OpticalEncoder

ServoProject

by Adam Bäckström

Getting the most out of your hobby servo

Video demo of project

Additional documentation for the project

Theory

Dependencies

Build instructions

• DS3225 Servo

• MG90S Micro servo

• Part list for robot and gripper

Legacy build instructions

• Brushed servo

• Coreless servo

• Micro servo

Project structure

ArduinoSketch

This folder contains the Arduino project for the Adafruit ItsyBitsy M0 Express boards.

Easiest way to program and configure the servos is through the configurationWizard.py script. Just run python3 ./ArduinoSketch/configurationWizard.py to get started. The script will ask if it should install any missing dependencies.

PLEASE NOTE! Windows users must use MSYS2 due to the the PyGObject package, see https://pygobject.readthedocs.io/en/latest/getting_started.html. After installing MSYS2 run the script with:

C:\msys64\mingw64\bin\python.exe ArduinoSketch\configurationWizard.py

Manually compiling the Arduino sketch

When compiling, the active configuration is selected by modifying the #include "*.h" line in the config/config.h file to include the desired config file. The configSelector.py script can be used to simplify the config selecting process by giving a drop-down list with all configs in the config folder.

The folder also holds a Makefile which can be used to compile and transfer the project. One benefit of using the Makefile is that the configSelector script is always executed prior to compiling. To be able to use the Makefile you must first install arduino-cli.

Arduino sketch dependencies:
  - Adafruit DotStar `source:` Arduino Library List
  - Eigen `source:` Arduino Library List

ArduinoLibrary/ServoProjectController

Arduino library for communicating with the servos.

View Example Arduino sketch

C++/Library

Holds the C++ library for communicating with the servos.

Dependencies:
  - GNU Make >= 4.2.1
  - gcc >= 9.3.0
  - boost >= 1.71.0

C++/Demo

Minimal c++ demo project.

View Example Code

C++/Example6dofRobot

Example 6dof robot project.

View Example Code

To compile run make. This creates the program ./executable with the following options.

Allowed options:
  --playPath            play the path defined in createPath()
  --gui                 open jogging gui
  --output arg          data output file
  --simulate            simulate servos

Dependencies:
  - Eigen >= 3.4.0
  - gtkmm-3.0 >= 3.24

CadFiles

Holds all .stl and the original Freecad files

PcbDesignes

Holds all KiCad projects for the electronics

Python/Demo

Python demo project.

View Example Code

Python/ServoProjectModules

Holds all python modules for the project.

Communication bus setup for demo projects

ONLY CONNECT THE SERVO TO 3.3V LOGIC!!!!

PLEASE NOTE! The bus controller needs to have a low latency to get fast communication with the servos. Most standard USB to Serial converters buffer the data and only transfers every 10 ms or so. This becomes a problem since the communication protocol will wait for the response from each servo before moving on to the next, adding huge delays.

To get the best communication speed it is recommended to use an "Adafruit ItsyBitsy M0 Express" (or similar ARM based Arduino) as the USB to Serial converter. Just program the Arduino with the usbToSerial.h configuration in the ArduinoSketch to get started. In usbToSerial.h you can also configure any regular servos you want to control together with the ServoProject modified ones.

How to switch to PWM interface version

ONLY CONNECT THE SERVO TO 3.3V LOGIC!!!!

Using the PWM interface is not recommended due to low resolution and high noise, but it is possible by modifying the configuration file. To enable PWM control replace the getCommunicationHandler() function with the version below.

    static std::unique_ptr<Communication> getCommunicationHandler()
    {
        Serial.begin(115200);
        auto com = std::make_unique<Communication>(SerialComOptimizer(&Serial));
        uint8_t pwmPin = 0; // Rx pin, ONLY CONNECT TO 3.3V LOGIC!!!!
        uint8_t controlSpeed = 14;
        uint8_t backlashControlSpeed = 2;
        float scale = 2.0f; // 2 units per us (4096 units == 360 deg)
        float offset = 1024.0f; // move to 1024 units (90 deg) for 1500 us pwm signal
        com->addCommunicationNode(
                std::make_unique<DCServoCommunicationHandlerWithPwmInterface>(1,
                    createDCServo<SetupConfigHolder>(controlSpeed, backlashControlSpeed),
                    pwmPin, scale, offset));
        return com;
    }

License

Open Source License

ServoProject is free software. You can redistribute it and/or modify it under the terms of Creative Commons Attribution 3.0 United States License.

To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/us/