I'm midway through a PhD in Physics in the United States. In my short time in academia so far, I've had several distinct kinds of collaborations. I've collaborated with peers who are working on understanding a new area together, with folks in other department who are doing applied work, and of course with my advisor.
Each collaboration has had its own unique structure. For example, in some of the applied work, my collaborators were interested in learning more about the details of my area, and in others my collaborators were just interested in getting results from me to plug in to their work. In some of the work with peers, each of us handled a distinct aspect of the work (and we understood little of the each other's aspect); in others, we worked together on the same problems and batted ideas back and forth.
Many of the collaborations have had the same kind of issue for me, though. Sometimes I feel like my collaborators owe me a certain amount of attention. (For simplicity, please consider that the collaborator is at the same level of seniority as me.) For example, once I was on the verge of a "breakthrough" and talking through it with someone would have made a big difference, but my collaborator didn't want to engage. For another example, once I was very confused about a particular question in an applied collaborator's area that was relevant to our project and they brushed me off when I asked for help.
Almost every collaboration I've had would have been improved in my eyes if my collaborators were more generous with each other. However, I know that there must be a line. The famous Hardy-Littlewood rules have an Axiom 2 which states that "There was no obligation to reply, or even to read, any letter one sent to the other". Clearly, other established researchers could feel differently than me.
My question is intended to elicit responses which flesh out the role of a collaborator, with a particular eye towards interactions with others on the team. When a researcher (student or established) agrees to be a collaborator with someone, what responsibilities are implicit in that?