Unfair Peer Assessment on a Group Project
You may not like this answer, but I think you should settle for equal grades.
The situation you describe is very common and so are the disputes you have wound up with. The expectation was that all should share equally and you didn't, apparently do that. You basically, rather than being the team leader/manager, took it on yourself to do all of the work. That wasn't necessary, but it is too late now to correct it. What you should have done (sorry) is to work physically together as a team. I suspect that you tried to divide up the work, making the problem bigger since you add the integration task to the work of the parts. It is a formula that has been proven to fail since around 1960, or so.
The instructor may be partly to blame for this if you haven't learned about project management in any modern style (say, agile), but, again, it is too late to go back.
In the real world, this also happens. Someone does more, others do less, or nothing, but the work is the important thing. In the education world, the learning is more important, actually, but not all students or professors recognize that.
So, in building the thing you have been a success. In managing it you have been less of a success. If you have learned something it is worth it.
Yes, the built in system rewards freeloaders, but you should have recognized that from the start and acted so that it didn't work out that way. The milk has been spilt.
I don't, however, disagree with the conclusion here of Vladhagen. Talk to your professor and get an opinion. But you should have done that by mid-term at least.
Never mind that your "partners" may get something that they don't deserve. Think about your own actions and what you have learned as well as what you haven't.
In my view, this project was pretty typical and so the typical grading scheme should apply - same grades for all.
Had someone else been team leader and closed you out, not giving you anything to do, or a way to be a success as a team, then, I think, you'd have a more valid complaint.
Of course, in the peer assessment that you write you can describe the project life as you see it. But your "teammates" will also do so.
50.29% seems like an incredibly specific number. Are you sure it wasn't 50.28%?
If your teammates have left the assignment for you to handle, could you not inform them that you have done the bulk of the work and will be filing the signed grade sheet accordingly unless they return and help? If they are ignoring you, it would seem like you could simply finish the project, take the bulk of the credit, and submit the grade sheet stating what you feel their contributions were. Inform the professor why they never signed the paper (a submission on their behalf, in absentia). If you have email records of your attempts to contact them, it seems like it would be relatively hard for your team to dispute your account.
I am somewhat unfamiliar with the UK grading system here, but it would seem that as long as you received high marks on the project, credit for who exactly did what will be conclusively irrelevant. Get the win and get off the pitch (so to speak). Does it really matter who made the most goals and passes?
If possible, I would show the professor what you have so far and seek his/her opinion. The sooner the better perhaps.
I will add that life rarely will split exactly equitably in terms of work load and recognition. "That's life."
I agree with everything written in the other answers and Buffy has given a particularly carefully worded response, however I wanted to add a UK perspective.
UK Engineering degrees are usually accredited by a professional body for admission to the Engineering Council to lead to Chartered Engineer status (this includes EE, CS, and other engineering disciplines). I am a member of such a professional body (as are most UK academics in the field) and am familiar with the accreditation processes from both the professional body and academic department side. During their undergraduate study my experience is that few students have made themselves familiar with the professional aspects of their degree and the requirements of the body that they will join in their later professional life as part of their practise. I am also familiar with the construction of syllabus content and degree programs that lead to appropriate accreditation and the assessment elements they must contain.
An engineering degree will be required to contain group work, not to make things easier for the assessor or to permit larger course cohorts to operate or for economic reasons of lowering the cost of delivering the course, but pedagogically to deliver certain learning outcomes. Achieving those learning outcomes and the degree to which they have been achieved is what determines (or contributes towards) the grade or mark for these courses. Experiencing group interactions is one of the learning outcomes; successful co-operation in a group is one of those learning outcomes. Learning and experiencing what can go wrong is often an implicit learning outcome. Interestingly, making the damn thing (the physical result of the engineering labour) is only a small part of the learning outcome.
Consequently, being the hero and doing the whole thing yourself is exactly NOT what a group project is about and can lead to reduced marks. I have even seen students given totally failing grades for sacking their team and doing it solo. Engineers with these qualities are not the ones that fellow professionals want to work with in their seriously large projects and hence the reasons for marking sanctions for group disputes over contribution. We need engineers that can work together and leave their egos behind.
Later in their degree students will learn more about project management, but it is often necessary for them to experience sink or swim to understand the need for such structured methods.
You would have got short shrift from me if you complained about your mark on one of my assessments!