## Introduction: Modular Bicopter

I created a Bicopter that can take off and land vertically. My purpose in writing this instructable is to showcase the critical elements of the Bicopter so that you can build your own as well. It will require much tinkering but that's what makes it fun and that's how we learn!

## Supplies

1. Counter Rotating Brushless Motors [2]
2. Lithium Polymer Battery
3. Servo Motors [2]
4. ESC (Electronic Speed Controller) [1 for each motor, 2 total]
5. Radio Transmitter and Receiver
6. Flight Controller (ex. kk2, px4)
7. Servo Extension Wires
8. Frame (preferably modular)
9. Soldering Iron & solder
10. 12-14 gauge AWG wire

Or, you can watch this video and I explain it: Supplies

## Step 1: Understand the Problem You Are Trying to Solve

I live in a densely populated location within California, however, I want to fly aircraft in my area. What if I need to deliver a package via drone? What if my drone breaks? How will I quickly fix it? In my analysis, the answer is to create a modular bicopter that takes off and lands vertically. Why you ask?

1. My two rotor bicopter spins its two larger rotors at an angular velocity slower than a 4 rotor quadcopter of equivalent class. In essence, the bicopter rotors accelerate the same mass of air to a velocity slower than that of quadcopter. Kinetic Energy is equal to one half the mass times the velocity squared. Therefore, by moving the air two times slower, the bicopter uses 4 times less energy in theory. This means increased payload capacity. Minute Physics does a good job illustrating this concept here.
2. I made my bicopter slender and "rocket-like" because I intend for the majority of its operation to be in the vertical direction. Suppose I drop this bicopter from an aircraft. If the bicopter has a lower cross sectional area, it will have lower drag. With lower drag, the bicopter can fall faster and climb faster as well so that it can reach it's destination more quickly.
3. A modular bicopter is easy to fix. If the structure is composed of replaceable, parts, if a piece such as a landing leg breaks, you can repair it. In my design, I 3D printed fuselages and legs so that they can be easily replaced if damaged.

## Step 2: Build the Bicopter Structure

To build the bicopter, I used PLA (Polylactic Acid), a 3d printed material. However, the bicopter can be built from a variety of materials. I built my first bicopter structure from cardboard, as seen here: Cardboard Bicopter. For 3d printing, I recommend first designing the bicopter in Fusion360 or Solidworks. From there, convert your design file to an STL file. Then, upload your STL file to a slicer program such as PrusaSlicer or Cura. The slicer program essentially converts your STL file to a set of x,y,z coordinates, called a g code that the print head will follow.

I also implemented screw like threads between the fuselages of the bicopter to increase ease of replacement. When 3d printing, I noticed that the prints would sometimes fail due to incorrectly tensioned belts due to loose screws; this resulted in many print failures. As a side note, I even tried to 3D print the motor bells, however the heat generated by the motor softened the PLA, warping the motor bell structure resulting in motor failures; this is an area of improvement, that perhaps you can make!

## Step 3: Integrate the Electronics and Control System

Solder Connections

I used a soldering iron in order to solder the wires of the ESC to the motor. Furthermore, I used a heat gun in order to shrink the heat shrink tubing over any exposed wire. The the three leads on the ESC will connect to the 3 leads on the motor.

No Solder Connections

The ESCs and servos each have separate wires extending from them that plug into a radio receiver or flight controller input.

Control System

I used a gimbal in the form of a ball and socket joint in order to vector the thrust of the motors for control. The gimbal is actuated via two servos for pitch and roll control. Spinning control or yaw control is done by changing the velocity of the propellers, a principle motivated by the conservation of angular momentum. I made a video explaining this concept here: Angular Momentum Lesson by me

The specific control scheme that this particular bicopter uses is Proportional-Integral (PI) control. I used a kk2 board to modify the P and I gains until stability was reached.

## Step 4: Test Your Bicopter!

Often times, my bicopters don't work, especially in the beginning as seen here, however, this seems to be a part of the process of learning and making your bicopter so that it can fly like this and beyond! I recommend wearing your safety goggles when testing your bicopter just in case this happens! I also recommend testing your bicopter in an area clear of people and pets.

As always, thank you Instructables for allowing the world-wide sharing of ideas!

Participated in the
Make It Fly Speed Challenge