CTR Electronics Pigeon 2.0 User manual

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Pigeon 2.0
User’s Guide
Revision 1.0
Cross The Road Electronics
www.ctr-electronics.com

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Table of Contents
1. Device description .....................................................................................................................................................5
1.1. Kit Contents........................................................................................................................................................5
1.2. Features..............................................................................................................................................................6
1.3. Electrical/Inertial Specifications.........................................................................................................................7
1.4. General/Mechanical Specifications....................................................................................................................7
1.5. LED States...........................................................................................................................................................8
1.6. Functional Diagram ............................................................................................................................................9
1.6.1. Mount Orientated Signals...........................................................................................................................9
1.6.2. Enclosure Orientated Signals ......................................................................................................................9
1.7. Changes between Pigeon 1 and Pigeon 2 ........................................................................................................10
2. IMU Error Sources....................................................................................................................................................11
2.1. Location –Center of Rotation ..........................................................................................................................11
2.2. Temperature ....................................................................................................................................................11
2.3. Gyroscope Sensitivity Error ..............................................................................................................................12
2.4. Avoid Magnetic/Ferromagnetic materials .......................................................................................................13
2.5. Vibration...........................................................................................................................................................14
2.6. Saturated inputs...............................................................................................................................................14
3. Calibration ...............................................................................................................................................................15
3.1. Temperature Calibration..................................................................................................................................15
3.2. Gyroscope Bias Calibration...............................................................................................................................15
3.3. Gyroscope Sensitivity Calibration.....................................................................................................................15
3.4. Accelerometer Calibration ...............................................................................................................................15
3.5. Compass Calibration.........................................................................................................................................15
4. Boot behavior ..........................................................................................................................................................16
4.1. Boot behavior - Test Results ........................................................................................................................17
5. Wiring ......................................................................................................................................................................19
6. Orientation Convention...........................................................................................................................................20
6.1. World Frame Reference.............................................................................................................................20
6.2. Euler Angles................................................................................................................................................20
6.3. Gimble Lock................................................................................................................................................20
6.4. Does X/Y Axis placement matter?..............................................................................................................21
6.5. Default Mounting Orientation ...................................................................................................................21
6.6. Custom Mounting Orientation...................................................................................................................21
6.6.1. Custom Mounting Orientation –Explicit Values ...............................................................................22
6.6.2. Custom Mounting Orientation –Phoenix Tuner ...............................................................................23
7. FAQ ..........................................................................................................................................................................24

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7.1. Is there a way to tell if the device is present/powered?..................................................................................24
7.2. How do I change the Mount Orientation? .......................................................................................................24
7.3. What changes do I need to make when upgrading from Pigeon (1) IMU to Pigeon 2.0?................................24
7.4. What are the requirements of Pigeon 2.0 when booting up? .........................................................................24
7.5. Does the device support CAN FD?....................................................................................................................24
7.6. Trying to keep robot from tipping over. Any suggestions? .............................................................................24
7.7. Closed-looping an Arm. Any suggestions? ......................................................................................................24
7.8. When Pigeon IMU boots, starting Yaw is not zero?.........................................................................................24
8. Mechanical Drawings...............................................................................................................................................25
9. Revision History ..................................................................................................................................................26

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TO OUR VALUED CUSTOMERS
It is our intention to provide our valued customers with the best documentation possible to
ensure successful use of your CTRE products. To this end, we will continue to improve our
publications, examples, and support to better suit your needs.
If you have any questions or comments regarding this document, or any CTRE product, please
contact [e-mail]
To obtain the most recent version of this document, please visit
www.ctr-electronics.com.

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1. Device description
The Pigeon 2.0 is an inertial measurement unit (IMU) that can sense acceleration, angular velocity, and magnetic
fields. With this information, Pigeon 2.0 can be used to sense a mobile platform’s pose, which then can be used for
a variety of applications.
1.1. Kit Contents
Each kit contains a single Pigeon 2.0 IMU.
IMU is preassembled and includes wire leads
for power and CAN bus.
The CAN bus wire leads are terminated with
3-pin pre-installed connectors (0.1” pitch).
One lead pair has a female connector, and
the other has a male connector. This way,
several CTR-Electronics CAN bus devices can
be daisy chained together.

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1.2. Features
•Nine Degrees of Freedom (3 Axis Accelerometer, 3 Axis Gyroscope, 3 Axis Magnetometer)
•Full AHRS: Yaw, Pitch, Roll
•Quaternion Output
•Gravity Vector Output
•Boot-up does not require stillness. Get useful heading information as soon as it is powered on.
•Kalman Filter fusion algorithm
•Gyro automatically re-biases after 4 seconds of no-motion
•Temperature Compensation for temperature sensitive components
•Temperature factory-calibrated
•Accelerometer factory-calibrated
•Gyroscope factory-calibrated
•No user-calibration required for accurate 6-axis fusion.
•Mount IMU in any orientation (not limited to horizontal or vertical orientation) (Note 1,2)
•Heading and Yaw are continuous, ideal for robot heading servos and motion control.
•Enclosure protects against debris
•Wide Input Voltage Range 6V –28V
•Protection Reverse Input Power Protection
•Polycarbonate housing prevents debris from entering inside device
•One wire lead-pair for power
•Two wire lead-pairs for CAN Bus (3-pin connector, one male, one female) for daisy chaining devices
•Robust bootloader and reliable field-upgrade (no physical button required, no “stuck states” that
requires user intervention)
•Wirelessly check, configure and field-upgrade using roboRIO Wi-Fi and Phoenix Tuner.
•Users can download software API binaries on our reliable Maven server (99.999999999% reliability)
•Hardware Simulation Support
•Supports CAN bus and CAN FD bus.
•Supported by CANivore and roboRIO use case
Note 1: Pigeon 2.0 can be configured for any mounting orientation. Other IMUs provide a fixed number of orientations, but
Phoenix Tuner/ Phoenix API can be used to select any orientation.
Note 2: When using Euler angles, user must avoid Gimble Lock conditions for valid Yaw, Pitch, Roll values. This is a limitation of
expressing pose using Euler angles, and not a limitation of the Pigeon IMU.

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1.3. Electrical/Inertial Specifications
Note 1:Device firmware currently selects ±1000 dps. Future software updates may allow configuration based on
customer feedback.
1.4. General/Mechanical Specifications
Outside Dimensions
1.77” x 1.77” x 0.51”
Weight
1.07 ounces (30.39g) w/ enclosure & wires
Supported Communication Protocols
CAN 2.0 (1Mbps)
CAN FD with CANivore
Boot Calibration (Note 1)
0 seconds
Gyroscope bias no-motion time (Note 2)
4 seconds
Mechanical Shock (Note 3)
10,000 g (duration 200 us)
2,000 g (duration 1 ms)
Maximum Free fall (Note 3)
5’
Note 1: Drift rate will start at DR BOOT.
Note 2: Gyroscope is re-biased after 4 seconds of no motion, which reduces drift rate to DR NO-MOTION
Note 3: Stresses above listed rating may cause permanent damage to the device.
Symbol
Parameter
Condition
Min
Typ
Max
Unit
Tamb
Ambient temperature
-40
+85
°C
Isupp
Supply Current
DC supply 12.0V
DC supply 28.0V
40
21
46
23
mA
Vdd
Supply voltage
6.0
12.0
28.0
V
ESD Rating
ESD Protection Contact Discharge
±30
kV
ESD Protection Air-Gap Discharge
±30
kV
Yaw Drift Rates
DR NO-MOTION
No-Motion Drift
0.12
Deg /
hour
DR IN-MOTION
In-Motion Drift
0.4
Deg / min
DR BOOT
Boot-Into-Motion Drift
1
Deg / min
Gyroscope Specifications
Range
Angular Velocity Measurement Range (Note 1)
±125
±1000
±2000
dps
Resolution
Resolution of angular velocity
measurement
16
bits
Accelerometer Specifications
Range
Range Acceleration Measurement
±8
g
Resolution
Resolution Acceleration Measurement
16
bits
Magnetometer Specifications
Range
Magnetometer Range
±1150
uT
Resolution
Magnetometer Resolution
0.3
uT
Accuracy
Compass Accuracy (with proper calibration
and placement)
1
deg

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1.5. LED States
The Pigeon 2.0 features 2 tri color LEDs that indicate CAN bus health. This feature can be used to confirm proper
CAN bus wiring. The table below shows the possible color states.
LED Color
Blink Pattern
Description
Off
Pigeon 2.0 is not powered/ plugged in.
Check power cabling to the Pigeon 2.0.
Yellow/Green
Only one LED will blink this
pattern.
Device is in bootloader, most likely because field-
upgrade failed in middle of event.
Inspect CAN bus wiring and re-field-upgrade using
Phoenix Tuner.
If device has valid firmware, turn device off, wait 10
seconds, and turn device on to boot strap it.
Red/Yellow
LEDs are never off –one of the
two colors are always illuminated
Hardware is damaged
Red Blink
Check CAN Bus health and connection to the Pigeon
2.0.
Yellow
Alternate Blinking (Note 1)
CAN bus detected.
Robot controller is not present on CAN bus, or Pigeon2
software object not created in user application.
Yellow
Simultaneous Blinking (Note 2)
CAN bus detected.
Robot is disabled.
Green Blink
CAN bus detected.
Robot is enabled.
Note 1: Only one LED is on at any given moment.
Note 2: Both LEDs are on at the same time.

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1.6. Functional Diagram
Signal paths are show in the functional diagram below.
1.6.1. Mount Orientated Signals
Note that the Yaw, Pitch, Roll, Quaternion, and Gravity Vector are compensated for the selected Mount
Orientation.
1.6.2. Enclosure Orientated Signals
The outputs of the gyroscope, accelerometer and magnetometer are not
compensated for the selected Mount Orientation.
These signals are biased/calibrated to canonical units. (Note 1).
As a result, these signals are referenced to the enclosure’s orientation.
If these enclosure-oriented signals are used, it is recommended to choose a
Mount Orientation that is reasonably horizontal or vertical so that Yaw, Pitch,
Roll, and Gravity Vector are also aligned to these signals.
Note 1: Magnetometer requires user calibration

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1.7. Changes between Pigeon 1 and Pigeon 2
Pigeon 2.0 is the next evolution in Pigeon IMU. Listed below are the differences between the latest iteration and
the original Pigeon IMU.
Note 1: Both Pigeon 1 and Pigeon 2 use a right-handed orientation, and Pigeon 2 defaults to Z-axis up (similar to Pigeon 1). However, Pigeon
2 uses an X forward orientation to better match the academic research papers used in the development of the product.
Symbol
Pigeon IMU
(Version 1)
Pigeon 2.0
Boot
Requirements
5 seconds of stillness
No requirements
6 Axis angle drift
(no-motion)
15 deg per hour
0.12 degrees per hour
6 Axis angle drift
(motion)
1 deg per minute
0.4 deg per minute (with 4 second no-motion event)
1 deg per minute (instantly after boot-up)
Axes conventions
+X points to right
+Y points to forward
+Z points to sky
Pitch is about +X
Roll is about +Y
Yaw is about +Z
+X points forward.
+Y points to the left.
+Z points to the sky.
Pitch is about +Y
Roll is about +X
Yaw is about +Z
Mount
orientation
Must be mounted flat
and level (Z axis pointed
up)
Mount in any orientation.
Orientation does not need to be purely vertical or
horizontal.
Pitch and Roll can be zeroed this way as well.
Enclosure
None
Polycarbonate Enclosure
Communication
CAN bus
Gadgeteer Ribbon
Cable
CAN bus
CAN FD bus (CANivore)
User
Requirements
(Indoor 6-axis
applications)
Temperature
Calibration for best
performance.
None for best performance.
Select Mount Orientation if using non-default orientation.
General Software
API Changes
PigeonIMU class
WPI_PigeonIMU class
Pigeon2 class
WPI_Pigeon2 class
getState () is not available –there is no need as the IMU is
always read.
getFusedHeading() is not available –there is no need as
IMU Yaw is the fused heading in all circumstances.
Use getYaw() instead.
Full Software documentation available at:
https://ctr-electronics.com/documentation

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2. IMU Error Sources
All IMUs are susceptible to accrued error due to sources of error listed below. However, this can be avoided by
following a few basic principles and careful IMU placement. The suggestions below are applicable to many IMUs,
including those available in FRC Robotics.
Below is information and instructions for how to root-cause each error source using features of Pigeon 2.0
2.1. Location –Center of Rotation
Due to the fusion between the accelerometer and the gyroscope, excessive and sustained g-force caused by
centripetal acceleration can impact the Yaw. This can be resolved by moving the IMU closer to the COR (center of
rotation).
The root cause can be confirmed by printing/plotting the accelerometer magnitude while spinning the robot at
maximum velocity. Ideally, the magnitude should be as close to 1G as possible.
Alternatively, the accumulated gyro Z value can be printed/plotted while performing a sustained high-speed
rotation. If the accumulated gyro Z value is more correct than the Yaw, it sufficiently confirms the root cause.
Procedure:
1. First drive the robot to immoveable flat obstacle. A wall works best against the robot’s flattest surface
2. Zero the yaw and accumulated gyro Z
3. Drive the robot in a zero turn at max speed for ~30 seconds
4. Drive the robot in the opposite direction at max speed until it approaches 0 heading.
5. Drive back up against the obstacle and read Yaw and accumulated gyro Z.
6. If root-cause is confirmed, move IMU closer to COR and repeat procedure.
2.2. Temperature
IMUs (in general) also drift due to subtle changes in temperature. This is primarily due to the temperature’s impact
on the zero-bias for the gyroscope. However, it can also affect accelerometer and magnetometer. One strategy to
reduce this is to continually re-bias the gyroscope whenever a no-motion event is detected (Pigeon 2.0 does this
along with other market IMUs). This combined with an environment where temperature does not change rapidly
can be adequate depending on the application.
Another strategy is on-the-fly compensation for changes in temperature. Pigeon 2.0 supports this as well and
comes out of the box with a temperature calibration. If the temperature calibration is called into question, the
user can disable it through a configuration parameter.

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2.3. Gyroscope Sensitivity Error
Gyroscopes may have a range in the reported angular rate of their measurements (despite being advertised as
being constant). As a result, a gyroscope will typically have sensitivity error. This can cause a consistent
under/over-reporting of measured yaw compared to actual rotation.
Pigeon 2.0 gyroscope sensitivities are factory calibrated. However different applications may require end-user to
provide additional trimming. The procedure below can be used to measure and trim the sensitivity error
correction.
This can be measured by the following procedure:
1. First drive the robot to immoveable flat obstacle. A wall works best against the robot’s flattest surface.
2. Zero the yaw and accumulated gyro Z
3. Drive the robot in a zero turn at max speed for 10 rotations
4. Drive back up against the obstacle and read Yaw. It should be 3600 (± expected drift for the duration of the
test) degrees.
5. Drive the robot in a zero turn at max speed in the opposite direction for 10 rotations
6. Drive back up against the obstacle and read Yaw. It should be 0 (± expected drift for the duration of the test)
degrees
Using table below, determine if sensitivity error is likely.
Step 4
Error is low
Step 4
Error is high
Step 6
Error is low
No sensitivity error
Possible sensitivity error
Step 6
Error is high
Inconclusive
Inconclusive

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2.4. Avoid Magnetic/Ferromagnetic materials
Most IMUs have some type of compass calibration procedure, including Pigeon 2.0. However, if the IMU is placed
in an area with severe magnetic disturbance, then minimally the benefit of compass is reduced, and maximally the
robot heading may be severely incorrect. Although many IMUs (including Pigeon 2.0) will automatically detect
invalid magnitude field strengths, depending on the type and direction of the distortion, the compass can still be
affected. For this reason, compass-features are often utilized in an outdoor setting in a chassis designed to
accommodate compass features.
The common disturbances are due to proximity to
ferromagnetic materials such as iron/steel and proximity to
magnetic materials (motors). Additionally, if an IMU is placed
within an extreme magnetic field (e.g., proximity to
neodymium, rare-earth magnets), the hard-iron offsets within
the magnetometer may permanently change, requiring a new
calibration. Care should be taken to ensure such magnets are
not placed near the IMU PCB (e.g., CTRE Mag
Encoder/CANcoder magnets).
This impact can be root-caused by waving a simple
mechanical compass in the presence of where the IMU is
intended to be placed. Look for any major changes in the
needle position as the compass is waved near the critical areas of the robot, while maintaining consistent
orientation between compass and Earth.
Next place the mechanical compass in the location where the IMU is meant to be placed. While the robot is
placed on blocks, drive all motors, chains, and articulators while watching the compass. If the compass needle
reacts to robot actuation, then IMU should be relocated, or simply avoid relying on compass features if the
application will allow it.
Phone compass applications (software) can be used to a lesser degree; however, a mechanical compass is best,
and are widely available for <$5.
Another means of confirming this source of error is to print/plot the compass magnitude as reported by the IMU
while moving the robot into various poses. This can be compared with the expected magnetic field strength which
can be determined with a Phone compass application, or with an online search such as…
http://www.ngdc.noaa.gov/geomag-web/
Any massive dip or rise in the magnetic norm may indicate magnetic disturbance.
However, it should be noted that there can be magnetic disturbance despite the norm not changing by much. For
this reason, the mechanical compass testing above is recommended.

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2.5. Vibration
Vibration of an IMU can cause errors by contributing noise to the accelerometer, gyro, and magnetometer.
Additionally, if the vibration is severe enough, a sensor input may see a saturated value. A common example of
this is vibration in the airframe of a UAV/drone (for example, and unbiased propeller).
2.6. Saturated inputs
Pigeon 2.0 will mark a sticky-fault if a sensor measurement is saturated. This is useful in determining if sensitivity
configurations are too high, or if the Pigeon physical mount needs dampening. Typically, a rigid mount to the
robot chassis is recommended, unless the IMU sensors are saturating, causing loss of information in the pose
estimation.

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3. Calibration
3.1. Temperature Calibration
Pigeon 2.0 is factory temperature calibrated. Additional user calibration is not necessary.
3.2. Gyroscope Bias Calibration
Gyroscope is factory calibrated. Additional user calibration is not necessary.
Additionally, the gyroscope’s bias calibration is automatically adjusted by firmware during runtime.
3.3. Gyroscope Sensitivity Calibration
Gyroscope sensitivity is factory calibrated. However, the required sensitivity precision may be application
dependent. As such there will be a future software update to allow for additional trimming.
If sensitivity error correction needs to be trimmed, calculate how many degrees your test rotation
overshot/undershot the expected result per rotation. Then configure the device with the overshot/undershot per-
rotation value.
Note that sensitivity error is positive if measurement overshot or produced a magnitude above expected value.
Similarly, sensitivity error is negative if measurement undershot or produced a magnitude below expected value.
Example below:
1. Perform test procedure in Section 2.3.
2. IMU reports Yaw travel from 0 deg to -3602 deg.
3. However mechanically IMU traveled -3600 deg.
4. Therefore, measurement overshot by 2 deg.
5. Set corrective error amount to +0.2 deg per rotation (See Phoenix API or Phoenix Tuner)
6. Retest using above procedure to confirm improved result.
3.4. Accelerometer Calibration
Accelerometer is factory calibrated. Additional user calibration is not necessary.
3.5. Compass Calibration
2022 Pigeon 2.0 release firmware supports a compass calibration that requires rotating about the three principal
axis.
A GitHub example will be made available demonstrating how to leverage this.
Compass can then be enabled via software configuration. Note that the 9-axis compass is recommend for outdoor
robotics applications where stray magnetic fields caused by the environment are minimized.
We recommend leaving the compass disabled for indoor robotics applications as this means customers can use
the Pigeon 2 as is, with no supplemental calibration procedures.

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4. Boot behavior
Most IMUs requires no-motion during boot-up to tare the gyroscope, thereby reducing yaw drift. This includes the
original Pigeon IMU (version 1.0), and several competitor IMUs.
Pigeon 2.0, however, does not require no-motion during boot-up.This is because Pigeon 2.0 can predict the
gyroscope bias during boot-up.This allows it to produce reasonable heading information immediately on boot,
even when in motion.
This is a particularly important feature to resolve complications due to:
•IMU is booting up in environment with vibration sources (fans, compressors, user-handling)
•IMU is booting up with extremely loud music in near proximity (also a vibration source)
•IMU is booting up while users are moving platform
•Cannot guarantee that users will ensure IMU is “ready” before executing robot action.
For more information on the drift rates in various configurations, see Section 1.3. Electrical Specifications.

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4.1. Boot behavior - Test Results
The test results demonstrating this feature is shown below. Test setup involved:
•Pigeon 1.0 (documentation suggests five seconds of stillness required)
•Pigeon 2.0 (stillness not required)
•Competitor IMU on roboRIO MXP port (documentation suggests five seconds of stillness required)
All three IMUs were mounted on a fixture that vibrates at approximately 7 Hz. IMUs were all power booted during
vibration and drift was tracked over time. The ongoing vibration prevents all three IMUs from performing no-
motion calibration.
4.1.1. Boot behavior –Drift Rates
Device
Change in Yaw over 30 sec
Drift
Pigeon 1.0 (Note 1)
+ 1.8 deg
3.6 deg per min
Other 2nd Generation
Competitor IMU (Note 2)
+ 20 deg
40 deg per min
Pigeon 2.0
- 0.10 deg
0.2 deg per min
Note 1: Pigeon 1.0 User’s Guide clearly states that IMU requires no-motion on bootup. We do not recommend deviating from
the product documentation during use. The gyro bias prediction is only a feature with Pigeon 2.0
Note 2: Competitor IMU Documentation clearly states that IMU requires no-motion on bootup. We do not recommend deviating
from the product documentation during use.

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4.1.2. Boot behavior –Accelerometer
Note 1: Source of vibration is in the Y and Z axis, therefore X-
axis measurements are reduced in comparison.
Legend
ax
Pigeon 2 Accelerometer: X Axis
ay
Pigeon 2 Accelerometer: Y Axis
az
Pigeon 2 Accelerometer: Z Axis
X axis
0.5 seconds per gradient
Y axis
2.5 mg per gradient

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5. Wiring
Pigeon 2.0 comes with wires pre-installed on it. The leads should be wired following the table below.
Color
Signal
Red
Vdd
Black
Ground
Yellow (Note 1, 2)
CANH
Green (Note 1, 2)
CANL
Note 1: The two yellow wires are electrically common.
Note 2: The two green wires are electrically common.

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6. Orientation Convention
6.1. World Frame Reference
Pigeon2 treats +X as the forward axis, +Y as the left axis, and +Z towards the sky (right-hand orientation). In
researching common axis orientations, this is a common way to define the world frame reference for ground-
based vehicles.
When the Pigeon is using the Default Mount Orientation, these axes match
the XYZ logo on the enclosure.
6.2. Euler Angles
For applications that require Euler Angles (Yaw, Pitch, Roll) to represent the
pose within the world frame reference, Pigeon2 performs the following:
•First calculate Yaw by rotating about +Z in the world frame reference. (Turning to the left is positive).
•From this new body frame, calculate Pitch about the IMU’s local reference Y’ (Pitching nose down is positive,
diagram demonstrates a negative pitch).
•Calculate a final Roll about the IMU’s local reference X’’.
Note that because Yaw is calculated first, it is done so in the world frame
reference (defined by gravity).Because of this, Yaw is defined as travel
about the plane orthogonal to gravity. Therefore, the Pigeon 2.0 does not
require being aligned to gravity for reliable Yaw.
6.3. Gimble Lock
Given the angle definitions used by Pigeon 2.0, Gimble Lock occurs when
the Pitch reaches near ±90 degrees.
At this location the tip of the airplane would be aligned with World Frame
Reference Z Axis.At this point Roll and Yaw cannot be distinguished from each other. As a result, the Euler
Angles are not reliable near this orientation.
For applications that require 360 degrees of vertical travel, it is strongly recommended to use Roll instead of
Pitch. Roll allows for complete 360 rotation with no risk of ambiguity. This is because Roll is the final calculated
angle and cannot introduce ambiguity if Pitch is sufficiently away from Gimble Lock.
Note that Gimble Lock is a limitation of using Euler Angles.In other words, there is always a location that
produces this erroneous condition. More advanced applications may avoid this by using:
-Gravity Vector
-Quaternion –which can provide the Line of Rotation (LOR), and amount of rotation over LOR
-Combinations of the above with or without Euler Angles
But for relatively simple applications (ground vehicle, single axis arms, etc.), simply choosing an IMU orientation
that will not encounter Gimble Lock is sufficient.