Just out of curiosity, when would you think these prototypes should be best built? Surely not on my free time, right?
If the company is not interested on listening to new ideas, and you're keen on participating in something you would like to help build, then perhaps this is not the right company for you.
I have a project right now that I am thinking of building a prototype for on my own time and pitching to my company, because the company will basically have to sell the idea to another business. Why would I do this? Because then I can say how much I want to be compensated for my idea getting the company new business.
I honestly wish you all the best, and hope that works for you.
Just please be aware that after you've delivered, you loose power for negotiation. Therefore I would probably rethink the timeline choosen for agreeing on a reward "then I can say how much I want to be compensated for..".
I certainly do not intend to deliver anything that works before asking for compensation, I intend to show something that works and then negotiate how much it is worth.
But only if you think it will demonstrate enough value to get you something you desire: cool work, a promotion, etc.
This requires a good understanding of what your managers and the larger organization will value, and whether they reward people who show they can deliver on those items. People's careers _do_ get bumped from these kinds of efforts, but I've seen a lot of engineers spend 40 hours prototyping something that management just won't value.
If the company is not interested on listening to new ideas, and you're keen on participating in something you would like to help build, then perhaps this is not the right company for you.