Please help me identify this yellow part with four arms and an axle hole This is part of a set (that's in a bag of partially built pieces) that I'm trying to identify. This seems like a unique part, and if I can identify the part, then maybe I can cross-reference it to the set.
That's a Technic Knob Wheel (32072):

https://www.bricklink.com/catalogItemIn.asp?P=32072&amp;in=S

It's not especially rare, but hopefully it will help you to narrow down your set identification search. Feel free to ask other questions if there's anything that we can do to help out.