Subject:
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Re: Shrimp, Lobster & more...
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 27 Feb 2001 21:13:24 GMT
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Viewed:
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927 times
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In lugnet.robotics, Mario Ferrari writes:
> Like Xanthra47 wrote, there's still room for the first shrimp that can steer
> :-)
>
> On this topic I have some ideas. I would use the four central wheels like
> tracks, blocking the inner ones in the turn (or slowing down them) while
> keeping the outers at full power. This means some slippage is required but I
> think it can work. The problem are the two front and bottom single wheels,
> we really have to turn them to make turnings possible. Maybe two turntable
> controlled by a single motor that turns them in sync (but opposite
> direction)...
The mechanism to steer these two wheels in sync would be a bit tricky,
though, considering that the wheels are suspended independently.
An easier and more flexible way is to steer the two wheels separately, but
attach a rotation sensor to each of the wheels, and keep them in sync
through software.
If I understand it correctly, the original Shrimp has 6 degrees of freedom
in terms of motion control (i.e., it requires 6 output ports for motion):
front wheel driving
front wheel steering
back wheel driving
back wheel steering
left two wheels driving
right two wheels driving
When it turns in-place, the four middle wheels will slip. (See
<http://dmtwww.epfl.ch/isr/asl/systems/shrimp/sld003.htm>.)
In addition to the car-like steering and turning-in-place, you may want to
try some other interesting maneuvers, like "crabbing"... (Steer the front
and back wheels sideway, like when turnining in-place, but drive the two
wheels in the same direction, dragging the four middle wheels along.
Sojourner had done it on Mars.)
> I also wonder what happens when SHRIMP tries and turns on a very rough
> terrain or while over an obstacle.
>
> Mario
I am wondering the same thing.
Sojourner has 10 degrees of freedom in motion control (all the six wheels
are powered independently, and the four outer wheels are steered
independently). A later prototype, Rocky 7, simplified the design to 6 DOMs,
while introducing some slippage while turning, similar to Shrimp. (See
<http://robotics.jpl.nasa.gov/people/volpe/papers/Jr7.ps.gz>.)
But now NASA is switching back to the old 10-DOM design. (See the email
attached at the end, from a nice person working at NASA.)
Your Shrimp in Lego is very exciting! Not only is the mechanism ingenious,
it also looks practical enough to be incorporated into a full-featured
mobile robot, controlled by two or three RCXs.
Cheers,
Hao-yang Wang
---------------- Begin Forwarded Message ----------------
Date: 1/30/01 2:40 PM
Received: 1/30/01 2:51 PM
From: Richard Volpe, volpe@helios.jpl.nasa.gov
To: Hao-yang Wang, hao-yang_wang@filemaker.com
Yes, MER will have 4 wheel steering. Rocky 7 was a concept design
for reduced actuation mobility. MER decided to reuse the Sojourner
design, scaled up.
Thanks for your interest -- Rich
Hao-yang Wang wrote:
>
> In the movie from JPL' Mars Exploration Program web site
> <http://mars.jpl.nasa.gov/mep/missions/rover_movie.mpg>, the 2003 Rover
> is shown to steer all of its four corner wheels while turning in-place.
> Does this means this new Mars Rover will have 10 degrees-of-freedom in
> mobility like Sojourner, but unlike Rocky 7, which can steer only two of
> its corner wheels?
>
> Thanks,
> Hao-yang Wang
>
> (Sorry for this uninvited email. Please at least give me a quick
> yes-or-no answer. Of course I will be the most grateful if you could also
> briefly explain why. :-)
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Message is in Reply To:
 | | Re: Shrimp, Lobster & more...
|
| Like Xanthra47 wrote, there's still room for the first shrimp that can steer :-) On this topic I have some ideas. I would use the four central wheels like tracks, blocking the inner ones in the turn (or slowing down them) while keeping the outers at (...) (24 years ago, 26-Feb-01, to lugnet.robotics)
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