Would anyone happen to know (or be able to measure for me) the center-to-center distance (across, not diagonal) of the mounting holes on the small muffin fans? Units in mm would be good. Also, are we allowed to use different muffin fans? If so, can we use a 6V one wired to the 12V circuit or would that be bad/disallowed? Thanks.
I can’t exactally remember the size of the holes in the muffin fan. Are you talking about the large ones? If so it was around 4 inches, but don’t take my word for it.
Running a 6v muffin fan on a 12v source would make that thing spin crazy fast, i’ve done it before, it doesn’t have any real problem except the fact that it’ll wear out/die a lot faster.
The muffin fans are measured so that each side is the dimension given.
IE a 120mm muffin fan should be a 120mm square…
Simple geometry from there…
sqrt((120^2) + (120^2)) = 169.705627 =~ 170mm
The above posts don’t really get me the answers I need. Can someone with the actual small muffin fan measure it, or someone who has the Inventor model measure it in there? And can someone who is knowlegable on the rules tell me if we can use a 6V fan? Thanks.
I dont have the fan in front of me, it somehow dissapeared, but I have to ask why do you wish to use a 6 Volt fan when 12 Volt fans are included? I dont believe there would be a problem with using the 6 volt fans except that they will burn out quicker, possibly in the middle of running a match or something which at that point your fets ( or whatever they are ) could get overheated.
Use the flow chart to see if you can use it and if it doesn’t put your electronics budget over then you could use it.
-Mike
If they are standard 40mm x 40mm fans (which I am almost 100% sure they are) the center to center distance (not diagnally) is around 32.5mm.
EDIT: Andy’s original shifting tranny had these mounted on it. That PDF should have the hole spacing too!
EDIT 2: Looks like he has it at 1.265", which confirms the 32.5mm within some uncertainty. A 4-40 should have plenty of wiggle room 
A fan has a motor, so unless you can find explicitly otherwise I would assume that it must be a kit motor driving it or no go.