How do you motivate co-founder/s to commit with you on an idea?

We use to sit and vote.

Understand what motivates them specifically and reframe how my idea can bring that to them. For example, if they care a lot about revenue, then you want to talk about how this idea can really increase your customer LTV.

I managed to do this 3x. It takes time. For sure not done in a day. I usually make a communication channel to talk about something that caught my interest. Make sure that I know what my partner's inner motivators are, and talk about those in our chat. Partner A is into 'design' Partner B is into 'prestige' Drop hints, data points, customer lists, design awards that other incumbents got on the industry, and work my way to influence like this. Then, I start sharing my prototypes. If I see them getting involved, I let them dabble at it. At the moment that you hear them say 'I wish I was working on (frank's idea) instead of what I am doing now' you know you hit a good spot. After that, you commit, they commit, and hopefully the morale still is up as you go through the long and taxing process of building business.

I subtly leverage hints, data points, customer lists, and design awards acquired by industry incumbents to gradually influence others.

Well, I just describe how their passions and experiences would work perfectly for the idea I'm working on and how their role would be important in the business and also a great learning experience for them.