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So I decided to build Crescent Rose from RWBY. Yeah this thing:
I wanted it to transform and retract back into a somewhat compact form. Specifically, I wanted it to extend out and be able to retract back to its compact form. After analyzing the movements I found the rod, and claw extension to be possible. The tiny horn-like mechanism on top of the claw I decided not to do, as my focus was the rod extension and the claw.
These were the options I ended up exploring.
If I just wanted Crescent Rose to open up and not retract, I would have used mostly springs. Springs are good for one way movement but that means you have to fold your mechanism back up manually. With my goal of opening up and retracting, I couldn't go this way.
Gravity powered with weights:
I considered gravity and weights to move the pole extensions out and flip open the claw. It would also allow the prop to retract under specific movements. I had to scrap this one because the amount of precision needed to build the parts was not possible for me with what I had.
Hydraulics and Pneumatics:
These would be a great application to Crescent Rose for the extension, but they are costly, heavy and are good for only the gun extension. These can extend and retract if needed but are no good for the circular movement of the claw.
Servos and Motors:
These are very versatile and would definitely be good for Crescent Rose. They too are costly and the means to control servos requires extensive knowledge of a microcontroller and programming. Motors, the DC kind, are simpler but you have less control over them. However, these are great for Crescent Rose as they can achieve both linear and circular motion.
Transfer of motion and combination with springs and gravity:
This was another idea where I would build Crescent Rose to extend and retract based on the movements I put on the prop. This would achieve the gun extension and the rest of the claw out easily and achieve retraction well enough. This option, in combination with springs and weights with gravity would be the best option for Crescent Rose overall.
Pure springs had to be scrapped due to springs only being able to achieve extension and not retraction. Pure gravity and weights had to be scrapped due to the complexity of Crescent Rose. Only limits to hydraulics and pneumatics were cost, I know how to use them. Servos and motors are also costly but I know how to use them too. Only limits to the combination option was time.
Ultimately, I decided on Pneumatics,Servos and Motors to power Crescent Rose. I did not go with the combination option even though it may be my best was because I didn't want any human involvement with moving the prop besides switches and buttons and because I had the money for it. Plus automatic effects with buttons just looks cooler.