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Omnibase Overview

This section documents the design and implementation of a custom holonomic base for FRIDA, a significant hardware upgrade intended to replace the DashGo differential drive platform currently in use.

Motivation

The DashGo platform, while functional, imposes constraints on the robot's navigation flexibility. Transitioning to a custom holonomic base offers several key advantages:

  • Omnidirectional movement — the robot can translate in any direction without rotating, enabling smoother and more precise maneuvers in tight or dynamic indoor environments.
  • Full mechanical ownership — being entirely designed and built by the team allows complete control over the platform's architecture, facilitating future improvements and adaptations tailored to competition requirements.
  • Improved integration — custom electronics and mechanical structure allow a tighter integration between the base, the arm, and the rest of the robot's systems.

Mechanical Design

Wheel Selection: Mecanum vs Omni

An early design decision was whether to use mecanum wheels or omni wheels. Both achieve holonomic motion but differ in their trade-offs:

Feature Mecanum Wheels Omni Wheels
Vibration & stability Lower vibration, greater stability More vibration
Space efficiency Larger footprint (wheels offset 45°) Smaller footprint
Push force Greater in all directions Lower
Max velocity Moderate Higher
Heavy load applications Preferred Less suitable
Cramped space navigation Moderate Better

After evaluating competition requirements — particularly the need to carry loads and operate reliably — mecanum wheels were selected as the preferred choice.

Mecanum vs Omni wheels comparison

Space efficiency comparison between omni-wheels and mecanum wheels

CAD Design

The base structure uses 4040 aluminum extrusion profiles as the main chassis frame. Motors are mounted with custom-designed motor mounts that adapt the actuator attachment to the extrusion profile geometry.

Omnibase CAD model

Proof-of-concept CAD model of the omnibase

Actuator System: ODrive S1 + BLDC Motors

Each of the four wheels is driven by a brushless DC motor paired with an ODrive S1 motor controller, following a quasi direct drive (QDD) approach inspired by the OpenQDD project.

ODrive S1

The ODrive S1 is a compact, high-performance FOC (Field-Oriented Control) motor controller designed for robotics applications.

Parameter Value
DC bus voltage range 12 V – 48 V (12S LiPo max)
Continuous phase current 40 A (with heat spreader)
Continuous power output 1600 W
PCB footprint 66 mm × 50 mm
Mass 35 g (55 g with screw terminals)
Communication CAN (isolated, daisy-chain), UART, USB-C
Onboard absolute encoder Yes — no homing required on startup
Control modes Torque, velocity, position, trajectory

Key features for this application:

  • Galvanically isolated CAN bus with daisy-chain connectors (J16/J17), allowing all 4 S1s to share a single CAN bus to the main controller without ground loop issues.
  • Onboard absolute encoder eliminates the need for homing routines when the robot powers on.
  • Compact form factor (smaller than a credit card) makes it feasible to mount directly on the base chassis.

The four ODrive S1 units are connected in a CAN daisy-chain, all communicating with the central STM32H755 microcontroller using the CANSimple protocol.

Electronics & Control Architecture

The control PCB is the central hub of the omnibase, designed entirely by the team. It interfaces the main computer with the four motor controllers and onboard sensors.

Control PCB

The schematic was designed in EasyEDA (V1.0) by Ximena Trejo. Full schematic PDF available here.

Base Omni Shield - Page 1: STM32H755

Base Omni Shield Rev 2 — Page 1: STM32H755 pinout

Base Omni Shield - Page 2: Peripherals and ODrive connectors

Base Omni Shield Rev 2 — Page 2: TJA1051, BNO055, BLE module and ODrive connectors

Key Components

Component Interface Role
STM32H755 — Dual-core (Cortex-M7 + Cortex-M4) main microcontroller; handles CAN communication, odometry, and BLE
BNO055 I2C (SCL/SDA) 9-DOF IMU (accelerometer, gyroscope, magnetometer) for orientation and odometry fusion; powered at 3.3V
TJA1051 CAN (CTX/CRX) CAN bus transceiver; interfaces the STM32 CAN peripheral with the physical CAN bus to the 4 ODrive S1s; powered at 5V
BLE Module UART (BLE_RXD/BLE_TXD) Bluetooth Low Energy module for wireless gamepad connectivity; 6-pin connector, powered at 5V
ODrive connectors ×4 30-pin Per ODrive: CANH/CANL, PWM, encoder channels A+B (ENCA/ENCB), GND
CAN termination — 2×60Ω resistors in series (= 120Ω) with 100nF capacitor to GND, per CAN bus standard
Power input Terminal block 2-pin PWR_5V input with power switch (SW_PWR_STM); 3.3V and 5V indicator LEDs onboard

Communication Topology

[Main Computer]
      |
    [STM32H755]
      |  (CAN via TJA1051 — CANH/CANL)
      +——[ODrive S1 #1]  ← CANH, CANL, PWM, ENCA, ENCB
      +——[ODrive S1 #2]  ← CANH, CANL, PWM, ENCA, ENCB
      +——[ODrive S1 #3]  ← CANH, CANL, PWM, ENCA, ENCB
      +——[ODrive S1 #4]  ← CANH, CANL, PWM, ENCA, ENCB
                                    [120Ω + 100nF termination]

      + [BNO055]     (I2C — SCL/SDA)
      + [BLE Module] (UART — BLE_RXD/BLE_TXD)

The STM32H755 acts as the bridge between the high-level computer (running ROS 2) and the low-level motor controllers. It sends velocity/torque commands over CAN to each ODrive S1, and also routes PWM and encoder signals (ENCA/ENCB) per motor. IMU data from the BNO055 is read over I2C for odometry fusion.

The PCB was designed in EasyEDA (V1.0) by Ximena Trejo, created and updated on 2026-03-09/10.

Software & Repository

The firmware and ROS 2 integration code for the omnibase is maintained in the team's repository:

The repository includes: - STM32 firmware (CAN configuration, ODrive control functions, odometry) - ROS 2 nodes for base velocity commands and odometry publishing - Configuration and calibration utilities

References