If you want to vary the speed within a stroke, then yes, you’ll need to use a low-level interface of one type or another. You can either use the direct serial interface (EBB commands), the [robopaint API](https://github.com/evil-mad/robopaint-mode-remote/blob/master/API.md “robopaint API”), or other means to do so. If you can say what tools or environment you are using to generate your vectors, I might be more able to point you in the right directions.