There is a wide variety of control interfaces available for power wheelchairs. The main objective is that people with all different sorts and grades of disabilities can control a wheelchair by themselves in a simple manner.
Within these control interfaces, there are two different types: proportional and non-proportional controls.
There is no universal protocol for power wheelchairs. Often, alternative controls are made for a single model or brand.
At mo-vis, we are faced with this reality too. However, we try to be as 'universal' as possible.