encoder_arm

encoder_arm.py

Overview

encoder_arm.py is a synthetic joint-position sensor that publishes pseudo-random encoder angles for the TIAGo arm at a fixed rate. It enables controllers, loggers, and dashboards to run when no real hardware is connected.

Interfaces (strongly-typed, stateless)

Direction	Topic	Semantics
Provided	/{robot}/encoder_arm	std_msgs/Int32 – simulated joint angle in degrees [0–359]

Contract

Pre-conditions

• Node launched with a valid robot_id CLI argument.

• Downstream subscribers expect arm encoder ticks at ~10 Hz.

Post-conditions

• Publishes exactly one Int32 per loop iteration.

• data field is an integer uniformly drawn from [0, _MAX_ANGLE].

• No other side-effects or retained state.

Invariants

• Loop frequency = _RATE Hz ± ROS scheduler jitter.

• Angle range fixed by _MAX_ANGLE.

Quality-of-Service KPIs

Metric	Target	Rationale
Message rate	10 Hz ± 0.5 Hz	Keeps controllers in sync.
Latency	< 100 ms	Prevents stale joint readings.
CPU load	< 1 %	Safe on onboard CPU.

Implementation notes

• Uses random.randint(0, _MAX_ANGLE) for angle generation.

• All logic resides in arm_encoder(); the main loop only maintains timing.

• Seed the RNG (random.seed(…)) before calling for reproducible traces.

Functions

arm_encoder()

Initialise ROS publisher and broadcast random encoder angles until shutdown.