Subject:
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Re: (Un)steerable Shrimp
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 2 Oct 2001 10:58:00 GMT
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Viewed:
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623 times
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"Brian Alano" <lego-robotics@crynwr.com> wrote:
> Elijah Meeker wrote:
>
> > ...it seemed to me that wheel
> > height was a defining aspect of the shrimp design.
>
> It seems so from the literature, but I wonder if rocker length also
> plays a part. There probably is a rocker arm length to wheel diameter
> ratio beyond which increasing the rocker length doesn't do much good.
I agree. In my SHRIMP II version I reduced the length of the front arm from
16 to 12 studs, and this affected negatively the maximum height of the
obstacle that the platform can overcome.
> The seminal idea was to climb the obstacle one axle at a time. To me
> this implies that one set of wheels should clear the obstacle before the
> next set engages the obstacle. However, the SHRIMP at
>
> http://www.bluebotics.com/products/shrimp/
>
>
> seems to not require that so rigidly.
Actually the rule is not so rigid. A SHRIMP can climb obstacles with more
than a single wheel at a time. The higher the number of wheels moving on
level terrain (or even better descending an obstacle), the more the push
available for the other wheels to climb obstacles. The parallelogram
configuration of the bogies converts that push into climbing ability.
>
> > Steering issues:
> >
> > [snip] I don't have any micromotors
> > but I am hoping they will have suitable power for turning the turntable
> > via a worm gear. If anyone is sure they won't I would greatly appreciate
> > a heads up.
>
> I'm pretty sure they won't work. They are s-l-o-w and w-e-a-k. Suitable
> only for moving light loads slowly.
I totally agree. Micromotors won't work.
> I recently saw a chart comparing all the Lego motors by torque and
> speed. Sorry I don't have the URL, but I know it's out there somewhere
> on the 'Net.
Maybe this:
http://web.mit.edu/sp.742/www/motor.html
> > Going to separate motors for front and back wheel raises the issue of
> > sensors for each. I currently have a rotational sensor, but am thinking
> > that I will likely wind up using a light sensor with an encoder strip.
> > Again, any suggestions would be welcome.
>
> Being less ambitious, I plan to use touch sensors to signal the center
> point of the front and rear steering positions, and not worry about
> precisely matching angles between the front and rear beyond that. (To
> conserve inputs, I also plan to multiplex the touch sensors on a single
> input.) Mario Ferrari managed to mechanically link his front and rear
> steering, but his pictures seem to have disappeared from his web site
> (after apparently taking quite a ribbing from his Italian
> contemporaries, I might add.)
Here's a temporary page where you can find the pictures of my SHRIMP II :
http://www.geocities.com/mario.ferrari/shrimp2/shrimp2.html
A full description of it will appear in my coming book "Building Robots
with Lego Mindstorms".
> Thanks for the pics. The SHIMP, for all it's promise, is quite a
> challenge to build. Every picture helps!
I join Brian's thanks. Nice job, Elijah, and nice pictures.
Mario
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Message has 1 Reply:
 | | Re: (Un)steerable Shrimp
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| (...) Hmmm, any ideas on maximum length? (...) Well rats. Now I am back to a flexible connection between the front wheel and the body, or put another motor on it, the latter being far less desirable due to weight. Maybe Graiger's sells rare earth (...) (23 years ago, 2-Oct-01, to lugnet.robotics)
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Message is in Reply To:
| | Re: (Un)steerable Shrimp
|
| (...) It seems so from the literature, but I wonder if rocker length also plays a part. There probably is a rocker arm length to wheel diameter ratio beyond which increasing the rocker length doesn't do much good. The seminal idea was to climb the (...) (23 years ago, 2-Oct-01, to lugnet.robotics)
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