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Steering Overview

The kart steers by wire: there is no mechanical linkage between the wheel and the front wheels. Turning the input (Hori wheel or RC stick) sends an angle setpoint to a dedicated ESP32 controller ("Steervo"), which runs a closed-loop position controller against a steering potentiometer and drives a Talon SRX motor controller by servo PWM.

The chain

flowchart LR
    input["Hori wheel axis<br/>or RC left-stick L/R"] --> teensy["Teensy (kart-core)<br/>axis → angle setpoint"]
    teensy -->|"STEER_SET<br/>(CAN, 50 Hz)"| steervo["ESP32 (Steervo)<br/>position loop (PID)"]
    steervo -->|"servo PWM<br/>(GPIO15)"| talon["Talon SRX"]
    talon --> motor["CIM motor → 50:1 gearbox → steering"]
    pot["steering pot (GPIO36)"] -->|feedback| steervo
    steervo -->|"STEER_STATUS<br/>(CAN, 50 Hz heartbeat)"| teensy

Division of labor

The two computers split the job cleanly:

Teensy (kart-core) Steervo (ESP32)
Maps the input axis to an angle setpoint (±30.00° full lock). Runs the position loop locally against the pot.
Sends STEER_SET at 50 Hz over CAN, with an ENABLE bit. Drives the Talon by PWM only when it is genuinely ACTIVE.
Watches the STEER_STATUS heartbeat; treats loss/fault as a steering fault. Reports measured angle, output, and fault bits at 50 Hz.
Owns the wheel→motion direction sense. Owns calibration, soft limits, and its own failsafes.

The Teensy only sends a target and watches the heartbeat; all of the control math and the steering-specific safety live on the Steervo. This keeps the steering loop running at a fixed local rate even if the CAN link hiccups.

Two enable gates (both required for motion)

The steering motor stays dead until two independent gates are cleared:

  1. Steervo compile gate — kEnableMotorOutput in firmware/steervo/src/main.cpp. While false, the Steervo commands neutral PWM even when fully ACTIVE, so you can validate the link, the pot, and calibration with zero risk of motion. It ships true now that steering is bench-validated.
  2. Teensy runtime gate — STEER ON / STEER OFF over the Teensy serial. This sets the ENABLE bit in STEER_SET, and defaults OFF at boot. It is independent of arm/drive: you can bring steering up without arming traction.

On top of those, the Steervo will not move unless it has a valid calibration and a fresh 50 Hz STEER_SET stream — so the motor is dead until you deliberately calibrate and enable it.

Where to go next

Stands-only build note

In the current traction-only bench build, the traction side ignores steering health so the (stands-only) traction path can be tested without the Steervo. Steering itself still works via its own STEER ON gate — the two are independent.