Recently NASA has made the first powered flight on Mars. They have deployed a drone called Ingenuity costing about $85 million. The helicopter was able to fly on about ten meters altitude (as of May, 7) over the surface of the Red Planet.
Coincidently, I have also built a flying drone. This looked like a good challenge and an opportunity to learn about unmanned aerial vehicles (UAVs).
Here is what I learned.
What you will essentially need is propellers, motors, and some way to power and control them.
|Part||Qty||Unit W. (g)||Weight (g)||Price (EUR)|
|Arm support (printed)||2||3.5||7|
|Base (v1.1) (printed)||1||30||30|
|Top (v1.1) (printed)||1||21||21|
|1100 mAh Battery 3S||1||117||117||14.72|
|2300 KV Motors 2204||4||25||100||14.02|
|ESC (4 in 1)||1||19||19||24.84|
|F3 flight controller*||1||17||17||18.87|
|Radio receiver (FS-iA10B)||1||17.6||17.6||19|
|UBEC 3A 5V||1||?||3.13|
|Bolts and nuts*||1||18||18||<10|
|Nylon spacers 40 mm||6||?||5.72|
|Motor anti-vibration pads||4||2.01|
* Approximate weight.
** Total price without LiPo charger (iMAX B6), radio transmitter, and camera. You can reuse those from other projects. The prices are given for indicative purpose only. The parts are not guaranteed to be optimal or cheapest.
The 3D printed frame was downloaded from Thingiverse: design called Peon230. Initially I printed everything in PLA. However, I have found out that, when crashing, base and top parts tend to break. Now, I use nylon for those two parts: they are lighter in nylon and do not break so easily. By the way, I did not use glue for platform adhesion when printing with PLA1. Printing directly on the glass platform gave parts a shiny finish.
ESC = electronic speed controller. Those translate control pulses coming from the flight controller into voltage actually driving motors. The ESC I used in this build contains actually four ESCs, permitting to control all four motors. That reduces the copter's weight, which is great.
UBEC = universal battery elimination circuit (DC-DC converter). Helped me to use a single battery both for the motors (12 V) and for the flight controller (5 V). UBECs are switching converters and they are recommended over linear DC converters, which dissipate a lot of heat when stepping down the voltage.
(Battery) 3S = 3 cells. Each cell contributes 3.7 V, therefore 11.1 V total. I used a battery with capacity of 1100 mAh. This battery gave me up to 15 minutes to fly.
Motor characteristics. 2300 KV: 2300 revolutions per minute (RPMs) per volt (with no load attached to that motor). Therefore, at 12 volts, these motors are expected to achieve 12 * 2300 = 27600 RPMs. 2204: 22 is the rotor diameter and 04 is the stator height. Larger motors give you more torque, which is related to the uplift force you want to generate. This is especially important when considering the vehicle's weight. Racing drones have high thrust to weight ratio enhancing their maneuverability and ability to rapidly accelerate Camera drones, on the other hand, have lower thrust to weight ratio making them more stable and easier to pilot.
The nominal voltage of a lithium-polymer (LiPo) battery cell (3.7 V) is actually closer to its storage voltage (3.8 V). When a battery cell is fully charged, it reaches 4.2 V. The battery should never be overcharged because of an explosion/fire hazard. Also discharging under 3 V is not recommended as the battery may break. It is a good idea using a balance charger that controls each cell individually. Be careful with your batteries. There exist special safety bags designed for LiPo charging. Never charge your batteries unattended.
Assembling a Drone
Soldering Motor Wires
First of all we need to make sure that our electronic part (flight controller, ESCs, motors, etc.) works properly. We solder three wires of each motor directly to ESCs. Please pay attention to the motor wiring as neighboring motors rotate in opposite directions. Then, we solder an XT60 battery connector.
In parallel to motors we solder a UBEC, not shown on the video2. We connect UBEC to power the flight controller from the same battery.
In this video we assemble the frame from earlier printed parts. We put motors, ESCs, flight controller, and the receiver on the frame. The flight controller is bolted on top of the 4-in-1 ESC. Then, we connect the radio receiver to the flight controller. We also connect flight controller output wires to ESCs. We could solder everything instead, but these connections are already good for the test. We test connection with a transmitter and the motors. We finalize the build by putting the remaining part of the frame on top.
It is crucial that your build is tight. No wire, nothing should be in the way of your propellers.
Tuning the Flight Controller
While your UAV may seem functional, it is probably not yet ready to fly. In fact, the flight controller is probably the most important part, it acts as a "quadcopter's brain". The controller interprets the received radio commands and the data coming from its sensors, most notably from the intertia measurement unit (IMU), to stabilize and steer the vehicle. In fact, without a flight controller it would be virtually impossible for a human to pilot a quadcopter.
To make sure the controller interprets the flight situation adequately, it has to be properly calibrated. To perform the tuning, I used Clean Flight software. However, there exist multiple alternative options, such as Beta Flight, which is a popular fork of Clean Flight.
Some of the Challenges I Have Faced
- Vibrations on captured videos from the quadcopter turned out to be mostly because of slightly damaged propellers (after emergency landings)
- The best way to position antennas turned out to be along the body. This way they don't get into the way if crashing.
- Regulations. In Europe, you need to obtain a special permission to fly a drone. Also there are very strict limitations where you can fly as a hobbyist.
This is my first racing quad. I am still learning to fly this thing.