How I Developed the Scout Flight Controller, Part 8: Taking Flight

Tim Hanewich
7 min readSep 11, 2023

This article is part of a series documenting the development of a custom quadcopter flight controller from scratch. For a list of the other related articles, please refer to the introductory article found here.

Now with the hardware assembled and Scout Flight Controller software uploaded, the quadcopter is now prepared to be powered up and tested.

Safety First

Before doing anything, take the necessary safety precautions when performing tests! This is a highly-powered quadcopter with sharp-ended propellers that spin at several thousand revolutions per minute. Any slight error or mistake can have very serious consequences. I will do my best to share what I learned while building Scout. I am not responsible for any physical harm or accidents.

Use safety goggles — By far, the number one thing you need to protect is your eyes. I had a close call in which the propellers came loose and nearly hit collided with my face or when the quadcopter lost control while in close proximity to my face. Eye protection is CRITICAL! Whenever you are powering up the quadcopter, for any reason, please use safety goggles.

Have a fire extinguisher handy — When using electrical components in a high-performance scenario like we are, electrical fires can happen. I had three incidents in which a small fire nearly started. On one occasion, an error in code caused too much amperage to travel through a positive and negative wire for one of the motors. The amperage must have been higher than the wires I was using were rated for because the two wires melted their casing and fused together. Clearly a catastrophic problem. Luckily I was able to unplug the battery before anything serious happened besides smoke and a small flame. On the other two occasions, and ESC burned out when the drone crashed. Simple things like this happen so it is best to take precautions. I purchased a small, inexpensive fire extinguisher and never powered up the quadcopter without this by my side.

A propeller snapped after a crash
An ESC burned out mid-flight

Wear gloves — The propellers have nicked me and caused deep cuts many times. In several of these scenarios, the cuts were so deep that they have already formed scars. I’ve learned that the worst place to have a deep cut from a propeller is on your hands. When powering the quadcopter on and handling it while powered (for testing purposes), wear gloves to provide at least some level of protection.

Make sure the propellers are tightened — When it comes time to power up the motors with propellers on, always ensure that each of the four propellers are sufficiently tight. I made the mistake of not tightening them enough during my early test flights. I quickly learned that not tightening the propellers enough will cause each of the four bolts to fly into the air and each propeller to release and act as a flying spinning blade with a random trajectory. Even losing a single propeller during a flight would be catastrophic. Ensure that your propellers are very tight. Retighten every 3–4 flights.

Test Without Propellers

Before fastening the propellers to each of the four motors, it is wise to perform a simple test first without propellers. Power the quadcopter up, switch into flight mode, and you should see each of the four motors spool up in their appropriate direction. Gradually apply a bit more throttle and you should see the motors spin faster. Input some basic commands (pitch forward, roll right, yaw, etc), and you should at least hear the motors increasing/decreasing speed to accommodate your commands.

This simple test ensures that your motors are working correctly before you introduce a safety risk by fastening propellers. Whenever you are unsure about some component of the drone (i.e. new software update, it just crashed, an ESC may not be working, etc.), first test with no propellers as a simple (relatively) risk-free assessment.

Always Tether

Until you have a certain number of hours of flight time under your belt and you are certain that the drone flies predicably and stably, always tether the drone to something heavy on the ground.

As mentioned in the previous article, you will need to find the approximate PID (proportional, integral, derivative) controller gain values that work best for your particular quadcopter. While testing this and handling the quadcopter yourself while in flight mode (manipulating its attitude manually to observe how it responds), tether it to the ground so just in case, if something goes wrong, it is not able to fly uncontrolled and damage something.

During development, I would tether Scout to my ottoman. It isn’t high-tech, but it works.

I looped four strings around the ottoman and through each mounting hole, below each motor, of the drone’s frame. The four strings give about 1.5 feet of free play but arrest any further movement along each axis (for the most part).

I used this set up during development. I would upload code, test the result, make a tweak to the code, and repeat this process until it was tuned properly.

After tweaking the code with the ottoman setup and feeling confident in the flight controller’s tuned parameters, I then tethered the quadcopter to the ground with several heavy pots and pans. I positioned each heavy pot/pan so the drone had only about 4–6 feet to fly.

Scout achieved its first flight tethered as specified above:

After ensuring Scout can fly predictably with it tethered like this, I then took it outside and opted for a much longer, single string leash. I cut a string of about 50 feet (grants a leash of 25 feet) and tied this through the frame of the drone and then through the handle of a very heavy pot. The pot, upside down, served as the “launch pad” for the quadcopter (it would sit on this when taking off to avoid the propellers hitting the grass). After functioning as the launch pad, it would then serve in flight as an anchor. If the drone lost control, it wouldn’t be allowed to fly off as this very heavy pot would hold it down.

You can see clearly see the white string that is serving as a safety tether in Scout’s demo flight video:

While testing your drone’s flight capabilities early in development, it is important to tether it to the ground! If something goes wrong, this ensures that it can’t fly off into the distance and potentially seriously hurt someone!

Airspace Restrictions

Drones like the ones built by DJI often come with sophisticated flight computer features. These features are there to aid the pilot in various ways. One feature that these drones come with is a GPS system paired with an airspace restriction map. Knowing its location via GPS and knowing the restricted air spaces in the area, DJI’s software will not let you fly in restricted air spaces over a certain altitude.

My barebones and homemade Scout Flight Controller comes with no such luxury. There is no GPS unit on board and no knowledge of restricted air space. As such, there is no software-based restriction on where the drone can/cannot fly. This puts the burden on you as a pilot to be aware of federal, state, and local airspace restrictions in the areas in which you live and plan to fly.

The responsibilities of piloting a drone to not end there — it is your responsibility to be aware of airspace restrictions, operating rules, drone related laws (i.e. do not fly over people/cars), privacy laws, fly zones, etc.

No Battery Indicator

I did not install a battery level indicator (voltage monitor) onboard Scout. This means that the pilot has no way of knowing the battery level while in flight. Be careful of this — I’ve learned that you will generally get a warning as the voltage dips to very low levels (the quadcopter begins to feel sluggish/needs more throttle input), but power will rather abruptly be lost when the battery is absolutely dead.

It is generally bad to run a battery down to this level though. To avoid any accidents, frequently change batteries and don’t fly for too long on a single battery!

FAA Registration

The Federal Aviation Administration (FAA) requires all drones that exceed 250 grams to be registered. If your quadcopter meets or exceeds 250 grams, you legally must register it with the FAA.

Conclusion

With the hardware assembled, Scout Flight Controller software uploaded, and functionality tested, the quadcopter is now complete! While this and the last few chapters walked through the development process linearly, it likely won’t be as easy as this series leads you to believe. Like with all software/hardware development, there will be challenges. There will be obstacles to overcome.

In the next chapter I’ll share some of the challenges I ran into and had to overcome to complete my most demanding project yet.

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