Fun with casters

Today is *almost* one of those throw-back posts where I reminisce about the awesome 80s.  Only I'm going to hone in on one specific part of that time period.

Did you ever have a Sit'n'skate?  Cause I did, and it was amazing.

via.

 Some people these days market it as the "Flying Turtle" by Wham-O.  The gist was that you sat on it, and as you moved the handles left and right, the toy started to move.  The more you oscillate the handles, the faster you go.  Very simple.  Yet very strange method of gaining momentum.  

I was trying to think through the mechanics of the motion, and found a few physics enthusiasts who like to write out models for things.  Well, this is the caster wheel principle, wherein the turning axis is in front of the wheel contact axis, causing a stability case where the wheel "wants" to follow the axis.  Think of a stroller or shopping cart.  The wheels will right themselves if they are pointed in the wrong direction.  Well, for this device, it is easier for the wheels to move forward when you turn the handles than for them to slide side-ways, which is the only other alternative given the torsion. Casters are taken advantage of in robotic systems, where casters give additional motion capability.

Also, there are new products on the market these days that take advantage of this mode of propulsion.  For example, there are these twisty skateboards called Ripstiks.  I saw a neighbor kid riding one a couple of years ago, and thought, "How can he be riding on two wheels?!"

A Ripstik. via.

Now a Plasma Carwhich is basically a sit'n'skate with a different posture.  The website says those wheels in front are just for stability, and don't really touch the ground.  So it's the same thing.  Caster wheels behind the axis of rotation.

 

Available at Amazon.com  You should watch the videos of the kids riding them there.  Pretty cool!

Have you ever thought back to a toy that you had as a kid that was so cool, and seen elements of it reinvented again and again?