Some help and/or advice needed please


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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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

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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.

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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D Herring

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