SBG Systems Ellipse Series User manual
Ellipse – Operating Handbook ELLI SEOHAIR
This operating handbook explains how to install and setup an Ellipse in airborne applications
such as aircraft, helicopter, or UAV. Mechanical installation is explained as well as software
configuration and magnetic calibration.
●
Mechanical installation with alignment, vibration and magnetic field considerations
●
Software configuration with motion profile, G S antenna lever arm
●
Magnetic calibration in case of magnetometers use
Mechanical installation
Inertial Systems are very sensitive to their environment and the location of the inertial system
into the aircraft is a key point to get accurate and reliable measurements.
Sensor accuracy can be greatly compromised if following instructions are not followed.
Vibrations
The Ellipse is designed to handle vibrations. Nevertheless in case of highly vibrating
environment, an efficient mechanical vibration isolation is required for proper operation. Silicon
dampers can be used for that purpose.
Ellipse placement in the aircraft
The vehicle coordinate frame is defined as follows:
●X axis points to the front of the aircraft
●Y axis points rightward.
●Z axis points downward.
The Ellipse MUST be mechanically aligned with the vehicle coordinate frame, as explained in
the following diagram. Alignment accuracy should be better than 0.5°.
Note: If a correct mechanical alignment is not possible, then a software alignment
can be used. lease refer to the Ellipse User Manual for such operation.
The main lever arm is the signed distance, expressed in the vehicle coordinate frame, FROM the
Ellipse center of measurements TO the vehicle desired measurement point. It can be used to
deport the velocity and position outputs to this specified location.
Only velocity and position outputs are affected by this main lever arm measurement.
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Ellipse – Operating Handbook ELLI SEOHAIR
Magnetic environment
If magnetometers are used for heading
observation, user should also consider the
magnetic environment.
The Ellipse magnetometers require for good
operation a clean magnetic field. The sensor
should be placed away from any magnetic
interference such as: DC motors, radios,
strobe lights, power supplies etc.
GNSS Antenna placement
GNSS antenna must be fixed with respect
to the Ellipse. It should have a clear view of
sky.
The G S lever arm is the signed distance,
expressed in the vehicle coordinate frame,
from the Ellipse center of measurements,
to the GNSS antenna. It must be measured
within 5cm accuracy.
In addition, this lever arm should be lower
than 10m for best performance.
Note: If the Ellipse is not aligned with the aircraft, lever arms are still taken to the
reference frame of the aircraft, with X pointing forward, Y to the right, and Z down.
This is also the reference frame of the Ellipse considering the re-alignment has
already been applied.
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- 3.51m
0.2m
ANT
IMU
Y
X
Z
- 2.5m
1.2m
IMU
Y
X
Z
Ellipse – Operating Handbook ELLI SEOHAIR
Dual G S Antenna lacement
Dual antenna systems installation will require special care in order to obtain optimal
performance:
●Same antenna type, same cables with identical lengths must be used for both
antennas.
●Both antennas must be turned the same way (connectors oriented in same direction)
●Both antennas must have the same view of sky when mounted on the vehicle.
●Both antennas must be placed on a ground plane (typically the aircraft's roof or wings,
horizontal bars), more than 10cm away from the ground plane's edges.
Once installed, the main G S antenna lever arm must be measured. It is the signed distance,
expressed in the vehicle coordinate frame, from the Ellipse center of measurements, to the
main G S antenna. It must be measured within 5cm accuracy. Then, the same should be done
for the second antenna.
recise lever arms can also be estimated in ost processing using Qinertia.
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Antenna 1
Antenna 2
Ellipse – Operating Handbook ELLI SEOHAIR
Software configuration
All Ellipse configuration is done through the sbgCenter interface, or using low level
communication protocol.
Note: At the first access, the Ellipse will have its default configuration. This data
output configuration should be used it you want to send logs to Support. Don't
hesitate to contact the Support Team for help.
Sensor
Motion rofile
For airborne application, several motion profiles are available:
●Airplane
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Ellipse – Operating Handbook ELLI SEOHAIR
●Helicopter
●Rotary Wing UAV
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Ellipse – Operating Handbook ELLI SEOHAIR
Alignment and lever arms
Here you can configure the alignment of the device and its lever arm in regard to the center of
rotation of the aircraft.
On the alignment settings you only need to set up the first two axis, then the third one will be
automatically computed.
Initial osition and Date
This parameter will matter if you are using magnetometers: the initial position and date will be
used to compute the magnetic declination.
In case you use magnetometers as a heading source, then a magnetic calibration is mandatory.
A 3D calibration should be preferred over a 2D one if possible. If a 2D magnetic calibration is
performed, it will be only valid locally, and should be re-done if the aircraft is in a different
geographic area.
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Ellipse – Operating Handbook ELLI SEOHAIR
Assignment
GNSS Receiver assignment
Here it is possible to select the serial port to receive the GNSS Receiver data, and select the
input Synchronization as well.
The Ellipse N and D GNSS are automatically set to “Internal” by default to select the on-board
GNSS Receiver. In addition, they accept In case the Internal GNSS Receiver is selected, the user
can also set an RTCM corrections input on any available serial port.
Other Aiding Inputs
You can enable Air Data aiding input for airborne application, in case you have such external
sensor available. lease note that Odometer is for Automotive applications, and DVL for Marine
applications.
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Ellipse – Operating Handbook ELLI SEOHAIR
Aiding
GNSS Configuration
lease check following point at the G S configuration level:
1. Choose this parameter depending on the G S you are using (NMEA, Ublox or Novatel,
Septentrio)
2. Set up the lever arm of the G S depending on its position on the aircraft (GNSS
Antenna placement). f your lever arm has been precisely measured within 1-2 cm, or
estimated by Qinertia, you can check the " rimary antenna Lever arm has been
measured precisely" box. This will optimize Kalman filter warmup-time and overal
performance.
3. Select Rough lever arm if you measured it within 5cm accuracy. If precisely measured
or estimated by Qinertia, you can select "precise lever arm" to optimize filter warm-
up time and performance.
4. Automatic rejection mode is advised for each parameter. Automatic mode
automatically detects the confidence so the Kalman filter knows it can rely more on a
parameter or less on an other.
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Ellipse – Operating Handbook ELLI SEOHAIR
Magnetic calibration in airborne applications
When magnetometers are used as heading reference, a magnetic calibration is mandatory for
normal sensor operation. Different calibration methods are provided, depending on accuracy or
ease of use requirement.
Light UAV calibration
As long as a UAV (fixed or rotary wings) is light enough to be held by a few persons, a 3D
calibration, made on the ground is to be preferred. The basic procedure is the following:
1. Install the sensor as described in previous sections, and place the whole system away
from external magnetic disturbances (buildings, other vehicles, etc)
2. ress “Start acquisition” button on sbgCenter calibration window
3. Rotate the system as much as possible. The main point is to cover the whole flight
profile, but a larger amount of points, beyond the flight profile will provide even
better results.
4. ress “Calibrate” and check calibration results. ress “OK” to finalize the calibration
procedure.
5. ower cycle the sensor if you need immediate operation after calibration.
Airplanes, helicopter and large UAV applications
In flight 3D calibration
This calibration will give the best results as it allows to map the magnetic field in real 3D so
that magnetometers readings are kept consistent even during turns and pitching.
In order to perform the calibration procedure, user can use the integrated sbgCenter calibration
tool, or a data-logger to store the “magnetic calibration data” outputted by the Ellipse during
calibration procedure.
rocedure
Once the aircraft is in steady flight at a reasonable altitude, the goal is to cover different
orientations which are representative of the flight domain of the aircraft.
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Ellipse – Operating Handbook ELLI SEOHAIR
The calibration accuracy does not depend on any precise orientation (facing true North for
example) and rather depends on how many significantly different orientations have been
covered. The calibration algorithms are able to map the 3D magnetic field in orientation that
have not really been covered during calibration; however, it is good to cover the full flight
domain to get the best results.
For example an Extra 300 aerobatic airplane should get the best results by performing several
representative aerobatic maneuvers in different directions in order to get a good 3D coverage of
the magnetic field. In the other hand, a Cessna 172 private airplane could only perform high
inclination eights to get optimal results.
rocedure tested on a private airplane
The following procedure has been tested with success on a piston private airplane.
The calibration starts in a steady flight. Two 360° turns will be performed decomposed in the
following steps:
Step 1: Calibration Start. ress “start
acquisition” button.
1. High bank right rolling – without
turning.
2. High bank 120° left turn
Step 2:
1. High bank right rolling – without
turning.
2. High bank 120° left turn
Step 3:
1. High itching: +20° then -20° then
return to level flight
2. High bank right rolling – without turning.
3. High bank 120° left turn
Step 4:
1. High bank 120° right turn
Step 5:
1. High bank left rolling – without turning.
2. High bank 120° right turn
Step 6:
1. High itching: +20° then -20° then return to level flight
2. High bank left rolling – without turning.
3. High bank 120° right turn
Step 7: Calibration end. ress “Calibrate” button, then “OK” button write the calibration data to
your sensor.
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Figure 1: Trajectory performed during calibration
Ellipse – Operating Handbook ELLI SEOHAIR
Once these tests are done the calibration can end. It is not crucial to perform exact 120° turns,
but the procedure should perform rolling points at significantly different headings. In addition
the pitching in the first turn should not be performed at the same heading as the one done in
the second turn.
Note: This procedure can be easily transposed to rotor-craft. The procedure can be
performed in a stationary flight, by making several pitching and rolling maneuvers at
different heading values. The goal is to expose the sensor to as much orientations as
possible.
Ground calibration (2D)
Although this method is not the most accurate, it's possible to calibrate the magnetometer on
the ground, using the “2D” calibration method.
The procedure is really simple and only requires a few steps on the ground to be performed:
1. Install the sensor as described in previous sections, and place the whole system away
from external magnetic disturbances (buildings, other vehicles, etc).
2. lace the aircraft on a horizontal platform. The aircraft must be kept horizontal (in its
line of flight level). This is the case with most tricycle landing gears airplanes, but this
should be a concern with conventional landing gears.
3. Calibration Start. Start the sbgCenter calibration tool and press “start acquisition”
button.
4. erform a 360° circle with the aircraft. The calibration mode has to be set on “2D”.
The aircraft should be at least 10m away from any metal building or other aircraft.
5. Calibration end. ress “Calibrate” and check calibration results. ress “OK” to finalize
the calibration procedure.
Note: For highest performance, please consider the 3D calibration.
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Ellipse – Operating Handbook ELLI SEOHAIR
Calibration result examples
On the following screen-shots, it is possible to see that the calibration coverage is not a full 3D
sphere but covers significantly different orientations. The first screen shows an example of the
calibration procedure explained above. The second one shows a calibration only performed with
a simple “8” performed.
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