Mini-Arm

The Mini Arm is a miniature version of the Desktop-Arm project with IK solver inspirations from Alberto Abarzua and Mithi Sevilla, a portable 6DOF 3D-printed robot arm with open-source models and code. Robot DH paramater numerical calculations referenced from:

• Mithi Sevilla
• Zenetio
• Ohara124c41.
• NitishPuri

This package does NOT use any symbolic math packagaes, only numpy, which makes this scalable to microcontrollers with the same kinematic configuration!

While this little machine can run on a 5V 2A DC adapter, it has other cool features:

• Runs CircuitPython on a Raspberry Pico W (wifi operated)
• All 3D printable components (aside from nuts & bolts)
• Total cost of hardware less than $60
• Weighs less than 1lb (0.3kg to be exact)
• Capacity to integrate more features

Where to start ?

This Github repository contains Installation and Quick Start instructions for the Mni Arm project.

Table of Contents

• Hardware
• Raspberry Pico W Installation
• Quick Start

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Hardware:

1. Building the arm

   • The full list of parts needed to assemble the arm can be found in the B.O.M.
   • Files for 3D printing can be found on HowToMechatronics with assembly instructions

2. Electrical wiring

   

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Raspberry Pico W Software Installation:

These install instructions were tailored using a Windows 10 OS. There are also setup instructions for Ubuntu and the Raspberry Pi too. There's also support for ROS if you want a challenge...

If plugging in your Pico for the first time, it should appear in your PC in boot mode with a couple files. You will need to install the CircuitPython UF2 file onto the Pico W.

1. Move the included CircuitPython (8.4.0) UF2 file into the Pico drive.
   • The Pico should reboot and display new files after dropping the uf2 file into the drive.
2. Flash code and libraries to Pico
   • Move the lib folder, settings.toml and code.py files from the Mini-Arm package directly into the Pico drive. This will flash the Pico with the code and libraries.
3. Configure communication with your Min Arm (USB or TCP/IP).
   • For USB Serial communication, it's ready as-is! Just plug a USB cable into the port exposed on the side.
   • For Wifi/Network usage, configure your network credentials in the settings.toml file and change the COMM_TYPE to NETWORK. You can use a serial console to see the host IP. There are several editors with CircuitPython or MicroPython support (Thonny, Pycharm, VSCode) but the easiest method I found was using PuTTY. Connect to the Pico with the assigned COM port, and press Ctrl+d to restart the code.

The arm should be good to go!

Note: You can also download the latest version of CircuitPython intead of using the provided version, the only risk being minor bugs caused by differences is versions. The Adafruit website has a guide on getting started with CircuitPython.

Quick Start

Xbox Teleop

When the arm first turns on, the LED will change to green to indicate successful connection to the network. A blue light indicates a successful connection to the server with a client. Open the xbox-client.py file and set COMM_TYPE to the same type set for Mini Arm in the settings.toml file. Plug in a controller, open a terminal in the directory containing the xbox-client.py file, then run the python file:

python xbox-client.py

Robot controller commands

Sending commands to either the TCP/IP server or serial to the robot requires an encoded string message. The commands currently supported are below:

Name	Parameters	Description
movemotor	MOTOR VALUE	Moves motor number MOTOR to absolute position VALUE (deg)
movemotors	[VAL1,VAL2,VAL3,VAL4,VAL5,VAL6]	An array containing values for each motor. Moves all the motors at once to the values included in the array from base-to-gripper
play	SONGNAME	Plays a tune from the selected SONGNAME if in the library
pose	[X, Y, Z, ROLL, PITCH, YAW]	Moves the end effector to an absolute coordinate pose frame with respect to the world frame. It is helpful to know where the robot EE frame is.
delta	[X, Y, Z, ROLL, PITCH, YAW]	Displaces the end effector from its current pose given the displacement values
robotinfo	none	Gives back information about the robot's current pose and joint state
gripper	VALUE	Moves the gripper based on the input received
debugon	none	Enables verbose feedback outputs for debugging
debugoff	none	Disables verbose feedback outputs for debugging

Serial Control

TO-DO

TCP/IP Control

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Robot control is done through the Unity version of the "AJ" GUI v1 (Link coming soon), or an SSH terminal to the robot. FOR TCP/IP, quickest way using a python terminal:

import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("YOUR-ROBOT_IP",1000))

Send a command like an sbsolute position [x, y, z, roll, pitch, yaw], where cartesian coordinates are in mm and orientation is in degrees:

s.send(b"pose [1755, 0, 2660, 0, 0, 0]")

Or open the gripper:

s.send(b"gripper 180")

The arm has a very limited library of themes (starwars or mii), but enjoyable nonetheless. Play a sound file by passing the name:

s.send(b"play mii")

License

Copyright 2022-2023 Jonathan Shulgach

This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, you can obtain one at https://mozilla.org/MPL/2.0/.