BB.Sensor.OpenLoopPositionEstimator (bb v0.15.0)

A "sensor" that estimates joint position for open-loop control systems.

This sensor subscribes to BB.Message.Actuator.BeginMotion messages from a paired actuator and uses easing functions to estimate the current joint position during motion. It publishes BB.Message.Sensor.JointState messages at a configurable rate.

Use this sensor with actuators that don't provide position feedback (e.g., RC servos, open-loop stepper motors). The estimator works with any joint type (revolute, prismatic, etc.) as it operates on raw position values.

Options

actuator - Name of the actuator to subscribe to (required)
easing - Easing function for position interpolation (default: :linear)
publish_rate - Rate to publish position updates during motion (default: 50 Hz)
max_silence - Maximum time between publishes when idle (default: 5 seconds)

Easing Functions

The following easing functions are available (see easings.net for visualisations):

:linear - Constant velocity (default)
:ease_in_sine, :ease_out_sine, :ease_in_out_sine - Sinusoidal
:ease_in_quad, :ease_out_quad, :ease_in_out_quad - Quadratic
:ease_in_cubic, :ease_out_cubic, :ease_in_out_cubic - Cubic
:ease_in_quartic, :ease_out_quartic, :ease_in_out_quartic - Quartic
:ease_in_quintic, :ease_out_quintic, :ease_in_out_quintic - Quintic
:ease_in_expo, :ease_out_expo, :ease_in_out_expo - Exponential
:ease_in_circular, :ease_out_circular, :ease_in_out_circular - Circular

Example DSL Usage

joint :shoulder, type: :revolute do
  limit lower: ~u(-45 degree), upper: ~u(45 degree), velocity: ~u(60 degree_per_second)

  actuator :servo, {BB.Servo.Pigpio.Actuator, pin: 17}
  sensor :feedback, {BB.Sensor.OpenLoopPositionEstimator,
    actuator: :servo,
    easing: :ease_in_out_quad
  }
end

How It Works

Subscribes to BeginMotion messages from the named actuator
When motion begins, captures initial position, target, and expected arrival time
Ticks at publish_rate during animation, interpolating position with easing
Uses GenServer timeout for heartbeat publishes when idle
Ensures final position is published even under system load