Microheli

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Walkera V120D01 microheli:

This is a 'tiny' heli:

Rotor span 27cm and all up weight 88 gramme.

Tiny yet it has a shaft driven tail with servo driven tail rotor pitch, 3 axis solid state giros coupled to an adjustable electronic flybarless system, a brushless motor and 10Amp speed control. All miniature versions of what you get on much larger helis.

The heli is incredibly tough - I have crashed many more times than captured on video - some 'bone jarringly' hard - and the only (non-cosmetic) damage was a set of stripped tail drive gears and a few nicks out of the blades - see crash video.

This page is relevant to many of the latest generation of fixed pitch microhelis, some will have flybars, some like this will be flybarless! Coaxial (dual rotor) helis are extremely stable and are therefore very easy to fly and not covered here.

Flybarless helis use gyros and electronics to replicate the stabilising effect of the flybar on conventional helis. The flybar acts as a gyroscope 'modifying' the control inputs from the servos therefore imparting some level of stability to the heli. The weight of the flybar blades (many have extra weights) has a dramatic effect on the stabilising effect. Higher weight = more 'stability'.

The simpler mechanical design (fewer moving parts) & lighter weight make flybarless systems more efficient and therefore can fly longer for the same battery charge. There are also less parts to wear, fail or damage in a crash.

Images below show the difference between a flybarless rotorhead and conventional rotorheads.

           
Flybarless fixed pitch rotorhead. Direct connection of the control arms to the swash plate. Very few moving parts, low weight and aerodynamic drag. Conventional flybar fixed pitch. The flybar has 'levers' that modify the inputs from the swash plate. About 6 moving parts for the flybar. Arodynamic drag from the flybar and lever mechanisms reduces efficiency. Conventional flybar CP (collective pitch) rotorhead. The flybar connects to the blades via the 'square' frame and internal levers - about 12 moving parts for the flybar system. Stabilising weights can be seen on the flybar. Coaxial, dual rotor heli - top rotor is stabilised by the heavy flybar. Lower rotor accepts control inputs. These are extremely stable helis and very easy to fly but have limited performance.

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Transmitter controls.

This video describes the actions of the stick controls on the transmitter. The sensitivity can be adjusted on many transmitters - this one has a 'half' control limit switch (top right) that effectively halves the rate of the sticks - this is very useful when starting to learn to fly. More advanced transmitter models will have programmable 'rate' and 'curve' - set these at the manufacturers recommended settings for your flying experience.

If you do not have adjustable rates just remember - VERY small stick inputs!

Many forums etc have a wealth of data and guidance on transmitter setups.

 

Takeoff.

If you have, or can make, a set of training gear for your heli there is an exercise to get used to the controls - skate the heli around the floor. I have not demonstrated this since a smooth hard floor is required, see the video when my homemade training gear catches the carpet! Get the heli light on the training gear and 'skate' around the floor, this gives a feel for the controls. Beware however that the control inputs when 'skating' are far less effective than when flying. ie: more input is needed to control the heli - due to drag on the ground.

As you become familiar increase power so that the heli is just off the ground and practice very low fly-skating.

If you don't have access to a smooth floor or training gear then you'll just have to go for it - hop off the ground and back down to get a feel for the takeoff power - careful of the very unstable transition zone.

The heli will tend to drift left on takeoff, this is due to the tail rotor having a net left push whilst counteracting the main rotor torque - compensation will come naturally with practice.

 

Hover.

If you have 'skated' the heli with training gear the transition to hover is very easy - increase power until the training gear is free of the ground and use the right stick (cyclic) to maintain position. It can't fall over with training gear and will be more stable due to the extra weight. Remove the training gear as soon as possible - the heli will be much more lively without the weight and drag.

Without training gear extend the lil' hops longer and longer, keeping the heli reasonably low, and maintain position using small inputs of the cyclic.

When very low to the ground a heli is more unstable than at higher altitudes, this is due to the ground effect - the ground acts as a barrier to the airflow from the rotors. Stable hovers at altitudes below approx' 1 rotor diameter are much more difficult due to this ground effect.

A way to imagine a hovering heli is to think of the it balancing on a ball (of air). If the ground is close the 'ball' is smaller:

Transitioning to side on then nose in hovering - try and put yourself in the 'pilots seat' so that you input controls relative to the direction the heli is pointing. This can take time to master, especially the nose in hover, as left and right are effectively reversed relative to your line of sight.

 

 

Trimming.

Adjusting the settings on the heli and transmitter to 'balance' the heli, ie so that the heli will not tend to preferentially drift in any one direction.

The first essential is to ensure that your heli is correctly assembled, the battery fitted properly and the heli not damaged, especially the main or tail rotor blades.

Ensure that the blades track correctly:

Hold the heli down by the skids, use a weight, run the main blades upto high power. Viewed from edge on do both blades follow the same path. If they need adjusting consult the manual or manufacturers web' site etc for tracking adjustment guidance:

Bad blade tracking

 

Good blade tracking

 

Check the trim when you are in a draught free environment, over level surface and well away from any walls, furniture etc. Microhelis are very sensitive to drafts and 'backwash' from nearby barriers, walls etc.

Do not be over critical in trimming the heli - I find a lil' forward bias useful.

 

 

Hovering, flying slow over an abrupt change in ground level effects the lift from the main rotor. The 'ball' of air is distorted and pushes away from the higher level! This decelerates the heli as it approaches the 'obstacle' and accelerates it off!

 

First flights

Transitioning to flying is just extending the duration of the hover and then moving in the desired direction rather than maintaining a stationary position. For the first few 'flights' bring the heli to a hover and gently push right stick forward and get a feel for how fast it accelerates, bring it back to hover and a lil' back stick to return to the start point (flying backwards so keeping the heli 'tail in').

Next hover around the room at a reasonable height in a 'triangle', sharp corners changing direction whilst almost in stationary hover. By flying a triangle the heli stays 'side on' avoiding extended time in the nose in position. As confidence builds slowly increase the speed and slow the rate of the turns - this will result in smooth curves, eventually 'circular' circuits around the room, and periods of 'nose in' flight. Practice circuits in both directions around the room, anticlockwise is generally harder due to the gyroscopic effect of the main blades.

Introduce a very small amount of roll into the turns, turning left a lil' left roll on the cyclic - be careful the speed of the heli and rate of turn may change rapidly unless fine roll control is used.

The effect of control inputs on power will soon become apparent - the more control inputs are used the less lift is generated by the main rotors. As the manoeuvres become more rapid and use greater control inputs more power will be needed to maintain altitude and rotor head speed. This is a fine balance when flying indoors since there is limit to how high you can go, and the mix of different furniture heights.

Flying low over furniture has its own complications. The heli can move in and out of ground effect as it passes over furniture. This can cause either sudden increases or decreases in altitude and or control response - all good practice!

   

What's Next?

Learning to fly in one consistent space is ideal - the walls don't move and the background 'view' is familiar. Once competent flying around one room move to a different environment, different shape room, furniture, even outdoors if you have a very calm day. These helis can be flown in significant wind conditions but it takes a lot of practice.

Precision flying - target landing, slalom gates, etc, add challenges that will stretch you and improve your skills.

The V120D01, like many flybarless helis has adjustable stability controls, this allows the flyer to reduce (or increase) the electronic stability, and adjustable 'servo extent' which limits the max travel of the servos. If the option is available slowly increase the 'servo extent' to maximum and reduce the stability to minimum.

On minimum stability a small fixed pitch flybarless heli will feel at least as unstable as a properly trimmed 3D capable CP (collective pitch) model - so if flying a fixed pitch heli has become easy upgrade to a fully aerobatic (3D) capable CP heli.

The stability of a flybar heli can be adjusted by reducing the weights (if fitted) on the flybar, but there is a limit. No fixed pitch heli with flybar will feel as 'unstable' as a CP heli - adjust the transmitter as far as possible to maximize control input range and accept when upgrading to a CP its back to school for a refresher course!

 

 

Crashes:

I've had scores of crashes learning to fly this heli - a few are on this video. Microhelis like this one are very tough - mainly since they are so light there is rarely sufficient inertia in a crash to damage much. The most important thing to remember it to SHUT OFF THE POWER - or you will strip gears, potentially do more damage to the rotors and rotorhead etc. Flybarless microhelis win hands down in this department since there are no small levers and links in the rotorhead to damage, flybar rotorheads can be much more fragile. Always thoroughly inspect your heli after any heavy landing or crash.

Flight simulators:

There are good and bad things with training on a flight simulator. They are great for getting 'thumb memory' and practicing manoeuvres but they are not very realistic (even the 80+ flight sim's in my experience) - it's all too easy on a sim' - the controls and even flight characteristics of the models may be realistic but without the full sensory feedback (3d vision, sounds, adrenalin, walls etc) there is a lot missing.

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