I've never managed a mechanical (assumed physical?) product before, but would say that the general approach of breaking down your themes or 'work types' and then allocating a % of capacity will still apply! You'll have to set your capacity in a way that is aligned with overall business strategy or goals.

Maybe you'll have more maintenance a compliance depending on the industry you work in, as a physical product needs to be reliable, functional, and in some cases, more 'safe' to use than other products.

Keen to hear more about your industry though before I can answer with more conviction.

Hope that helps?