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Amulet is an open-source, three-phase brushless motor controller designed for EPFL Xplore legged-robot actuators. It is compatible with moteus firmware and targets higher-current quasi-direct-drive builds, with published specifications of 12–44V input and 100A peak phase current. Its reported 1,500W peak electrical power is a project claim—not an independently verified continuous rating.
What Amulet is—and who it is for
Nguyen Vincent’s Amulet (ΛMULET) is a motor controller for custom robotic actuators, particularly quasi-direct-drive actuators in legged robots such as quadrupeds. It controls three-phase brushless motors and follows a moteus-compatible firmware approach, making it an open-hardware alternative for builders working in that ecosystem.
That compatibility does not make Amulet a drop-in replacement in every robot. The project describes its pinout as nearly one-to-one with the moteus n1 to ease firmware porting, but a finished system still depends on the specific motor, encoder arrangement, wiring, power stage, cooling, and firmware configuration.
Amulet specifications
| Specification | Published Amulet value | Qualification |
|---|---|---|
| Input voltage | 12–44V | Project specification; Vincent Nguyen’s 2024 announcement separately describes use with a 10S battery. |
| Peak phase current | 100A | Published project specification. This is phase current, not a stated battery-input current rating. |
| Peak electrical power | 1,500W claimed | Reported by Hackster as a project figure that could change after further testing; not an independently certified or stated continuous rating. |
| Control MCU | STM32G474 | Project specification. |
| Control rate | 15–30kHz | Project specification. |
| PWM switching frequency | 15–60kHz | Project specification. |
| Communications | CAN-FD, up to 5Mbps | Project specification. |
| Position sensing | Two onboard 14-bit encoders | Listed in project specifications and Hackster coverage. |
| Cooling | 12V fan cooling | Project specification; the design also provides a low-side-switched fan connector. |
| Board dimensions | 69.67 × 76.7mm | Project specification; mass is not stated in the cited project materials. |
In a separate 2024 announcement, Vincent Nguyen described 30A nominal and 100A peak current when using a 10S battery. Those figures should not be read as a general continuous-current guarantee across the full 12–44V input range.
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How Amulet compares with moteus
Amulet is best understood as a moteus-compatible design with its own power-stage and thermal choices, not as a controller proven to outperform every moteus model. The figures below come from project specifications and official moteus documentation; they are model-specific reference points, not results from a controlled head-to-head test.
| Comparison point | Amulet | moteus reference models |
|---|---|---|
| Input-voltage envelope | 12–44V, according to project specifications. | Model-specific values are not stated here as a shared envelope; the cited official documentation gives individual power figures at 28V, 30V, or 36V. |
| Peak phase current | 100A, according to project specifications. | n1: 100A; x1: 120A, according to official hardware documentation. |
| Peak electrical power and conditions | 1,500W claimed by Hackster’s report of the project; the report says it may change after more testing. No standardized test conditions are provided in the cited material. | r4.11: 900W peak at 30V; c1: 250W at 28V; n1: 2kW peak at 36V under the documented 30kHz condition; x1: 1.3kW peak at 36V. See official moteus documentation for model-specific conditions. |
| Encoder count and resolution | Two onboard 14-bit encoders. | Not stated in the cited moteus reference materials. |
| Cooling provision | 12V fan cooling, a fan connector, and FET packaging designed for external heatsinking on both sides, as reported by Hackster. | Not stated in the cited moteus reference materials. |
| Dimensions and mass | 69.67 × 76.7mm; mass not stated in the cited project materials. | Not stated in the cited moteus reference materials. |
| CAN-FD interface | 5Mbps listed in project specifications. | Not stated in the cited moteus reference materials. |
| Firmware compatibility | Described as compatible with moteus firmware. | moteus firmware is the reference ecosystem; compatibility with Amulet is the project’s stated design aim. |
| Assembled-board availability | Current retail availability is not established by the cited project documentation, announcement, or coverage. | Not stated in the cited reference materials. |
The published 100A phase-current figure and reported 1,500W peak place Amulet in a high-current design space shared with moteus n1 and x1. That is a comparison of published figures, not evidence of equivalent sustained output: the power claims have different levels of qualification and the available material does not provide a common test protocol. Amulet’s 69.67 × 76.7mm board and fan provision also point to a different packaging and thermal strategy.
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What changed in Amulet’s design
Vincent Nguyen said the pinout is “almost one to one similar to the moteus n1 controllers” to make firmware porting easier. The larger changes are in power generation and thermal handling rather than a wholly different control concept.
- Additional rails: The power section includes a 12V rail and a low-noise 3V3 rail for the ADC reference.
- Filtered buck inputs: The buck-converter inputs use a pi filter.
- More bulk capacitance: The design increases the number of bulk capacitors to support a higher peak-power target.
- More cooling options: Hackster reports that the FET package can be cooled from both sides with an external heatsink, alongside a low-side-switched fan connector.
These are design choices intended to support the project’s power and cooling goals. They do not, on their own, establish measured thermal limits, reliability, or electromagnetic-compatibility performance.
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Can you build or buy an Amulet?
The project is presented as open source, and Vincent Nguyen’s 2024 announcement says fabrication documents were released. That supports reproducing or adapting the hardware from the project files. The announcement also names PCBWay as the manufacturer and assembler of the project boards; it does not establish a current commercial retail channel for assembled Amulet controllers.
Before committing to a build, check the project’s own documentation for the current hardware files, bill of materials, assembly notes, and firmware instructions. The available cited materials do not establish a current finished-board seller or guarantee that every file or component remains available.
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What to check before using it in a robot
A high-current controller is one part of a power system, not a complete safety solution. The moteus project documentation warns that its designs include moderately high-power electronics; the same practical care applies when building around Amulet.
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- Confirm that the battery, connectors, wiring, and protection are suitable for the intended voltage and current. Use appropriate battery protection and fusing.
- Plan the enclosure and thermal path around the actual motor load and operating duration. The project’s peak figures are not a substitute for a continuous-current or thermal rating.
- Verify encoder wiring, motor phase connections, and firmware settings before applying full power.
- Test progressively with a safe setup and appropriate monitoring rather than assuming firmware compatibility proves the complete actuator is configured correctly.
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