How to Build a Low-Cost RC Combat UAV

Building an RC aircraft can be as expensive or inexpensive as budgets allow. If you plan to chase other pilots in the air on a path of mutual destruction, keep expenses low and build a disposable flying platform. In this case, using a sheet of rigid construction insulation fits the bill with the bonus of a UAV that is fast and maneuvers well.

There are components that must survive from one craft to the next such as the radio receiver, BLDC motor, LiPo battery, and control servos, provided the invading UAV’s propeller does not chop through these parts, which can happen on occasion. That is why a combat builder will acquire inexpensive flight components and protect them with durable enclosures.

Figure 1 details the overall dimensions of the parts to be fashioned from partial sheets of ½ in. and 1-½ in. thick, pink, rigid polyurethane insulation available at most building centers. The dimensions and shapes can be modified to your preference, but keep the overall mass of the craft similar to maximize the motor’s ability to carry the structure and maintain good flying characteristics.

Figure 1: Combat UAV foam parts. (Image source : Don Johanneck)

Duct tape and hot glue are the adhesives of choice, with some parts requiring filleting to bolster sidewind forces. Parts cut using a CNC or by a skilled hand fabricator may be redesigned to have tabs and slots that cut down on the need for reinforcement and often provide an option for quick repair. An example of a CNC cut sheet is included in the blog resource links.

The sides of the triangular body can be reinforced with thin plywood strips or ½” channel plastic sheet rock edging to reduce wing warping during extreme maneuvers. Hot glue and a layer of duct tape on the top and bottom of the strips will help keep them in place and add strength. The fins may also be reinforced with triangular strips of foam or “fillets” hot glued at the root of the fin where it meets the body. See Figure 2.

Figure 2: Reinforcement techniques. (Image source: Don Johanneck)

To speed the transfer of components from a destroyed plane to the new platform, a unified motor mount and flight control module can be built or 3D printed. Any configuration will do if ventilation is provided for components that may get hot during flight. The example in Figure 3 shows a wooden spacer between the motor and the 3D printed parts. The brushless motor can become hot enough during flight to soften 3D printed material, which could result in motor mount failure, leading to a crash and adjacent component damage. Hold the components onto the plane by cutting slots in the body and installing Velcro straps. Sample STL file links are provided below for experimentation.

Figure 3 : Modular components. (Image source: Don Johanneck)

The aircraft is controlled in flight by setting the throttle level and manipulating the control surfaces. For this design, only elevators for pitch and ailerons for roll are needed but they are combined as “elevons.” Most radios have provisions for using elevons and include instructions on-screen or in the manual on how to set them up. Servos can be added to the platform using hot glue, 3D printed mounts, or making mounting holes in the body. Control horns can also be 3D printed or cut from wood. For the servo/elevon control linkage, a section of stiff wire was crafted from inexpensive utility marking flags found at many hardware stores.

For this aircraft, I prefer to use a 4250 size 800KV motor with a twelve-inch pusher prop. I also use an 80-amp ESC with a uBEC for receiver power. A 4500 mAh 4S LiPo battery provides a nice amount of power and flight time without getting excessively heavy. A complete blog on RC Power System Basics is available in the DigiKey Resource Library. Share this blog with friends and get a combat team up in the air!

Important Note: Never fly alone in case the unexpected happens and you need emergency assistance. RC aircraft like this are great fun to experiment with and engage in combat. Never forget the craft is powered by a strong motor turning a sharp propeller at high RPM. Although you may be tempted to launch the craft from below, you will realize that as the craft leaves your hand, the spinning propeller is traveling toward your hand. Side launching or using a custom, hands-free launch platform are the safest methods. To watch how launching is done properly and for some RC combat fun, watch DigiKey’s “How To Get Technical” video on “Explore R/C Night Flying with NeoPixel LEDs.”

Design Files

Combat Plane CNC Layouts:

Combat Plane Modified

Combat Plane 3D Print STL Files:

Combat Box

Combat Box Lid

Combat Motor Mount

Combat Servo Mount A

Combat Servo Mount B

Combat Horn A

Combat Horn B