Subject:
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Re: Has anybody successfully added an RCX to 7471 Mars Rover?
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Newsgroups:
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lugnet.org.ca.rtltoronto
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Date:
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Sat, 24 Jan 2004 07:31:57 GMT
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Viewed:
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577 times
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In lugnet.org.ca.rtltoronto, Kelly McKiernan wrote:
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My issue is how to motorize the wheels without making it look
stupid, ie having giant motor pods on the ends of the “suspension”.
You can’t do it with micromotors (not enough torque)...
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Have you actually tried it with six of them? Perhaps geared down? I know,
that’s criminally slow, but the real things only move (at top speed!) 2
cm/sec... I’ve only got 2-3 gear motors, but I suspect it might work for a
lighter version. I know this is getting away from the simple “motorize the
LEGO-supplied model” ideal, however.
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I’ve been thinking that maybe it could work (not optimally, but it’d move) by
redesigning the two center non-swivelling wheels with a motor on each, slaved
from the same RCX control. Properly geared down, it may have enough oomph to
move the full mass of the rover+RCX slowly, probably about the same speed as
the real-life version. That’s a lightly ugly solution. Other motors could then
use input to steer, point the PanCam Mast and comm dish, etc. At that point
it’d also be possible to put sensors on and write a “follow the line” program
too. But that’d undoubtedly take more time than I’ve got before mid-February.
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Well, halfway there!
I’ve replaced the middle tire assemblies with some stepped-down motors and
attached them to the actual unit. The wires are threaded up through the guts of
the structure and hooked up to the RCX. Success! It moves and moves well, at a
believable pace (not sprinting, not sluglike).
Note the removal of the middle tires in the above shot. The motorized assemblies
are at bottom. They’re a bit blocky, but once they’re mounted and the rover is
on its wheels, you can’t tell.
There’s a closeup of the motor itself. Note the motor axle uses a small gear,
which meshes with the much larger gear behind the tire itself. The motor is not
incredibly sturdy, but it does have 10 studs locked, which seems to be enough to
keep it solid while moving.
Using the above configuration, I was able to get it to move smoothly over the
carpet. The steering connections between wheels is very loose, and any little
bump in the road shifts a tire just enough to make it wander drunkenly. Kind of
fun to watch, really.
Now, to lobotomize the rest of the rover to fit in the RCX. The cavity is almost
exactly the width and length of an RCX, as if they designed it to work this way.
Most of the “extra” functions (unfolding the “arm”, moving the comm dish,
folding up the solar panels, erecting the mast, etc) need to be stripped to make
room for the RCX, if there’s any possibility of putting the central solar panels
back on flush. The above is my halfway-finished hack job. One note: I’m having
to redesign the outer structure to be sturdy enough to support the solar panels,
now that some of the central stuff is coming loose. I also need to find a way to
keep the steering mechanism unencumbered, which takes up the bottom half of the
body core.
It’s an ugly scalpel job that will leave scars, and frankly I don’t see how I
can make it any more fragile, but I’m shooting to have this completed by
tomorrow’s touchdown of Opportunity. Cross your fingers!
Kelly
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