I wanted to build a four-legged robot, but actuators are expensive, so I decided to design my own. I created a modular system with the goal of making every component reusable and the robot itself scalable. The target weight for this robot dog is around 5 kg. Each actuator is built around a BE4108 BLDC motor paired with a custom FOC controller for electronics,. For the mechanics, there is an inner ring that will be machined (currently in resin for prototyping) and an outer shell. currently there are 3 variants of the gearbox model: cycloidal, planetary, linear (with ball screw). For prototyping, I am using the B-G431B-ESC1. The custom FOC controller is based on an STM32G491 and uses a TMC6200 gate driver, plenty of integrated features. the target for all the parts of this robot is to be scalable.