Open Melt 2

Short Version: Open Melt 2 is out – and now it’s Arduino based. Full documentation for Open Melt 2 is on Github.

A translational drift (“Melty Brain”) robot spins its entire body, but is controlled directionally by an embedded system that modulates motor power.

This requires precise tracking of rotation speed. It has potential use in combat robotics – but is not common due to being perceived as difficult to implement.

Open Melt has its origin in the mid-2000’s – when I developed a series of 1lbs and 3lbs Melty Brain combat robots based on the ATmega168/328 microcontrollers.

Compared to some other approaches the system is simple:

• An accelerometer measures centrifugal force in order to calculate RPM-
• Each rotation a heading LED is illuminated to indicate the “front” of the robot
• The driver intuitively corrects for any minor errors in tracking as they steer

This system works pretty well – and I’ve won a few fights with it.

I eventually open-sourced the project as “Open Melt” – and it’s been used by a handful of combat robot builders.

But over the last decade – Open Melt became out-of-date.

The old system depended on a high-g (200+g) accelerometer with analog output. Increasingly accelerometers favored I2C interfaces – and 200+g analog ones became harder to source (and weren’t available on convenient breakout boards).

Adding I2C support to the original version could address the issue – but the code wasn’t up to my current quality standards. All functionality was crammed into main.c. Patching it up would make that situation worse. Revisiting it made me think, “who wrote this cruft?!”

So Open Melt needed a major refactoring at least.

Before I started – I took a moment to reflect: “What is the purpose of this project?”

Make translational drift accessible to more combat robot builders – and try to keep it that way into the future.

So – it was clear Open Melt should move to Arduino. This makes the system far less intimidating to people without a background in embedded software development.

(If you haven’t played with Arduino in a while – checkout the Arduino 2.0 IDE – it’s not awful!).

With Open Melt 2 – code quality is more of a priority. Good practices (high cohesion, low coupling) are followed. While functionality is largely the same – it’s implemented across seven different modules instead of one. Code for translational drift logic, motor control, accelerometer and radio control are all cleanly separated and have well-defined interfaces.

Next time swapping the accelerometer won’t be an existential crisis for the project.

Moving to Arduino also gives Open Melt the potential to run on non-AVR microcontrollers (not tested).

Detailed plans are now provided for a 3d-printed Antweight (1lbs). I haven’t fought with this robot yet – but it’s held up well in testing.

It’s almost a complete how-to-guide on building a Melty Brain robot.

Have fun – but please remember:

Building and operating a robot of this type, even in smaller versions, is inherently dangerous. By choosing to use the provided code and plans, you acknowledge the risks involved. The creator of these plans cannot be held responsible for any injuries, damages, or losses that may result from the use of this project.