To reiterate that point- Personally, I see royalties vs. up front as a risk management issue, and would choose to reward my acceptance of risk financially.

For example, If I had a map I would normally charge $150 for ($50 deposit, $100 after completion, with delivery of the artwork after final payment was received) I might be willing to consider a royalty scheme that would ensure I would get compensation based on expected sales, most likely in a declining balance.

Here is a purely fictional example....

If you are retailing the product for $10 and expect to sell 100 copies (based on past performance of comparable products) I would probably ask for $50 up front and a $1.50 per unit sold for the first 100, and $.25 for every unit after that.

So, if it under-performs and only 50 sell, I make $50+$75=$125 ("loosing" money).
My breakpoint is 2/3 expected sales (67 units) where I make the $150 I'd have asked for with no royalty scheme in place.
If it performs as expected, I get reward for sharing the risk and get $200 ("bonus")
If it perform really well, say triple the expected sales, I get reward for sharing the risk, (but at a reduced rate) $50+150+200x$.25=$250

I've made a few such deals and "Lost" on more than I've "won"...

-Rob A>