Freestyle quadcopters: a drone without a gyro, a racing drone in concept—Do I need to write a full sentence about them? Okay—they will bend a classically trained pilot's mind. I know this because they've bent mine. If you back up a blog, you will find a breakdown of quadcopter aerodynamics. That post still bears truth, but like the difference between concept and practice, the concepts must fundamentally find their way into the human situation. Enough hobble-gobble psycho-speak already, I can talk about lift all day, but you're trying with pain to the temples and with strain to the irises to keep your drone from climbing out of range or crashing, and preferably at any one altitude in between those two extremes! You just want it to stay put! Okay, not just stay put, but be able to make your drone fly to where your mind desires it to go.
Here, I grin like a keeper of secrets. I can do that.
"What?" you exclaim.
Yup. And I know that pride comes before the crash.
Of course, it makes sense that it's possible to hover on, fly toward, circle around, climb over, split between, and duck under things without a gyro. It's possible, or freestyle quadcopters would long ago have been a product that joined the failure-to-launch club. Now, to be honest as Abe, "My drone-bilities are a far cry from Pulitzer Prize winning," but I would feel confident enough to put on FPV goggles (which I've never done), pick up an FrSky transmitter (which I have), and fly a real freestyle drone till it had 10% battery remaining.
How?
For me, my leap forward sprang out of the dramatic, hard to interpret, Shakespearean building blocks: the Pitch-Power relationship and the Bank-Yaw relationship. If you wrap your mind around these two groups of concepts and start screaming at your thumbs to obey, soon they will. Let me break it down a bit and I'm sure you'll better follow my trail from early frustration to intermediate success.
The Pitch Back and Relax Concept
If we are discussing the pitch and power relationship, we are again talking about the vector on top of Alfalfa's, the Little Rascal's, head. Your throttle—yes that super-throttley-throttle that will wildly climb your drone up 60 feet per second—affects both altitude and forward movement. Cool? "Cool." And pitch affects both altitude and forward movement. Cool? "Cool, wait-what?" Both pitch and power control the same two things. (I'm quite sure that you've ascertained this from your own experiments.)
It's learning the balance between these two control inputs that will take your hobby from frustratingly choppy to satisfyingly less choppy. If you pitch forward, more power is required to maintain altitude. Add too much power for the amount of forward pitch and the drone climbs, too little and the drone descends. The hard to scale wall is the fact that the rates of throttle and pitch are different (non-linear), i.e. the inputs are mind-numbingly independent and intertwined at the same time. Don't get discouraged. This concept won't float for you without practice, so try this:
Find a long, straight stretch (preferably in a drone simulator) and focus on maintaining altitude after takeoff. Then pitch forward while maintaining altitude (increasing power). Pitch forward more and add more power. You can legally fly up to 100mph in the USofA per the FAA, and if you picked a long enough stretch, with these inputs and the right drone, you soon will be illegally speeding while practicing the first half of this exercise. That's right: the first half. The second half of the exercise is the reverse. It's pitch backward and throttle backward enough to maintain altitude until the drone is slowing down.
Speaking of slowing down, in order to do so, you'll either need to let air-drag slowly slow you down or you'll need to pitch backward to the point that the lift vector starts pulling you backward, i.e. the FPV camera of the quadcopter will to some degree be sticking up into the sky. It's this unsettling feeling of falling backward, or losing view of the horizon, that I avoided in my first two weeks of simulating, that once I embraced and practiced for thirty minutes, gave me control of the speed and altitude of my drone! A frog-leap forward for me! Hence the title of this post is dedicated to this act of trust. Like a child learning to float in the community chlorine tank and having to lean back and relax, I had to learn the pitch back and relax the throttle concept to gain control of my wild-style forward trajectories. You'll bump and balloon at first on your runs back and forth, but it works! (Or at least it did for me.)
Now for Bank and Yaw: The Coordinated Turn
Bank and Yaw are related like ketchup and cucumbers. Independently they make sense, but together...foggle-woggle. Yaw is the merry-go-round. Bank is the teeter-totter. But neither by itself turns the quadcopter in forward flight (note the italics on forward).
Independently, yaw works to turn the potential vector or trajectory of the sUAS, but only the potential vector and only in a perfect hover before a trajectory has been set. If you're reading this, you will have already succeeded, like me, in performing many skidding turns like a Tokyo drifting car by using yaw alone and then pitching in the new direction you want to go. But truth be told, this drifting was the instigator to many of my crashing headaches up until last week when I started applying the concept of a coordinated turn.
Get this, if pitch and power are dedicated to forward speed and altitude control and a quadcopter newbie can separately gain control of the quad’s direction with the other inputs, bank and yaw, they will have in their grasp all the rudiments of drone flying! GET THIS, if pitch and power are dedicated to forw...okay, reread the last sentence if you want the full effect. Here's the trick:
At Slow Speeds more yaw than bank is needed to maintain a coordinated turn. A coordinated turn is nothing more than the quad not drifting sideways into the turn (a slip) or over-rotating into the turn (a skid).
At High Speeds more bank than yaw is needed to maintain a coordinated turn. (Reread the "A coordinated turn is" sentence above for the full effect ...yada ...yada ...yada.) Try this:
Once you get the hang of the "Pitch Back and Relax" exercise above, set a speed and altitude and then practice coordinating your turn for that speed. It will be a balance of bank and yaw; try banking first and then adding yaw to match. Then change the speed (which will change the turn-radius) and practice setting the new balance of bank and yaw.
A "turn-radius eureka" happens after you have a handle on speed control (pitch and power) and a handle on the coordinated turn (bank and yaw). (And it's not a eureka because you already know it, but here it is anyway):
The slower you go, the sharper you can turn (with a coordinated turn and without losing your forward momentum/speed).
The closer to SR-71 Blackbird speeds you are, the wider your turn will be. In more substratal terminology: if you need to turn more fast...slow down!
Ahh...how relaxing it is when these two aerodynamic relationships are matched up like Romeo and Juliet, and Benedick and Beatrice. Hopefully, my next topics (the aiming point and the twitching-thumbs technique) will prove to be less dramatic.
Keep Relaxing (In that summer pool)
-Josiah Hutchison
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