In this series on how to build a FPV racing quadcopter, the main components that we are going to be using are the ZMR 250 carbon fiber mini quadcopter frame, the Open Pilot CC3D flight controller, Emax 12A SimonK ESCs (electronic speed controllers), DYS BX Series 1804 2300KV brushless motors, the FlySky FS-T6 radio transmitter along with the FlySky FS-R6B 6-channel receiver and a Fat Shark FPV system. Our sponsor URAdrone.com also makes a nice DIY combo kit available which would also work out quite nicely for following this build.
A FPV racing quadcopter may sound intimidating but really it is quite a simple multirotor consisting of five very basic systems:
- 1)The Frame: Is the physical "body" of the quadcopter.
- 2)The Power Distribution System: Distributes power to the system or systems of the quadcopter and includes a power source such as a battery.
- 3)The Flight Controller System: Interprets the signals from the radio control system and sends the appropriate response to the electronic speed controllers which in turn control the power sent to the motors.
- 4)The Radio Control System: Is controlled directly by the pilot and sends the appropriate signals to the flight controller system.
- 5)The FPV or First Person View System: Allows the pilot to "see through the eyes" of the quadcopter via a camera system; simulating being on board the actual aircraft which is known as the first person view.
The ZMR250 carbon fiber frame kit consists of two bottom frame plates, an upper frame plate, camera damper, four rubber damper grommets, four landing legs, four arms/booms, a camera frame (front frame piece), eight standoffs and required screws and nuts (above photo). For this build we want to mount the battery underneath the quadcopter racer rather than on the upper deck as is common with most of the other FPV racers. Our logic in doing this is to maintain as low a center of gravity as possible. For example, which is going to handle a high speed turn better, a transport truck or a Ferrari? The Ferrari obviously because of its lower center of gravity. In comparison, which quadcopter racer is going to handle high speed maneuvers better, the one with the battery mounted on the top deck or the one that keeps the weight as low as possible (to the horizontal axis of the motors)? Again, the latter is obvious. However, for us to do this we are going to have to make a very slight modification to the two bottom frame plates.
In the above photo, you'll notice that one of the rectangular cutouts in each of the bottom frame plates has been outlined with a gold Sharpie marker. Using a Dremel and carbide bit lengthen each of these cutouts by a few millimeters to allow for a XT60 or Deans T-plug battery connector to pass through the frame. This will allow us to mount the battery under the quadcopter racer and have nice clean wiring from the battery to the power distribution system. (IMPORTANT: As we assemble the frame these modified cutouts need to be to the rear of the racer.) Once this is complete take one of the bottom frame plates and pass two velcro battery holders through the slots as shown in the photos below.
We will now take the other bottom frame plate and add our standoffs. In the photo below, we have marked the standoff mounting holes with a gold "x".
When mounting the standoffs it is important to use a very small amount of blue Loctite Thread Locker on the threads of each of these screws because later on they will not be easily accessible for tightening if they should loosen from vibration (below three photos).