Aerobot Quadcopter Project

Project Goals:

• Build a robust, sturdy and reliable platform on which various equipment can be mounted.
• Add a GoPro camera for aerial photography use.
• Add "intelligence" equipment (FPV, OSD and GSM sensors and controllers) and configure the bot to fly autonomously.
• The internet of things - turning the bot into an IP device.

Bill of Materials:

Required Parts

Parts:

• Frame:  
• 1 x DJI Flame Wheel F450
• Mass: 282g, Price: $32
• Motors:  
• 4 x NTM Prop Drive 28-30S 800kv
• Mass: 65g, Price: $16
• Propeller:
• 1 x 10 x 4.5 SF Props
• Mass: 15g, Price: $4
• ESC's:  
• 4 x HobbyKing 20A BlueSeries
• Mass: 39g, Price: $11
• Battery:
• 1 x 4s Turnigy 4000mAh
• Mass: 437g, Price: $32
• Flight Controller:
• 1 x HobbyKing KK2.1 Flight Controller
• Mass: 55g, Price:$30
• Connectors:
• 1 x Deans Ultra Plugs (1 pair Male/Female)
• Mass: 40g (per pair), Price: $3
• 12 x Gold Bullet Connectors (3.5mm - female)  
• Mass: 30g (per pair), Price: $5

Total Mass: 1.5kg,  Expected Thrust: 1.2kg x 4 = 4.8kg
Cost: $220

Other Parts:

• Transmitter: my trusty Spektrum DX7
• Receiver: Spektrum AR6100e
• Miscellaneous:  soldering iron,  solder (rosin core), power and ground electrical cable (12-gauge, about 6 inches of each), heat shrink insulation, velcro straps, cable ties

Choice of Parts

DJI Flame Wheel F450 Frame

After reviewing many articles on the subject, I elected to go with a quadcopter setup using the DJI F450 frame.  This provides a cost-effective setup for a first time project like this while also providing a decent amount of space on which to mount equipment plus sufficient payload-carrying capability PLUS, most importantly, there is a ready supply of spare/replacement parts available. Additionally, DJI provides an ingenious integrated power distribution system embedded in the metal hubs which saves space and facilitates ease of setup.  While DJI offers a so-called "ARF" kit (which sans a battery, receiver and flight controller can hardly be described as ARF) which combines, in one box, the frame, motors, ESC's and propellers, I opted to select the various components based on my requirements of wanting ample lifting power, low weight at a low price. 

NTM Prop Drive 28-30S 800kv

The prop drive 28-30S 800kv provide incredible amounts of torque for such a small motor.  At just $16 each and weighing in at just 65g, these motors when equipped with a 10x4.5 slow flyer prop, should produce approximately 1.2kg of thrust!  We selected a very big 4s Turnigy 4000mAh battery (for an unbelievably low price of $32!).  This weighs in at a whopping 437g and contributes approximately one-third of the takeoff weight and was selected in an attempt to allow the vehicle endurance time of, at least, 15 minutes. 

HobbyKing KK2 Flight Controller

For the flight controller, a HobbyKing KK2.1 was selected - this is the latest version of the flight controller designed by legend, Rolf Bakke.  While this flight controller does not include some of the high-end features found of the expensive controllers, it contains more than enough features for now and at a price of only $30, is a great to get in the game.  Eventually, I expect to replace this with a fancy controller (like the NAZA flight controller which can run $200 or more depending on the features needed), but before spending the money, I prefer to know exactly which additional feature I would like.

 

Assembly

 

Assembly begins by attaching a female Deans ultra plug to the battery and creating matching pigtail using the male Deans ultra plug and some short pieces of 12-gauge wire for each the power and ground connections (or alternatively buy a prefabricated pigtail with a male plug).  Be careful not to cross-wire this; connect the male and female plugs to verify this.  Then solder the pigtail connection to the appropriate terminals of the power distribution  board (PDB) on the hub by soldering the red wire to positive '+' and the black wire to negative '-'.

Next, the ESC's are prepared by soldering three female bullet connectors to each of the three (black) wires that will attach the ESC to a motor.  Once complete, the arms are attached to the hub (with the white arms at the front and the red arms at the back), the motors mounted to the arms using the screws provided with the flame wheel kit, an ESC is attached to each arm using cable ties and connected to that motor using the bullet connectors.  At this time the positive and ground wires coming off the ESC can each be trimmed to length and soldered to the appropriate terminal points on the PDB.  For future reference, the side of the quadcopter containing the white arms is designated to be the front and the side with the red arms is the back.  This orientation will be maintained for the rest of the assembly and beyond.  The use of the red and white arms will further all us to identify the direction that the quadcopter is pointing when it is far away.  

At this stage, the assembly is just about complete.  All that remains is to add the receiver and the flight controller and wiring it all together (receiver connects to the left side and motors connect to the right side of the KK2 board.  The receiver was mounted, using double-sided tape, to one of the side panels (the other will be used for the GPS and FPV equipment. In order to mount the flight controller, I simply used the foam padding container that it was shipped in by hot gluing the controller board to the padding and gluing the padding to the mounting plate on the hub.  Using the padding provides the dual benefit of both protecting the flight controller from damage (in the event of a rough landing) as well as reducing the transmissions of vibrations from the frame to the flight controller.  Testing of the receiver and the KK2 flight controller can be now be conducted in order to verify that all is working correctly.  It should be noted that the KK2 gets its power via the ESC on motor 1.  Unless motor 1 is connected (and the battery is attached to the PDB), the flight controller will receiver no power.  Once testing of the KK2 is complete and satisfactory, the top plate of the hub can be attached.

Before attaching the propellers, it is necessary to ensure that each of the motors is rotating in the correct direction.  Each motor is given an identifying number starting with the front left motor which is assigned the number 1 and then continuing from with the front right and then proceeding in a clockwise fashion.  It is essential for effective yaw control that diagonally opposite motors spin n the same direction.  By convention, motors 1 & 3 should spin clockwise while motors 2 & 4 should spin counterclockwise.  In order to spin the motors, we must first arm the KK2.  This is achieved by using the left stick in the transmitter and moving it down (zero throttle) and to the right.  Holding it there for a couple of seconds will arm the KK2 and increasing the throttle stick will now cause the motors to spin.  It should be very quick and easy to verify the direction of rotation of each of the motors.  The direction of rotation on any motor can be easily reversed by disconnecting two of the wires between the ESC and the motor and switching them (yes, you can switch ANY two wires, it does not matter which to and the motor will reverse - this characteristic of a stepper motor).

At this point we are ready to mount the propellers and begin tuning the flight controller.  We want to ensure that the gyros are zeroed out on a level surface and will then go about messing with the P and I gains on the controller to ensure that the self-leveling mode is stabilizing the quadcopter's flight.  This will be useful for FPV flying and aerial photography while reducing the overall agility of the vehicle.  Here is some video of the quad spinning up for the for time and performing its very first aerial test.  The goal here is to tune the controller.