In the Sentinals Campaign, the ease with which characters utilized the basic Invention rules quickly unbalanced the campaign. For the Vanguard Campaign, I have redesigned the rules surrounding inventions.
A character must spend one invention idea in order to gain a permanent idea for an invention. The Invention Idea requires Skill or Knowledge of the subject matter – or viable reason in game terms that it could be pulled off.
You get Int % chance to successfully invent the idea. You then must Spend one Character Point to get the roll. If the roll is failed, you can try again next level by spending another character point – the percentage chance is cumulative per level.
Example: character has INT of 13 first attempt -- 13% chance of success Second attemt -- 26% Third Attempt -- 39% etc.
Subject to quality % roll at game master discretion