit to Jonathan Challinger for picking up on that obscure detail. At the same time, recorded vibrations increased dramatically, but I do not believe it was "real" and might have been errors in the data. After that, the Pixhawk may have blacked out before impact as the Baro log ends before getting close to zero.

At this point, I suspect that the loose battery made contact with some of the traces on the GPS carrier board. It may have shorted the power lines, causing the Vcc to drop momentarily. Or it might have shorted the I2C or UART comms lines, causing many possible problems in the code. Hopefully we can figure out exactly what happened and make the code more robust to that type of failure in the future.

In the meantime, and regardless of future code improvements, I will be gluing that battery to the carrier board of all my units. There is also a battery in the Pixhawk that should probably receive the same treatment. I would encourage 3DR to glue these in the factory in the future. The early failure of this unit was largely due to the extreme vibrations caused by the gas engine, but it's probably just a matter of time until it happens to other units subject to lower vibrations.

Damage to the helicopter was not as bad as I expected, but anytime you crash something like this it is going to be expensive (the blades alone are $200). I will most certainly rebuild it and keep going. This type of failure is always going to happen when you do something new and difficult. I will take measures to protect the GPS from vibration on the rebuild.

I would like to point out that, due to safe flight practices, nobody was at risk in the crash. I was using a local RC aircraft club field at a time when few people were there for these initial test flights, and the helicopter was more than 300 feet away from me when it happened.

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