Subject:
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Re: SHRIMP building was: Re: High Strength Powered Steerable pivot wheel
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 22 May 2001 10:54:39 GMT
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Viewed:
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970 times
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"Brian B. Alano" <lego-robotics@crynwr.com> wrote:
> "Nickle, Steven (2511)" wrote:
>
> > A steerable shrimp is a challenge.
>
> In the near term, I've opted out of the "steer in place" requirement. That • way I
> go from four outputs to two. With an 8-wheel SHRIMP, I steer like a • four-wheel
> steered (FWS) car does at low speed. Also, I don't have to worry about the
> friction of skid steering, which I found to be a major problem in my • 8-wheel
> Micro-SHRIMP (micromotor-powered SHRIMP).
You drive all the wheels together in the same direction (first output), and
use a motor to steer the front and rear groups in sync (second output). Is
this what you mean? Very clever. You cannot steer in place but I suppose
this is not going to be a strong constraint, considering that in place turns
would probably be not possible anyway on the rough terrains SHRIMP is
designed for .
> > Also the number of motors keeps things interesting
> > also.
>
> I'm concerned about the power drain of my nine motors (9 x 250ma? = • 2250ma!). I'm
> thinking about powering the drive motors from a large battery box • controlled by a
> micromotor and polarity switch. But that will add so much weight, maybe • two 9v
> battery boxes in parallel would be better...
>
> What's been the experience of those who have run that many motors • simultaneously
> from the RCX?
My SHRIMP worked pretty well when driven by the RCX, though not showed in
the pictures. I'm currently working to a 4WD rover that features a motor for
every wheel, and the RCX has no problem in supplying them. When you double
the numer of motors, their individual load halves (well, not exactly, we
should consider friction) and the drained current decreases accordingly. I
suspect that your nine motors will absorbe much less current than 250mA
each, unless your SHRIMP is climbing a very steep slope.
Since you used just two output ports, you could split your 8 traction motors
in two groups of four wired to separate ports.
I wouldn't add a the weight of six more batteries in a battery box. The
additional weight would reduce a lot your ability to climb obstacles, and
would make weights balancing much more challenging.
If you're open to some non-Lego solution, you could use the same group of
batteries to supply the RCX *and* the polarity switch for the motors at the
same time. You can take the power directly from the batteries inside the RCX
using an external wire (no harm to your RCX and no need to modify it). Or if
you own an RCX 1.0, you can use a battery box to supply the switch and the
RCX through a custom cable.
Mario
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Message has 2 Replies:
 | | Re: SHRIMP building
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| (...) Yes, something like this: | is a wheel pointed straight, \ and / are wheel turned left or right = is the body Going straight: | | |==| |==| | | Turning left: \ \ |==| |==| / / Turning right: / / |==| |==| \ \ Disclaimer: I haven't actually (...) (24 years ago, 23-May-01, to lugnet.robotics)
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