Simple and relatively cheap Octocopter using All in One Pro multiwii Flight Controller. So after the successful build of my Hexcopter I decided to try an Octocopter. This would be built using the same construction of the hex (and quad) and would also use the same motors, esc’s and propellers. I like to keep it simple and it also means I only have to worry about one spare for all the models as they all use the same bits. A2212 13T 1000KV brushless motors, 30Amp basic Hobby Power (simple) ESC's, and 10" 4.5 propellers.
Step 1: Design and mechanical build
So to start with I drew out a basic design and worked out the minimum dimensions needed for propeller clearance then looking at the sizes of fibreglass sheet I could get choose 12" * 18" as a good starting point. This fibreglass sheet was squared of and then the corners marked out for the tube mounts. This design uses 4 off 600mm 12mm diameter carbon tube and I was able to buy this cut to length from eBay. The motor mounts I choose were a plastic type which requires the tube to be drilled at each end whilst not hard to do the clamp type are a lot more convenient but 10 times the price.
So you can see in one of the pictures the holes for the mount are drilled 5mm from the side and 6mm from the adjacent edge and spaced 28mm apart. The corner hole is shared with the other clamp. Once you have all the holes drilled you can position the clamps and the tubes (with the motor mounts) and true up all the tubes with reference to the edge of the fibreglass sheet.
Step 2: Wiring
I then decided to screw in place the motors and do all the wiring. The power wiring was done firstly in pairs for each corner then the pairs were joined to make one side with a dean’s plug for the battery and the same on the other side. And the last connections were made from each side to a power distribution board to allow both sides to be connected together and allow other items to pick up power conveniently.
Step 3: Flight controller
When it came to mounting the "All in one Pro" flight control board I decided the correct place was in the middle and that mounting the board on rubber absorbers would be a good idea. so I firstly cut a spare piece of PCB fibre glass board and shaped it to a doughnut then marked out and drilled the 4 holes that would hold the flight board, then with the doughnut in place I drilled through the board into the main board and temporarily screwed the board down whilst I then drilled the 8 holes through both plates to fit the rubber mounts. Once happy with the drilled holes and with an arrow to show the front (and top) the plates were unscrewed and the rubbers fitted and Fight control board screwed on top with small spacers.
Step 4: Add batteries and go flying!
Then I choose to fit the batteries on either side, to allow the Velcro strap to go through the main plate I drilled and then slotted a hole using a 3mm diamond drill bit. Connect all the wires as per the multiwii website and that is it! Well not quite!! when I first finished this I fitted two batteries and gave it a try in the garden, all seemed ok but when you tried to take off it would fight against it's self? And eventually be on the floor seemingly struggling to take of. It was also most like it didn't have enough power to take off? Anyway to cut I long story short I had to play with the PID settings and then managed to get it to fly. Currently it’s "SO PLANTED" it almost jumps back to horizontal!
After playing with this model for a while I can report it has loads of power and if given some good stick input will disappear upwards!
Also worth noting whilst I was having a good (aggressive) fly around one of the propellers failed and I was very easily able to bring the model down to the ground, in theory the model should fly with two motors failed, but I wouldn’t like to try it!