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Hexacopter

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19.01.2010 The set "MK Basisset Hexa" ist available again in the Mikrokopter Shop. Ordered one set together with a 35 MHz R/C receiver. 30 minutes later the shop displays sold out for the set.
21.01.2010 Parcel was handed over to DHL.
22.01.2010 Parcel has arrived. Unfortunately I'm out of town for the weekend. Assembly starts on Monday.
25.01.2010 Mounted the motors to the arms, installed cables, soldered and mounted LED tapes. Joined arms with centerplates. The package is missing the nyloc nuts
26.01.2010 Started soldering the brushless controllers.
27.01.2010 Soldered and mounted BL controllers and Flight Control.
28.01.2010 All cables soldered, mounted landing gear and camera plate. First test: LEDs shining bright and 4 motors running. Have to patch Flight Control to hexa mode.
31.01.2010 Configured Flight Control, matched hood, fixed propellers, charged batteries. First test in the backyard. Power is good, Hexa starts to hover. Seems to be easy to handle, but not for me. Two forced landings in the snow without damage. Have to practise on a more open terrain.

First test
First test
07.02.2010 Longer hovering flights in the gym. Casual drifts and runaways resulting in harsh landings. But the handling slowly improves. Next time I must try the altitude control.
13.02.2010 Testing altitude control in the backyard. Using altitude control together with some expo on nick and roll levers make flying a bit easier. Hovering works good now and I dare to go higher. Next task is to exercise yawing.
20.02.2010 Visiting the local Quadro scene at the "Lichtwiese". Due to the weather only one pilot is there. After 12 minutes flight time I'm going home again with cold fingers.
21.02.2010 Boom! My second appointment in the gym. Getting closer to the Hexa after two long flights to better hear the beeper. With my left hand over the hood I smoothly push the throttle. Suddenly the Hexa sets full power, pushes towards the roof and falls down. I'm bleeding from two cuts in the face and beeing taken to the hospital. From the first glance the copter looks severely damaged but after all most of the parts are still in good shape. All propellers need replacement, one arm is bent and two motors went loose. The FC is damaged at one mounting hole but still looks OK. About the cause I can only guess. Possibly the altitude control was left switched on and went crazy while still on ground. However, it could just have been an operator error. I will stay away from the gym for the next time. And of course away from rotating objects.
15.05.2010 Within the last weeks all missing spare parts have arrived. After the FC turned out to be beyond repair I had to buy a new one together with two arms, a hood and one engine. The engine test revealed a bearing damage for two other engines. Since I don't have the tools to replace the bearings I ordered two Roxxy 2827/34 on ebay. Those have a longer shaft and different color but are otherwise same as the 2827/35. This time I limited the Max Throttle to 160 which is still enough power for a unloaded coper. Test flights went succesful this weekend. The copter season is opened again!
11.07.2010 Received a camera mount from LCC-Shop. It weighs about 330g and looks very stable. Unfortunately ist doesn't fit underneath the Hexacopter. I have to reengineer the aluminium arm and make a new camera plate from 1mm-Epoxi. Connecting the servos to the FC works immediately, provided that the FC already has a second RECOM regulator. Some test flights still show a slight camera tilt but the video is quite stable. Time to get a HD camera.

Camera mount with roll-nick-compensation
Camera mount with roll-nick-compensation
03.10.2010 Two months ago I decided to buy a Samsung WB2000 camera, mainly for its HD video feature. Now the Hexa has to carry a payload of almost 500g, which seems to make no problem. First test flights with camera mounted showed issues with the autofocus and "floating" pictures. It seems like the autofocus is only active at the start of a video recording. So, when starting the recording on ground, the focus is adjusted to close-up range, which leads to blurred pictures when airborne. A workaround is to direct the camera into the sky when starting the recording. The floating pictures are caused by the cameras image stabilisation. Switching off both mechanical and digital stabilisation results in a better quality for aerial videos. A first video can be seen here. The video sequences already look good for ascent and hover flight but for descent they start shaking, which maybe comes from the Mikrokopters attitude control. Even after balancing out the propellers and damping the camera mount this effect would not completely disappear. Altogether the image quality of the WB2000 could be described as moderate. The pictures are missing a bit contrast and especially for the green colors the resolution is low. To be fair I wouldn't expect movie quality for that price segment. Expensive digital camcorders probably offer a better quality but have the disadvantage of a sparse wide angle. So I will keep the WB2000 for now - hopefully it won't fall out of the sky ruggedly.
20.10.2010 The Hexa accompanied me on my vacation to France and thus I was able to gain some experience in filming aerial videos. Quickly I observed the relatively short mobility range of approx. 50 Meters. Beyond that range it will get difficult to distinguish the aircrafts outline. To some extent the LED strips are concealed by landing gear and camera mount. To perform more spacious flights one needs either FPV equipment or computer aid, in other words, an autopilot. So I set myself the target of developing an autopilot for the Mikrokopter. It shall be based on a 10Hz GPS and the MK3Mag compass. To get a feeling for the difficulty and estimate the required computing power I started with developing my own flight simulator. After that I wrote a quite simple autopilot and ported the code to AVR-C. It turned out that a 8-Bit microcontroller like the XMega64 could easily process the code at rates of 10Hz and more. As soon as I start with the project I will link it here.

12 December 2010, Achim Walther, Mail