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Adding support for a new servo

⚠️ Warning: This documentation is only intended for servos that communicate via the Dynamixel Protocol (v1 or v2), such as the Robotis Dynamixel or Feetech servos.

  • Create a new file in the service folder (or a subfolder such as feetech or dynamixel), for instance sts3215.rs in the feetech folder. Make sure to add its declaration in the parent module (for instance in [./feetech/mod.rs]) as they must be explicitly declared in Rust. Something like this:
pub mod sts3215.rs

  • Add the servo definition in the new file. You can use the MX as a template. The macro should defined the name of the servo, the protocol version used and then a list of all registers with their name, address, access, type and conversion type (can be set to None to get the raw register value).

  • Between the protocol version and the registers, the definition can state what a caller of the raw address API needs to know to make sense of the bytes. Every entry is optional and they come in this order: resolution: 4096, (encoder steps per turn), word_order: big, (default little), supports_sync_read: false, (default true), supports_broadcast_ping: true, (default false), baudrates: [(1_000_000, 0), ...], (baud rate and the value of the baud rate register), factory_baudrate: 1_000_000,, homing_offset_sign: -1, (present = actual + sign * homing_offset; needs a homing_offset register), operating_modes: [(position, 0), ...], (needs an operating_mode register) and encoding: [(present_load, sign_magnitude(10)), (goal_pwm, twos_complement), (goal_position, unsigned)], for registers whose sign handling differs from their integer type (signed types default to two's complement, everything else to unsigned). See sts3215.rs. They are exposed as INFO, MODELS and the encoding of each RegisterInfo, and to Python as static methods of the controller class.

  • Finally, add the servo registration in the servo root module [./mod.rs]. You can specify all variants supported by your servo definition. This registration allows for the scan function to detect your new kind of servo.

By doing this, you will be able to use the servo in the same way as the other servos. The servo will be automatically detected and registered when you run the scan function. You can then use it in your application.

It will be available in the rust lib but also the python bindings.

Conversion types

If you want to define custom conversion function for a register (such as transforming the raw encode position to radians for instance), you need to define a struct that implements the Conversion trait.

See the AnglePosition for an example. You can see that the position register uses the AnglePosition conversion type.