|Settings for the DX6i|
The Goals for this tutorial
The first step in learning to fly a helicopter is getting it up into the air into a stable hover. Fortunately that's relatively easy for Blade models. But once in the air even the Blade helicopters will have a tendency to drift one way or another, or move in a circular motion referred as TBE (Toilet Bowl Effect).
Trimming for hover is the first goal in setting up the model and the DX6i. It is done with a combination of transmitter (Tx) adjustments, and if necessary adjusting the linkages on the elevator and aileron servos. The second goal is learning how to use the mixing feature of the Tx to correct deviation in forward flight. All references to the sticks are for Mode 2 configuration where the left stick controls rudder/collective pitch/throttle and the right stick cyclic (elevator/aileron).
The Controls: Real vs. Models
Collective and Throttle
In a real helicopter is vertical stick between the legs called the "cyclic" which controls the forward/backward pitch(elevator) and left/right roll (aileron) of the rotor and helicopter body by changing the relative feathering angle and lift of the rotor blades, one increasing in pitch angle and the other decreasing by the same amount as the rotor blade pivots or "feathers" on rotor head. On "Mode 2" RC model transmitters used for helicopters the right spring-loaded control stick is the cyclic control.
Real helicopter and collective pitch (CP) models control overall thrust and lift generated by the rotor blade by varying the angle of both blades together, or collectively, via a lever called the "collective" similar. In a real helicopter it is a lever, similar to the hand brake on some cars, which rises from floor on the right side of the pilot seat. As the pilot lifts the lever up the pitch of both blades increases, generating more thrust and lifting the helicopter off the ground.
On a collective pitch helicopter the rotor turns at a constant speed. But like a car going up a hill when the collective pitch is increased more power is needed to maintain rotor RPMs. On full-scale helicopters there is a motorcycle-like throttle grip on the end of collective which allows the pilot to easily vary the throttle in coordination with changes in collective pitch. Most helicopters also now have cruise-control like automatic adjustment of power as pitch changes.
On CP model helicopters the collective pitch and throttle are both controlled with the forward/backward movement of the left stick. Coordination of throttle and pitch is done by adjusting separate curves set on the transmitter, increasing throttle as pitch is increased. For inverted flight a second set of "Stunt"curves are created with a V shaped throttle curve with will increase power similarly when collective pitch is > 0 (normal) and < 0 (inverted)
Smaller RC helicopters like the Blade micros do not have adjustable collective pitch. The blades are set at a fixed pitch (FP) and the motor speed is used to control thrust and lift. This makes the model easier for beginners to fly. But the downside of Fixed Pitch is, quite literally, that the model will fall like a rock if the throttle is lowered much beyond the point lift = gravity.
Control of Yaw (where the nose is pointing)
If the rotor blade on tail of a single-rotor helicopter stops working for any reason the body of the helicopter will spin in the opposite direction according to Newton's third law of motion: equal and opposite reaction. In the case of a helicopter under power the body reacts oppositely to the torque of the driven rotor.
On most full-scale helicopters flown in the U.S the main rotor turns counter-clockwise (CCW) and the orientation of the nose is controlled with a pair of pedals which change the pitch and thrust of the tail rotor spinning at the end of the tail boom. The thrust from the tail rotor pushes the boom CCW to counteract the CW spinning of the body which would otherwise occur. The pedals are referred to as "anti-torque" pedals (not rudder) because that's what they do: counter the torque of the main rotor with the tail rotor. The deviation of the nose from the desired direction of travel is called "yawing".
On single rotor RC models, including Blade, the main rotor turns clockwise (CW) and the tail would spin in the opposite direction, CCW, without the tail rotor. The orientation of the body in relationship to the rotor tilt and direction of travel (yaw) is controlled by sideways movement of the left stick on the transmitter, commonly but erroneously referred to as the "rudder" stick.
Larger RC single-rotor models control the tail in the same way as a full-scale helicopter via changing the pitch of a shaft- or belt-driven tail rotor. That method does not scale down effectively so micro helicopters use a separate electric motor to drive the tail which are not as responsive.
When executing a CW spin of the body the motor on the tail of a mSR or 120SR must speed-up above the level needed to balance the main rotor torque and fly straight. When the body of the model is spun CCW to the right the tail motor must slow down and let the torque of the main rotor spin the body. As a result of this cause and effect these models will be more responsive and easier to control when performing tail initiated turns and pirouettes in a CW direction than CCW. The direction of the main rotor also affects turning. In a CW turn the rotor banks in the same direction the rotor is turning. In a CCW turn the rotor banks opposite the direction of rotation.
On twin rotor coaxial models the main rotors turn in opposite directions so one counteracts the torque of the other. When a rudder stick input is given on the Tx the model changes the relative speeds of the two motors and causing the body of the model to turn or "yaw" clockwise (CW)or counter-clockwise (CCW). A single rotor helicopter uses a tail rotor on a boom to counter the torque of the main rotor.
Setting up the Spektrum Transmitter
Now that we are on the same page about what the sticks on the Spektrum Transmitter control and what those control functions are called we can start programming it. I'll assume you've read the user manual and are familiar with the controls and instead discuss the most practical way to use them.
The advantage of the Bind-N-Fly concept is the ability to program and control several different airplanes or helicopters using the same transmitter. The transmitters, depending on model, have between 5 and 11 discrete channels for controlling functions on the models. For an electric helicopter five channels are used:
The transmitter is set-up differently for CP and FP models. For the FP blade model it is necessary to set the SWASH TYPE menu to "1 Servo - 90°" The 90° refers to the difference between the two control arms on the swash plate, not the angle of the flybar relative to the main rotor.
Swash Balls, Dual Rates, Expo and 5-in-1 'Turbo Boost'
Many different levels of performance can be programmed on the DX6i transmitter (Tx) via what are called Dual Rates and Exponential (Expo). Dual rates can be used to lower the maximum travel of the servos and limit power of the main and tail rotors to less that 100% of maximum. Expo slows the response of the control sticks so a minor movement of the stick does not cause a big unexpected movement of the model.
On the model itself there are two ways to change its responsiveness. The swashplate on Blade models has two sets of balls with different lengths. Out of the box the links are set on the shorter balls. Moving the links to the outer balls causes the rotor to move more when the same amount of servo travel. The 5-in-1 receiver is also programmed with a high/low rate which is controlled by using the Ch. 5 GYRO channel on the Tx like an on/off switch. When GYRO rate is less than 50% the 5-in-1 will be in low rate mode and limit servo movement and motor power. When the Tx sends a Ch.5 signal greater than 50% to the receiver it switches to high rate which increases throttle, rudder and servo travel by 15%.
The Pros and Cons of 'Training Wheels'
Remember when you first learned to ride a two-wheel bike? You might have started with training wheels on the back to keep the bike from crashing until you learned how to balance, pedal and steer all at the same time. All the things mentioned above are the RC helicopter equivalent of training wheels designed to "numb down" the action of the control sticks. That may seem like a good thing for a beginner, but with the controls numbed too much down the delay in seeing the heli react proportionally when a stick input is made will can result in making larger than necessary stick movements to get the heli to react, causing overcorrecting. That can quickly become a vicious cycle ending with the heli circling out of control and hitting something.
One of the advantages of learning to fly with the mSR and 120SR is that they are self-correcting and if well trimmed hover hands off. Having learned to fly both with minimal problems and crashing I think much of conventional wisdom for setting up a dual rates and expo for other less inherently stable helis isn't as necessary with them. Stop for a moment and consider this: once your 120SR is trimmed properly and rises into a stable "hands off" hover, learning to reign back and moderate the stick movement will have the same effect as dialing in lower dual rates and expo when you try to move it out of the hover into FF. Smaller stick inputs will be needed and they will have a more immediate and predictable effect on the flight of the heli.
Before numbing down the controls you might want to try flying a few times with 100% D/R and EXPO set to INH. One of the advantage of learning to fly with the Blade models, particularly the coaxial ones, is their ability to hover hands-off when properly trimmed. That means they don't go anywhere unless the sticks are moved and if the sticks are moved very slowly, learning to waiting for the model to react, its possible for even a beginner to fly in control with no "dumbing down" of the sticks. If you manage to keep it in the air that way it's a clue you don't really need to numb the controls and get up the learning curve a bit faster; you'll only need to train your thumbs once.
Give Yourself Room to React
The main difference between a skilled pilot and a unskilled one is reaction times. A skilled pilot can avoid a crash into the floor or wall by reacting quickly with the correct stick input. A beginner needs more time to react correctly and that translates into needing more space for flying. The biggest mistake beginners make is trying to fly indoors in too small as space. They wind up crashing and damaging parts before ever managing to trim the model into a stable hover But if you start with high rates with a 120SR don't do it in your living room or driveway. Wait for a calm morning or evening and find a field where there is nothing within 100'. Get it 25' into the air in a hover and then MOVE THE STICKS VERY SLOWLY until you learn how stick movement changes the attitude and altitude of the heli. When set to high rate on the Tx and Rx it doesn't take much input to get a well trimmed 120SR moving and make corrections.
TRIMMING AND MIXING FOR FF:
Step one is getting it up into the air into a stable hover. With a well trimmed 120SR that's just a matter of applying throttle and then letting go of the sticks, so let's start with setting the throttle curves for a mid-stick hover. But first let's set the GYRO switch so it will activate the high dual rate on the 5-in-1:
RATE SW GYRO
Now flip the GYRO switch to 1 (5-in-1 high rate mode). The extra 15% doesn't make much difference in throttle or servos unless max. inputs are used so I leave mine in high rate all the time.
Step 1 - Set-up throttle curve for hover when throttle stick is centered
I set my throttle curves so my helis hover when the stick is centered, making both sticks centered an easy to find "no hands hover" control baseline.
With throttle curves adjusted so the heli hovers when the stick is centered, getting off the ground into a stable hover is just a matter of cracking the throttle enough to spin up and balance the main and tail rotors then pushing the throttle stick past half way to get it rising off the ground smoothly but quickly. Once it is in the air at the desired height moving the stick back to center stops the climb and puts it into a hover.
With my 120SR I found that 30% - 40% throttle was required for hover, so I set my high rate STUNT curve to 0 - 30 - 40 - 65 -100 my NORM curve to 0 - 30 - 40 - 65 - 80
If you try those settings on your DX6i you'll find the curve is steeper than linear in the beginning, flatter in the middle, and more or less linear beyond the hover range. That reflects how I want the heli to act: get up off the ground into a hover quickly and smoothly, then react in a slower predictable controlled way when ascending or descending from hover and have linear response when I need emergency power to recover from a too rapid descent.
Note: On a CP heli NORM is typically used to create a linear curve for scale flight and STUNT is typically is used to create a V shaped throttle curve for 3D inverted flight. I don't see a compelling need for two radically different throttle curves on a FP heli like the 120SR if flown outdoors so I keep everything except the H value the same on mine and keep it in STUNT mode all the time outdoors. On the rare occasions I fly it inside I use NORM to slow ascents out of hover and keep it off the ceiling.
Step 2 - Trim for hover
Get it off the ground in a large open space into a hover, take your hands off the controls and observe how it drifts.
Trim correction for the rudder can be done two ways: switches on the console or the sub-trim menu. Trim correction for the elevator and aileron can be done three ways: switches on the console, the sub-trim menu, and adjusting the length of servo linkages.
I like to trim in two steps. I keep the console trims centered and INITIALLY use the sub-trim menu to adjust and quantify numerically how much trim is needed for hover. Then once I have an idea what corrections are needed I'll re-zero the sub-trims for aileron and elevator and adjust the linkage to get the same stable hover. You can skip the sub-trim step for aileron and elevator and adjust the links immediately, but since HH flight tests and adjusts its products only minor sub-trimming should be needed. My 120SR only required 8 units of left rudder and 8 units of left aileron to achieve hover. 100 sub-trim units move the servo about 40% off center so 8 units moved it about 3% off center; not enough that I thought it necessary to change the linkages.
Step 2 - Set Mixes for Forward Flight
When the heli is moving the side of the clockwise turning rotor facing the direction of travel will generate more lift than the other side of the blade moving away from the direction of travel. So in forward flight the left side of the rotor generates more lift and the heli will tend to skew to the right. As it skews to the right the gyro will adjust the tail rotor to try to keep the tail following the nose.
One of the best tips I read for learning to fly a heli was "watch the main rotor shaft". Changes to the main rotor shaft predict where the heli is heading next. In FF seeing the main shaft tilt more to the right is a clue that a left aileron correction will be needed.
After flying the 120SR a few times and correcting for FF deviation using the aileron and rudder sticks land the heli and unplug the battery. Go to the monitor screen of the Tx and see how the elevator, rudder, and aileron indicators on the monitor screen move with the same amount of stick movement you used when flying. After seeing how much your stick corrections changed the aileron on the monitor, go to MIX 1 and set ELV > AILE and change the R rate value until you see the same amount of aileron movement on the monitor when you move the elevator the same amount you did when flying. To correct for skewing to the right you'll need to enter a minus value for R. The L rate is used to correct aileron when backward elevator is applied, so if you don't fly backwards fast you can leave it at 0.
If after correcting the aileron FF trim with MIX 1 you may find that the heli flies level but the tail is yawing left or right. First recheck and adjust your hover rudder sub-trim as necessary to keep the tail steady in hover. Once hover trim is verified repeat the same process for MIX2: First fly the heli and make a constant rudder correction with the stick in FF, then using the monitor as a guide use MIX2 to enter a ELV > RUDD mix to get the same amount of rudder movement when the elevator stick is moved.
My 120SR was skewing to the right in FF and using the monitor I found I needed ELV > AILE R - 60 units to match the corrections I'd been making with the stick to keep it straight. Next time I flew the heli with that -60 ELV>AILE mix it flew dead straight. There was some minor yawing of the tail but not enough to worry about mixing out. My mSR requires both ELV > AILE and ELV > RUDD mixing to keep it straight in FF.
Assigning both MIX1 and MIX2 to the AIL D/R switch on the console (SW = AIL) will allow you to turn them on and off for comparison with and without with the switch over the right stick.