Inertial Electric Assist – Metromotive

submited by

Style Pass

2021-06-19 05:00:05

I’m currently working on an ebike build, and the bike that I’m using has some quirks that make it difficult to fit a conventional bottom bracket torque sensor, or to add switches to the brake levers for activating regenerative braking (and such switches also only provide a single level of regenerative braking, rather than one that is proportional to the desired braking level).

Having done a lot of thinking about acceleration in micromobility vehicles recently, I came upon the idea of not actually measuring torque at all, but inferring it from other measurements. This was validated when a friend of mine mentioned a project that showed promising results from just such a scheme.

What follows is a combination of planning and specualtion for this build, but is also might generalizable to other vehicle types. If it works, it would provide a potentially cheaper alternative to conventional torque/force sensors while also providing proportional regenerative braking.

An electric assist vehicle is one where an electric motor multiplies the effort of a human to propel the vehicle. That is to say it incorporates a controller that seeks to make \(F_{motor} = F_{human} \times gain\). This type of control scheme is extremely common for electric bicycles, as it provides a very intuitive way of controlling the motor’s output.