Hidden Blade Top 5 Specs & Constraints

Top 5 Specifications

  1. The device shall conceal a 7” blade within a container.

The blade will need to be long enough to protrude outside of the container while also having enough blade inside the container to retain the blade in position.

  1. The blade tip shall move at least 3.5” from the edge of the container when the system is engaged.

This amount of protrusion from the container will make the device comparable to those in the Assassins Creed videogames

  1. The mechanism shall withstand a point load of 10 lbf on the tip of the blade.

This point load can be in any direction and represents bumping the extended blade against an object. By resisting this force, the blade can be more robust and confidently used for cosplay.

  1. The system shall be electronically powered by a battery

The current design consists of an Arduino, flex sensor, and servo motor. These are powered by a battery since it wouldn’t make sense for the user to be next to a non-portable power supply.

  1. The system shall have a non-threatening aesthetic and geometry

Sharp things, pointy objects, and straight edges tend to trigger alert responses in people. The device needs to have curved edges and no sharp edges or corners. The use of a draft blends the device with the user’s arm better than an orthogonal wall.

Top 5 Constraints

  1. The device shall measure less than 2”x 8” x 2” to be comfortably attached to an average-sized user’s arm

This was estimated using a ruler and hyperextending a long sleeve shirt around the wrist.

  1. The device shall weigh no more than 5lbs to be comfortably carried by the user.

This was estimated by attaching dumbbells to an average-sized user’s arm and using that to estimate a comfortable weight to carry around.

  1. The device shall be capable of a quick disassembly

This is required for emergency access to the internals and deactivation of the blade mechanism.

  1. The blade shall be made of plastic to reduce potential hazards

Using a 3-D printer can prove beneficial for the rapid prototyping stage but for the model I want to build, I also want to make the blade out of plastic to prevent accidental cuts or stabs.

  1. The device’s color shall make the device easy to conceal

Dark colors make the device easier to conceal. However, black will trigger an alert response in people since black is subconsciously associated with dangerous things. An army green color or maybe a dark navy blue could prove to be non-threatening and concealable.

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2 Comments. Leave new

  • Ryan Cochran
    April 10, 2021 5:07 pm

    Hi Gary,
    This is awesome and I actually thought about making one too initially for the final project. I am interested in seeing how you will actuate the device to trigger the blade to extend and retract with it being electronically powered. Will the flex sensor act as a pressure sensor and when the wrist is moved in the correct direction it will release the blade and then when the wrist is moved back it will retract? I am super excited to see how this turns out!

  • Hello Gary,

    This is a super cool idea! Ive always been a fan of assassins creed. I think it is smart to go ahead and make it out of plastic as when I thought about making it I had the vision of it jamming into the palm of my hand!


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