You get the weed whacker appliance for the Mech (if you don't have it, it's in Captain Zigg's room hanging from the ceiling) and press space to hit the blade and they will move. The Multi-tool stops it so Sprocket can open the door for you. Don't believe that the Multi-tool MOVES the fan. (That's what a lot of people say)
its in the museum on mainstreet of steamworks island :)
It's Steamworks Island #14th Island
(The solution is at the related question "How do you beat Steamworks Island")
the crab on steamworks island is next to the living quarters
you go all the way to the top where the gear is than use the multi tool if you don't have the multi tool than just go to the cantina in the beginning of steam works island
You go to Steamworks and head to the museum and there is the Deogen
pound it with the mech's weed whacker
steamworks island
There is a video walkthrough at the related link below. There are written WikiAnswers solutions at the related questions, as there are for all Poptropica islands. (How do you beat Steamworks Island) (What is the walkthrough for Steamworks Island)
Steamworks island
you can get it on the far left of steamworks island, past the living headquarters.
how to do the bridge terminal on poptropica's steamworks island