Mounting Plate

Mounting Plate – definition

A mounting plate is a rigid mechanical interface used to attach sensors, compute modules, enclosures, antennas, test fixtures, or custom payloads to a mobile robot. In UGV practice, the term does not mean only a flat piece of metal or polymer. It means a defined structural surface with known hole patterns, load limits, stiffness, and reference geometry. The mounting plate affects payload placement, cable routing, sensor alignment, vibration transfer, and center of mass.

In mobile robotics, a mounting plate is part of the integration stack. It connects the mechanical layer to the electrical and software layers. A LiDAR mounted on a plate must keep stable orientation relative to the robot base frame. A camera bracket fixed to the plate must preserve extrinsic calibration. A compute box mounted on the same plate must stay within thermal and vibration constraints. In ROS 2, the components attached to the plate are typically represented as frames in the TF tree, often linked to base_link or a dedicated payload frame defined in URDF according to REP 103 and REP 105.

On Leo Rover and Raph Rover, a mounting plate is commonly used as the top payload interface. It allows rapid installation of research hardware such as 2D LiDAR, RGB-D cameras, GNSS/RTK receivers, mast assemblies, Jetson-based computers, and custom electronics. In this context, the plate is not a cosmetic accessory. It is a mechanical reference that influences navigation quality, localization repeatability, and field robustness.

Why a mounting plate matters in mobile robotics

On a UGV, payload integration changes robot behavior. Even small changes in height, mass distribution, or sensor tilt can degrade perception and control. A mounting plate provides a repeatable way to install equipment and document the resulting configuration.

From an engineering perspective, the plate supports four functions:

Mechanical fixation – keeping the payload attached under static and dynamic loads.
Geometric referencing – preserving known sensor pose for calibration and TF publication.
Load distribution – spreading forces across the chassis instead of stressing a single point.
Integration support – enabling cable management, spacing, thermal clearance, and service access.

For autonomous navigation, sensor pose stability is critical. A few millimeters of displacement or a few degrees of roll or pitch error can affect point cloud registration, occupancy mapping, or visual odometry. This is especially relevant for SLAM systems that fuse LiDAR, IMU, and wheel odometry.

Key mechanical parameters

A mounting plate should be specified with measurable parameters. These values determine whether the plate is suitable for a given sensor stack or compute payload.

Parameter	Why it matters	Typical engineering note
Material	Controls stiffness, mass, corrosion resistance	Often aluminum, steel, FR4, carbon composite, or 3D-printed polymer
Thickness	Affects deflection and resonance	Thicker plates reduce flex but increase mass
Hole pattern	Determines compatibility with sensors and brackets	Should be documented in CAD and assembly drawings
Maximum payload	Prevents structural overload	Must include dynamic loading, not only static mass
Flatness and tolerance	Important for sensor alignment	Relevant for LiDARs, stereo cameras, and GNSS masts
Mounting height above chassis	Changes field of view and center of mass	Higher placement improves visibility but increases roll sensitivity
Ingress compatibility	Important for outdoor operation	Plate openings should not compromise enclosure protection

When the payload is elevated on spacers or a mast, the effective bending moment increases. A simple static estimate is:

M = F × d

where M is the bending moment, F is the force from payload weight or acceleration, and d is the perpendicular distance from the support point. On rough terrain, dynamic acceleration can make the effective load several times higher than the static weight.

Mounting plate in ROS 2 and URDF

The plate itself is a mechanical part, but in ROS 2 it often appears in the robot description. This is useful when the plate defines the pose of sensors or custom payloads. The standard ROS convention is to model rigidly attached components in URDF and publish the transform tree for downstream nodes. REP 103 defines coordinate conventions, and REP 105 defines common mobile platform frames such as map, odom, and base_link.

If a LiDAR is mounted on a plate above the chassis, the sensor frame should reflect the real offset. That offset is then used by SLAM, Nav2, point cloud processing, and visualization tools.

<link name="mounting_plate_link"/>

<joint name="base_to_mounting_plate" type="fixed">
  <parent link="base_link"/>
  <child link="mounting_plate_link"/>
  <origin xyz="0 0 0.085" rpy="0 0 0"/>
</joint>

<link name="lidar_link"/>

<joint name="mounting_plate_to_lidar" type="fixed">
  <parent link="mounting_plate_link"/>
  <child link="lidar_link"/>
  <origin xyz="0.12 0 0.03" rpy="0 0 0"/>
</joint>

For quick validation, the transform can be checked from the ROS 2 CLI:

ros2 run tf2_ros tf2_echo base_link lidar_link
ros2 topic echo /tf_static

Sensor integration on Leo Rover and Raph Rover

On Leo Rover, the mounting plate is typically used for lightweight research payloads. Examples include a 2D LiDAR for indoor mapping, an Intel RealSense depth camera for obstacle detection, or a small GNSS receiver for outdoor experiments. Leo Rover uses a Raspberry Pi-based onboard compute unit by default and supports ROS 2. Because the base platform is compact, payload mass and placement should be controlled carefully.

Typical considerations for Leo Rover include:

Do not obstruct the wheel envelope or suspension motion.
Keep the LiDAR above splash level but below a height that significantly raises the center of mass.
Preserve service access to power, USB, and network interfaces.
Avoid flexible printed brackets for sensors that require stable extrinsics.

On Raph Rover, the same concept scales to heavier payloads. A mounting plate may support larger LiDAR units, industrial compute hardware, battery-backed enclosures, multi-sensor perception rigs, or agricultural and inspection payloads. The higher payload capacity allows more complex assemblies, but resonance, cable strain relief, and environmental sealing remain critical.

Common failure modes and trade-offs

A poorly designed mounting plate can introduce errors that appear to be software faults. In practice, many localization and perception issues start as mechanical integration problems.

Common failure modes include:

Plate flex causing time-varying sensor pose errors.
Vibration coupling into IMU or camera data.
Misaligned drilling leading to incorrect TF values.
Insufficient clearance for connectors or cable bend radius.
Excess payload height reducing stability on uneven terrain.

The main trade-off is between stiffness, mass, and modularity. A thick metal plate is stable but heavy. A thin polymer plate is easy to prototype but may deform under load or temperature. Slotted universal patterns improve compatibility but reduce local stiffness compared with a plate optimized for one payload.

Documentation and verification

For research and field deployment, the mounting plate should be documented like any other robot subsystem. The minimum documentation set usually includes CAD files, hole pattern dimensions, mass, material, assembly torque guidance, and the resulting URDF or TF configuration.

A practical verification workflow is:

Measure the installed sensor pose relative to base_link.
Update the URDF or static transform publisher.
Check frame alignment in RViz.
Run a short SLAM or localization test and compare repeatability.
Inspect for loosening after vibration or off-road driving.

This workflow is especially important when Leo Rover or Raph Rover is used as a repeatable research platform across multiple experiments.

Normative references and standards

In ROS-based mobile robotics, the most relevant references for components attached through a mounting plate are the ROS frame and description conventions rather than a single dedicated robotics standard for the plate itself.

REP 103 – Standard Units of Measure and Coordinate Conventions.
REP 105 – Coordinate Frames for Mobile Platforms.
URDF documentation – robot links, joints, and fixed transforms in ROS.
Manufacturer mechanical drawings – for LiDARs, cameras, GNSS units, and compute enclosures.

These references define how the mechanically mounted payload should be represented in software, which is essential for reproducible navigation and perception results.