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[DPRG] segway

Subject: [DPRG] segway
From: Chuck McManis cmcmanis at mcmanis.com
Date: Tue Dec 3 18:34:01 CST 2002

At 05:39 PM 12/3/02 -0600, cbrenizer wrote:
><I meant to send this to the entire list, too>
>I had wondered if a third wheel device costing 3 or 4 hundred dollars
>would have happier customers than the multi-thousand dollar segway (I
>know I'd be happier paying less and it probably wouldn't need much
>electronics, since it wouldn't have to be self balancing)

This is a common mis-perception. Two wheel, three wheel, or 18 wheel, you 
have to deal with torque of a vertical human body. The value proposition of 
the Segway is not about balance, its about inertial mass management.

Consider a human standing on a "trolley" (you can imagine any number of 
wheels on it) moving forward at a velocity "V" When you decelerate your 
momentum (mV) is converted into a torque that is related to how far your 
center of mass is from the trolley. The harder you decelerate, the more 
torque you experience and the more likely you are to fly off the thing.

The Segway, manages your momentum by changing the torque angle inversely 
proportional to your rate of deceleration (that is to say you "lean back") 
which causes your relative torque moment to be 0 (or put another way it 
keeps your angular momentum 0) so that you perceive the declaration as 
increased acceleration along your vertical axis. This translates in a shear 
force on the wheels and ground.

Basically you don't fly over the handle bars because you are never being 
pushed toward them and conversely when it accelerates you don't fall off 
the back.

Now you could put a tilting platform on your trolley and have it do this 
compensation (think of a coffee cup holder for your that uses gimbals to 
keep the cup level in the face of changing accelerations.)

So to completely replace what the Segway does on a multiwheel vehicle is 
you would need to first have a platform that could roll over the kinds of 
terrain that a Segway does and can turn in place (this is essential for 
navigating human targeted environments), and then you need a hydraulic 
platform (or a fast electromechanical one) that could keep your inertial 
acceleration vector vertical in real time.

The neat thing about the Segway is that it does both of these with exactly 
two motors.

--Chuck





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