Quad Post

Overview

The Quad Post is a 3-DoF motion platform that uses four vertical actuators positioned at the corners of a rectangular frame. It provides motion on three axes: heave (up/down), pitch (forward/backward tilt), and roll (side-to-side tilt). Quad Post platforms are popular for their simplicity, reliability, and strong heave response — they excel at reproducing the feel of road surfaces, braking, acceleration, and cornering.

Because all four actuators operate on the same vertical plane, the Quad Post relies on the Overallocation Factor to prevent “tripoding” — a condition where one actuator lifts off the ground due to uneven loading.

Getting Started

1. In the Sim Config tab, click the “+” tab to add a new component.
2. Select Quad Post (3 DoF) from the dropdown.
3. Enter your rig dimensions or adjust the defaults to match your hardware.

Note

The Quad Post does not currently include hardware-specific presets. Enter your dimensions manually.

Configuration Parameters

Rig Dimensions

These measurements define the rectangular footprint of your four actuator positions:

• L1 (mm) — Front edge width: The distance between the two front actuator mounting points, measured center-to-center.
• L2 (mm) — Side length: The distance from front to rear actuator mounting points, measured center-to-center along the side of the frame.
• L3 (mm) — Rear edge width: The distance between the two rear actuator mounting points, measured center-to-center.

Tip

Measuring tip: Measure from the center of each actuator’s mounting bolt or pivot point. The frame does not need to be a perfect rectangle — L1 and L3 can be different widths if your front and rear actuator spacing differs.

Actuator Settings

• Travel (mm) — The total stroke distance of each actuator from fully retracted to fully extended. At rest, the platform sits at the 50% travel position (half the stroke above the base).
• Overallocation Factor — Controls how aggressively the platform uses actuator travel when multiple axes move simultaneously. Default: 1.0.

Danger

Important: For Quad Post platforms, an Overallocation Factor of 1.0 is strongly recommended. This ensures all four actuators stay within their stroke at all times, preventing tripoding. See Overallocation Factor for details.

Travel Limits

Set the maximum range of motion for each axis:

• Heave (mm) — Maximum vertical displacement from center (positive = up, negative = down)
• Pitch (degrees) — Maximum forward/backward tilt angle
• Roll (degrees) — Maximum side-to-side tilt angle

Actuator Layout

The four actuators are named by their position:

Actuator	Position
Front Right	Right side of the front edge
Rear Right	Right side of the rear edge
Rear Left	Left side of the rear edge
Front Left	Left side of the front edge

Each actuator reports its own travel value and park percentage. When the platform pitches forward, the front actuators extend while the rear actuators retract (and vice versa). When it rolls right, the right actuators extend while the left actuators retract.

Common Setups

Standalone Quad Post

A Quad Post by itself provides heave, pitch, and roll. This is sufficient for most driving simulations where lateral and longitudinal G-forces are simulated through tilt cueing (pitch for surge, roll for sway).

Quad Post + Surge Layer

For rigs that want dedicated forward/backward motion, add a Surge Layer component alongside the Quad Post. The Quad Post handles heave, pitch, and roll while the Surge Layer adds a separate surge axis.

Quad Post + Traction Loss

Add a Traction Loss component for a dedicated rear-end slide actuator. The Quad Post provides platform motion while the Traction Loss actuator simulates oversteer and loss of grip.

Tuning Tips

• Overallocation Factor = 1.0 — Keep this at 1.0 for Quad Post platforms. Higher values risk tripoding.
• Start with conservative travel limits — Quad Post platforms have limited angular range compared to hexapods. Start with pitch and roll limits around 5–8° and increase gradually.
• Monitor overallocation warnings — Enable DEBUG log verbosity and watch for overallocation messages. If they appear frequently, reduce gains in your motion profile (especially heave, pitch, and roll in the Primary Cue).
• Heave is your strongest axis — Quad Post platforms excel at vertical motion. Use heave gain aggressively for road surface detail, curb strikes, and suspension effects.
• Use Manual Control to verify — Before connecting a game, use Manual Control to sweep each axis individually and confirm correct direction and range of motion.