Arm Twister Skin Stretch Project

Skin stretch can be applied to a person's arm by twisting in opposite directions, in a manner similar to indian burns that kids do to each other. We want to make a portable device that is easily attachable to a person's arm so that we can study the responsiveness to skin stretch while the body is in motion (running, jogging, walking, etc). Part of the challenge is to make the device easily adjustable to differences in arm shapes and sizes.

Current Prototype:

I learned a lot from the initial prototyping (see InitialPrototypes) about what materials and methods work for attaching something to the arm. For this first pass, I only wanted to have one ring rotate relative to the arm to cause skin stretch, instead of two counter rotating rings for proof of concept purposes. This prototype idea can be easily extended to the two counter rotating rings and currently in the process of doing that.

Based on the sorbothane prototypes, we realized that sorbothane or silicones are well suited to stay in contact with the skin (no slippage). Also, contact with the skin at many discrete areas creates bunching effects between the contact areas, which causes more sensation than if the contact were continuous all around the arm. Since timing belts have evenly spaced teeth (especially at finer pitches than I could cut by hand in sorbothane), I started coating timing belts with dragon skin silicone (see TimingBelts).

The timing belts actually serve two purposes in the prototype: contacting the skin and twisting it, and conveying the rotation from the motor.

Solid Works CAD model:

Picture of Prototype Device:

Current Activities:

MelodyBlog - (starting in May)

ArmTwister2

Things to think about:

• Bunching effects
• Some slippage vs. no slippage
• Materials
• Testing
  • how many degrees, speed of rotation, etc.
  • running, walking, standing on treadmill?

-- MelodyWu? - 11 Jun 2007