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8th International DAAAM Baltic Conference

"INDUSTRIAL ENGINEERING

19-21 April 2012, Tallinn, Estonia

CAMERA GIMBAL PERFORMANCE IMPROVEMENT WITH

SPINNING-MASS MECHANICAL GYROSCOPES

Tiimus, K. & Tamre, M.

Abstract: This proof-of-concept study was

done to research the advantages and

disadvantages when combining spinning-

mass gyroscopes with an electro-

mechanical gyro stabilized camera gimbal

mechanism on a small vertical take-off andlanding (VTOL) rotorcraft and to show that

a method like this has the potential of

being used. As spinning-mass gyroscopes

conserve angular momentum, they can be

used to maintain system orientation and

also to eliminate vibrations dispersing

through the airframe. The experiment

started by attaching a small gyro stabilized

gimbal on a miniature VTOL rotorcraft and

performing flight tests and logging the data

about the base position angles inconjunction with the gimbal mechanisms

output shafts position and ability to

compensate these rotational movements.

After that, 2 spinning-mass gyroscopes

were taken from inside missile guidance

units and implemented to the system by a

special pivoting mechanism. The tests were

performed again after upgrading the

mechanism. Although the overall take-off

weight of the platform increased, the

video-image quality, which was the mainevaluation method, was significantly

improved.

Key words: VTOL rotorcraft, UAV gimbal,

Inertial Measurement Unit, Motion

control, Spinning-mass gyroscope

1. INTRODUCTIONFast developments in the field of small

unmanned multi-rotor-configurationrotorcraft have begun to push aside

conventional helicopters due to their

simple mechanical build, relatively low

cost and secure operation. Being simple to

construct and build makes them also very

lightweight compared to other VTOL

machines. For this reason, multi rotoraerial vehicles are highly maneuverable

and stable in non-windy conditions, but

very prone to stronger wind gusts, which

makes them oscillate and vibrate in a lot of

occasions. This may affect the used

instrument, especially video cameras with

CMOS sensors.

For this reason, a study was performed to

see, whether or not combining spinning-

mass gyroscopes help to improve theoverall performance of a the electro-

mechanically gyrostabilized camera

gimbal. Spinning mass gyroscopes

conserve angular momentum (1) and add

synthetic inertia to the system.

(1)

By combining mechanical gyroscopes and

a positioning gimbal by a specialized

mechanism, which takes precession and therotation of the spinning-mass gyroscopes

axes into account, it is possible to eliminate

the base motion (in this case VTOL

rotocrafts airframe rotational movement

(Fig.1)) from affecting the picture.

The obtained result would find many

applications where improved gimbal

precision and eliminated vibration are

crucial like laser illumination, distance

measuring, target surveillance and other

similar application areas.

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Fig. 1. Y6 Multirotor VTOL rotorcraft

without gyrostabilised gimbal

2. SYSTEM DESCRIPTION2.1. Developed gyrostabilizedmechanismThe objective of the study was to find a

solution, which improves the performance

of a 2-axis electromechanically gyro-

stabilized camera gimbal [1](2) mounted

on a Y6 configuration multi rotor VTOL

rotorcraft (Fig. 1). The applicable small

gimbal is not roll-stabilized although it can

be used in Roll-Pitch confirugarion if

needed.

Fig. 2. Electro-mechanically gyrostabilised

camera gimbal test platform

The mechanism uses DC planetary

gearhead motors with integrated

incremental encoders. Absolute position

for each axis is retrieved with a binary

code disc and an optical switch. The

system uses 3 coordinate systems ground

(0), base (1) = IMU and gimbal (2) (Fig.

4).

Fig. 3. Coordinate systems: 0 - ground, 1

base/IMU and 2 gimbal output

At system startup, the optical switch

detects its relative position to zero angle

and seeks to according direction until the

front is reached (Fig. 5 and 7). At this point

the incremental encoders readout is reset

[6] and gimbal is ready for operation.

Fig. 4. Tilt mechanism

Fig. 5. Block diagram of motor controller

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Fig. 7. Tilt actuator: planetary gearhed DC

motor with integrated encoder, controller

and absolute positioning sensor (optical

switch)

Now the IMU (SBG Systems IG-500A)

detects the rotational movement of the base

and outputs Euler angles = (, , ) [5]

for yaw, pitch and roll to represent its

spatial orientation. This information is

processed in the main controller and output

to motor controllers by I2C bus (Fig.6). The

amount needed to compensate for the base

movements is calculated and with encoder

feedback, the mechanism axes rotate the

required amount.

2.2. Adding spinning-mass gyroscopesSpinning mass mounted on a gimbal on a

base maintains its orientation based on the

principles of angular momentum [3]. The

higher the rotating speed and the mass of

the spinning body, the higher the applied

momentum is needed to deviate the

gyroscopes angle of rotation. Coming upwith a mechanism that allows to constantly

maintain the angle of rotation to the 0-

coordinate system or in other words

removing the angular base motion [4] is

one of the key task for this study.

Precession of the spinning axis occurs

when a force is affecting the spinning mass

[3]. Although, if the angular speed and/or

mass of the spinning wheel is high enough,

the axis will hold its position and nodeviation occurs.

The mechanical test platform uses two

modified spinning-mass gyroscopes (Fig.

8) on 2 DOF-gimbals, so that their

rotational axes cross. This mechanism

itself is mounted on a separate gimbal,

which can pivot in all 3 rotational axes in

relation to the base. The electro-

mechanically gyrostabilized servo

mechanism is mounted underneath the

pivoting point so that the center of mass is

Fig. 6. Block diagram of system processes before implementing spinning-mass

gyroscopes

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slightly on the lower side thus making

gravitation level the system when there is

no sideways acceleration occurring. In

other cases, the mechanical gyroscopes

resist the input force that is caused by

accelerating and decelerating the aircraft.

Fig. 8. Spinning-mass gyroscope from a

missile guidance system

This implementation adds a fourthcoordinate system between the base and

the gimbal output (Fig. 9). Coordinate

system 1 is now solely the rotorcraft

(base), 1A is the spinng-mass mechanical

gyrosystems frame and also the IMU, and

coordinate system 2 remains the servo-

driven output.

Fig. 10. Coordinate systems: 0 - ground, 1 -

base, 1A - , 2 gimbal output

Because the coordinate system 1A can

rotate along with the spinning-mass

mechanism, an additional feedback unit is

needed on the pan axis to sum up in thefinal mechanical output of the gimbal. For

this application an absolute encoder is

needed (Fig. 9), because incremental

encoder would also need indexing, which

is impossible in this case.

The gyroscopes used in this experiment

were removed from a missile guidance

system and during testing they were

powered up using compressed air.

2.3. Multirotor test platformThe base for testing the gyro stabilized

mechanism was a custom Y6-configuration

multirotor VTOL platform (Fig. 11 & 12).

This allowed the gimbal to be mounted in

front of the aircraft so that the spinning-

mass mechanical gyroscope system

Fig. 9. Block diagram of system processes after implementing spinning-mass gyroscopes

Spinning

mass

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pivoting point is at the same level with

aircrafts rotational center (Fig. 13).

Fig. 11. Multirotor VTOL rotorcraft

platform with gyrostabilized gimbal

2.4. ResultsThe aircraft has a standalone flight

controller which can also be used to log

flight data. When this information was

compared with the according data from the

gimbal mechanisms IMU unit, it was seen

that spinning-mass mechanical gyroscopesgreatly reduced the amount of

compensation amplitude that was

necessary for the camera gimbals output

shaft to remain level. Most of the base

movements were canceled by the spinning-

mass gyrosystem. Another advantage is

seen when comparing the pre and after

results of a CMOS block camera image.

There was no rolling shutter artifact seen in

the image, when the mehcanical

gyroscopes are used. CMOS sensors are

known to be very prone to vibrations and

sudden sharp movements.

Fig. 12. Multirotor VTOL rotorcraft in test

hangar

3. FUTURE DEVELOPMENTSThe proof-of-concept with this system was

achieved. Future plans include gathering

all the necessary data to develop the

methodology and procedures to calculate

exact parameters for the spinning-mass

gyroscopes. Another important task is to

construct customised driving motors for

gyroscopes that allow constant and long

operation. Finding the correct balance

between the spinning masses and their

angular velocities allows getting optimum

overall mass and saves energy.

4. CONCLUSIONThe objective of this study was to find a

method to take advantage of syntheticinertia provided by spinning-mass

Fig. 13. Test equipment layout on the aircraft

S-M gyroscopes

Mechanisms

pivoting pointGimbal output axis

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gyroscopes to help in stabilizing a electro-

mechanically gyrostabilized camera

gimbal. The results were satisfying and the

most significant part is the fact that there is

no need to void the biggest advantage of

multi rotor aircraft, which is being verylightweight and agile, by adding additional

mass to the frame of the vehicle to cope in

gusty weather conditions. Instead it is

possible to modify the gimbal suspension

type and use it in conjunction with

spinning-mass gyroscopes to keep the

gimbal level plus eliminate almost all

vibrations. The fact that the gimbal is

moving independently from the crafts

frame allows to use smaller and lighter

servomotors which are used to direct theused instrument to the desired position.

This somewhat also compensates the mass

of the mechanical gyroscopes. Additional

research needs to be done.

5. REFERENCES1. Tiimus, K. & Tamre. M. Camera

Gimbal Control System for

Unmanned Systems, Tallinn

University of Technology, 2010

2. Ghosh, M. Moment of Inertia andNutation of a Captured Gyroscope,

The College of Wooster, 1998

3. Spinning Mass MechanicalGyroscopes, US Dynamics

Corporation, 2006

4. Nettmann, E.F. Comparison ofGyro-Stabilized Camera Mounts for

the Motion Picture Industry,

Nettmann Systems International,2011

5. Guinamard, A. IGN-500A AHRS,SBG Systems, 2009

6. Merry, R.J.E., van de Molengraft,M.J.G. & Steinbuch, M. Velocity

and acceleration estimation for

optical incremental encoders,Eindhoven University of

Technology, 2010

6. CORRESPONDING ADDRESSMSc. Kristjan Tiimus

Department of Mechatronics, Tallinn

University of Technology

Ehitajate tee 5, 19086 Tallinn, Estonia

Phone: +372 5177186

E-mail: kristjan@helicam.ee

7. ADDITIONAL DATA ABOUTAUTHORS

1) MSc. Kristjan Tiimus, Prof. Mart Tamre

2) Title of Manuscript: Camera Gimbal

Performance Improvement With Spinning-

Mass Mechanical Gyroscopes

3) Full Address of all authors:

Kristjan Tiimus / MSc. / Department of

Mechatronics, Tallinn University of

Technology / Ehitajate tee 5, 19086.

Tallinn, Estonia / kristjan@helicam.ee /

+372 5177186

Mart Tamre / Prof. / Department of

Mechatronics, Tallinn University of

Technology /Ehitajate tee 5, 19086.

Tallinn, Estonia / mart@staff.ttu.ee / +372

6203202

4) Corresponding Author: Kristjan Tiimus,

Tallinn University of Technology,Ehitajate tee 5, 19806, Tallinn, Estonia