I just wanted to de-lurk to mention that I've completed construction of a working LEGO Difference Engine. (i.e. a Babbage Engine)
It has over 200 gears, 20 shock absorbers, and is about 18 inches tall by 25 inches wide. It is purely mechanical in nature, requiring over
100 turns of the crank for each answer.It can evaluate any polynomial of the form ax^2 + bx + c, up to three digits.
Enjoy!
----- Andy