Subject:
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Re: Fishing for a tasty linkage/gearing/robotic building thread...
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 13 May 1999 16:13:16 GMT
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Viewed:
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1654 times
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"S. Crawshaw" wrote:
> On Thu, 13 May 1999, Paul Speed wrote:
>
> > Or third, a synchro drive constrained to a ninety degree
> > throw. This is simpler than the independent wheels since it doesn't • <snip>
> > The most complicated part of this will be getting the drive train
> > snaked through whatever rotation assembly you have. Most of the
> > synchro drives you will see examples of use the turntable pieces.
>
> Surely the only reason there's usually complication is that the assembly
> needs to be able to rotate any amount in either direction. If 0-90 degrees
> is the total range, then there are lots of really simple solutions.
>
> [This next bit is irrelevant to the 0-90 constrained synchro drive]
>
> > I do not have any of these so I have experimented with several
> > other linkages. I won't go into them here... they are an
> > implementation detail.
>
> That's a bit of an understatement - and I'd love to hear how many other
> ways you found to make a synchro drive: I've only heard of one way
> that doesn't use a turntable (uses a differential instead)
I have a fully functional version that doesn't use either - or any special
parts. I wish I had a digital camera to take some decent pictures. I have one
photo taken with a Polaroid. I'll put it on my web site tonight. In the mean
time, I'll try to describe the method here. I highly recommend "Sensors and
Methods for Mobile Robot Positioning" by J. Borenstein, H. R. Everett, and L.
Feng to anyone doing this type of construction. Syncro Drive discussion is
located in section 1.3.4.
The problem to solve is getting power to the drive axle while maintaining
rotation of the same axle. In my solution I use the vertical power shaft as the
only support for the drive assembly. As you will see, the lack of structural
integrity is compensated for by the steering mechanism, which limits the design
by only allowing approx. 170 degrees of turning. Quite a limit for full syncro,
but quite acceptable for the 0-90 needed by this discussion.
(Use a non-proportional font for all diagrams)
The single drive structure is quite simple - the ascii art makes it look
complex :)
A
P A P
*********A*********
* A * A - power axle
W * A * W D - drive axle
W * A * W F - free wheeling axle
W * A * W G - 90 degree gearing
W * GGAGG * W P - steering posts
W * A G * W W - wheels
DDDDDDDDDDDDDDD FFFFFFFF
W * G * W
W * * W
W ************* W
W W
W W
(side view)
This depicts a vertical power axle, a 90 degree gearing, and a horizontal drive
axle. Note that the drive axle only extends to one side of the structure - the
opposite side is a free-wheeling axle for a second wheel to be attached to
provide stability - only one wheel is driven.
The 'P's at the top are the key to steering. These are posts to which are
attached rods which converge at the center of the mechanism at the steering
column; which uses idler arms to push/pull the rods and in doing so, rotate the
syncro structure.. The steering linkage also provides quite a bit of added
stability.
WWWWWWWWW WWWWWWWWW
. .
P----------------*----------------P
..... I ..... A - power axle
. . I . . I - idler arms
. A . S . A . P - steering posts
. . I . . S - steering column
..... I ..... W - wheels
P----------------*----------------P
. .
WWWWWWWWW WWWWWWWWW
(top view)
Steering works by turning the steering column. Be aware that the steering
linkage must be located above the wheels; the rotation of the assemble will
bring the wheels underneath the linkage.
Steering four sets of syncros can be accomplished by locating two sets of idler
arms offset by 90 degrees on the same steering column. They must also be
displaced enough to prevent the steering rods from interfering with each other.
I can provide further details if anyone is interested. I will also place a
description on a web page if there is any interest. I have not up until now for
two reasons: lack of photos, and design limitations. This design has some
severe limitations in steering ability which would be lessened if it could
obtain a full 180 degree turning angle.
-Wes
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