Subject:
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Re: Designing a bipedal robot leg
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 21 May 2002 01:44:39 GMT
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Original-From:
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Andy Gombos <{gombos_2000@earthlink.}StopSpam{net}>
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Viewed:
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830 times
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My comments are interspersed, with no delimeters. I hate OE. :P
----- Original Message -----
From: "PeterBalch" <PeterBalch@compuserve.com>
Cc: "[unknown]" <lego-robotics@crynwr.com>
Sent: Monday, May 20, 2002 5:27 PM
Subject: Designing a bipedal robot leg
Andy
> If you were to design a leg for a bipedal robot, how would you do it? • Would
> it have a knee, or a moveable ankle?
> Both.
Intresting. Sounds like that will solve many of my problems by itself. By
keeping the feet and ankles straight and flat, I had to move the weight a
great distance. By tipping the ankle, I may need to move no weight at all.
*Bot description clipped*
> Would you use pneumatics, motors and
> cables, or the various muscle wires or pneumatic muscles available?
> Motors. It's too hard to keep everything in the right phase using Lego
> pneumatics.
Wonderful. Of course I am using pneumatics to simulate a muscle more
realistically. I was going to use motors, but the weight and power transfer
issues were smaller with pneumatics. Hopefully there will not be a "phase"
per se, but rather a tipping of the ankle via a small cylinder, then large
ones perform the necessary walking motion. The ankle is let down, and the
step is taken. Without a precise timing requirement (my earlier bot
required ~.5 second between the foot leaving the ground and the foot
touching the ground to remain stable, almost impossible for any Lego device
with any precision. Much engineering has gone into allowing the cylinders
to fully extend and retract along the full range to create the movement.
This should simplify the control issues a bit.
> Would shortening the distance between the legs
> help in this?
> Do you mean the side-to-side distance between the legs? Yes. The closer
> they are together the easier it is to transfer the weight from one to the
> other. All bipedal walking animals keep their feet as close to the centre
> line as they reasonably can. Only bipedal hopping animals keep their feet
> apart.
Perhaps that will lessen the COG shifting requirements too. My first model
was the maximum # of studs wide - the length of the longest Technic beam.
> As an aside: I also attempted 6-legged walkers. I initially assumed that
> they should be steered by taking longer or shorter strides on the left or
> right sides. It doesn't work at all well. The design assumes that the • front
> and rear feet will slip sideways. However, the forces generated by the
> longer strides are insufficient to overcome the sideways friction. The • feet
> slip but forwards and backwards - not side to side.
> My eventual successful design used Ackerman sterring - like a car's front
> wheels. The front legs of the walker could turn to one side of the other.
> It's tricky to get the drive to then while they are turning; the drive
> shaft must be the same "kingpin" that each leg steers on. Ackerman • sterring
> at both the front and rear would be even better.
Different steering methods are needed for different kinds of robots. The PDF
"Where am I" provides a good overview of the drawbacks an advantages of
different types of steering and locomotion - unfortunatetly it does not
discuss walking robots, although the Ackerman design and equations are
listed.
Thank you for all your help - perhaps I will get it to work this time.
Andy
> Peter
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Message is in Reply To:
 | | Designing a bipedal robot leg
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| Andy (...) Would (...) Both. Many years ago, in the days before RCXs, I constructed a few walking bipeds with knees. I found the problem with swinging a large weight around to maintain balance was that the momentum of the weight often toppled the (...) (23 years ago, 20-May-02, to lugnet.robotics)
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