Here’s the nearly completed mechanism that makes the three fans move on each side of the head. Note that the schematic in the previous post shows the left side of the head and this is for the right side of the head. Still have a little bit of relief machining to do and drilling the fan blade mounting holes. After that I can attach the fan blades and power them up!
In several scenes in the movie Stargate you can see how the fans on the sides of the Horus and Anubis helmets rotate in a progressive manner, with the upper fan moving the greatest amount and the lower fan moving the least. It’s a really cool effect and the set of three fans on either side of the helmet was made to move using a single servo. There’s not a lot space in that area of the helmet so it has to be a fairly compact mechanism.
In order to replicate this I created a kinematic model of the mechanism using a free program from Autodesk called ForceEffect. This is a great bit of software that allows you to plot motions of all kinds of linkage mechanisms. I would have killed for software like this back in the day (20+ years ago) when designing suspension mountain bikes as I used to plot kinematics manually on paper. The fact that you can use an app like this on your phone or tablet is just awesome.
Unfortunately the photos I have of the original mechanics are not direct side shots and a fair bit of modification/extrapolation was required to get the proper range of movement, taking into account the necessary leverage ratios and clearances. The original helmet mechanics used helper springs to overcome the high leverage ratios- I have the benefit of modern digital servos that are much more powerful than the analog servos used when the film was made. The downside is that digital servos use more power and are noisy but that’s the price you have to pay…