From NewAtlas:
We have seen a few different takes on Vertical TakeOff and Landing (VTOL) drones over the last few years. The idea behind such approaches is to harness the typically longer range and greater payload capacity of fixed-wing drones and mix it with the superior agility of multicopters, allowing them to take off and land in tight spaces.
Some of these have been developed for military purposes, such as the HQ UAV and the Batwing-like AirMule, but others, like the VTOL Kestrel and SkyProwler are aimed more at hobbyists. In developing the delftAcopter, the researchers have set out to build a drone that can be used to carry medical supplies to tough-to-reach areas.
The electric drone takes the form of a miniature biplane, an aircraft design that uses two wings stacked on top of one another which became popular in the early years of aviation following its success at the hands of the Wright brothers. While some VTOL drones use tilting propellors to switch from vertical to horizontal movement, the delftAcopter itself changes orientation as it makes that transition.
Prior to takeoff, it sits upright with the propellor spinning horizontally, just like a helicopter. Then as it reaches the desired height, it shifts its position by 90 degrees so that the propellor is facing forward and it is thrust in that direction, allowing it to zip along at up to 107 km/h (66 mph). With a 10,000 mAh battery onboard, the aircraft can fly for up to 60 minutes on a single charge.
The delftAcopter is capable of entirely autonomous flight, including takeoff, forward flight transition and landing. It can travel beyond the operator's line of sight and maintain a connection through an Iridium satellite connection, which the researchers actually claim allows it to be controlled from anywhere on the planet.
It uses Parrot's S.L.A.M.dunk developer kit along with a fish-eye stereo camera to gather video, and uses an inertial measurement unit (IMU) and GPS to track its position during flight. The craft weighs 4 kg (8.8 lb) and also features obstacle avoidance and the ability to pick out safe landing zones.
The team is set to put the delftAcopter through its paces at the upcoming 2016 Outback Medical Challenge. The event takes place in Australia and tasks competitors with building an autonomous aircraft capable of retrieving a blood sample from a stranded person located at an inaccessible site around 30 km (18 mi) away.
Drones have emerged as tools with great potential when it comes to search, rescue and disaster relief situations. Various drones have been tested for these purposes in the US, the Swiss Alps and across Africa, a particularly suitable candidate due to rough terrain and the lack of paved roads and infrastructure to move cargo by land. The delftAcopter will have its chance to demonstrate its wherewithal at the Outback Medical Challenge between September 27 to 29.
Comments
Interesting numbers!
So, we aim for 9.2A at 35 knots, and 20A during hover. Both with 2 x 6S in parallel (i.e. 4kg AUW). It can lift up to at least 4.2 kg with good controllability, we did not test the limit yet. It can stay hovering for a long time (never tested longer than 20m, got too boring after that).
We use a phone/modem connection with a self designed pcb for the Iridium sat comm.
Looking forward to the competition days!
Hi Kevin.
Out of interest what is your current draw in hover and in cruise@knot, your max lift (kg) in hover and max range @cruise with that platform? If your interested our QP for the OBC is doing 45A hover, 4.8A cruise@40knots, 4.4kg lift on a 2.6kg AUW, of which 1kg is battery (2x.4S 6.6Ah). We expect to fly less than 1 minute in hover over the course, but it will happily do 15min on a battery.
Are you using the Rockblock for sat comms? We've opted for a less glamorous (but much more cost effective and better throughput) 3/4G mobile connection with backup multipoint telemetry radios. Originally we wanted to do fully autonomous (type 2) but CASA wanted continuous comms when we asked last year.
@Chris, thank you!. We have not experimented with larger control surfaces in practice. However, the moment we started using our current surfaces in the hover control loop greatly increased controllability. I suppose that if you really want to, you can rid of them, at the cost of reduced yaw control. But considering that, 1) it is imperative to keep hover time to a minimum for efficiency, 2) how much we still need the tip props to do proper yaw control ( we actually felt the need to upgraded to extremely powerful tip props, we use the same kind as from high end race quads)... 3) landing this thing autonomously on unknown terrain with wind is quite a challenge already, we have chosen to keep them for this design round.
@Thomas, Iridium is used as the datalink. We can send thumbnails of possible Joe locations to GCS, and we can upload commands (e.g. kill, go to way-point, abort take off, etc). For the rest, the Paparazzi autopilot is flying autonomously in "NAV" mode (including searching and selecting Joe if the Iridium thumbnail link fails).
What kind of control do you get through the Iridium link? Using Sat phones here is still hit and miss and is regularly down for a few minutes. I suppose you have the ability to choose your base station site so that you have the best possible view of the sky. Would you use it to control the machine in guided mode or something similar (I'm not familiar with Paparazzi's controls)?
Great work and a novel approach! Have you tried larger control surfaces or large vertical control surfaces on centerline to aerodynamically counter torque? Curious if that would allow you to ditch the anti-torque motors, lighten up the load and allow greater efficiency.
Thanks Jason.
In the early design stage we considered that we may need to land with the wing in parallel with the wind. Since the competition will go ahead with up to 30 knots wind, we needed quite some torque to make that happen with such a big wing.
In terms of the swash plate design, mostly we have had trouble with control of a very lightweight rotor with a very long wing attached to it. Normal helicopter gyroscopic control is not possible, it becomes a mix between the gyroscopic effect and the aerodynamic effect. Great research material though, papers are pending!
Awesome work!
I think this fear of traditional helicopters being "complex" is over hyped due to lack of understanding/experience with traditional style heli's. If you look at our 3D Helicopter brothers, they are pushing RC Models to the limits and extremes well beyond that of any quadcopter I have ever seen, and, not having any issues with "mechanical complexity". The swash plates and control mechanisms on RC Helicopter models are very robust and quite simple, especially if used well below their maximum design capabilities.
Great work guys! Definetly one of the most innovative approaches to the VTOL Plane solution I have seen in a long time!
One more question... How come you used two anti-torque motors? Was 1 insufficient?
Thank you all for the post and for the encouraging words!
Let me clear up a few things:
The standard configuration is 2 6S batteries of 4500mAh each. Depending the weather conditions during the Outback challenge we may go for 3 of those, or vary with 3500mAh.
To make a comparison with a helicopter, we think that in general the DELFTACOPTER should be able to get more range at higher speeds, due to its fixed wing advantages. Time is of an essence during the competition (and in many other real life situations as well). Adding extra weight scales pretty good during the forward flight part of the mission.
The fact that the DELFTACOPTER is fully electric ,although making it far more difficult to get the range and speed, does save in operation costs. We have not needed to do any maintenance other than that caused by crashes during testing. The swash plate seems quite reliable in this sense, and the main motor as well as the tip motors are direct drive. (we did need to change ESCs from to different makes at random intervals, it seems they are not happy with spinning up of such a large propeller)
Our big design trade off is in the main propeller. It is designed for both hovering and forward flight in mind, meaning it has to deal with an extreme pitch range. In theory the custom made design was made more efficient towards the forward flight regime, but we lack practical comparison data how this worked out in terms of efficiency. In any case, it is a compromis. Cruise speed depends on the weight configuration, but currently we estimate around 18 m/s, we may operate it at higher speeds in case of windy conditions.
The tip rotors are indeed only for anti torque, and only during landing (although we use them during take off as well, since they are there anyway). Since we do autonomous landing at unknown terrain in possibly windy conditions, the vision system needs a yaw stable aircraft to be able to make for controlled obstacle avoidance and landing.
We don't need a gimbal for the camera system, as the Parrot SLAMdunk has 200 degrees view angle. Indeed it is looking straight down in hover mode, straight back in forward flight mode.
Indeed we use Paparazzi as our autopilot software. It gives us the freedom at engineering level to implement the transition and other special control algorithms needed for it to fly. Many changes for the hybrid control already have been pushed to the master branch, the rest will come after the challenge. The flight plan based structure also allows us to easily create custom autonomous missions, as required in the challenge.
Lastly,
Due to the Outback challenge requirements, we need to have datalink to the aircraft at all times. We have therefor added iridium satellite communication to the UAV, such that we can operate it from anywhere on the world.
How much more efficient in forward flight is compared to a conventional elicopter? How fast is the cruise speed? 10000mAah means nothing if you don't state the voltage... (it's 12S, so 44,4 Volt, right?)
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