Asking to get paid for academic research work I am currently a student working for a professor full time over the summer on science / engineering research projects. My first meetings with this professor took place during the spring semester. During these meetings, the professor agreed to hire me and agreed (in speech only) to pay me for my work. No specifics were ever discussed and the remark about paying me was made casually. I have signed no financial paperwork of any kind at any time. If I were to get paid, I would almost certainly be paid minimum wage. After this meeting, payment for my work, which I have been doing most of the summer, has never been brought up again by the professor or anyone around them.

I have not brought this issue up to the professor because: 


The experience working on the projects I am being assigned is metaphorically worth its weight in gold to me right now. It is both work I am intensely interested in pursuing, and also a great resume experience listing for potential future employers.
I am in a financial situation that allows me to offer my time for free. Since this is my first experience working on academic research, I did not want to be turned down by the professors I asked because of money. I also will almost certainly need to ask this professor for a letter of recommendation for future internships to very selective companies in the same industry as this professor. I also know this professor regularly communicates with high ranking industry professionals who work at the same companies as I want to apply to. Thus, my relationship to this professor is of paramount importance above all else.
I will almost certainly be working for this professor through the end of the next academic year (however, I will have to work part time during the school year since I am a student). I have considered the possibility that it might be wiser to wait until I have worked for this professor longer before asking to be paid for my work. As far as the feedback on work I have already performed, I seem to produce results that are on par or better than they are expecting, and I deliver my results on or ahead of schedule.


All of this said, I still would like to get paid (however small an amount it may be) for this position since I am working full time and, when I was hired, the professor I work for did (again, verbally only) say I would get paid. I feel like I am in an awkward position here, and I am unsure what the best way bring this topic up is. How should I bring this up to professor if at all?
Given that payment was offered but just not followed up on, it is entirely possible that this professor does not realize that he never got around to the paperwork for paying you. (I say this having seen that exact scenario play out more than once.)

I would recommend just bringing it up casually, e.g.: "When we spoke in May, you mentioned the possibility of payment. Is that something we can arrange now?"