Canberra UAV Demonstrates Helicopter Flight with Downstream FBL Controller

I wanted to bring attention to the work that Tridge and the rest of the CUAV team have done to demonstrate the possibility of flying a Helicopter with a standard FBL controller handling the rate control duties.  They have been testing gas powered helicopter for next round of the Outback Challenge which will require a long-range VTOL aircraft.  Helicopters are a natural target for this mission of course.

Several of the CUAV team are experienced RC helicopter pilots, but not as familiar with installing a Pixhawk on a helicopter which can be difficult, especially in the case of gas engine helis.  As such, they were more comfortable having a normal Flybarless Controller handling rate control. In this case, the Skookum Robotics 540.   Tridge has made changes to the code which allow for a pure control pass-through from the RC Rx, through the Pixhawk, and straight to the FBL controller. This pass-through occurs in Acro mode, whereby the Pixhawk running ArduCopter has no effect on the flight control, so even if the Pixhawk should have a major AHRS/EKF failure, the helicopter is still controllable. 

Of course, the Pixhawk is capable of controlling a Helicopter without any FBL system, and this is the most common arrangement.  But the possibility of running an FBL controller in series with the Pixhawk helps lower the barrier to entry for many existing RC Helicopter pilots.  And also offers helicopters similar failsafe-function to airplanes, where they can survive the loss of the autopilot.

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Comment by Andrew Tridgell on March 10, 2016 at 2:34pm

thanks for posting this Rob!

The method we're using is SBUS chaining, so we use a FBL controller with SBUS input (a skookum 540), and use the SBUS output port of the Pixhawk. That means just 1 simple cable between the Pixhawk and the skookum, which keeps wiring nice and simple

Comment by Mark Omo on March 10, 2016 at 2:44pm

@AndrewTridgell are you planning on using this in the OBC for redundicy?

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Comment by Chris Anderson on March 10, 2016 at 2:54pm

Gas can and five-foot blades! My hat's off the heli guys for sheer courage. 

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Comment by Chris Anderson on March 10, 2016 at 2:55pm

PS: I assume "FBL" stands for flybarless? New term for me...

Comment by Matt™ on March 10, 2016 at 3:04pm

The most amazing thing is how you can get it to fly while the blades are going so slow!  jk...

Comment by Andrew Tridgell on March 10, 2016 at 3:04pm

@Chris, yes, FBL is flybarless. There are a huge number of people flying flybarless helis around the world. What we've shown is you can add a full autopilot to one easily, but still have the peace of mind that your first takeoff (in ACRO mode) will fly exactly the same as it does before you add the autopilot. So you can switch to an autopilot mode once you're at a safe height to test control and know you can recover in your familiar FBL mode with one switch.

I'm hoping this capability will encourage more people to try autonomous helis. They really are incredibly capable machines, and not utilised nearly as much as they should be.

You can buy a heli that can fly at 150km/hr for a couple of hours, and handle high winds with ease, while doing high precision vertical takeoff and landings. No other UAV type really comes close.

@Mark, we're using both quadplanes and helis. Our current plan is one will be the retrieval aircraft and the other the radio relay. Which will do what role isn't clear yet. In reality it would make more sense for us to concentrate on one or the other, but they are both such fun we didn't want to miss out by only doing one type

Comment by Rob_Lefebvre on March 10, 2016 at 3:27pm

There's nothing scary about gas.  Gasoline is safer than LiPo batteries.

Go to any club and ask them how often they've had a fire resulting from a gas airplane crash, or any other reason (the gas cans don't catch on fire if you overfill them). Then ask them how many LiPo fires they've had.

Operational safety is up to the operator.  Treat the vehicles like harmless toys, and somebody will get hurt.  Treat them with the respect they deserve, like you would any other dangerous power tool (Chainsaw, powerset nailer, posthole digger) and you can accomplish your task with speed and efficiency.

Comment by Mark Omo on March 10, 2016 at 3:51pm

@AndrewTridgell I was more referring to the control system redundancy, as I am unsure of what happens if the co-processor on the Pixhawk fails.

Comment by Andrew Tridgell on March 10, 2016 at 4:11pm

@Mark, the stm32 IO co-processor handles SBUS output, so if that fails then the FBL would be starved of input and the vehicle would crash

For our OBC heli the petrol ignition would also cut however, as the pulses to the PWM ignition switch would stop, so the heli would be safe as the blades will lose energy quite quickly.

Comment by John Bond on March 10, 2016 at 7:14pm

Wow, a flashback to the 1990s.  Gas helis were pretty much the only rotary-wing choice then.

Heli autopilots have always had pass-through modes.  It's almost a must for someone who flies helis manually as they need to be able to revert quickly to a comfortable mode if the autopilot does something unexpected.  It's something that fixed-wing pilots and those who only fly more automated systems often don't get because the margin for error with a heli is so much less.

It is kind of interesting what "manual" flight control has become.  If you don't like what your "full" autopilot is doing you can switch to a pass through mode which uses a simpler autopilot (OK, stabilization system).  The days of "manual" control being the ability to only move control surfaces based on sight and sound are pretty much gone.


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