Some help and/or advice needed please

Posted by Scordicus on January 26, 2009, 6:56 pm

Hi,

Although quite used to electronics, I have never ventured in to the world
of robotics and I have an idea which I would like to implement, but I
don't know if it's possible, so I would really appreciate some advice
before I blow wads of cash on something that may not work as desired lol..

OK, here's what's required.. I'm building a model dockside railroad that
has a roll-on roll-off ferry that will move a few box cars on it, I wish
for the ferry to wait 15 minutes, move away from the dock turn through 90
degrees to reach it's opposite point (it's not a sharp turn) and come to
rest about 14-16 inches away from where it started. Wait 15 minutes, then
return to the point of origin and start the cycle over again. This process
would be relatively slow, as ferry's are!

Now the ferry is 12 inches long and 6 inches wide so space underneath for
a drive mechanism is not really a problem. I thought about using something
like a line following robot although without going in to it too deeply, it
seems that they only follow white on black or black on white.. Water is
blue or blue/green so that presents one problem.. The second problem is
how to get it to reverse along the same line, and to move smoothly and
slowly.

Is it possible to enable a line following robot to run in reverse? Or
would having two (one at each end underneath the ferry, dragging the other
when idle work?)

Would a line following robot be accurate enough to line up the railroad
track when it returns to the docks if it's moving slowly enough? If so,
how thin could the line be?

Is it possible to build some thing that would accuratley home in on an
infared beam or laser? Or something similar to do away with the line?

Any advice or suggestions would be more than welcome to help me out with
this particular project.

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Posted by cadcoke4 on January 26, 2009, 7:23 pm

On Jan 26, 6:56 pm,
webmaster_at_budgetwebsiteservices_dot_co_dot...@foo.com (Scordicus)
wrote:

> I wish > for the ferry to wait 15 minutes, move away from the dock turn through 90
> degrees to reach it's opposite point (it's not a sharp turn) and come to
> rest about 14-16 inches away from where it started. Wait 15 minutes, then
> return to the point of origin and start the cycle over again.

If I understand you correctly, the ferry starts with its side against
the shore. Then, it moves sideways for a short distance before
turning 90 degrees to travel the rest of the distance.

I don't see a need for robotics in this instance, unless you want to
do so just for the sake of demonstrating the use of robotics.

I suggest that you use 2 underwater cables, one attached at the bow,
and the other at the stern of the ferry. A wench system pulls the two
cables in parallel, to pull the ferry away from the shore, and then
the one attached to the stern lags behind a bit, to force the boat to
proceed normally. A similar process happens at the other end. It may
be necessary to add some additional hardware to force them to not get
hung up, or pivot the wrong way. Perhaps the two connecting points are
not exactly center, but towards the left and right sides
respectively. Then, you never permit them to get so close to each
other that the ferry might turn the wrong way when it does its 180
turn.

It may also be possible to do this with one underwater cable. But,
cause the ferry to turn parallel by putting some mechanical apparatus
underneath the water at the dock side. But, I don't have a good idea
about that off the top of my head.

Joe Dunfee

Posted by D Herring on January 26, 2009, 11:50 pm

Scordicus wrote:

> OK, here's what's required.. I'm building a model dockside railroad that
> has a roll-on roll-off ferry that will move a few box cars on it, I wish
> for the ferry to wait 15 minutes, move away from the dock turn through 90
> degrees to reach it's opposite point (it's not a sharp turn) and come to
> rest about 14-16 inches away from where it started. Wait 15 minutes, then
> return to the point of origin and start the cycle over again. This process
> would be relatively slow, as ferry's are!

...

> Would a line following robot be accurate enough to line up the railroad
> track when it returns to the docks if it's moving slowly enough? If so,
> how thin could the line be?

Alignment is questionable; it may be helped by angled guide wires
sticking out from the port. The lines usually need to be fairly
thick, maybe 1/4" or 1/8". With experimentation in materials, it
should be possible to use an infrared line which isn't human-visible.
Line tracking can conceptually go both ways, but most kits assume a
single direction.

> Any advice or suggestions would be more than welcome to help me out with
> this particular project.

Idea 1: Attach your ferry to a locomotive engine and have it drive
slowly across a stretch of track set below ground level. Then you
don't have to mess with a whole different system. When things break,
you have spares and expertise handy, and you know the alignment should
be good.

Idea 2: Use a jigsaw to cut a curve through a sheet of blue plastic.
This curve is now the track for your ferry. Attach one or two
pieces of thin piano wire to the fairy, pass them through the plastic,
and attach them to washers on the other side. Use a pulley system to
pull it back and forth.

Idea 3: Attach strong magnets to the base of the ferry, put it on a
thin non-ferrous sheet, and use strong magnets on the other side to
move it around. Again use a hidden track or the like. May require
wheels or bearings underneath the ferry. This may have alignment
problems.

Idea 4: Mount the ferry to the floor; move the table around it. ;)

- Daniel

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