Fix Instant Flip and Learn to Fly
« on: August 21, 2018, 08:37:20 pm »
How to Fix Instant Flip
Your First Takeoff
Learning More

Your first flights should be Line Of Sight, and this post assumes you are flying LOS, but also discusses the standard FPV turn around a tree.

To fix instant flip, all of these must be done correctly before first flight:
- Use the default Flight Mode Switch of Stabilized 1 which is Attitude mode (Input -> FlightModeSwitchSettings) for your first flights; at least until you feel comfortable with flying.
- Stabilization->ZeroTheIntegral must be enabled.
- Quadcopter motor direction MUST be CW CCW CW CCW for NW, NE, SE, SW (or other settings must be made).  See Vehicle page.  Also see Vehicle page for other aircraft type motor directions.
- Must plug ESCs into FC in correct order.  See Vehicle page.
- Must put correct prop type on each motor.  See Vehicle page.
- Two wrongs do not make a right, you cannot correct for incorrect motor direction by using the other prop type.
- The FC must be mounted right side up with the arrow pointing forward (or see this or this to allow for rotated mounting).  For Revo/CC3D/Sparky2 that is also with the ESC (servo) connectors on the top right side.
- ESCs must be calibrated reasonably well.  Here is one way / the best way to calibrate them all at once.
- Read the next section "Your First Takeoff" because there are several piloting mistakes that also cause instant flip.

Your First Takeoff:
- Review the Instant Flip section to make sure it is built and configured as well as possible.
- Don't "help it stay level" during takeoff.  Use just the throttle to "jump" up to knee high.  Do not move any other stick.
- Don't take off from the side of a slope.  On the ground it winds up the PIDs in the same way that "helping it stay level" does.
- Take off quickly, as soon as you start the motors.  Do not slowly increase motor speed.  Jump up to knee high.
- Don't fly in the wind.  Perfect calm is the best to reduce drifting away.
- The longest grass you can find that isn't so long as to get stuck in props on takeoff is the best place to take off.  Hard landings aren't quite so hard in grass.
- Always be ready to zero the throttle if it starts to drift away.  Better to fall down and risk a broken prop than to push a bad situation and make it worse.
- Always be ready to zero the throttle the instant it touches the ground in anything like a crash.  Any time a motor is jammed (upside down, grass in the prop, etc.) you must immediately zero the throttle to help avoid burning the motors or ESCs.  Likewise, if one or two motors don't start normally, they only jitter back and forth a little, stop immediately and check for a bad motor wire to avoid burning more things out than are already burned out.
- First tests: Blip the throttle up and back down just a little bit (don't move any other control till much later); then blip up a little more, and back down; more and more till it lifts and gets off ground for a second.  If it always flips something is wrong; go back and fix it; check the instant flip section.  It should come off ground and stay level.  Now you know how much throttle it takes to lift off.
- Flight rule to keep in mind:  Always fly with the tail pointing toward you (nose away from you), so both you and the quad are facing the same way, like you are both in line (queue) waiting for checkout at the store.  For now this is as simple as "Start in this orientation and never touch the yaw (rudder) control."
- Take off quickly, as soon as you start the motors.  Do not slowly increase motor speed.  Jump up to knee high.  Practice aLtitude control with the throttle stick.  Don't touch the other controls.
- Cut the power off before it drifts away.
- Adjust trims after each "landing" :) to help it avoid drifting.  If there is any wind, be aware that your trims are compensating for the wind too and if you hovered pointing in the other direction, it would drift twice as bad.
- If it is drifting it is hard to fly.  Always make sure it is trimmed out as well as possible to make flying easier.

Learning More:
- Learn to control aLtitude first.  Don't touch the other controls.
- After several trim adjustments it will stay in one place better and give you more time to practice holding your aLtitude reasonably.
- When you can control aLtitude fairly well, use roll (left-right banking) and pitch (forward-backward banking) to keep it right in front of you and avoid drifting away.  Don't use yaw yet, except in tiny amounts and only to keep the tail pointed straight at you when really necessary.
- Learn yaw (rudder, the control that makes it spin like a top spins) last.  Until then, don't mess with yaw.  Yaw will mess you up.  When the nose points towards you, both roll and pitch will be backwards.
- Practice moving around with throttle, roll, and pitch.  Do this a lot.  Don't use yaw yet.  Practice, practice.
- By now, you should be good at hovering in one place.  While hovering in front of you, get comfortable with moving the yaw, but limit it to within 45 degrees left to 45 right.
- Make sure you are well trimmed so that the hover drifts as little as possible.
- Get the idea of what this step is asking before starting.  Bumping a little bit of forward pitch will make it drift forward.  Start in a hover that is pointing almost straight away, but a little left too (say 15 degrees) and bump forward a little to make it drift a few meters (yards).  Then move the yaw right to make it point 90 right and bump a little forward pitch.  Now you are drifting left to right.  Don't let it get very far the first time, just a few meters.  Move the yaw stick left (rotate 180 left to change your 90 right to point 90 left) and then bump forward pitch and it will stop.  Bump forward more and you are drifting right to left.  Use right yaw to point 90 right (like the first time), and bump forward again.  Repeat.  You are learning to fly left right left right back and forth.  Notice that the nose never points straight at you if you do it this way.  That is important.  Practice, practice, extending the distance and correcting for drift.
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- Remember to avoid having it point straight at you.  If it gets a long way away, fly it backwards to get it back.  You can also use backward pitch for braking if you want.  At this point, you are kind of driving it around like a car.
- If you want to make a course correction remember that you need to bump the forward pitch after steering the yaw.  Over-steer the yaw, bump forward, reduce the yaw over-steer to make the nose point straight in the direction of flight.
- At this point, you are good enough to fly it around in straight lines, using pitch for speed and yaw for "steering", like driving a car.
- Extend what you just learned, the left right left right with stops at each side, into continuously moving slow horizontal figure 8's with the nose always in the direction of flight and turns pointing away from you on both sides of the 8.  You are just using pitch to make it go forward and yaw to drive it around like a car while you maintain altitude with throttle.  The flight pattern below never has the quad pointing straight toward you and stretches your concept of heading without ever doing the difficult "nose in" orientation.
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(V i e w   F r o m   A b o v e )

    > > >             < < <
 /         v       v         \
^            \   /            ^
^              X              ^
^            /   \            ^
 \         v       v         /
    < < <             > > >

            you are
- When flying your figure 8's and you get flying above a slow drift speed, you will notice that you must keep the nose more toward the center of the circle than straight in the direction of flight.  You also have to pitch forward continuously to hold it in the circle.  This is a lot like driving a hovercraft that slips in the turns.  Practice the figure 8 at a higher speed.  Flying like this actually allows you to fly beyond where you can see the orientation of the quad.  Keep it moving forward and steer with yaw.  Not really recommended for beginners though.
- What I will call a standard FPV turn is actually close to what you were doing with the figure 8 at high speed.  Generally, it's hard to see the tree you are using for the center of your FPV turn, because it is straight out the left side of the aircraft, so to make a left turn around a tree it is common to line it up to fly past on the right side and yaw to point the nose almost straight at the tree so you can see it as you fly by.  So generally speaking you use yaw to keep the nose pointed toward the tree and use forward pitch (instead of left roll) to hold it in the circle around the tree while the momentum from your straight line speed carries you forward around the tree.
- Now comes learning banked turns.  Instead of skidding through the turns, nose toward the center, with forward pitch creating a shallow bank to hold you in the circle, the correct way is to keep the yaw pointing straight in the direction of flight (like an airplane flying in a circle) and use some roll banking to hold you in the circle (again like an airplane).  This is the coordinated, banked turn, and is the standard turn for all aircraft.
- All helicopter type aircraft needs more thrust in a turn.  This is needed to avoid loosing altitude.  For shallow banks, the amount is almost unnoticeable.  For a 30 degree bank you need 15% more power.  For a 60 degree bank you need 100% more power.  For a 90 degree bank you theoretically need infinite power.
- If you are running defaults, you are running Manual thrust mode.  CruiseControl thrust mode will automatically calculate and apply the additional thrust needed.  Some people consider this a crutch.  Others consider it a labor saving device.  Select it typically in Input->FlightModeSwitchSettings->Stabilized-1->Thrust.  (Press Save.  :) )
- A quad flies as well in any direction (forward, backward, left, right or anywhere in between), so you are only keeping yaw pointing forward for other reasons, like later flying FPV or full sized aircraft.  In fact you can do these figure 8's with yaw always pointing in a single compass heading and using roll and pitch, but that isn't optimal when you are "inside" the aircraft and always looking out the front of it.
- Fly the figure 8's with the yaw always straight in the direction of flight and get used to how much roll banking you need for various speeds in the turns.  Putting just one or two clicks of forward pitch trim (Still flying Attitude mode) may help you maintain a medium speed.  Otherwise you will need to keep it moving with a little forward pitch.  Reducing your yaw stick sensitivity (rotation rate) may make the yaw easier to control in the turns.
- Practice horizontal figure 8's with the nose always in the direction of flight and the left side turn generated by flying away from you and leftward, then turning hard left to wind up point rightward before it gets back to you.  The right side turn is generated by flying away from you and rightward, then turning hard right to wind up point leftward before it gets back to you.  This pattern has the quad pointing straight toward you twice, and requires you to mentally switch from tail-in through a short period of nose-in and back to tail-in orientations.
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( V i e w   F r o m   A b o v e )

    < < <             > > >
 /         ^       ^         \
v            \   /            v
v              X              v
v            /   \            v
 \          ^     ^          /
    > > > ^         ^ < < <

            you are
- Everyone should learn to hover "nose in" (nose pointed toward you).  You may use the wrong control once in a while, but you should be able to recover from it.  You should be able to rotate with yaw, in either direction, to any heading, and hover at that heading.  It may not be pretty, but you should be able to do it.
- At this point, you can fly.  You just need practice and self direction on what to try.

For completeness:
- Transmitter trims, sub trims, etc. should really stay centered (where you had them during the transmitter setup wizard).  For ATtitude mode, you should set trims back to neutral and instead you should adjust Attitude->RotateVirtual to compensate permanently.  If it is drifting forward you subtract from pitch.  If it is drifting left you subtract from roll.  At least you must do this before trying Rate mode flight, which will be messed up by the trims.  In Rate mode, you will never need trims.  They are always centered.  Automatic gyro calibration trims it for you perfectly every time.
- Understanding and setting up failsafe is the difference between loosing an aircraft to a fly-away and getting it back, maybe with zero damage.  Beepers and LEDs help retrieval too.  Understanding the telemetry RSSI meter built into modern transmitters can help you find a downed aircraft.
- Understand lipo batteries.  Never ever fly them dead.  They become permanently damaged.  They might survive it once if you immediately (minutes) begin recharging them using a Nicad charger setting and switch to Lipo charging as soon as it will take it.  Store them at 3.8V per cell in a cool place (not in a hot car).
- Buy some "8S lipo alarm" on eBay for $1 shipped.  Set them to 3.7V and land when the alarm sounds.  IT is that or make bad guesses at how long to time each flight.
- Understand and try some flight modes and thrust modes.  For learning stunts Rattitude with CruiseControl is good.  For just zooming around FPV or LOS, you may like ATtitude with ALtitudeVario (it won't arm in AV thrust mode though).  If you have a Revo class FC with GPS fully configured, you can do RTB on signal loss or switch position and VelocityRoam is an excellent flight mode to set up.
- Rate mode and similar modes (Acro+, RateTrainer) don't have automatic levelling when you center the sticks, and are considered by many to be superior, especially for stunts and FPV.  For instance, long straight fast flight requires you to hold forward pitch in Attitude mode, but in Rate mode only requires you to touch the pitch long enough to change it from it's current angle.
- In general, but particularly for FPV, you should always have an ATtitude mode on your switch.  It is the only thing that works (besides GPS modes) when your video suddenly gets really bad.  In Rate mode, the video gets flaky, you bump the roll stick how much you think you need, 5 seconds later the video comes back for a split second and you see you are upside down.  You crash.  In Rate mode, you loose orientation a hundred meters away, without ATtitude you crash.
- One common cause of oscillation (wobbles) in flight is that the default PIDs are tuned for fast ESCs and you can't use PWM@50Hz on even a single ESC without retuning.  To fix this, use at least PWM@490 or PWMSync for ESC protocol / speed (Output page).  See
« Last Edit: November 22, 2020, 08:45:32 pm by TheOtherCliff »