Notes from

Also, no gearbox means there’s a lack of inertia, which is a major advantage from a safety perspective in robots and machines. If a car starts rolling down a hill, the inertia built up makes it very difficult to stop quickly. A similar thing occurs with a gearbox: If you have a motor that runs at 4000 RPM and a 100:1 ratio gearbox, an instantaneous stop is not possible. The gearbox needs time to slow down.