Director's Cut: A nice place to fly - Hexacopter in Cameroon / Africa

One of my videos - the MM6 cameroon video - received more than 1000 likes on Vimeo, and about one million views in total (until march 2013). Thank you all very much!! Here I present the Director's cut, showing some additional scenes and longer sequences.

 Watch the video here.

If you don't know the original video, I recommend to watch it first, and then decide if you would like to see the extended Director's cut: https://vimeo.com/18873955

 

GEMiNi in the TV

A pretty spontaneous interview for a report on the new i-phone app of the European Space Agency (ESA).
Radio Bremen TV asked me to do a quick FPV flight in their foyer:

Video: ARD Nachtmagazin

Flower power!!

Wind tunnel test data

This morning, I did some wind tunnel tests with the GEMiNi chassis. The GEMiNi was designed for FPV air races at high flight velocities, therefore the aerodynamic properties are important (well, it was also designed to look good of course...). I measured the aerodynamic forces generated by the frame (excluding the influence of the propeller's downwash) at a flight velocity of 12 m/s (= 43 km/h, maybe half the top speed) in a wind tunnel using a 2-axes force balance.

Angles of attack between 0 (hovering flight) and 90 degrees (vertical climb) were tested. The angle of attack is defined as the angle between the oncoming flow and the propeller disk. Both the lift coefficient (perpendicular to the oncoming flow) and the drag coefficient (parallel to the oncoming flow) were determined for each angle of attack (n = 3). The coefficients are based on the planform area of the copter.

Four different setups were tested:

• "canopy-tilt-" refers to the hexrotor without canopy and without the inclination of the rotors. This setup is very much comparable to a conventional, standard hexrotor like e.g. the MM6.
• "canopy+tilt-" includes the canopy, but no rotor inclination.
• "canopy-tilt+" is without canopy, but with rotor inclination.
• "canopy+tilt+" is finally the GEMiNi as I am currently flying it.

The results reveal that the inclination of the rotors has a large positive effect on the overall performance. In combination with the effect of the canopy, the rotor inclination reduces the negative lift by 17 % to 70 % at angles of attack relevant to fast forward flight (10° to 45°). Negative lift pushes the copter down in forward flight and must be compensated by additional thrust. This would reduce the maximum flight velocity and requires additional energy.

Lift coefficient vs. angle of attack. Large lift coefficients at angles of attack between 10 and 45° result in lower thrust requirements to keep the copter in the air. The application of a canopy and rotor inclination enhances the performance.

Additionally (and more importantly), the drag of the copter is reduced by 14 % to 40 %. Aerodynamic drag slows the copter down, so any reduction is clearly beneficial.

Drag coefficient vs. angle of attack. The drag of the copter is reduced quite dramatically by using the canopy and rotor inclination. Top-speeds will be much higher compared to the conventional setup.

To conclude: The analyses have shown, that the canopy and the rotor inclination both improve the aerodynamic properties of a hexrotor substantially. Higher top speeds, respectively a larger endurance during cruising flight will be possible. The additional weight of the canopy is negligible and will hardly influence these conclusions.

P.s.: It is constantly raining here in Bremen, and I am going snowboarding tomorrow, so the outdoor flights are a bit delayed...

Done. Looking forward to first outdoor flights...

What I really dislike in small copters is that they have the same amount of cables as larger ones, but almost no space...
The very first flights were done yesterday night. I used the default parameters from the BOLT S|2, and it seems to fly very nicely. There is a bit too much power, I prefer when my copters hover at about 50% throttle (like the BOLTs). This one hovers at 33% throttle. However, the GEMïNï is built for speed, and too much power will certainly not harm. It will also be possible to carry the GoPro HD Hero I think. The GEMïNï looks amazing in hovering flight...: Due to the tilted rotors, the tail hangs a bit lower than the rest (see my 3D animation), which gives it a crazy look :-D .  

Here are some images I shot this morning:
 

More propeller tests

Recently, I discovered some small counter-rotating propellers that I didn't know before. I ordered some and did some tests. The red 4x4.5" props look really good, nice thin airfoils and a good precision. During the tests, they made the least amount of noise, and are currently my preferred ones. The performance of the 4x2.5" props is even better, but they have a pretty terrible sound and seem to be less balanced. Both propellers outperform the AirAce propellers, but this is not really a surprise because the AirAce have a smaller diameter and more blades. What is also interesting is the weight of the propellers. A propeller with a lower weight potentially has a lower moment of inertia which is beneficial for the control loops:

• AirAce: 2.1 g
• 4x2.5": 1.5 g
• 4x4.5": 1.3 g

So this is an advantage for the 4x4.5" propellers, especially because the weight of this propeller is more concentrated to the center, which should further lower the momentof inertia.

The difference in endurance is quite dramatic, up to additional 2.5 minutes (+20 %) are possible when using the 4x2.5" instead of the AirAce.

Test setup

Left to right: 'AirAce', '4x4.5', '4x2.5'

Static thrust vs power input (@ 12 V)

Endurance vs take-off weight

GEMiNi, frame + canopy

Here are two images of the current status. Green is the favorite colour of my girlfriend ;-) . There will soon be an additional one in purple I fear...

GEMïNï progress...

I just realized, that I haven't yet posted an image of the PCB that I am using since half a year in the BOLT S|2 and soon in the GEMiNi. It is really small and weighs around 1 gram. It contains the minimum number of parts possible + 3 LEDs:

Thermoforming the canopy also worked pretty well once I found the correct temperature. I tried Vivak (PET-G) and black Polystyrol:

The chassis should be finished very soon, I am really looking forward to putting everything together...!

GEMïNï motors arrived

Yesterday the motors arrived from hobbyking (Turnigy C1822-2100KV). As usual with small motors, the shafts were all way too short to attach a propeller. Three-bladed props do not really work nicely with the provided prop-saver... Hence the original shafts had to be removed. It was pretty hard to exchange all motor shafts, as they have a very tight fit with the bell, and they are additionally glued with cyano. Some "nail polisher remover" and some heat helped a lot to remove them. The quality of the motors is really good.

I did some tests and compared them with the Robby Roxxy 1815-25 that I use in a similar copter (the BOLT). Both motors have the same size and the same weight, Surprisingly, the turnigy motors have the exact same performance as the much more expensive Roxxy motors. The increased KV number leads to an increase in the peak RPM and thrust.

The endurance with these motors will be around 8 minutes (the aerodynamic efficiency of the GEMiNi will be higher than that of the BOLT, because coaxial motors have somewhat higher losses - a factor of 0.75 to 0.8 is a good approximation).

The only thing that is really different between the motors is the price per motor:
9 € Turnigy (incl. taxes...)
27 € Roxxy

GEMïNï - further canopies ...

Still waiting for the motors and ESCs, I was playing around with the canopy design:

Shrediquette GEMïNï from W. Thielicke on Vimeo.

Shrediquette GEMïNï

Holidays are copter days... I spent some time during holidays to design a new FPV hexacopter. It will be equipped with the AirAce props that I used in the BOLT and some cheaper hobbyking motors (2200 RPM/V, ca. 15 grs.) + turnigy Plush 6A ESCs + a 1000 mAh 3S lipo. I also designed a canopy for the copter which I will print in 3D, thermoform from 0.5mm plastic sheet, and eventually laminate with carbon fibre. The propellers are tilted 10° forward in order to decrease the angle of attack of the copters body in forward flight, which will hopefully decrease the net aerodynamic drag in fast translational flight. I am hoping that this copter will be able to fly even faster than the BOLT. The GEMiNi is slightly larger, the max. dimension is 315 mm from propeller tip to propeller tip (diagonally). I will use the CCD-Killer camera, and an Airwave module for video transmission. The CCD-Killer is still my favorite camera in terms of image quality and exposure control vs. weight and size.

Ever since I built my first tricopter, I wanted to build a canopy that somehow resembles the Limulus, an impressive animal that seems to have survived from the primeval times... In 2008, I started to draw some 3D canopies for the DLX tricopter but never finished them.

I like the design of the Limulus ("Horseshoe crab") a lot, but in 2008 I didn't know how to create the chassis from the 3D model. Now I have the opportunity to print the model and to build it using thermoformed flat film. The thermoformed model will serve as negative cast. I never laminated complex shapes with carbon fibre before. Probably the first attempts will not look very nice...

Here are some pictures of the GEMïNï and early prototypes:

I am currently putting together a list of all the things I need for the new copter. I will use the Shrediquette xMega controller with the MPU gyroscopes / accelerometers. Hopefully the copter will be finished in the first quarter of 2013. After finishing this copter, I will most likely take a slightly longer break from my hobbies.

Ein BOLT für alle Fälle - RC Flight Control 3/2012

RC Flight Control 3/2012 title page

In the latest issue of the "RC Flight Control", there is an article about my BOLT Y6 hexacopter. The article is about how and why I designed the copter and there are some details about my previous copters. Paul again shot some nice photos, one of them is on the title page. A preview of the magazine is available here:
RC Flight Control PDF Preview 3/2012

At least in Germany you should be able to get a copy of this magazine in every larger newspaper store.

IMAV 2012 and new xMega Board

As some might have noticed, I didn't post news in this blog for some months. But now I  can announce my new xMega based control board and some news from the IMAV 2012 competition.

IMAV2012 in Braunschweig, Germany

We (team Akaflieg Bremen = Tumba & me) were participating in the IMAV2012 competition. In principle, the contests were similar to last year(s), see IMAV2011 post.
It was great fun again, all our copters worked very good and reliable. Also the video link was very stable, even at longer distances (we always use 5.8GHz 25 mW AV transmitters and a diversity receiver with directional antennas). The indoor autonomy competition was pretty challenging (see video below). These are the results for our team:

• Outdoor Autonomy: 3rd place
• Outdoor Flight Dynamics: 2nd place
• Indoor Autonomy: 1st place
• Indoor Flight dynamics: 1st place

I am not 100% sure about the results of the other teams, if you have information on this, please tell me, I'll add it to this post.

The conference and the competitions were so much fun, thanks to everybody that was there!!! See you next year in Toulouse hopefully....!

Here is a video from a local TV station that did a short documentary about our IMAV2012 preparations:
http://www.youtube.com/watch?v=SM-ugRY_AR8

And here is a quick video from our competition flights:
http://www.youtube.com/watch?v=E2fwMWeuqGw

And finally another short TV spot by RadioBremen TV:
http://www.radiobremen.de/fernsehen/buten_un_binnen/video38606-popup.html

I participated with two copters, the BOLT and my new BOLT S|2. Both copters use the ATMEL xMega32A4, which runs at 3.3V and with 32MHz. It is a very nice and powerful controller. One of my copters uses the ADXRS / ADXL IMUcube, the other uses a MPU-6000 IMU.

 New xMega board

The new control boards were developed in cooperation with other Shrediquette users from the german website Roboternetz.de . The goal was to make them as small and simple as possible with as few components as necessary. The final xMega board for the MPU6000 IMU only measures 16 x 18 mm, and it is capable of driving six motors with hardware PWM. The xMega board for the ADXRS/ADXL IMUcube measures 19 x 22 mm. Well, the time for my hobbies is still decreasing, but I want to keep my project open source of course. So I decided to upload the PCB Layout + schematics + the source code that I am currently using for both boards. But they are not really documented, they are not optimized at all, and they do not work with my GUI. But maybe some of you can make use of some parts of it:
xMega_ADXRS layout, schematics, source code
xMega MPU60X0 layout, schematics, source code

Pictures from the IMAV 2012 competition 

(Taken by Tumba and Matey)