Justa learning to fly

After getting home and replacing a prop (and ordering shitloads more), it was time to start taking flying lessons.

The KK2.0 has a nice feature called 'auto-level' which will keep the copter mostly level when no other inputs are being sent to it. I soon found out that i had to adjust some P/I gains down to prevent the copter from oscillating when in that mode. Currently, it flies quite nice with it enabled.

Auto-level is rather awesome in that it keeps the copter from trying to fall over all the time. It is rather like trying to balance a broom on your fingertip, otherwise. You constantly need to adjust to prevent it from going somewhere you don't want. This is true for auto-level flight, too..only just not as much. The challenges are as such:

Controlling Height

This is first thing to work on. It's already exciting/nerve-wracking to watch your propellers spin up and your aircraft trying to get off the ground... Will it work ? Will it fly properly ? Nothing is preventing it from crashing and burning to the ground EXCEPT YOUR NON-EXISTENT FLYING SKILLS.... Great.

The issue here, though, is to get all four legs off the floor as simultaneously as possible. If one sticks to the ground while the others are airborn, the aircraft will start to turn around that one leg, changing your orientation and require you to adjust that soon after takeoff.

The first flight of a new copter can be challenging for the above reasons, but once you know that the device is basically flight-worthy, it's best to simply pull it off the floor as quick as possible without giving TOO much impulse... because....

... once you're airborne , you're "loose" and subject to all kinds of effects.

When flying low ( 50CM or less) you are subject to extra lift generated by the wind generated by your propellers hitting the ground and reflecting back up, giving your copter an extra push up. Your copter gets pushed up higher than that point , loses the extra lift, descends again.. gets lift, goes up, loses lift, descends...and there you continue oscillating, unless you compensate just enough for this to stop.

When adding thrust, it's easy enough to see how much you need to add to increase the rate of climb. When removing thrust, this isnt always as clear. Going up is kinda a linear thing. Going down is more of a logarithmic thing. Soon gravity starts pulling you down faster and faster and before you know it, you have to compensate to prevent your aircraft from hitting the floor hard. Sometimes, you need to REALLY hit the throttle to prevent it from smacking down hard. If you do, be careful to also RELEASE the throttle quickly enough when it's clear you're rising, or else you'll find yourself flying at 30 meters height, giving you an impulse to quickly release the throttle.. and so on.. and so on.

Another challenge that you'll deal with soon enough is the reduction of lift when making other maneuvers.. When banking forwards/backwards or left/right, you will also loose some height. This is also partly true for spinning around your axis. So in all these cases you need to add a little of throttle to compensate.

Lessons learned

• At liftoff, be a little bold and pull off the floor as quickly as possible.
• Gain height to avoid backwash from making your height oscillate
• Do all adjustments carefully and in moderation. Be wary of overcompensation!
• Don't let the aircraft gain too much negative vertical speed (fall), it is hard to compensate for!

Landing

The first thing you will learn after take-off is a quick landing. It's inevitable. I won't quote the ancient saying about it...

The trick of landing is in not damaging the plane or endangering anyone. It's as easy as getting the knack of the point above, controlling your height. If you manage to hover close to the ground, landing is as simple as cutting the throttle for the aircraft to drop nicely on the floor. A drop of 20CM's isnt going to kill it if the ground is sand or (preferred) long-ish grass.

It's often best to simply cut the throttle and make a clean drop instead of trying to be fancy and try and land the feet of the aircraft onto the floor while there's still (too much) throttle causing upwards thrust. A little sidewind while the aircraft is crabbing closely across the surface could be enough to have one side of it snag behind something, make the aircraft tilt and lurch and bury a rotor into the sand (or grind across the concrete). Or worse, if the auto-leveller starts adding thrust to the rotor and makes the whole thing lift off again uncontrolledly.

Lessons learned

• A clean cut of throttle is the most efficient. Doesn't matter if it's 20cm above the floor; especially if you were about to drift into something (or someone!)
• Landing is best done on semi-solid surfaces. Short grass works well enough, as does sand/mud/dirt. Concrete/asphalt can cost you a propeller if things go awry.
• When landing in/on surfaces like tall grass or weeds, it's best to cut throttle as quick as possible when hitting things; unless you like untwining grass from rotor-axles.
• DISARM your craft after landing. Really, do it! Reaching for the aircraft to re-position it can easily make you adjust the throttle-stick without realizing it. A cut on your finger is one thing; a lost eye a different story altogether.

Understanding velocity

Some quadcopter control boards will allow you to fly the aircraft in a way that lets it take care of handling velocities. Push the stick forwards, the aircraft will move forwards. Release the stick and it will stop in it's tracks. Or rather, the board will make the aircraft stop in it's tracks by applying counter-force , tilting the aircraft backwards to apply reverse thrust and restrain the craft's forwards momentum.

This is not the case with the controller that I use currently (KK2.0). This requires that the pilot keeps in mind that when you're making the aircraft go forwards at 20KM/h, you'll need to apply back-thrust sooner-or-later or you'll soon lose sight of it; or end up ramming into some object/tree/person at 20KM/h... Ouch.

Like with handling objects in no-gravity situations (outer space), once you start adding velocity to an object, you'll also end up having to apply counter-thrust to reduce the relative velocity to zero, in the end. Much the same is true for flying quad-copters, except that it only counts for two of the three axis (just X/Y , not Z (up)). Also, unlike in space, there is of course friction and your aircraft will lose relative velocity sooner or later. The amount of friction, however, is like you're trying to control a hockey-puck across an ice-rink with just a big fan at your disposal. Sure, you will be able to move it around, but the amount of instantaneous power available is simply limited. It's not like a car or bike; there are NO such things as 'grip' or 'brakes'.

Lessons learned

• Learn to plan your movements. Don't add uncontrolled velocity into directions you don't have clear or can compensate for.
• Keep orientation very clear (see next point), it's crucial to knowing what direction to apply velocity to.

Keeping orientation

This is perhaps one of the more hard things to get a proper grip on. It helps if you're used to top-down racing games on the PC and can keep track of what is left/right/forwards/backwards even when your view on things is being re-adjusted all the time.

The issue is three-fold.

Your view is not travelling WITH the aircraft, just aimed AT the aircraft. You will lose focus of the device at some time and wonder what is front and what is back. You will need to read the behaviour of the aircraft as you adjust the controls and deduce from that how it's oriented

You will need to learn to deal with compensating for looking at it from all kinds of weird angles. You will start by looking at it from above but soon you'll see the underside of the aircraft. You'll likely fly it away from you,and then forwards is still nicely forwards.... Soon you'll drift sideways though, maybe fly back and let the craft pass you, turning furwards into backwards and backwards into forwards... switching left/right too... Be prepared for this before you let it happen. Anticipate.

Sometimes, you just want to get things 'in order' again by adjusting the orientation so that 'forwards' is simply 'away from you' again. This involves adjusting the spin of the aircraft with the X-axis on the same stick that also handles the throttle on it's Y-axis. This can be a bit of a tricky thing to work with; controlling height can be challenging enough on it's own, let alone if it's coupled with figuring out orientation and compensating for it.

Lessons learned

• It's easiest to keep 'forwards' the same direction as much as is possible.
• Adjust orientation when you have the opportunity for it, you'll thank yourself later.
• Be sure to anticipate the effect a flight-maneuver may have on it's (relative) orientation to you. An overhead pass flips everything around.

Terrain and Physics

This is one of the more 'obvious' points, but I thought I'd mention it here anyway.

Unless you're flying in some completely flat grass-land, you'll most likely end up meeting some terrain here and there. Nice features to fly over, things to circle around, skim across, etc.

Remember that your aircraft keeps itself in the air by virtue of the lift it's propellers generate. They will create turbulence , stir up dust, make sand and twigs fly up and about ... It may make you lose sight of the aircraft , it might knock a twig against a propeller, it might even cause a branch to start swaying and knock against the aircraft...

... which brings us to the important part. Once the function of any of the propellers becomes impaired, the flight-worthiness of the aircraft is directly affected. It has NO gliding ability to speak of. All that keeps it in the air is the lift from it's rotors and the brains that control it in the right way. Both the electronic brain that adjusts directly based on gyro/accelerometer information , as well as the brain in the pilot's head.

So be sure to take overhanging branches, trees, laundry, powerlines, etc into account when flying, as well as the undergrowth. Tall reed, swirling leaves, etc, can all have a serious impact on your craft's ability to stay in the air. If you're lucky the rotor will simply end up catching on a piece of weed and wind itself around it. If you're unlucky, you approached said weed at 60KM/H and are soon watching how it hits it, spins out of control and does it's last cartflip.

Lessons learned

• A quad-copter is not a plane. It has no surfaces that generate lift other than the rotor-blades
• A quad-copter typically flies low enough to be impacted BY and have impact ON the terrain in the proximity
• Anticipate movements and changes in the terrain.