Maxon Arduino Library

Introduction

This repository is a custom Arduino Library for controlling maxon motors connected to an epos4 via an RS232 communication with the Arduino Framework.

The library was written using the following documentation:

• EPOS4 UART Commanding (low level UART packet format)
• EPOS4 Communication Guide
• EPOS4 Application Notes (commanding register sequences)
• EPOS4 Compact 50/5 Hardware Reference (for epos pin out)
• EPOS Studio for registers values

The library is implemented in an asynchronous, non-blocking fashion. The core of this mechanism is the tick() function, which must be called as frequently as possible inside your main loop. Each call to tick() checks whether the EPOS4 has sent a response or if a new command needs to be issued. If no action is required, it immediately returns control to your code, allowing your application to remain responsive while still maintaining reliable communication with the motor controller.

A basic example can be found in the examples/BasicExample directory. It demonstrates how to use current treshold homing and Profile Position Mode (PPM).

Currently, the implemented functionalities are limited to the EPFL Rocket Team Icarus project needs, with support for current threshold homing and profile position homing. However, the library is designed to be easily extendable, allowing additional features to be integrated as needed.

Installation

You can install this library in two different ways depending on your development environment.

Method 1: Using PlatformIO

1. Navigate to your PlatformIO project folder.

2. Inside your project, go to the lib/ directory.

3. Clone the repository into the lib/ folder:

   git clone https://github.com/EPFLRocketTeam/2025_I_AV_SW_MAXON_ARDUINO.git
   

If your project itself is under version control (e.g., a GitHub repo), it is recommended to add the library as a git submodule instead.

4. Build your project. PlatformIO will automatically detect and include the library.

Method 2: Using the Arduino IDE

1. Download the library as a ZIP file from the green Code → Download ZIP button.

2. Open the Arduino IDE.

3. Go to Sketch → Include Library → Add .ZIP Library….

4. Select the downloaded ZIP file.

5. The library will now be available under Sketch → Include Library in the Arduino IDE. It can be included as:

   #include <epos4.h>
   

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Hardware setup

What you need:

• Maxon EPOS4 controller
• RS232 to TTL adapter (for Arduino connection)
• Arduino board (e.g., Arduino Uno, Mega, Due)
• DC motor connected to the EPOS4
• Power supply for motor + controller

What is RS232

RS232 is a long-established serial communication standard that defines how devices exchange data over a physical link. It specifies both the electrical voltage levels and the data frame format needed for reliable communication. Unlike logic-level serial signals, RS232 operates with higher positive and negative voltages (typically between ±3 V and ±15 V), which makes it more robust against noise and suitable for longer cable runs in industrial or laboratory environments.

At its core, RS232 uses the same data frame pattern as a UART, but with different voltage levels. This makes it practical to interface RS232 devices with microcontrollers like Arduino, since the UART protocol is natively supported — for example, when you call Serial.println(), you are directly using the UART hardware. Moreover because UART is asynchronous, it does not require a shared clock line, which allows simple and non-blocking read/write implementations.

Since the Arduino’s UART pins operate at logic levels (typically 5 V or 3.3 V), they cannot be connected directly to an RS232 interface such as the one on the EPOS4. The RS232 voltage levels (±3 V to ±15 V) would damage the microcontroller if applied directly. To bridge this gap, a dedicated RS232 transceiver is required, acting as a translator between the two standards.

Wiring example

The following section shows a wiring example for controlling the epos4 with a teensy4.1. I used an epos4 compact 50/5, the RS232 connector is probably the same across epos4 versions. The epos4 compact 50/5 does not require a seperate power supply for the logic part of the controller, thus only one power supply is required, this may not be the case for other epos4. Note that the power gnd and logic gnd are seperate, logic gnd must be connected to the Arduino gnd (RS232 is a 3 wire protocol !!!).

For convenience here is an extract of the EPOS4 Compact 50/5 Hardware Reference.

EPOS4 library description

High Level Functions

Low Level Functions

This section explains the low-level abstraction of the EPOS4 library, focusing on how serial communication is implemented to interact with the EPOS4 motor controller.

Overview

The low-level layer provides a direct interface with the EPOS4 over UART, handling:

• Serial frame construction and transmission
• CRC16 error checking
• Character stuffing (DLE duplication)
• Sending and receiving object dictionary read/write requests

It abstracts the raw EPOS serial protocol and ensures that higher layers can reliably read/write objects without handling communication details.

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Serial Protocol

The EPOS4 uses a Maxon-specific serial protocol (based on CANopen frame concepts).

Frame Structure

A typical EPOS4 frame has the following components:

Field	Size	Description
Start of Frame (DLE)	1 byte	0x90 – indicates start of frame
Start of Text (STX)	1 byte	0x02 – indicates frame payload begins
OpCode	1 byte	Command type (0x60=Read Object, 0x68=Write Object)
Length	1 byte	Number of data words in the frame payload
Data	N bytes	Node ID, Index, Sub-index, Value (little-endian)
CRC Low/High	2 bytes	CRC16 over OpCode + Data
Character Stuffing	Variable	Duplicate 0x90 bytes in the payload

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Character Stuffing

To avoid confusion with the DLE (0x90) start byte, any occurrence of 0x90 in the payload is duplicated:

void EPOS4::addStuffedByte(std::vector<uint8_t> &frame, uint8_t byte) 
{
    frame.push_back(byte);
    if (byte == 0x90) frame.push_back(0x90);
}