Hi, I am not in an engineering field but there are common themes to all PhD research and from what you’ve said, I don’t think you need to worry. The aim of your project is to design some software to achieve a specific task, and then to beta-test it? Your research element will be in working out the best way to create the software and also, the best way to validate it. So I think you will be awarded your PhD based on your journey from initial idea of designing the software, through to building and evaluating it. As with any project you’ll defend the way that you achieved this and reflect on how it might be improved. If your software does not function in the way it should (and so, does not fulfill the original aims of the project) then this would not mean PhD failure as long as you can defend the choices you made along the route from design to final product. I hope that offers you a bit of reassurance but to put your mind at rest, I think you should talk to your supervisor about your concerns. Best of luck with your work.