In the Return of the Jedi, there is an amazing scene where Luke and Leia chase down scout troopers on speeder bikes to protect their mission to take out the Death Star shield generator. The speeder bikes are capable of high speed travel and require skill and fast reflexes to fly. The FPV view from the speeder bikes is breathtaking as they fly between the giant trees, barely missing them.
The popularity of quadcopters has developed into a new hobby of FPV quadcopter racing, where instead of flying the quadcopter by looking at it, the pilot uses FPV goggles. Flying this way gives you the feeling of sitting on the quadcopter while you are flying. You get to experience the racing drone as if you were sitting on the drone while piloting.
The development of the FPV racing hobby was fueled by the development of smaller, mini quadcopters. Before this, larger quadcopters were flown, but lacked agility due to their size. The miniaturization of electronic components and motors, reduced the size of quadcopters, and thereby increasing their agility due to the highly favorable power to weight ratios.
When looking at a racing quadcopter, you may wonder why motors are placed in a rectangular configuration as compared to the typical square configuration. The square configuration is the most stable. However, racing drones need more agility. This is accomplished by purposefully designing the racer with a planned amount of instability. Fighter jets are also designed this way. They rely on active computer control of the aircraft to maintain stable flight. For racing drones, the rectangular shape introduces a relative instability along the roll axis, which allows quicker turns and maneuverability.
For racing drones, it is possible to reach speeds up to 120 kph. However, top speed is not the key driver in quadcopter racing. Maneuverability is much more important and is driven by the control response time, flight stability, and turning response of the quadcopter. Acceleration is also important, since you want to be able to reach your top speed quickly when coming out of a corner. Typical flight times of a racing quadcopter is about 5 to 8 minutes.
The frames provides the lightweight rigidity needed for the quadcopter structure. The sizing of the racing quadcopter frame is measured diagonally from one motor axle to the other. A 250 mm frame is typical of racing quadcopters. It is also possible to build a quadcopter frame using a 3D printer. You can look online and find the plans to print your own quadcopter frame. The distance between the main body and struts establishes the maximum size of propeller the quadcopter can support. Typically, a propeller size of 5 inches is used.
The frame usually has two levels and connected using spacer screws. You have the option of going with a G10 fiberglass sheet or carbon fiber frame. G10 frames are cheaper than carbon fiber, but are not as light, and do not provide for flexibility. With carbon fiber frames, you need to know that they are electrically conductive, so you need to ensure that the battery is isolated.
Motors and Propellers
Brushless motors are used for building and flying racing quadcopters. Motors are specified by a their size, and their motor velocity constant designated as KV. The KV value is the number of RPMs that the motor will turn when 1 volt is applied, but with no load attached to the motor. You can think of this as the revolutions per volt, but the RPMs will decrease once you add a propeller. Also, a higher KV does mean more RPMs, but it also gives less torque. The motor size is specified by four numbers, with the first two numbers designating the diameter of the motor stator in millimeters, and the last two numbers are the length of the stator.
You want to be sure that you pick the right propeller for your motor. An oversized propeller will provide for poor performance, while a propeller that is too small will not make maximum use of the motor. The motor manufacturer will provide recommendations for the propellers to be used with the motor over a range of voltages. Also, be sure to get extra propellers, for when you crash.
Electronic Speed Controls
For stable, and controlled flight, the onboard flight computer determines how fast each motor should spin using input from onboard sensors, and its control algorithms. The electronic speed controls take the input from the flight computer to control the motor speed. Each motor has its own electronic speed control.
The flight computer is the brains of the quadcopter, and links to the receiver and the ESCs. This controller takes your input commands, along with data from onboard sensors and converts that into commands to the ESCs. Typically racing flight controllers are simple, and do not include functionalities like the incorporation of GPS.
This is obviously what powers the quadcopter. Batters sized in the range of 1300 to 1800 mAh are commonly used on racers. There is fine balance to be achieved when deciding on the battery power, and the corresponding motors, and ECS that can support the voltage. A power distribution board is commonly used to provide a link to all powered components from a single node.
The biggest barrier to entry into FPV drone racing is the video equipment. You need a camera, a video transmitter, and a set of FPV goggles. These components are a bit on the pricey side, but are needed for stable flight control of the drone. You need to have video transmission over a good range, with very low latency.
You may need to obtain an amateur license in order to operate your video transmitter. Check with your local communication authority to find out if this is the case. There are numerous options for picking the video transmission frequency, and output power. Be sure to pair this properly with the reception capabilities of your video goggles.
You have the option of using a small security camera for our vision system, or go with an action camera such as a GoPro Hero, or a Mobius camera. You could power the camera with a separate battery, but can also link everything to the main battery.
FPV Quadcopter Racing Summary
If you are looking to get into FPV quadcopter racing, you should be warned this is not an inexpensive hobby. To start off with, there are quadcopter racing kits available that have all of the parts that you need to build your racer. With a bit of experience, you can start making tweaks, adjustments and improvements and eventually move onto designing and building your own quadcopter racers.