The best senior project in any engineering field is a project that the senior comes up with on their own. The senior should be eager to test out and demonstrate many of the topics that they've learned in their schooling. The scope of the project should be limited to a difficulty level that will be within the time and financial budget of an undergraduate process. Building and deploying a new Mars rover on Mars would certainly be a spectacular project but far beyond any individuals resource.
I do recommend that your project should involve several people handling different aspects of the project. Most engineering work happens today in teams of different engineers with different disciplines and assignments.
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"Don't disturb my circles." translation of Archimedes last words
Well I was watching a show on nano technology the other day, and saw a new procedure for operating on the eye where a very small device was injected into the eye and navigated through the eye to a blood vessel to deliver a payload of medicine used to unblock the vessel enabling sight again....The object was controlled by 8 electromagnets encircling the eye, with a joystick type controller....If you could expand on this concept for some other procedure that would be cool....
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All living things seek to control their own destiny....this is the purpose of life