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Building an octocopter for $30








little
          octocopter



I wanted something that would be able to lift cameras yet be harmless and made of parts that are both cheap and easily available. The end result matches all my expectations. It has a stable flight yet can be controlled in gusts of wind. With a1000 mAh battery it can stay in the air for 13 minutes. Below is a demo flight on a windy day.







Eight motors?


I just took the motherboard of an Eachine H8 (alias JJRC H8 Mini) and doubled the amount of motors. One quadcopter can be bought for $13 and parts like a motor or a set of propellers cost around $2.

www.banggood.com/search/eachine-h8.html

www.ebay.com/sch/i.html?_nkw=jjrc+h8+mini

www.ebay.com/sch/i.html?_nkw=jjrc+h8+mini+parts

The motors are a little further away from each other, to reduce the interferences between the propellers. In an original Eachine H8, the motors shafts are 55 millimeters apart. Here they are 63 mm apart, at the ends of balsa rods of 80 mm, 6 by 6 mm cross-section.

The motherboard doesn't know that they are two motors at each end instead of one. The two motors are simply soldered in parallel; they will receive the same power. The wires come from a thin USB cable.



wiring of
          the motors of an octorotor



Not every motherboard will be able to adapt itself to such a change. This one motherboard could barely control a quadcopter with 120 mm balsa rods. When I replaced it with a Hubsan X4 H107L motherboard, it completely failed.

The motor wires also act as suspensions for the motherboard. I learned that trick when my first Eachine H8 became unstable. At first I failed to understand that the problem was caused by a propeller blade that was slightly bend downwards. This caused vibrations that disturbed the accelerometers on the motherboard. Raising the motherboard so that it would only hold by the wires did help a lot, because the vibrations were less transmitted to the motherboard. Then finally I lightbulbed that I just had to bend the blade back in place.



octorotor
          motherboard on suspensions



Balsa wood?


Don't use balsa wood. Maybe better build a structure with carbon fiber rods or build a stronger balsa structure than I did. I do like my structure but it breaks easily. I often have to repair it with superglue (pour a lot on each side, wait till it sinks in, lightly push the parts together, wait till the glue forms filaments when the parts are pulled apart, breathe on the parts to activate the polymerization, push the parts strongly together, they will hold in seconds, then let cure ten minutes or so till the next flight). The battery in the image below is a 500 mAh double capacity one for Hubsan X4 quadcopters.



broken
          octorotor



The motors are first tightly wrapped in common polyester sewing thread, with a drop of superglue to hold down. Then both the flat end of the balsa rod and the side of the motor get a big drop of UHU hart glue soaked in. A minute later the parts are pushed together and the excess glue is shaved away. Then the position of the motor is checked and enforced using a ruler. The assembly is left to dry for a few hours then finally the excess thread above the balsa rod is removed.



octorotor
          motor glued in place



To do what with?

The video below may seem to be one more dull drone flight with a cheap low resolution camera and a bad landing. But think again. Did you ever see a drone video wherein the flying drone records the surrounding sounds? I soldered away the microphone of the Y2000 camera and hung it 1 meter below the device, connected to the camera through two 100 microns varnished copper wires. The sound emitted by the propellers is so weak that it can barely be heard.







If you need a better camera, a Y3000 or a 808 #16 have higher resolutions yet about the same weight. Be careful: "808" cameras are sold for $7 but they have a low resolution. To have a high resolution it needs to be a "#16" one. Also do take into account the type of lens. The narrow lens of a Y2000 or Y3000 camera sees the world through a keyhole while an 808 #16 with a 120° lens will yield a more open image.

www.aliexpress.com/wholesale?catId=0&SearchText=y3000+camera

www.banggood.com/808-NO_16-HD-120-Degree-Mini-Camera-Module-7g-p-82197.html



Eric Brasseur  -  April 11 2016
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