FBL Helicopter World Review

: Graupner Fbl Helicopter World Review FBL Helicopter World Review RADIOS

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First of all we should point out that the

Graupner R&D team in Germany did all the

programming of the FBL system. Experienced

helicopter pilots from the European and Asian

scene supported them by extensive flight tests

and improving internal control algorithms. The

hardware is manufactured, like most electronic

devices coming from Graupner/SJ, at their

headquarters located at South Korea.

The Graupner flybarless system is based on

2.4 GHz HoTT receivers (usable for pattern

and helicopter applications), that are equipped

with 3-axis gyro sensors right from the factory.

These receivers are the GR-24 Pro 12-channel

(3xG+3A+3M+Vario) and the new, 9-channel

GR-18 (3xG+3A+3M+Vario). I will mainly focus

on the GR-24 Pro receiver, because it is a perfect

choice up to 700/800 size machines, but small

enough to fit 450 size helicopters.

According to information from Graupner/SJ it is

not finally decided whether to bring out the metal

cased GR-18 ‘3D’, shown at the Nürnberg Toy

Fair. Nevertheless the plastic housing is totally

up to the job and saves weight. The helicopter

flybarless software can be downloaded very

easily from their homepage and transferred to the

gyro-equipped receiver via the update manager

PC program (as used with other Graupner

REVIEW

At the ROTOR Live 2014 fair in Germany,

Graupner launched their HoTT

flybarless system for model helicopters

by demonstrating it on the flight line

and it created lots of interest. Of particular

interest is its total integration into existing 2.4

GHz HoTT gyro receivers by simply doing a free

of charge software update. It also offers the

ability to perform model setup and parameter

adjustments wirelessly and very comfortably

via the radio, which has to be regarded as a

groundbreaking feature in the industry. We

checked out further details and want to show

how the Graupner SAS works in practice.

Graupner/SJ’s

FBL System

More ToTal InTegraTIon: The all-new graupner hoTT flybarless sysTeM

rS/ptureS Fred Annecke

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collective, you check the correct collective, cyclic

and rudder effective stick directions by using

the Tx servo reverse menu. Tx sub trims remain

untouched as the flybarless system zeros all stick

functions (=> yaw rate defaults) during every

boot up sequence. Gyro ‘Axis Assignment’ is an

easy job… Using the gimbal sticks, we select

roll, elevator and rudder in sequence and when

tilting the helicopter towards the correspondent

HoTT devices). When buying a new HoTT gyro

receiver, pattern and helicopter applications are

implemented and ready to run out of the box.

Updating an existing device takes a few seconds

and existing adjustments will not be overwritten.

A particular highlight is that the whole

communication and adjustment of the SAS

software is via the Tx telemetry menu, in my case

a mx-20, or mz-24 HoTT. Thanks to bidirectional

data transfer, there is no need for a separate user

interface, smart phone or even push buttons on

the unit itself. The transmitter is present anyway

and acts as a wireless data terminal with an

easily read display. All FBL related model data

and adjustments are stored in the receiver itself.

One of the most important demands of the

Graupner developers was making the initial setup

of a new model as easy as possible without

losing flight performance later on. For this the

Graupner flybarless software is divided in two

layers, the ‘Base Setup’ and ‘Expert Mode’.

When doing the initial setup of a new model

helicopter, the first step is to switch the bound

HoTT receiver to ‘Heli’ mode. Having done this,

the flybarless software is active and ready for

adjustments. As with all other inputs, this is done

by using the Tx telemetry, going through Base

Setup menu first. The menu structure itself is

built like a book, which can be thumbed through

forwards or backwards from page 1 to 4, by

pressing the transmitter buttons.

On each of these theme specific ‘pages’,

related sub points are listed. Electronic

swashplate mixing is performed inside the

receiver/flybarless system itself, so the Tx has

to be set to 1 servo swashplate (no mixing). All

servos need to be plugged into the receiver in a

given order, as shown in the manual.

All basic steps that have to be done first are

listed on the last two pages of the Base Setup

menu! This makes some sense (?) because these

points are only necessary once for a given model,

so control loop related parameter settings can be

reached very quickly on the first pages without

going a long way round (*).

After selecting the swashplate type (90°, 120°,

135° or 140°) and rotational direction (initiates

the correct pitch => rudder/cyclic => rudder feed

forward direction and pirouette compensation),

the next point is to set the servo travels. By

collecting all three (or four) servos together in a

group, you can go through all the possible norm/

rev combinations by simply clicking one button –

thus avoiding the irritating trial and error of setting

the servo direction individually.

Having obtained the same directions for

Graupner/SJ’S FBL SyStem

Graupner/SJ’s

FBL System

The brand new 9 servo GR-18 gyro receiver with integrated SAS serves 8 channels at the front

and 1 at the rear, which can alternatively be used for external telemetry devices

The GR-24 Pro serves 12 servos and external

telemetry sensors can be plugged in

On top we have the UHF PCB (giving 2.4

GHz antenna diversity), lower PCB with servo

signal processing and sensor arrangement.

Plastic housing is internally ‘metalized’ for

shielding reasons

GR-24 Pro (12 channels) and GR-18 (9 channels)

include SAS for model helicopters together with

the proven 2.4 GHz HoTT protocol

The GR-24 Pro is a 2.4 GHz HoTT receiver and SAS in a single housing. It comes factory equipped

with 3-axis gyro, 3-axis accelerometer and variometer, which opens the door for future interesting

options

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Graupner/SJ’S FBL SyStem

The Graupner receiver/SAS unit sitting in the back of my trusty Mikado

LOGO 500SE

The GR-24 Pro unit performs excellently in a big 700 - my Compass 7HV

Ultimate was one of the test bench during lots of flights

A GR-24 Pro is compact enough even in a small and light helicopter like the

WARP 360 – it gave impressive flight performance using the factory settings!

The GR-18 is first choice for small helicopters like the WARP 360 The Raptor E700's chassis provides too much space for the

GR-24 Pro

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direction, the system stores the necessary gyro

reaction, confirms it, and it’s done.

The rest of initial setup is a familiar routine. For

older analogue and modern digital servos, we

are able to adjust the refresh rate for swashplate

and tail rotor. It is possible to run standard rudder

servos with 1.5 ms or special, narrow pulse

gyro types of 960 and 750µs. In order to get a

perfectly horizontal alignment of the swashplate

and zero collective pitch of the main blades,

the system switches off the control loops after

selecting ‘SWP S1/2/3 centre’.

Now we can perform the necessary fine

adjustment very comfortably by using fingertips

on the Tx touch pad. The same is true for the

rudder servo centre offset. A pitch gauge is a big

help while adjusting the necessary swashplate

servo travel in the menu to achieve the required

7º cyclic pitch. After this we limit the maximum

possible swashplate tilt angle without binding

and fix max. and min. collective range. The same

is done with the left/right throw limits and rudder

servo/tail pitch slider.

‘Swashplate Rotate’ is only needed for multi

blade rotors that need a virtual offset. System

internal ‘Expo’ should be left ‘YES’ as per the

factory default. This gives 25% on roll/ele, and

30% on tail in order to smooth the response

around centre a little bit for the first flights. If you

want to run your own Expo in the Tx, you simply

select system internal Expo ‘NO’ and choose

flight mode dependent values. Cyclic and rudder

yaw rates are adjusted by using the transmitter

servo travel volumes in general. As these values

can be switched using the flight mode, it is not

necessary to run bank switching in the SAS itself.

During dozens of test flights with different size

and weight helicopters, 80% travel volume/0%

Expo on swashplate and 70% travel volume/30%

Expo on rudder, was found to be good overall

values for response and smoothness. The only

control loop parameter adjustments that are

necessary in the Base Setup menu are optimising

cyclic and rudder gyro sensitivities during flight.

If you want to run a crisper cyclic response,

you increase ‘Direct Stick’ input – it could not be

simpler. Running the factory default settings and

only using the Base Setup menu, will give very

good results for most helicopters. If you want to

make the gyro sensitivity head speed dependent,

you can set an aux Tx input function for this

particular axis and change its value via the flight

mode switch.

Expert Mode

As mentioned, ‘Expert Mode’ will probably

be needed in a few cases. When switched to

‘YES’, the previously near empty Base Setup

menu pages for swashplate and tail rotor will be

filled with many more adjustment options. Now

you have direct access to internal SAS control

loop parameters (for example P: proportional,

I: integral, D: differential), each of which can be

adjusted and will change the flight characteristics

– as described in the typically extensive Graupner

user manual.

For us one interesting point might be the

‘Speedflight’ optimisation. By changing this value

you damp the tendency of some helicopters

(or better said: its particular rotor head/rubber

damper/blade stiffness combination) to track

any wavelike characteristics during high-speed

runs. ‘Hovering Stability’ comes factory preset

to ‘Normal’. High or Low makes the helicopter

more stable for beginners or more aggressive for

3D maniacs. In case you want to improve holding

power of your tail during brutal collective inputs,

you can adjust ‘Torque’ (collective and cyclic feed

forward value) on this page.

A meaningful feature is the system implemented

logging function. With this, internal parameters of

the flybarless system are continuously written to

the Tx SD card via the downlink. This data can

be a helpful in the case of problems and can be

analysed by the Graupner service team.

In Flight

Now the most important question is: how

does the Graupner flybarless system perform

during flight? To find this out, I converted several

helicopters in my fleet to the new system and

checked out their characteristics during lots of

test flights. Result: all of them were very easy

and exceptional quick to setup – thanks to the Tx

based, wireless adjustment procedure.

In all cases after having done the compulsory gyro

gain optimisation during the initial flight, the Base

Setup menu was more than adequate to get a very

well performing model. It seems that the factory

default settings were very accurately matched.

Graupner/SJ’S FBL SyStem

When opening the telemetry menu of a

Graupner transmitter you have access to the

receiver/SAS units, after switching to ‘Heli’ you

are in the ‘Base Setup...’

...and ‘Tail Adjust’ (Tail Gyro Sensitivity)

‘Base Setup Control’ scrolls through the initial model parameters

Gyro Axes Assignment is a single step – the

last page

...with ‘Swashplate Adjust’ (SWP Gyro

Sensitivity and Direct Stick)...

When switching to ‘Expert Mode...’ ...swashplate and tail rotor menus become live with addition control loop parameter adjustments

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very quickly change parameters

via telemetry, if wanted just for a

short try, is a really great bonus –

when/if anyone experiences this

you will not want to do without it!

Conclusion

From my point of view,

Graupner has done a very good

job with their HoTT GR-24

Pro and GR-18 gyro receiver

integrated flybarless system.

The wireless easy initial set up

via the transmitter together with

excellent flight performance will

ensure it becomes a serious

market contender. When taking

into account the other matching

Graupner/SJ products such

as the ESC (with integrated

telemetry) and external HoTT

sensors, we have to think about

a cleverly thought out complete radio control

system.

(*) Hint: when holding the ESC button on a

mx-20 HoTT Tx for a longer time, you will directly

enter the telemetry menu. With this little trick

you get direct, lightning quick access to the SAS

parameters. MHW

Even hard, sudden bursts of full negative pitch

during high-speed manoeuvres every time gave a

neutral dive, without any tendency for undercuts.

While mounted in my little Compass WARP 360,

the internal Expo on swash and rudder gave an

instant comfortable and relaxed flight feel without

further adjustment of the parameters.

‘Cooperation’ with the ESC governor mode

(often a problem with small models with a low

rotor mass and short tail booms) worked well

without tail wagging or slow periodic oscillation

(a previous mounted SAS needed some control

loop fine-tuning).

With the big Compass 7HV Ultimate running on

12S LiPo, after initial flights the internal Expo was

switched to ‘NO’ and all expo settings were done

in the Tx in order to get a very crisp and direct

main rotor, but a smooth tail around centre. For

the rudder I am using the very reasonably priced,

but lightning quick Graupner/SJ HBS 770BB MG

servo (high voltage, brushless motor) which does

an excellent job.

We already discussed the values for servo

travel volumes (=> yaw rate) and Expo in the

transmitter, which were also confirmed in the

Raptor E700. A total no-brainer was my GR-24

Pro equipped Mikado LOGO 500SE. Right from

the very first lift off this model gave a feeling of

stick confidence seldom felt before when flying it.

The GR-24 Pro pirouette compensation feature

seems to be a system favourite. The ability to

Graupner/SJ’S FBL SyStem

Works well in the Raptor E700

Provides confidence in the 7HV



PRODUCT GR-24 Pro (3xG+3A+3M+Vario)

SERVO CHANNELS 12

TRANSMISSION 2.4 GHz HoTT (FHSS)

OPERATING VOLTAGE 3.6 – 8.4 V

DIMENSIONS 46 x 31 x 14 mm

Internal 3-axis gyro, 3-axis accelerometer,

variometer

Aux. External sensors possible

UPDATE via Internet

WEIGHT 18 g

ORDER NO. 33583

EURO RETAIL PRICE €199.95

PRODUCT GR-18 (3xG+3A+Vario)

SERVO CHANNELS 9

TRANSMISSION 2.4 GHz HoTT (FHSS)

OPERATING VOLTAGE 3.6 – 8.4 V

DIMENSIONS 46 x 21 x 14 mm

Internal 3-axis gyro, 3-axis accelerometer,

variometer

Aux. External sensors (instead of channel 9

servo outlet selectable)

UPDATE via Internet

WEIGHT 14 g

ORDER NO. 33579

Dislike

No FBL version GR-12 (3G+3A+Vario)

receiver available

Likes

Totally integrated SAS/HoTT gyro receivers

Wireless adjustments via Tx

High performance flight characteristics

Low priced

Good in the

WARP 360 too!

Graupner/SJ products are distributed in the

UK by Logic RC, Tel: 01992 558226,

Email: mail@LogicRC.com

For further information, please visit their

website at www.LogicRC.com

UK RRP:

P-33579 GR-18+3xG+3A+Vario HoTT 9ch

receiver £139.99

P-33583 GR-24 PRO 3xG+3A+3M+Vario

HoTT 12ch receiver £169.99

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