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An Autopilot in the clouds – part 3

This article is part three in a series, describing some of the inner workings of an autopilot system - even though the description is specific for this particular system, a lot of principles are generic and can be used to describe a variety of auto pilot systems.

Today we take a look at the maneuver system.

 

Maneuvers

For each type of vessel, there is a library of maneuvers. Some are common for all vessels and some are specific for a specific type of vessel or configuration.

A maneuver can either be of a simple nature, like turning right until another maneuver is issued by the autopilot, or a more complex maneuver that has some logic embedded (timing etc.) or is changing flight path dynamically based on data from sensors etc…

A maneuver can be synchronous or asynchronous, meaning that it either does something quickly (ie: issue a roll correction command) then terminates, or it does something that takes a while (ie: navigates the drone to a waypoint) which it does in it’s own thread and reports back to the main system when it’s finished. Asynchronous maneuvers has a built-in kill switch, which can be activated by the autopilot if certain conditions arise - ie. the rangeguard system triggers, the statemachine wants to change state etc., or the maneuver simply takes too long to execute. Maneuvers can also be temporarily paused.

 

Example - The simple maneuver

Suppose the drone is in the air and you’ve just activated the freeflight mode (which means that the drone is controlled manually by the operator). If you issue a turn left command, the system issues a turn left maneuver. Since the maneuver only does one thing, send a left flap down, right flap up command to wing servos, the maneuver is considered simple and only takes a few milliseconds to perform. The drone starts to turn and will continue to do so until the operator issues another command or the auto-part of the autopilot takes over for some reason.

 

The advanced maneuver

Once it’s time to get the drone safely back to earth (and we are talking a flying wing here), the autoland maneuver is executed. This maneuver could be a simple turn-off-the-engine-and-lets-hope-for-the-best type of thing, but I’ve made it a bit more dynamic.

The strategy is to let the maneuver store the planes heading and try to keep that heading all the way until the plane has landed. Furthermore we want to keep the engine running (a little bit) until we are a few meters over ground to have some thrust for steering.

The maneuver is asynchronous, because we want it to terminate when the plane is safely on the ground and the state machine can transcend to the safe state.

The maneuver starts by subscribing to the telemetry coming from the plane sensors. This ensures that each time the telemetry is updated, the autoland maneuver is fed the new data.

The maneuver then stores the current heading and locks in on it, by applying correctional turns if the plane starts to point off that heading with more than 10 degrees.

At the same time it tells the engine to spin slowly (approx. 15%).

Then it waits for the altimeter to tell it that it has sunk below 2 meters altitude. When it does, it turns off the engine completely but keeps applying correctional turns if the plane starts to head outside it’s chosen heading.

The maneuver also listens to the gyros and accelerometers. When no forward motion is detected for a period of time (a few seconds), the maneuver considers it’s job done, and issues a maneuver done signal back to the main system, which will trigger the state machine to change to safe mode.

One curiosity is that maneuvers can utilize other maneuvers to get their job done, ie. the general "flying through waypoints" maneuver, uses the simpler "fly to one waypoint" maneuver to get to each waypoint.

 

Next time

Initial flight testing, log analysing and optimization

Previous posts

http://diydrones.com/profiles/blogs/an-autopilot-in-the-clouds-part-2

http://diydrones.com/profiles/blogs/an-autopilot-in-the-clouds-part-1

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CAD Drones Announces Engineering Services To International Drone Community!

At CAD Drones we design and engineer custom drones for customers who have unique payloads.  Whether you need a 24 inch aerial drone to carry a GoPro or a 60 inch Quadcopter to carry a $5,000 camera system we can design, build, program, and test a custom drone for you!  We're the experts in Engineering Aerodynamically sound Sea, Air, and Land based drones.  We're willing to take on projects/contacts that are big or small.  Need 3 Prototypes for a new commercial division within your company?!  We are more then willing to take on the task of people those for you.  Need 300 Programmed, Tested, and Proven drones for your Universities new up and coming Unmanned Vehicle System Degree?  We can meet your needs and exceed them!  We use state of the Art CNC machines and 3D Printing Technology to prototype and test our 3D CAD Models of your custom drone vehicle.  Every CAD Drones Vehicle you receive will be above and beyond the current "brand name" vehicles being Jerry-rigged to meet commercial needs.  This modified toys present many problems within the commercial drone industry.  For starters the vehicle was not engineered to carry the payloads that are currently being used on these vehicle systems.  When the CG and weight of the drone changes you are now running your electronics, batteries, sensors, and overall equipment at a lower rate of consistency while in operation.  If Firefighters in a state like California for example need low-cost aircraft Designed, Engineered, Built, Programmed, Assembled, and even Tested we can achieve this and go above and beyond expectations.  If repair or maintenance is needed on your "CAD Drones" vehicle our company is more then willing to assist you in getting it up and running again.  By 2020 our goal is to be the #1 (Leading) Company in the World in Engineering Commercial Drones!!!  We take Tested, Tried, and Proven electronics with the hardware setup and payload in mind.  Our "First Goal" as a company is to get Top-Notch CAD Drone Vehicles into the hands of as many Farmers in the Midwest as we possibly can!  We believe strongly in using our skills, expertise, and vehicles to make farming safer by allowing farmers the ability to make smarter decisions when deciding when and where to spray pesticides and deal with diseased crops.  If you would like us to undertake a project for you or you want to become a "Project Based Contractor"  for CAD Drones, LLC please contact me via email at:

JoshuaAllenJohnson@gmail.com or check out our website at CADDrones.com 

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How 3DR tests camera gimbals

With our partners AES. This is a great way to really quantify performance!

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Screamy: A durable lost UAV alarm

Hello pilots!

I'd like to introduce you all to Screamy, our lost aircraft alarm. We launched a kickstarter campaign today to get this special product into your hands: http://kck.st/1wDiV5y

Put this on your valued multirotor or model aircraft and make sure you never lose it!

Thanks!

Kelly Miller

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What a simple orthomosaic and DEM can do

https://www.youtube.com/watch?v=3odtsy6l_KE

Using Orthomosaic and Digital Elevation Model to create 3 D model is nothing new. But normally it will require lots of computing power and knowledge. Skyline's TerraBuilder and TerraExplorer make it easy for the average people to make 3D video from an orthomosaic and DEM. For sure there are lot's of other functions within the software, I think just a 3D fly around video create by my recent aerial mapping work will enable my client understand his land better as he can view the area at difference angle and prospective.

I just learn some very basic function and will need proper training to fully utilised the powerful software. I find very limited resource in the net to help the learning process. Any idea ? 

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