Cozmo Functions


Cozmo is a complex distributed embedded system with the following main parts:

  • robot
  • cubes
  • charging platform

The robot can be subdivided into:

The Wi-Fi communication controller is responsible for the following functions:

  • Wi-Fi communication
  • over-the-air (OTA) firmware updates
  • NV RAM storage

Once Cozmo is powered on, the communications controller remains always powered on to maintain Wi-Fi communication.

On connection, the robot transmits its serial number with the HardwareInfo message and firmware version with the FirmwareSignature message.

The RTIP controller is responsible for:

  • OLED display image decoding
  • speaker audio decoding
  • camera image encoding
  • accelerometers
  • gyro

The body controller is in charge of:

  • left and right tread motors and encoders encoders
  • head motor and encoder
  • lift motor and encoder
  • backpack LEDs
  • backpack button (on newer models only)
  • Bluetooth LE communication (to cubes and charging platform)
  • IR LED
  • cliff sensor
  • batter charging

The body is powered on with the Enable message. The BodyInfo message communicates the body hardware version, serial number, and color.

Cubes use Nordic nRF31512 MCU. They are communicated with over Bluetooth LE and provide access to:

  • LEDs
  • Accelerometers
  • Battery voltage

Some charging platforms (aka “pads”) can be communicated with over Bluetooth LE. They contains 3 RGB LEDs that can be controlled, similar to cube LEDs.

The following sections provide more details on the use of each function.


Wi-Fi is activated automatically when the head board is powered on. The robot operates in access point (AP) mode.

cozmoclad defines a SetBodyRadioMode message that seems to allow changing the Wi-Fi channel but it is unclear how it can be used with the Cozmo protocol.

WifiOff Shutdown

Backpack LEDs

The 5 Backpack LEDs can be set controlled with 2 messages:

  • lightStateCenter - controls the top, middle, and bottom RGB LEDs.
  • LightStateSide - controls the left and right red-only LEDs.

Each color is defined by a 5-bit value for a total of 32768 colors.

See examples/ for example usage.

Backpack Button

v1.5 and newer Cozmo models have a backpack button.

Button press and release events are communicated by the ButtonPressed message. It is immediately available on connection and does not require Enable to be used.

The RobotState message has a backpack_touch_sensor_raw field but it seems that it’s value does not change as a result of button presses.

See examples/ for example usage.


The left and the right motor speeds can be controlled directly using the DriveWheels and TurnInPlaceAtSpeed messages. The motors can be stopped using the StopAllMotors message.

The actual speed of wheels is measured with Hall magnetic sensors. The values for each wheel can be read through the lwheel_speed_mmps and rwheel_speed_mmps fields of the RobotState message.

In addition, the and TurnInPlace message can be used to turn to a specific angle.


The robot maintains a world frame internally. It’s position and orientation with respect to it are transmitted every 30 ms or about 33 times per second with the RobotState message.

If the robot is unable to maintain correct position and orientation, for example because it is picked up or pushed, it will communicate this with a RobotDelocalized message.

The origin (0,0,0) of the world frame as well as “pose ID” can be set with the SetOrigin message. This is usually done on initial connection and and on receiving a RobotDelocalized message.

The timestamp in RobotState messages can be synchronized using the SyncTime message.

Path Tracking

The robot can traverse paths, composed of lines, arcs, and turns in place, described in world frame coordinates. The AppendPathSegLine, AppendPathSegArc, and AppendPathSegPointTurn messages can be used to build paths.

The last composed path can be executed using the ExecutePath message. One of it’s arguments can be used to request the reception of PathFollowingEvent message when path traversing finishes.

The status filed of the RobotState message has a robot_pathing flag that indicates whether the robot is currently traversing a path. The curr_path_segment filed indicates which segment is being traversed.

The ClearPath message can be used to destroy an already composed path. The TrimPath message can be used to delete path segments from the beginning or the end of a composed path.

See examples/ and examples/ for example usage.


The head motor can be controlled directly, using the DriveLift and SetLiftHeight messages. SetLiftHeight is always followed by an AcknowledgeAction message before the lift start moving.

The actual lift height can be read through the lift_height_mm field of the RobotState message. The lift_inpos flag of the status field indicates whether the lift is in position or in motion.

The motor can be stopped using the StopAllMotors message.

The robot measures the angle of the lift, relative to its lowest possible position. It is calibrated similar to the head motor.

See examples/ for example usage.

OLED display

Images can be displayed on the robot’s OLED 128x64 display using the DisplayImage message. To reduce display burn-in, consecutive images are interleaved and only half of the display’s rows can be used at a time and the effective display resolution is 128x32.

The Cozmo protocol uses a special run-length encoding to compress images.

Display and audio are synchronized by audio messages (OutputAudio and OutputSilence).

AnimationState message which can be enabled using the EnableAnimationState message provide statistics on display usage.

See examples/ and examples/ for example usage.


The OutputAudio message can be used to transmit 744 audio samples at a time. The samples are 8-bit and u-law encoded.

Speaker volume can be adjusted with the SetRobotVolume message.

AnimationState message which can be enabled using the EnableAnimationState message provide statistics on audio usage.

See examples/ for example usage.


Cozmo can send a stream of camera images in 320x240 (QVGA) resolution at a rate of ~15 frames per second.

The EnableCamera message enables camera image reception and the EnableColorImages message allows switching between grayscale and color images.

The camera gain, exposure time, and auto exposure can be controlled with the SetCameraParams message.

Images are encoded in JPEG format and transmitted as a series of ImageChunk messages. The header of the JPEG files is not transmitted to save bandwidth.

The ImageImuData message provides accelerometer readings at the time of capturing every image to allow for motion blur compensation.

See examples/ for example usage.


The IR LED (aka head light) can improve the camera performance in dark environments.

The IR LED can be turned on and off using the SetHeadLight message.


The RobotState message communicates accelerometer readings which represent acceleration along the x, y, and z axes.

In addition, the robot automatically detects and communicates 2 types of events. The RobotPoked message is sent if the robot has been moved rapidly by an external force along the x or y axes. The FallingStarted and FallingStopped messages are send if the robot is moving rapidly along the z axis.

See examples/ for example usage.


The RobotState message communicates gyro readings which represent angular velocity around the x, y, and z axes.

See examples/ for example usage.

Cliff Sensor

The robot has a “cliff sensor” that measures the distance to ground below the robot. This allows detecting cliffs and detecting when the robot is being picked up or put down.

The RobotState message communicates the raw cliff sensor readings.

In addition, the robot can be made to automatically stop when a cliff is detected with the EnableStopOnCliff message.

See examples/ for example usage.

Battery voltage

The RobotState message communicates raw battery voltage readings.

NV RAM Storage

The robot provides access to some amount of non-volatile memory (aka NV RAM) intended to store two main types of data:

  • unit-specific parameters (ex. camera calibration data and cube IDs)
  • mobile app data (ex. sparks and unlocked games and tricks)

The NV RAM storage is backed by the head’s ESP8266 controller external SPI flash. It is a NOR flash which drives the following specifics for its use:

  • an erase operation is needed before a write operation
  • data is erased in pages

The NvStorageOp message allows performing read, erase, and write operations. Data is addressed by the tag field and only the values enumerated by NvEntryTag can be used. Using any other address results in a NV_BAD_ARGS. Tags smaller than 0x80000000 are direct NOT flash memory addresses. Tags larger than 0x80000000 are virtual addresses that seem to be stored in the NVEntry_FactoryBaseTagWithBCOffset area.

NvStorageOpResult messages communicate results of NvStorageOp operations.

A backup through the mobile app, preserves the data behind the following keys:

  • NVEntry_GameSkillLevels
  • NVEntry_Onboarding
  • NVEntry_GameUnlocks
  • NVEntry_FaceEnrollData
  • NVEntry_FaceAlbumData
  • NVEntry_NurtureGameData
  • NVEntry_InventoryData
  • NVEntry_LabAssignments

See examples/ for example usage.

Firmware Updates

Cozmo firmware updates are distributed in “” files that seem to contain firmware images for all three of Cozmos controllers - the Wi-Fi communication controller, the RTIP controller, and the body controller.

The “” files start with a firmware signature in JSON format:

    "version": 2381,
    "git-rev": "408d28a7f6e68cbb5b29c1dcd8c8db2b38f9c8ce",
    "date": "Tue Jan  8 10:27:05 2019",
    "time": 1546972025,
    "messageEngineToRobotHash": "9e4a965ace4e09d86997b87ba14235d5",
    "messageRobotToEngineHash": "a259247f16231db440957215baba12ab",
    "build": "DEVELOPMENT",
    "wifiSig": "69ca03352e42143d340f0f7fac02ed8ff96ef10b",
    "rtipSig": "36574986d76144a70e9252ab633be4617a4bc661",
    "bodySig": "695b59eff43664acd1a5a956d08c682b3f8bd2c8"

This is the same signature, delivered with the FirmwareSignature message on initial connection establishment.

See docs/ for more examples.

There seem to be individual signatures for each controller but the structure of the files is not known.

The firmware image is transferred as-is from the engine to the robot, using FirmwareUpdate messages. It is divided into 1024 B chunks that are numbered consecutively, starting with 0. Each chunk is confirmed by the robot with a FirmwareUpdateResult message with status field set to 0.

Firmware transfer completion is indicated by the engine with e FirmwareUpdate message with chunk ID set to 0xFFFF and data set to all-zeros. The robot confirms firmware update completion by sending a FirmwareUpdateResult message that repeats the last chunk ID and has a status field set to 10.

Bluetooth LE

“Objects”, that can be connected to over Bluetooth LE announce their availability with an ObjectAvailable message periodically. The ObjectAvailable message contains the object type (e.g. light cube 1, 2, 3 or charging pad) and the object factory ID which identifies it uniquely.

The ObjectConnect message is used to initiate or terminate a connection to objects, using their factory ID.

Connection establishment and termination is announced with the ObjectConnectionState message. It contains a temporary “object ID” that is used to identify the object for the duration of the connection with it.

Cube LEDs

Cubes have 4 RGB LEDs that can be controlled individually.

A cube has to be “selected” first, using the CubeId message. A subsequent CubeLights message sets the state of all 4 cube LEDs.

Cubes can be programmed to perform simple LED light animations autonomously using the LightState structure and the CubeId.rotation_period_frames field.

See examples/ and examples/ for example usage.

Cube Battery Voltage

Cube battery voltage is communicated periodically with ObjectPowerLevel messages.

Cube Accelerometers

Cube accelerometer value reception can be enabled with the StreamObjectAccel message and are communicated every 30 ms with the ObjectAccel message.

In addition, the robot performs basic cube accelerometer ata processing and provides basic events with the following messages:

  • ObjectMoved
  • ObjectStoppedMoving
  • ObjectUpAxisChnaged
  • ObjectTapped
  • ObjectTapFiltered


To play animations, AnimationState message have to be enabled first using the EnableAnimationState message.

Animations are controlled with the StartAnimation, EndAnimation, and AbortAnimation messages.

Keyframes are transferred with the AnimHead, AnimLift, AnimBody, AnimBackpackLights, RecordHeading, TurnToRecordedHeading, and OutputAudio messages.

See examples/ for example usage.