Originally Posted by SteveCallas
Rotating the blades is easy - even when they turn 90 degrees and offer up significant resistance. What I am worried about is that the voice coil has to shift the blades from 0 degrees to the desired angle, not the fan motor.
Poor analogy, but stick your arm outside your car window while driving fast and keep your hand out flat to act like a wing cutting through the air. Now twist your wrist so that your flat hand is now perpendicular to the air movement. The load on your arm changes, but it's ok, your deltoids and pectorals can take it, they are strong. That's like the fan motor - no sweat. The voice coil/magnet in this is your forearm muscles that twist your wrist, and they aren't nearly as strong. Yet they will have to precisely control the exact angle of the blades (your flat hand) while overcoming that resistance. Not easy for a voice coil or for your forearm. Am I missing something?
From personal experience I can tell you that it doesn't take much force to pitch the blades.
First, here's a link to a page on my website very briefly detailing my diy rotary sub attempt. EDIT - I'm not allowed to post a link. Maybe later.
It was never completed but the pictures are kind of cool.
Me and another guy challenged each other to build one with an absolute max budget of 4% of the cost of the retail version ($560). The other guy bailed almost immediately but I continued. The budget restraint was the first mistake.
The second mistake was using an rc helicopter swashplate and accessories, but that was the only way we could come in under budget. Once I had it mocked up with everything in place except the driver, I was able to pitch the blades (not shown in the pics) by hand and it took surprisingly little force on my part.
At that point, after playing with it for a couple of hours, I noticed that the rc heli parts had already started to wear out. That was the main reason I abandoned the project. It would be easy enough to finish and have a fully functional model but I don't want to destroy the driver for a subwoofer that requires regular maintenance. (I also don't have anywhere to actually use the thing so there's not much point.)
Anyway, the point is that the concept is pretty simple but rc heli parts are not the way to go, and I'm not a machinist so I quit. In the unlikely event that I try again one day I'll have a good long chat with soho54 first, that guy really knows what he's talking about. I just wish I had talked to him before I ever started...
At least I got a cool looking paper weight out of this exercise and it only cost me a couple hundred bucks.