Intro: Simple Plywood Tricopter.
Nice tricopter project using 3mm plywood for the frame and a full size servo for the yaw. No fancy pivots or hinges or tiny servos which break!
Using cheap A2212 brushless motor and Hobbypower 30A ESC. 1045 propellers and easy to use KK2.1.5 Flight control board.
Step 1: Design and Cutting Out.
I was really pleased with how this model turned out. i always use the same method for my models but this time i took it a step further by reducing the material used.
When you print out the plans it is very important to make sure the plans have been printed at 100% with no scaling. each arm should be 200mm long.
So basically once you have printed the plans out you will find that the whole model will fit on a piece of 3mm plywood 300mm * 300mm which you need to double up as each bit needs to be cut twice. meaning you only need a piece of plywood 300 by 600mm or 1 foot by 2.
You will need to stick the plans onto the wood using a stick glue and then carefully cut out all the bits. Each time you cut a bit out make sure the slots are the correct size and that corresponding bits fit together.
The design has been carefully considered to use the same bits in different places, so for example the two stationary arm are obviously identical, but so are the top and bottom of the arms and in fact the top and bottom are symmetrical so will fit either way around. When you have finished building this model you will only have 3 small bits spare and all these bit are associated with the servo arm.
Once you have cut out all the bits you then need to drill all holes, and once you have done the holes you can then peel of the paper. (that's the beauty of using stick glue)
Step 2: Gluing the Bits Together.
I spent some time on the design making sure bits would fit together securly. Before you start gluing all the bits together you should test build the arms first just to make sure you will be able to slot all the bits together.
My preference is to use gorilla glue. For a start it works really well and only takes 2 hours to set. But if you are new to Gorilla glue make sure you follow the instructions as you need to wet one surface of the wood and apply the glue to the other. then you must clamp the bits together while the glue sets. ALSO its is very important to keep the glue of your skin so either wear gloves or use an applicator.
you could use a PVA glue but that can take a lot longer to dry and if like me you are impatient then waiting for glue to dry is no fun! This whole model was started on Friday evening and was flying by Sunday lunch.
Step 3: Electrical Fit Out, Motors and ESC's.
The speed this model came together was really impressive. once all the bits were glued then its just a matter of slotting the arms onto the central hub (but don't glue) and the add the yaw motor mount using two M4 * 16mm screws with nylocks.
To mount the motors i have used the motor mount which comes with the kit. To get the holes in the correct place i position the motor mount (without the motor fitted) and holding the mount in place drill the first hole. Then i place a M3 screw in the hole and drill the opposite hole, again i place a M3 screw in that hole and then drill the last two. In this manner you should get all the holes to line up correctly when you fit the motor.
You can see in the picture above how i have fitted the motors and threaded the motor wires through the arms and out of the hole. This makes for a nice clean model and keeps all the wires out of the way. The motor wires are then soldered straight onto the ESC, this gets rid of the 3 wires and connections you would normally have from ESC to the motor. At the power wires to the ESC i have added 4" extra red and black wire and like the motor wires these have been fed through the arm and are all joined together in the area in between the center section.
Whilst i was soldering the motor wires onto the ESC i also choose to add the wiring to the lights. As shown in one of the pictures this was soldered onto the pads on the other side to the main power wires.
Step 4: Yaw Servo.
This design has made use of a full (normal) sized servo. The reason being i tried a small tricopter (HJ-Y3) which used a mini 9 gram servo, and very quickly realised that this was the weak point. Even though the gears were metal it did not stop them stripping at the slightest crash! also the model was made from fibreglass which seems to break very easily.
SO the servo i have used is a Bluebird servo, it happens to be a high speed metal gear servo but i think you could get away with a standard servo. BMS-631MG.
As shown in the picture and explained in the vid the servo is mounted with the horn on the side of the motor and then its just a short link of piano wire to the motor mount above.
I designed the motor mount to only have 20 Degrees movement up and 20 Degrees down, from the testing i have done so far this seem to be plenty. I also believe that limiting the movement of the motor mount helps to protect the servo.
Step 5: KK Flight Controller and Settings.
I have used the KK 2.1.5 flight control board for this project. I really like the simplicity of the board and the fact that you can make changes on the board without having to connect to a computer or use bluetooth to a phone/tablet.
Depending on how you want to fly this model will depend on how you mount the flight control board. If you wish to fly the model as a "Y" with two motor at the front then the board arrow should point in the middle of the two. If however you wish to be awkward (like me) and want to fly configured as a upside down "Y" the the board arrow should face the front motor. IT DOESNT MATTER WHERE THE SERVO ARM IS. As far as the flight controller is considered the servo is just used to change the yaw of the model and no matter where it is it will always cause the model to rotate.
If you are flying the default Tri then the KK will show you the motor number and tell you the motor direction. however i don't think it really matters as long as you get two in one direction and the last one going the opposite way. But for clarity motor one should be clockwise as should be 3. and motor 2 should be counterclockwise. unlike mine! (but is still works)
Once you have connected all the ESC and the servo (in position 4) then you can connect you battery and configure the controller. Motor layout should be Tricopter with servo in 4. Then i checked how the model worked without the propellers, with the throttle up to start the motors move the model around in a circle and confirm the servo is moving in the opposite direction to oppose the action. In my case it wasn't moving in the correct direction meaning the model would have spun out of control. To correct this you need to go into mixer editor and scroll down to channel 4 (the servo) and change the rudder value to -100. While you are at it change the self level setting to always on in the mode page, and finally to get you stared up the P Gain to 75 in the PI editor.
Step 6: Finishing Touches and Improvements.
When i first tried this model i squeezed the battery in between the central sections, this worked ok but i decided to change the design to add a better position. also the battery need to be off-center to counterbalance the weight of the servo.
Also i added holes in the new central bits to allow a tie wrap to be interested to fix the arms into place.
This model is very nice to fly and really fun. i cant wait to fly in a bigger field and she what it can do!
Second Prize in the
Make it Move Contest