I recently had a need to look under the floorboards to check on some pipework and the only easy access was a knothole less than 20mm diameter. A cheap borescope (£7.00 on eBay) gave a good picture but was difficult to manouvre to see what I was looking for. An unwound wire coat-hanger and electrical tape prove no solution so I quickly printed up a borescope steering mechanism based on what little information I could find on medical endoscopes.
I have put a video on YouTube https://www.youtube.com/watch?v=QbhHUqesBow showing the steering mechanism doing its thing with an inset picture showing the view from the borescope camera. I have avoided puting up a video showing what I found under the floor as it would distress anybody even slightly arachnophobic. I have put together a fairly comprehensive description of how to make this in a PDF file in the Thing Files