Nguyen Vincent's Amulet Is a High-Power Moteus Alternative for Brushless Motor Robotics Projects
Delivering 100A peak phase current and 1,500W peak electrical power — possibly more — the open source Amulet really packs a punch.
Robotics student and hardware engineer Nguyen Vincent and EPFL Xplore colleagues have designed an open source brushless motor controller, with a legged robot project in mind and offering up to a 100A peak phase current: the Amulet, built atop the existing moteus design.
"Amulet was developed specifically to be integrated in our custom quasi-direct drive actuators for a quadruped robot. We've decided to develop our own motor controllers to have the highest amount of flexibility when it comes to some of the most crucial hardware," Vincent explains of the project. "The amulet controller is a modified version of the moteus controllers, providing higher peak power, thermals and cooling capabilities and more. It runs a modified fork of the moteus firmware."
The compact Amulet offers, Vincent claims, a 100A peak phase current and 1,500W peak electrical power — both potentially to be revised upward following further testing. With that sort of power, there's no surprise to find it has integrated cooling support through a low-side switched fan system, and there are two 14-bit encoders included for positioning — with everything controlled by an STMicro STM32G474 microcontroller, delivering 15-60kHz pulse-width modulation (PWM) switching rate and 15-30kHz control rate.
"The pinout is almost one to one similar to the moteus n1 controllers," Vincent says, "to port the firmware more easily. The main changes are done in the power generation section, which includes a 12V rail as well as a low-noise 3V3 rail for the ADC [Analog to Digital Converter] reference. The buck inputs are filtered through a Pi filter. The number of bulk capacitors is also increased to reach a higher peak power."
"The FETs [Field Effect Transistors] were chosen with a package that can be cooled on both sides," Vincent continues. "This reduces the thermal resistivity of the package, which means that the FETs can be more efficiently cooled with an external heatsink. A low-side switched fan connector can also be used for cooling."
More details on the project are available on Vincent's Hackaday.io page, while KiCad project files, Gerbers, and schematics are available on the Xplore Research robotic dog GitHub repository under the permissive Apache License 2.0