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The Creativity of it: The Lazy Man's Sword

This is a simple mechanism that uses a motor. And it converts circular motion to linear motion. It is an easy setup and I ran through a couple of different iterations when designing it.


The Project itself is located here:

The Lazy Man's Sword!

With this sword you can eat a sandwich and battle a dragon at the same time. Yup! No more Arm fatigue when you wield this sword! Check it out here: The Lazy Man's Sword

I am not sure when this idea came to me. I just remember jotting it down and referring to it at a later point. The major idea was a sword that swung up and down of it's own power without having to move your hand.

I also had this thought that I wanted it to have a distinct chopping motion almost like a guillotine where it would rise and fall, slapping into place with a distinct noise.

The only real challenge to the project was figuring out a nice system for the motion that was easy to do and looked reasonably good.


Book: Ingenious Mechanisms for Designers and Inventors

I started my search by referencing a pair of books I have called "Ingenious Mechanisms for Designers and Inventors". Lot of good mechanical stuff in these books.






The cam mechanism

My first attempt was to use a cam mechanism. Picture that white cam spinning in a counter-clockwise direction. It will push the sword up as it spins. then we get to the cutoff on the cam and it releases the blade to slap back into the closed position. The rubber band (blue) is what pulls it back.






There were a couple of issues with something like this though. Foam board would be no good for the cam so I made one out of wood. But, the rubber band caused a sideways pressure on the blade. Not the rubber band itself but the pushing up of the cam on only one side.

So, I made two cams out of wood. And mounted one on this side of the sword and one on the other side. This way it got an even and straight pushing up.

But.... I couldn't find a good balance with this setup. I couldn't get the rubber band to be strong enough to pull the blade back, yet be weak enough so the cams could push the sword easily. It kept getting jammed. A bigger and more powerful motor could have over come this but I figured there must be a better way.

So I did some more research of simple machines and decided to go with something called a type 3 simple lever.

The three types of simple leversI ended up choosing a simple lever for the mechanism. Think of a seesaw.

Let me explain the three types of leves. They are important when you consider force and distance traveled.

For type 1 everything is equal. It takes an equal amount of force to get the motion on the other end. And the distance you push creates an equal distance on the other end.

For type 2 you have to push a longer distance to get a small motion but, you can press with less force.

For type 3 You have to push harder but for less distance. You get more distance traveled on the motion end.





So, for the sword I went with type 3. This way my small motor didn't have to turn large circles. It could turn smaller circles with more torque and it would give a big swing in the sword blade.


Simple lever type 3 in the sword

Can you see how it works as a simple lever? As the motor turns it pushes that wooden piece, exerting force and pushing the sword blade up, then pulling it back down. We have to exert a bit more force but we get a bigger swing for the blade.

And this system pushes the blade up then pulls it back down. So there is no need for a rubber band. And that takes the sideways pressure off. I only needed tomake this mechanism on one side of the sword. No need to mirror it on the other side of the sword.


And that's it! Figuring out how to do this project was a fun exercise in making a simple machine with a purpose. Now I can fight dragons, ogres and other creatures without my arm getting tired. The sword does all the work for me.



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