DIY drone: Lesson 2. Frames..

Contents

Introduction

So, before you start assembling your drone, the first step is to choose a frame. You can execute it yourself, or use ready-made solutions (UAV frame kit). As you may have noticed, different types of frames and configurations can be used to create multi-rotor UAVs. Therefore, in this section we will consider common or basic types of frames, materials of execution, as well as issues related to design.

Types of UAV frames

Tricopter

  • Description: UAV, which has three beams, each of which is connected to a motor. The front part of the tricopter is considered to be the side of the junction of two beams (Y3). The angle between the beams can vary, but is typically 120 °. To counteract the gyroscopic effect of the uneven number of rotors, as well as to change the steering angle, the rear motor must be able to rotate (achieved by installing a conventional RC servo motor). To exclude the use of a servo from the assembly, use the Y4 design
  • Advantages: Unusual appearance of the drone. It achieves the best flight characteristics when flying in the forward direction. Price (requires fewer motors and ESCs to build).
  • Disadvantages: Asymmetric design. Requires the use of a servo. Difficulty in the execution of the back beam (since the servo must be mounted along the axis). Not all flight controllers support this configuration.

Quadcopter

  • Description:"Quadrocopter" drone that has four beams, each of which is connected to a motor. For " X configurationconfiguration
  • Advantages: Most common multi-rotor design. The simplest and most versatile design. In the standard configuration, the arms / motors are symmetrical about two axes. All flight controllers available on the market can work with this multi-rotor assembly.
  • Disadvantages: Lack of redundancy (if the system fails, especially in the elements of the power plant, the drone falls).

Hexacopter

  • Description: The Hexacopter has six beams, each of which is connected to the motor. The front part of the hexacopter is considered to be the side of the junction of the two beams, but the longitudinal beam can also be considered as the front.
  • Advantages: If necessary, the hexacopter design allows the easy addition of two additional beams and motors, which will increase the total thrust, as a result of which the drone can lift more payload. In the event of a failure of one of the motors, it is possible that the drone will be able to make a soft landing and not crash. Modular frame design. Almost all flight controllers support this configuration.
  • Disadvantages: Bulky and expensive construction. Additional motors and parts increase the weight of the copter, therefore, in order to get the same flight duration as a quadrocopter, it is necessary to install more capacious batteries.

Y6

  • Description: Construction Y6 is a type of hexacopter with at the base, not six beams, but three, each of which is connected to a pair of coaxially mounted motors (a total of 6 motors). It should be noted that the lower propellers project downward thrust.
  • Advantages: Fewer components compared to hexacopter. Lifts more payload compared to quadcopter. When using counter-rotating screws, the gyroscopic effect is excluded, as in Y3
  • Disadvantages: More expensive compared to a quadrocopter due to the use of additional parts that are equivalent in cost to the hexacopter parts. Additional motors and parts increase the weight of the drone, which means that in order to get the same flight time as the drone, you will need to use a larger battery. As practice shows, the thrust obtained on the Y6 is slightly lower than that of a conventional hexacopter, probably because the lower rotor affects the thrust of the upper rotor. Not all flight controllers support this configuration.

Octocopter

  • Description: Octocopter has eight beams, each of which connected to the motor. The front part of the hexacopter is considered to be the side of the junction of two beams.
  • Advantages: More motors = more thrust, and therefore increased redundancy, allowing the drone to navigate with confidence with heavy and expensive DSLR cameras.
  • Disadvantages: More motors = higher price and larger battery. Due to its high cost, it is relevant only for the professional sphere.

X8

  • Description: The X8 design is still an octocopter, only not with eight, but with four beams, each of which is connected to a pair of coaxially mounted motors (a total of 8 motors).
  • Advantages: More engines = more thrust, and therefore increased redundancy. More likely to gently land the drone in the event of a motor failure.
  • Disadvantages: More motors = higher price and larger battery. Due to its high cost, it is relevant only for the professional field of activity.

UAV size

UAVs come in a variety of sizes, from the Nano, which is smaller than the palm of your hand, to the larger one, which can only be transported in the back of a truck. For most users who are just getting started with the drone hobby, the optimal size range offering the greatest versatility and value is between 350mm and 700mm. The frame size is the diameter of the largest circle that crosses each of the motors. Parts for UAVs of this size have a wide range of prices and the largest selection of products available.

Materials of UAV / Construction

Below are the most common materials of execution used for the manufacture of frames for multi-rotor drones, respectively, the list is not complete. Ideally, the frame should be rigid with the least possible transmission of vibration.

Foam rubber (Foam) - as the only material for the manufacture of UAV frames is rarely used, and, as a rule, in combination with a rigid frame or reinforced structure. Can also be used for strategic purposes; as a protection for rotors (propellers), chassis, often acts as a damper. Foam rubber can be of different types from soft to relatively hard.

Wood - if the priority is the cheapness of the structure, then wood is an excellent option that will significantly reduce the time of assembly and manufacturing of spare parts. parts. Wood is quite hard and is a time-tested material. It is important that perfectly straight wood is used in the manufacture of the frame (without bending and deformation).

Plastic - available for most users only in the form of plastic sheets. Tends to bend and as such is not ideal. Great for making roll cages or chassis. If you are considering 3D printing, you should take into account the production time interval (it may be easier to buy a UAV frame kit). 3D printing of parts has worked well for small quadcopters.

Aluminum - comes to the consumer in various shapes and sizes. You can use sheet aluminum for the body, or extruded aluminum for the drone beams. Aluminum is not as light as carbon fiber or G10, but price and durability are the main advantages of the material. Instead of breaking or cracking, aluminum tends to bend. To work with the material, only a saw and a drill are required.

G10 (a type of glass fiber) - despite the fact that the appearance and basic properties are almost identical to carbon (carbon fiber) is a less expensive material. It is mainly available in sheet format and is used to realize the upper and lower frame plates. Also unlike carbon fiber, the G10 does not block RF waves.

PCB (Printed circuit board - dielectric plate) - in fact an analogue of fiberglass, but unlike the latter, they are always flat. Sometimes used as top and bottom frame plates to reduce the number of parts used (for example, a power distribution board is often built into the bottom panel). Frames nanoprinted circuit board

Carbon fiber is the most sought after material due to its light weight and high strength. The manufacturing process is still entirely manual. As a rule, simple forms are mass-produced, such as flat sheets, tubular components; execution of complex three-dimensional shapes is carried out to order.

Additional considerations

  • Gimbal - most often used to stabilize the camera (FPV / Aerial photography). As a rule, it is installed under the frame in accordance with the UAV's center of gravity. Can be attached directly to the frame or by means of rails. For image stabilization, it is recommended to use two or three axis gimbals. Requires an increase in the length of the landing legs.

  • Payload (transport) - in the amateur sphere is something of a luxury, so how any additional weight not only reduces flight time, but also leads to the rejection of the use of additional elements that could add key functions to the drone. When designing, it should be understood that the transport case should be as light as possible and at the same time strong, and the cargo itself should be rigidly fastened, excluding any movement in flight.

  • Landing feet - despite the fact that some UAVs land directly on the frame (usually are excluded to reduce weight), the use of landing supports in the design will provide a gap between the lower part of the UAV and an uneven surface, and also in the event of a hard landing, they take a blow, increasing the chances of saving such important elements of the drone as the camera, suspension, battery and frame.

  • Installation - despite the fact that the design and manufacture of a drone is much easier than a conventional helicopter, the location of each element should be considered at the very beginning of the design process.

General installation guidelines:

  1. When creating a frame from scratch, it is important to ensure the exact position of the four mounting holes through which the motors are attached to the frame...
  2. Most motors for frames from 400mm to 600mm have the same mounting hole pattern, which allows a frame from one manufacturer to be used and motors from another.
  3. The location of all additional components should ideally be symmetrical about one axis, which later will help to facilitate the search and adjustment of the center of mass of the drone.
  4. Ideally, the flight controller should be located in the center of the circle (and as such in the center of mass) connecting all motors.
  5. The flight controller is usually attached to the frame using struts, rubber dampers, or double-sided tape.
  6. Many manufacturers use the same mounting hole pattern for the flight controller (eg 35mm or 45mm square), but there is no current “industry standard”.
  7. The battery is heavy enough, and if the center of mass of your assembly has moved a little, you can adjust it by moving the battery slightly.
  8. Make sure the battery mount plays a little, but at the same time ensures that the battery is securely held in place.
  9. Velcro straps are often used to secure batteries, however it is a good idea to add double-sided tape between the battery and the frame.

Guidelines

Step 1: See what materials and tools for their processing are available in your disposal.

  • If your arsenal is not enough to implement a custom frame, or you just want a professional frame, consider purchasing a UAV frame kit.
  • Even if the frame is made using the correct tools and basic materials, it can still have structural weaknesses causing excessive vibration or displacement. The manufacturing process requires keen eyesight and experience.
  • When making the frame yourself, think over the fastening of all the necessary elements of the drone; motors, electronics, etc.

Step 2: List any additional (accessory) parts that you plan to include in the assembly.

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  • It can be one-, two-, or three-axis gimbal for a camera, a parachute, an on-board mini computer, a payload, long-range electronics (as a rule, it makes the assembly heavier and larger), floating equipment etc.
  • The resulting list of additional / auxiliary parts will give an idea of ​​the dimensions of the drone and calculate the total mass.

Step 3: Think about the estimated frame sizes.

  • A large frame is not necessarily a great potential for a drone, and a smaller frame may not make assembly cheaper.
  • A drone built on a 400 - 600mm frame is recommended for beginners.

Step 4: Design, build and test the frame.

  • If you purchased the UAV frame kit, then you have nothing to worry about in terms of strength, rigidity and build.
  • If you decide to design and build a frame from scratch, it will be important to check its strength, weight, and make sure the structure can withstand vibration (minimal bending).
  • Consider using specialized modeling software (many are free, such as Google Sketchup) to design the frame and ensure the dimensions are correct.

Now you have a frame and you can move on to the next lesson.

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