Armour – open source robotic arm control software.

This project was designed to be a replacement for the useless software provided with the Dobot robotic arm, but should work well with any robotic arm that can be modelled using Denavit-Hartenberg parameters.
This is in a very, very early stage, and is only a console app at the moment, allowing control of the arm through the keyboard.

Firmware

The current implementation uses G-Codes as the protocol for arm control and assumes that your arm is set up for one degree per mm.
I use the repetier firmware which works pretty well but any 3D printer firmware should work.

Host software

Obviously this software is the host software but it’s not the greatest tool to use to test your connections and pin assignments. For that I use the repetier host.

Dobot

The dobot is configured with the three axes laid out in the following arangement.

Wiring the Dobot with RAMPS

I’d recommend using the RAMPS 1.4 driver board as it provides outputs for all functions relating to the arm.

Here is a picture of the RAMPS board wired up to the Dobot outputs.

To wire up the arm start by putting 3 jumpers across all 3 microstepping switches beneath each controller – this will set controllers to 16 times microstepping.

Then put the A4988 stepper drivers into the slots shown in the image and connect the stepper cables.

You’ll need a 12V power supply for the RAMPS board, connected to the green connector in the image above. I used the one that came with the Dobot by chopping the jack off the end and wiring it in.

Also put a jumper across the middle and inner pins next to the servo connectors to power join the VCC to the servo VCC.

Endstops

For some reason the people who made the Dobot decided not to implement any kind of end stop on the arm. I assume they intended to use the 2 axis angle sensors that are mounted on each segment. I couldn’t find any code that would allow me to hook into these sensors so I opted for the simple route and put some physical end stops in. I’m also not sure how they intended to get over the gyroscope drift issue.

Y and Z

The switch mounting block can be 3D printed from the stl file in dobot/HomeSwitchBlock.stl.

X axis

The X is mounted to the bottom plate and uses a small roller wheel micro switch. The mount can be 3D printed from dobot/ArmXEndStop.stl

This mounting reduces the range of the X axis to about 250° but it’s worth it for a usable X end stop.

Configuring the repetier firmware

• Download the Arduino IDE if you don’t already have it.
• Download the latest version of the repetier firmware.
• Open Repetier/Repetier.ino in Arduino
• Open configuration.h and overwrite it with the contents of dobot/Configuration.h
• Compile and program the arduino mega
• Open Repetier host and confirm that all the arm functions are working. Servos can be adjusted using M340

To run this project you’ll need visual studio. Set the start up project to “ConsoleArmControl”. That is the main entry point at this stage.
Currently set up with

When adding to the project where possible develop with TDD.

Forward kinematics

The forward kinematics uses a series of Denavit-Hartenberg matricies with parameters specified by the arm being controlled. For now this is the Dobot arm parameters but could be any arm.

Inverse kinematics

The inverse kinematics uses a hill climbing algorithm to identify the correct set of joint variables. With a randomized restart when a local maxima is reached.

This is not the most efficient algorithm but I don’t know enough maths to improve it at this point. If someone who understands IK better can write a better algorithm I’ll happily merge a pull request.