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DPRG: Eric's walker

Subject: DPRG: Eric's walker
From: Eric Yundt eric at sssi.com
Date: Tue Mar 23 14:52:18 CST 1999

David Philip Anderson wrote:
> 
> Howdy
> 
> Eric,
> 
> >  http://www.doorbell.com/yatu/images/leg_lines_full_stroke.gif 
> 
> most cool!  

Thanks!  I'm going to shrink it a little and put both front and
back leg-lines together in syncrhronous harmony for a zen-like
demonstration of YaTu4b's standard stroll.

> 
> How does the walker turn? 

Vertical turns should be pretty easy.  I think I'll be able to walk up
a 12-15 degree rise fairly easily -- with a 2 DOF belly balance and
super-grip shoes perhaps even up a 20-25 degree rise.  Walking downhill
I'll be able to handle a degree or two more on the drop (COG is shifted
slightly back of physical center.)

For regular turns in the horizontal I'm going to first attempt the YaTu
shuffle.  If that doesn't work well enough I'll break down and add an
additional passive degree-of-freedom to each (? hmmm...) leg.  If that
doesn't work, I'll take the normal route of 3 DOF per leg.  I had hoped
to originally just go straight for the 2 active and 1 passive DOF per
leg, but I left enough freedom in the design to add the additional DOF
per leg if needed so I figure I'll first try it 2 DOF per leg.

There are several forms of the YaTu Shuffle but they all are somewhat
based on the 4-legged soldier's about-face twist/slide move.  For
example, starting from YaTu's standard end-of-stride stance...

END-OF-STRIDE STANCE (EOSS):

      4
        +---+
        | ^ | 2
        | | |
        | | |
      3 |   |
        +---+
              1

A right turn could (still "in theory" FBO Barry's belly) be done like...

For definition:

        (#) - leg fully lifted
        {#} - leg dragged (partially lifted)
        --> - arrow indicates direction of push
              (opposite of leg movement)

RIGHT TURN FROM EOSS:
====================================

               
     (4)       
        +---+ 2         All at the same time, the left back leg
        |  /| |         pushes forward, the right front leg pushes
        | | | V         backwards, the left front leg is lefted and
      ^ | | |           the right back leg is barely lifted and 
      | |   |           with body shifted slightly is left to drag
      3 +---+{1}        backwards.
       
       

Or another way this might work... is tanklike:

      ^
      |
      4 +---+ 2         The left side legs all push forward at
        |  /| |         the same time the right side legs push
        | | | V         backwards.  This does require slippage.
      ^ | | |           Slippage could be accounted for by having
      | |/  |           the flexibility provided by a 3rd passive
      3 +---+ 1         degree of freedom if need be.
              |
              V

Another way might be the rearing horse/pirouette method...  This
is best demonstrated from the standing-up-straight stance (SUSS):


      4 +---+ 2         This method really demands good shock
      | | ^ | |         absorbtion.  It begins with a backwards
      V | | | V         lunge using the 3 legs not on the rear
        | | | ^         turn side.  It can be enhanced greatly
        |   | |         with a 2 DOF belly balance.  The right
      3 +---+(1)        back leg is lifted and moved back.
      |        
      V        



     (4)+---+(2)        At the critical point of the back-lunge
        |   |           the right back leg is planted and pushes
        |   |           backwards, the left back leg pushes 
      ^ |   |           forward, and front two legs are lifted.
      | |   |           This creates a twisting wheelie motion
      3 +---+ 1         that lands with Robot slightly turned.
              |
              V


I'm still working out the physics of the break-dance turn method
but it looks promisihg, especially for situations where there is
not room for a large turning radius and no room for rearing back.

Oh well, any other ideas?


- --
Eric  -  yatu at ytech.com                         _mm_==_ F      .___   
                                             [===========]     |   ---__
First he could roll and then he could walk.   |\ \888/ |\      | DPRG  _--
A bit more brain and soon he will talk.       | \      | \     |---__--
                                             /  |     /  |     |
http://www.dprg.org/yatu                    /_  |_   /_  |_    |

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