Monday, October 31, 2011

Helicopter Beginners Guide

Introduction

I should cover the basics of helicopter safety first, i wont go into flight safety, or pre-flight checks just yet. Just basic precautions to take on the ground whilst building or modifying your helicopter.


Specifically, until you are confident with the mechanics of the RC helicopter, and are in a informed position to start the mechanical set-up of the aircraft, do not connect the Li-Po battery to the helicopter. There are many reasons for this, but all will end in the helicopter trying to spin its blades at 2000 rpm, causing injury and/or damage. Once in a position to setup the helicopter mechanically, it is ok to connect the battery to the speed controller, but remove prior to this the three wires going to the motor, to prevent the helicopter trying to spool up.

The T-Rex 500 The T-Rex 500 with the front canopy removed

This is valid specifically for a electric helicopter, but is also valid for a nitro heli, except it is more difficult to accidently start a nitro heli. This guide is written in a fashion aimed towards electric helicopters, as this is what most new pilots will encounter. Most of the principles are the same, except the motor and speed controller is replaced by an engine and a servo. That is not to say electric helicopters are for beginners, its just a lot of the simple ready to fly sets are electric. Electric helicopters are available up to the 90 size IC range, and perform as well as, if not better than there IC counterparts.


I will cover the basics of all of the components in this guide as well, but i go into more detail about specific articles on other pages within this site. Also, see my subsequent articles on how to learn the basics of RC helicopter flight, and achieve a stable hover.


In this guide i will use the T-Rex 500 as the example, to guide you through the various components of the helicopter. I am not however recommending this as a beginners model. Under one-on-one tuition it is possible to learn on this aircraft, and in fact its flight characteristic can be set to be very docile and beginner friendly. But it is aimed more towards the mid to high end range and competition flight, they are also many times more expensive than a basic ready to fly box set, that a beginner should be aiming for.

Note

This section is essentially a glorified glossary of terms. I will go into detail on all of these subjects in other sections of the site. Such as radio setup, mechanical setup, flight training etc.Tthis is also a multipart series, so check back soon for more updates.

Helicopter Mechanics A modern carbon fiber helicopter airframe The frame serves as a support to the helicopters mechanics Airframe

Usually injection moulded. But also on more expensive models constructed from carbon fibre, and Aluminium. Providing a rigid frame to piece all of the components together, and transfer the power between the motor and rotor head. It also serves as a frame to hold the electronics. Modern pod and boom sport models, are semi exposed except for a fiberglass painted canopy that covers the first half of the airframe via some simple retaining clips. This aids in orientation of the aircraft whilst in flight, and helps to improve aerodynamics.

A belt driven tail drive unit Tail drive unit from above, we see the pitch slider and mixer arm Tail

Between the tail unit and main frame is the tail boom, it provides a route for the tail drive system and control linkages. It is necessary to have the rear rotor blades at a larger diameter than the main rotor blades away from the main frame. Usually there are also two support structures coming from the base of the helicopter frame, to a fixed point along the boom to aid structural rigidity. This is also where the horizontal stabilizer fins are located, a bit further towards the rear we find the vertical stabilizer connected to the tail drive unit. The power is normally transferred to the tail from the main motor via a belt drive, but it is also possible to have torque tube drives, that have a fixed drive shaft powering it. The rudder control on the radio controls the yaw of the helicopter via changes in pitch of the tail blades.

120 degree three servo swashplate 120 degree three servo swashplate connected to the cyclic servos Swashplate

This is one of the most important parts of a RC helicopter, it is how the movements from the servos are transferred to the rotor blades, and finally translated into a movement of the helicopter in the direction required. It allows the stationary helicopter frame and servos to apply movement to the spinning blades pitch. In order to produce propulsion in a certain direction, as the blades spin, at certain points along the circumference of the rotation, the pitch of the blade changes, thereby creating more lift on the left side than the right for example. This will then cause the helicopter to move to the right. This is the Aileron control on the radio, and produces a sideways banking motion. It is the same theory for the Elevator control, it rocks the swashplate forwards and backwards, like the Aileron moves it from side to side.

Top down image of the main rotor head Flybar support and mixer arms Rotorhead

Relatively simple compared to the swashplate, as most of the control mixing has been done there. The main components here are the blade grips, they are able to rotate to allow for the changes in pitch of the individual blade. Also on the rotor head is the flybar, this is to provide a mechanical form of stabilization to the inherently unstable aircraft. To provide control to the rotor head, we have a complex mixture of washout arms, bell crank arms, mixer arms, pitch control arms and flybar control arms. All working together to keep the helicopter in the air. I wont go into detail on these in this section, as the particular setup varies from one helicopter to another. I will however go into more detail in the mechanical setup section of this website.

Complete head unit removed from the helicopter and swashplate Mixer and bell crank arms connecting the swash plate to the rotors

A combination of rotor pitch and head speed gives the helicopter lift. When applying increasing pitch on both blades at the same time, this will produce lift, but also increased drag effects will reduce the head speed. On a modern transmitter, the throttle, and pitch are mixed to counter act this and keep a constant head speed, this is also where a engine governer comes into force on a nitro model.


To calculate head speed, we look at the rating of the motor, so a 3000 Kv motor will rotate at 3000 rpm per volt. So the T-Rex 500 runs at 22.2 v. This means the motor will spin at 66,600 rpm when the full voltage is applied, it then makes sense that at half throttle, we will have 33,300 rpm. It is then a simple case of working out the ratio between the teeth on the motor pinion and main gear to give us our head speed. So as an example, if for every one turn of the main gear, the motor turns 40 times, we would have a head speed of 1665 rpm.

Align 60A electronic speed controller The motor mounted on the helicopter Speed Controller and Motor

Unlike a nitro model where we have a mechanical mixture control and servo, on a electric helicopter we have a brushless motor and electronic speed controller [ESC]. The speed controller acts as many units in one. Supplying the appropriate voltage to the motor, providing power to the electronics, controlling headspeed, battery level warnings, and many more features. Most ESC's will have a built in battery eliminator circuit (BEC) to maintain the correct voltages to the receiver and ultimately the servos and gyro. If you have a nitro model, this will be a separate unit, and the helicopter electronics will have there own, smaller Li-Po batter pack. The ESC usually will connect to the motor via 3 cables, positive, negative and data. it is important when working on your helicopter on the ground, to disconnect the motor from the speed controller, to avoid accidental arming and spooling up.

Align GP750 servo Two of the three cyclic servos Servo's and Gyro

If you have a 120 degree swashplate you will have 3 servos mixed to control the swashplate movement. This is known as eCCPM, the controls are mixed on the transmitter, to allow the three servos to control the four directions of motion applied on the cyclic control. Some helicopters use 90 degree non-ccpm swashplates, but on the majority of current helicopters these are much less common. A quick visual inspection of your swashplate will allow you to identify easily which type you have.

Tail servo Tail pitch control unit

Lastly we have the tail servo, usually attached directly to the tail boom, or tucked away inside the main frame below were the tail boom interfaces with the frame. This provides the control for the pitch of the rear tail blades, to allow the model to yaw and rudder control. However, it is necessary to incorporate a gyro between the receiver and servo, to control the position of the tail. Due to the force of the tail rotor, it will generally always want to move. Also looking at the laws of motion, once moving it will want to continue on that path until operated on by an external force. So a gyro counteracts this. It keeps the tail locked steady in one position, when you give some left rudder, it moves left, but the moment you stop the control input the tail comes to sharp stop. Without this you would have to be constantly balancing the tail, and the other controls. No easy task.

The T-Rex 500 ready for action When not in use, keep the blades safe with the foam blade caddy Overview

So that completes are introductory lesson to the basics of remote control helicopters, this was meant as a simple overview, check back soon, and explore other parts of the site for more in-depth tutorials on RC helicopters. It may all seem confusing at first, but it will become second nature within no time at all.

Sunday, October 30, 2011

E-Flite Blade RC helicopter review

Introduction

I thought i should give an overview of some of the more economical micro and sub-micro remote control helicopters out there. As i know these are popular routes into the hobby. One brand that has shown a great deal of excellent micro and small RC helicopters is E-Flite. These are typically fixed pitch or coaxial micro helicopters, small, cheap and fun. Such as the Blade mSR or the Blade CX2. Usually easy to control indoors, but much harder to master. E-Flite have a number of models in there range, but ill just cover a few of the most famous concepts here. Also note, Align are now entering this market, and they will be releasing their T-Rex 100 micro helicopter shortly.

Blade mSR micro helicopter Next step up from a coaxialReady-to-fly or bind-an-fly4 channelStable and responsive"Almost" indestructibleExcellent after market support

The Blade mSR is a super sub-micro RC helicopter that fits perfectly in the palm of your hand. It is a good choice after learning with a coaxial helicopter such as the MCX or the CX3. It is recommended over the 120 SR, as it is slightly easier to control and less expensive in a crash. It weighs in at an incredible 1 ounce, which is astonishing to be honest. Considering it crams in all the usual goodies such as gyro, servos, DSM2 receiver and motor ESC. Along with a selection of the other Blade helicopters it is available as either bind-an-fly or ready to fly variations. It uses a single, fixed pitch rotor, and is ideal for flying around the living room on a cold winters day. Also an excellent gift for a more experienced pilot, due to the "wow" factor of such a capable super micro machine.

Blade mCX micro helicopter Ultra-micro indoor flyingTest flown and factory assembledEverything needed to fly in one box1S 3.7V 110mAh Li-Po includedExcellent precision compared to other coaxials

A micro version of the CX/CX2 range. It is the entry level coaxial contra-rotating helicopter. A good choice for the beginner pilot, it is super stable and easy to control. Like the rest of the Blade range, it utilizes a Spektrum DSM2 receiver and can be teamed up with a compatible Spektrum controller, or the one provided in the ready to fly package. The package has everything required to get in the air for a single price. Parts are cheap, and due to the size and weight it is very crash tolerant. As usual for this type of helicopter, is is best suited to indoors flight.

Blade mCX2 micro helicopter All the best bits of the mCXUpgraded precision swashplateCoaxial counter-rotating headLED lights

In keeping with the original mCX, it is an updated version, with a few extra features for slightly more advanced flight. It is still easy to fly, and anyone can have a go. But for the more advanced pilot, the swash is now user controlled via various parameters, allowing some tuning of the flight characteristics. Larger motors, LED's and a bigger battery means more fun, and greater flights. Essentially an advanced coaxial remote control helicopter.

Blade 120-SR micro helicopter Smaller than micro sizeReady to FlyStability of a coaxial helicopter2.4GHz DSM2 receiver

The Blade 120 SR is a gorgeous little heli. It sits on the line between a small coaxial helicopter, and a sub-micro fixed pitch model. But, it uses only a single rotor. It achieves the stability of a coaxial, but with the agility of a single rotor. Which makes this a nice stepping stone up from a coaxial model. It is available as either a bind-an-fly, if you already have a spektrum DSM2 compatible transmitter. Or as a ready-to-fly unit complete with controller. It hares many similarities with the mSR, essentially just a bigger, faster, better version. If you have got to grips and are confident with a coaxial model, then either this or the mSR is a perfect choice.

Blade CX3 micro helicopter Heading lock gyroCoaxial stabilitySpektrum AR6100e receiver100% factory assembledBlade CX2 compatible parts

If you are after scale on a small budget, then this RC helicopter is for you. It is a faithful representation of a MD 520N Police helicopter, and it certainly looks the part. Utilizing a coaxial drive system for super stability, it will be hovering in minutes. The counter-rotating head means that almost anyone can pick up the controls and have a blast. Sub-micro servos allow full backwards, forwards and banking motions of the cyclic controls. The heading lock gyro means it will stay fixed on a rock solid course until you tell it otherwise. As a first heli, it is definitely recommended, and it is sure to give hours of fun.

Saturday, October 29, 2011

Aerial Photography: Maxi Joker 3

Minicopter, makers of the Joker 3

The Joker 3 is the latest model in a long line of field tested Joker helicopters. What began in 2000 with the Joker 1, the first high-end 90 class electric RC helicopter, has evolved over the years to become one of the most popular and universal models ever developed. The strength of the Joker in the beginning was it's enormous flexibility, whether as a beginner model, fitted to a scale fuselage, an aerobatic model, or simply a fun model to fly.

The Joker 3 complete with a basic aerial photo setup

Technology pushed things further, and with the advent of the first lipo batteries in 2004 there was a need to protect the very expensive batteries by creating a chassis that protects the valuable contents in the event of a crash. From this need the Joker 2 was born, primarily in the iteration of the Maxi-Joker. Because of its (smooth flying characteristics) and extremely low vibration it has become, and remains one of the world's most popular photo helicopter. As an aerobatic model, the Joker 2 was the first 12s battery powered helicopters.

The industry has shifted in recent years, the development of Flybarless electronics and falling prices of Lipo batteries coupled with an increase in reliability have brought many changes to the RC heli industry. Scale Heli flyers desired a drive shaft to be able to integrate the mechanics into lighter hulls. Aerobatic pilots wanted more maneuverability and less weight without compromising the chassis strength.

The Joker 3

It is precisely this basic idea of the expensive components of a helicopter in a compact, stable, and protective carbon chassis that has remained a design requirement. This typically yields around 200 grams more weight when compared to extreme lightweights on the market but costs from crashes are significantly reduced. The guiding principles of a joker are: low cost, low wear and long life.

Thus, all components of the joker are lovingly created in small batches with very tight tolerances. The same techniques are also used in the new model, the Joker 3. Concept The basic concept of the Joker 3 is to once again increase the quality. The Joker 3 in contrast to its predecessor gets a freewheel unit on the main rotor shaft and a split drive gear. Additionally the rigid tail rotor drive allows for a perfectly easy running gear, both in flight and autorotation. The freewheel on the Joker 3 is a 15mm(!) strong clamping body that allows for a total weight of up to 20kg. An additional feature is the main and tail rotor are decoupled from each other by a second freewheel, this led to increased smoothness on the 3DD and was carried over to the Joker 3.

The Joker 3 mechanics

"The very good and quiet running primary drive belt has carried over to the Joker 3. Of course the increased use of such a mechanism brought about increased manufacturing costs. A basic requirement of Joker kit must be that it costs less then 1000 euros, a requirement that they have stuck to to date. The solution to this problem was called value analysis. This is a process to optimize cost intensive production processes. A principle of our production was and is a mixture of self-manufacturing and suppliers of manufactured parts from precision oriented shops in Germany. Of course the lion's share has always been produced in house. Manufacturing process have been partially broken down to several companies and, above all, the in house manufacturing processes have been optimized. Thus it became possible to only incrementally increase the cost of the Joker even though commodity prices rose sharply in some instances."

So with the Joker 3 compared to the Joker 2 you get almost the same price for more helicopter. The good news is that the total weight of the Joker 3 is 200 grams lighter then Joker 2.

Features A fully kitted out Joker 3 aerial video unit Extremely stable and rigid chassisIntegrated host of Flybarless electronics in a well protected chassis.Compartments for components above the flight battery as well as optimum antenna position.Integrated battery slot for up to 12s/5000 mAh BatteryEngine mount acts as a cooling plate for the ESC, a small buffer battery can be mounted above the esc.Additional freewheel clutch between main-and tailrotor, an easy to mount and remove torque tube driveEasily removable tail boom for transportation and maintenance purposesPrecision scissor linkage on the tail rotor featuring 9 (!) bearingsPrecision swashplate with double ball raced swash holder and swash drive with 8 bearings.Direct CCPM linkages to the swashplate without the old push-pull linkages.Robust flybarless rotor damping with different hardnesses.Product family As the basic models we offer five alternatives: Joker 3 with belt driven tailrotorJoker 3 with TT driven tailrotorMaxi-Joker 3 with belt driven tailrotorMaxi-Joker 3 with TT driven tailrotorJoker 3 fuselage mechanic without main- and tail rotor and specific trainer attachments.

Particular emphasis was placed on the Joker 3 to give it the most flexibility possible. So in addition to the basic models you can also choose between the following alternatives:

Belt driven tail rotorMFS II main rotor instead of the paddle-less "V" rotor headBeginner Kit with specially tailored parts such as rotor blades, shorter tail boom, belt drive of the tail rotor and full upgradability to full-sized joker (8s-operation).Enlarged sub-chassie for enthusiasts of Li-ion or LiFe cells.Stabilizer or bracket for the rear strutsPlatform for gyro, or flybarless system that will not fit between the upper chassis plates.Technical data: Rotor diameter: up to 1.60 m (Maxi-Joker to 1.80 m)Weight without battery: 3250 gramsFor engines with 6mm or 8mm shaftTail rotor diameter: 290 mm (Maxi-Joker 330 mm)Reduction: Engine to main rotor: - depending on the Motor between 1:9 and 1:13,6 (7 levels)Main rotor to tail: - 4,8:1Recommendations for extreme performance Maximum: Engine: Kontronik Pyro or Köhler actro 32-3Control: Kontronik Jive 80HVLipo: SLS ZX 12s/3700 to 12s/5000 mAhBlades: Radix 690 or 710 mmTail Rotor Blades: Radix 105 mmFlybarlesselektronik: AC-3XServos: powerful digital servosReceiver: 2.4 GHz

View the original article here