A 3D printed ducted fan UAV prototype

Though Ducted Fans UAVs as of now are not very common, my personal opinion is that this will change in the future, since they have certain advantages over other concepts. Just one single engine is necessary which makes the use of internal combustion engine more viable than for multi-rotors. Also a transition into a very efficient horizontal flight is possible (with modifications).


 This is a project which started in 2001 as a Ducted Fan VTOL in a configuration where the centre of gravity is located beneath trust vectoring giving the  advantage of stability. Since there were no hobby autopilots available at the time, it was only equipped with one gyroscope and a mechanical mixer to control the vehicle around the vertical axis. The vehicle was destroyed on the first flight with minor success.


With the uprising of small accessible autopilots and increasing knowledge, the concept of this configuration was given up in favour to a concept with the centre of gravity above the control surfaces. The lack of time and the high effort to create relative complex moulds for composite sandwich parts and the parts themselves slowed down the progress. A new upcoming technology (3D printing) changed  this project again. 3D printing is perfect for complex shaped parts in low quantity. It is perfect for creating objects with surfaces curved in two directions (like on a duct). For a prototypes where the minimal weight is not primary, 3D printing might be the best solution such as with this project.


I modified my CAD model of the Ducted Fan VTOL UAV for 3D printed plastic parts. I also built a 3D printer which fits my purpose with a built volume of 40cm diameter and 40cm height.

3D printing has further an advantage that mounting brackets and other small parts can be included in the structure.  In conventional building methods they are usually added in a later stage of fabrication. This reduces the time for mounting servos and other parts which can be a very time consuming task. In this prototype mountings for servos are already included in the structure. The control surfaces are directly connected to the servos and extremely light. Most of the structure consists of 0.35 mm (1/72”) to 0.5 mm (1/48”) thick walls with rips to stiffen it out.

Originally I had planned to equip the UAV with a self built autopilot. This autopilot is based on a Beagelbone as a processing unit connected via (real-time) Ethernet to a micro-controller which serves as an real-time interface between the sensors and actuators. This has the advantage that the processing unit can be exchanged according to the requirements by any other computer with a Ethernet port. The disadvantage is that compared to other available open source systems the developed system is in a very immature stadium. So I decided to use an autopilot based on the PX4 which I recently used for other projects and has a huge community.


The UAV is powered by one 3 cell LiPo battery with 3500mAh. The outside diameter of the duct is 30cm (12”), the height is 55cm (22”) and the take-off weight is about 1.2kg (2.6 pound). It has not yet performed its first flight, but some bench tests have been conducted. The produced trust is sufficient, but no measurements have been taken so far. Also the stators together with the control surfaces do a great job in elimination the reaction forces form the motor. Wool threads were fitted to the stators inside the duct to see if any airflow separations occur, which would inevitably cause a loss of control. The same will be done for the inlet to see if any separation occur trough influences like wind gusts or extreme manoeuvres.

Once the missing parts arrive the next step will be a free test flight equipped with analysis equipment (threads on the inlet, outlet and the stators recorded by multiple cameras).  Together with the recording function of the autopilot this should maximize the information gain to improve any non perfect test flight. This will hopefully happen soon and I will give an update.


Personally I can't imagine doing that kind of work anymore without a 3D printer. Even though the parts might be not perfect with a home made printer and composite materials might be more suitable, 3d printed (prototype) parts can greatly improve the manufacturing efficiency and let you concentrate on the task you really want to achieve. In my case it is to bring this Ducted Fan UAV into the air and modify it that way that it can be used as part of a fully automatic Unmanned Aerial System.

By fully automatic I mean a system which consists of a box which has a power- and internet connection which opens on command, the UAV takes off, fulfils its mission (possibly makes a transition into a efficient horizontal flight) lands fully automatic into the box ,and gets recharged or refuelled. This box can be located on the top of any building or tower or on a boat/vehicle. The user exclusively concentrates on the mission.

Currently I am looking for people who share similar interests for cooperation or collaboration. If you are interested or you know somebody who could be interested then feel free to contact me at: info (at) arminstrobel.com

More pictures can be found here arminstrobel.com.

Views: 4201

Comment by johnkowalsky on May 25, 2015 at 1:31pm

You say ducted fan I say tailsitter ;-)

Comment by Rob_Lefebvre on May 25, 2015 at 3:56pm

Very cool. Nice work.  I've been thinking of doing the same thing, making a ducted fan copter on a 3D printer.  

Comment by Andrew Rabbitt on May 25, 2015 at 5:54pm

Yeah!  Stick some wings on the side of it and make it transition to horizontal flight...


Moderator
Comment by Gary Mortimer on May 25, 2015 at 9:34pm

I'm +1 for tailsitter as well ;-) Dusty bin flies again! How do you handle the yaw with a single prop have you designed in some compensation as well in the body? I found I needed bags of surface dedicated to yaw with a single prop that meant less (but enough) for stability. 

Comment by Dan Neault on May 26, 2015 at 3:33am

I did mine at Shapeways, two years ago, and it came out real smooth. People should consider this if they wish to pursue co-axle airframes :)

 

Comment by Hans H. on May 26, 2015 at 4:34am
Very interesting! Will you test IC engine as well?

Do you print the walls with only one layer of 0.35 mm? Do you think it is strong ? How much does it weigh?

Was it difficult to build a larger 3D printer? Due to the constraints with the 12 " propeller, do you think it will be very difficult to build an even greater 3D printer to fitt a 20" propeller?
Comment by naish on May 26, 2015 at 7:33am

Great work...keep us updated!

Comment by patrice.rance on May 26, 2015 at 9:12am

I think i can give you some advises after my tests of singlecopter

https://www.facebook.com/patrice.rance/videos/10206758020857588/?l=...

Comment by patrice.rance on May 26, 2015 at 9:14am

In my case 3S batterie was not enough ! I put a 4S and it was better.

Comment by Armin Strobel on May 26, 2015 at 2:02pm

Thanks for the great comments.

@ johnkowalsky  You are right. Tailsitter might be a better name, or Monocopter, ... hope it flies and doesn’t sitt on its tail.

@ Rob Yes it is my plan to put some wings on it for a transition. But at first I will fly it without wings. Though the transition is a difficult part. I will avoid that by hopefully accelerating vertically on a speed which is sufficient for the wing to generate lift in the horizontal and then do the transition.

@ Gary I do have 4 stators with a asymmetric air-foil after the propeller. They are pretty big and have a high lift coefficient. I hope they are enough. If not I go back to my CAD model and add a 5th or 6th.

@ Dan  Nice work! Do you have a picture of the whole vehicle?

@ Hans Yes that will be the ultimate aim to have a bigger vehicle with wings for transition and an efficient IC engine and a precision landing system with automatic refuelling. I stay for now with the electric engine since it is easier to handle for now. But as you pointed out, at some time I hope this vehicle grows up.

The duct it self is just one layer and is certainly strong enough since there are just aerodynamic forces and the shape helps against buckling. In on of the pictures you can see that I added some rips to further stiffen it and to keep the shape during printing. Other parts have thicker walls. The weight over all is around 1.3 kg. For the next version I will weight every part separate.

Building a 3D printer was not really a challenge. More so the tweaking that you get the quality and the results you are satisfied with and/or fit your demands. I see no reason why it should not be possible to building an even bigger one. But consider the the printing time. My printer is relative loud and the duct needed 25 hours to print. So try to put the printer as far as possible from your bedroom :-). If you built a bigger one then stiffness will be an issue, but that is solvable.

@ naish Thanks! I will post here as soon as I have a nice video of a flight.

@ patrice  Great work. I love simple solutions. What (autopilot) did you use for stabilisation? I started with 3 cells that I have still the option to add one if needed. It is a starting point. Tell us more about your singlecopter.

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