First flight

After connecting up the motors, and the battery (props still removed!), the moment of truth was there... No smoke! So no electrical shorts yet. Then for the first time ever spanning up the motors! I had attached a piece of sticky-tape to the motor shafts, so that I could see the turning direction (the tape bends due to the forces of the air, and stays deformed after stopping the motors). Of course, two out of 4 turned in the wrong direction, so I had to swap two wires per motor to get that corrected. I had deliberately connected the motors with bullet connectors, both for modularity, and for being able to quickly correct this.

After swapping the wires, and one last check of the spinning directions, it was time to mount the props. Again, observing the turning directions.

Then, outside, with the quad in my hand - looking out for the diameter of the props to be well clear of anything, especially my arms - a first spin-up. With about 1/3 throttle, I tested out if the corrections of the stability control bit of the software were working in the right direction. Otherwise, the thing would not fly, of course.

Now, as you can see from that short footage, there's not much room in my back yard, so the actual first flight would have to wait until the weekend. We spend most of our weekends at "the camping", where we have a chalet on a decent size piece of land. Plus, right next to the camping there is a large clearing in the forrest. That is mostly sand and some grass, so reasonably crash friendly 😉

My fist test flight was also the very first flight for me, with any RC object ever. So I was a little nervous. Did not quite know what to expect. Especially because this was a highly experimental quad, which had also never flown before. And there was one thing I was sure of: the PID parameter valies would be way off...

So I decided to focus on PID parameters first, even before actually flying. The PID parameters are the factors with which stability corrections are multiplied. The letters stand for Proportional, Integral, and Derivative, respectively. And that relates to the error that is observed. The accelerometer "tells" the controller the position in space (attitude) of the aircraft, and the receiver "tells" the controller what the transmitter stick positions are, so now we have an actual attitude, and a "wanted" attitude. The difference between the two is the Error. Of course, we want the Error to be zero. The controller must therefor calculate a correction for the next loop of setting the individual motor PWM values.

The P-factor is the easy one to understand. It's a constant with which the error is multiplied, in order to calculate a correction. So if the Error gets twice as big, the correction gets twice as big too. Then as the Error approaches zero, so does the correction.

The I part uses previous error values (say the last 10), and adds them together. This value also needs to be zero (Errors have positive value in one direction, and negative in the opposite direction), to ensure that there is no drift. Again, a correction is calculated, much like with the P parameter.

The D part uses the previous Error, and compares (subtracts) it with the current Error. It sort of detecteren the "closure rate" of the Error becoming zero. If the closure rate is high, the correction can already become smaller, to prevent over corrections. This actually dampens the P value correction.

So, again with the quadcopter in my hand, I set the P value to a certain value. It seemed to do OK, so I then increased the P value. It felt far more stable in my hand, correcting any rotation much stronger than before. I repeated the proces to the point where it started oscillating. That means that the P factor is overcompensating the Error, so it needs some dampening. So there comes the D factor increase, until oscillations are gone. I left I on zero for now, and decided I would give it a try.

My very first hover! Slowly increasing the throttle until the quad lifted about 30 cm off the ground. It moved to the right, so I overcompensated to the left, and crashed!... First prop gone within 10 seconds! 😃 Now, you know that you are going to crash a couple of times, and that props are the first things to go, so I had a couple of them laying around, ready for use (balanced!).

After a couple of tries, the quad flew reasonably stable, and I got a little bit more used to operating the transmitter. Specifically to being more gentle on the sticks 😉