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Posted by on Aug 17, 2015 in Blog, Ramblings, Reviews

A New Era of Flight Control

A New Era of Flight Control

Goodbye DJI

Having had my second flyaway, and as usual no response from DJI, my trust in them and their flight controllers is just not there anymore. So I won’t be using anything made by them again. Ok, maybe their high density plastic multirotor arms but nothing else. But what else is there, Flight Controller-wise ? Quite a bit of choice, as it goes…

After some exhaustively lengthy research, I have narrowed my choice of flight controller for my TBS Discovery Pro rebuild to either a 3DRobotics Pixhawk, or an Eagletree Vector. I also looked at the APM 2.6, CC3D, Naze32, Hobbyking’s KK2.0,The Unmanned Tech All-in-One and a few more besides, but decided that the cheaper acro boards were not really for me, given that my main focus is smooth, slow, sail-plane style aerial video, not screaming it round a forest with high-speed mini-quad action, to which the smaller, cheaper boards, without GPS seem more suited.

The Semi-final

Eagletree Vector

I really like the Vector, and Eagletree in general, and the Vector’s in-built OSD is probably the best there is, AND it comes with a GPS mast (!) but several videos I saw revealed it to have a pretty awful GPS loiter mode – I saw far too many videos with horrible toilet-bowling, and read too many threads saying you can’t get a stable loiter on a quad with a Vector. And I need a stable loiter, so that sort of made the decision for me. The winner is, therefore…

Pixhawk by 3DR

Will it fit in a Discovery Pro ? Let's hope so.

Will it fit in a Discovery Pro ? Let’s hope so.

This really does tick all my boxes for flight controllers you might be able to trust. It’s open source code, which means it is future-proof, and constantly being tweaked and improved by pilots and engineers all over the world. There are hardly any reports of flyaways, which is most definitely something I am extra cautious about, and just everything about its history, construction, documentation and components instill me with confidence that if I set it up perfectly I can restore my lovely Disco Pro to its original glory AND give it a ton more features along the way.

Most importantly, if it crashes for any reason I will be able to find out why and what happened, something that was always a mystery with DJI controllers.

I’ve added the 3DR 433 MHz telemetry system so I will be able to monitor my position on a map and get a plethora of real-time flight data as I’m in the air, and record the measurements of all the various sensors for later review should anything untoward happen.

We’ll also be adding autonomous flight capability to the setup, and the Pixhawk comes with an ever-expanding set of useful and creative flight modes that will add a whole new angle to my flyings. I’m particularly looking forward to ‘Circle Point-of-Interest mode’, and the geo-fencing capability which means I can never fly illegally or out of range without having to think about it too much.

Missing in action

I’ve also had time to sort through the wreckage of my flying machine, and work out exactly what needs replacing to recomplete the build.

The final damage looks like this…

  • 2 x DJI Arms (nothing untrustworthy about those)
  • 4 TBS gimbal parts
  • 1 x Discovery Pro Top Board (expensive)
  • 4 x Leg extensions
  • 1 x Pixhawk flight controller, with GPS, telemetry, PPM encoder, and peripheral kit (external USB / LED)
  • 3 x new batteries, LiPo 4S, 4500 mAH
  • Assorted new connection bits – we’re moving  from Deans to XT60
  • 1 x replacement on-craft battery alarm
  • 2 x Graupner 9 x 5 props
  • 1 x Gimbal Roll Motor (cable on original was severed at the base as the gimbal support arm crumpled)

So, it was around £800 to play again. More if I also find out drive motors or ESC’s have failed in the crash. Thank goodness the GoPro 4 survived, and I have plenty of work on at the moment !

If I didn’t enjoy the challenge of the build I would have chipped in another £200 and just bought a ready-to-fly 3DR solo, complete with inbuilt Pixhawk 2 – time will tell if that would have been the better idea :)

Setup & Test. Rinse & repeat.

DJI, unreliable as their flight controllers are, without doubt, the easiest to set-up.

Now I am faced with the considerably more challenging task of making the Pixhawk work with not only my Discovery Pro, but also with my Walkera Devo 10 transmitter, which might not be quite up to the job. This is going to involve some messing about with input channels, and a lot of pre, during and post-build calibration and testing.

Or it may get replaced with a reasonably priced FrSky Taranis, which is what everyone else uses with the Pixhawk. I may go down that route if the PPM encoder I’ve ordered with the Pixhawk gives me ‘channel problems’. And it might do so, because I have to route channels 6 and 8 directly into the TBS Pro mainboard to control gimbal pitch and camera switching. Will the PPM encoder deal with the missing channels ?

Connections...

Connections…

The Pixhawk supports up to 6 different flight modes at a time, and it’s a bit of a mission to get my Devo 10 to address all those with a combination (mix) of 2 switches, one 3-position, and another 2-position. I also need to control the gimbal’s pitch via the Discovery pro’s inbuilt circuitry, and make sure that the RX1002 can cope with the Failsafe reporting methods that the Pixhawk requires.

Once I’ve put it all together and done the basic calibrations and setup, Pixhawk features an Auto-tune flight mode where it will spend 5-7 minutes tuning pitch and roll gains by itself until they are optimum for my craft. It also has 4 separate fail-safe detections, Return to launch, and Land Modes, dual-redundant magnetometers with Extended Kalman Filters to spot discrepancies between them and therefore hopefully avoid GPS error-based flyaways.

The reward for a relatively time-consuming setup should be a flight controller with almost every parameter imaginable fully configurable, tunable specifically to my setup and recordable (not to mention visible in real-time during flight) and a machine capable of full flight autonomy, with as many (free) waypoints as its memory can handle (at least 50).

And of course, we are future-proof for at least 3 years and there are regular updates to firmware, offering extra features and improved safety with every version, and all for free. There are comprehensive manuals and forum help available, and a really nice community of people, so I’m looking forward to my second ‘from scratch’ machine build and my adventures with a brand new flight controller !

Happy Flyings

Aero J