5 replies to this topic

[JustFloating]

Hi there, my name's Tim. I'm currently a mechanical engineering student at Cal Poly, and we build a float every year to be in the Rose Parade in Pasadena. I was recently put in charge of animating the train on the front of the float. (Here's a picture of the concept for the float; you can see the train on the red suspension bridge: http://www.asi.calpoly.edu/rose_float)

So what does this have to do with ski lifts? The train is going to be running back and forth down the track, and we decided the best way to animate this would be to have a series of pulleys running the length of the track housing a steel cable that would be attached to the train at one point, kind of like an upside-down ski lift.

I've thrown together a test track in our lab to help me get a finalization of what I'll design.



There's a 12 degree incline with a 30 degree bend in the track immediately after, which lends itself to some tricky geometry with the pulleys (pay no mind to the nylon pulley, it's currently serving no purpose).

Here's a picture of the kind of pulleys and cable I'm planning on working with:



What I've been stumped on is figuring out the best way to attach two ends of the cable, as well as figuring out how to attach the train to a section of the cable, without causing the cable to derail off the pulleys. I've thrown together two pulleys and the train being pulled by rope, and this issue kept cropping up. Any advice you folks could offer would be greatly appreciated, even if it's just pointing me in the right direction to figure out more. Let me know if you need to know more,and here's the album with a few more pictures: http://imgur.com/a/K5ikm#0

Thanks for reading, cheers!

[Kelly]

I think what you’re saying is you want to attach the “cable” to “itself” and to the “car” and have it go around the pulley’s.
I am not sure if the pulley’s and cable have been purchased or were selected from the supply bin at the school or are materials that were given for the preliminary design stage…but perhaps there is a simpler way…
 1700-german-carriage.jpg (125.16K)
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I see a potential problem with the size or diameter of the cable…I suspect it will be too stiff and heavy to be of much practical use.
That’s ok, a cheaper and better solution is available.
The construction ropeways in the renaissance period in Italy used fiber rope with great success (actually everybody did until steel was invented) as it is more flexible and much lighter.
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You can find hemp, cotton or manila rope at the local hardware store or on your neighbor’s clothes line. The more flexible the better.
Also used in that time period was the idea of vertical pulley’s. They self align the rope and support the rope…in fact the horizontal bullwheels seen on ski lifts is somewhat a newer concept.
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For the drive pulley friction I suggest using less tension and a double wrap around the drive pulley. I have a friend Craig who has a tram in his office that works just fine on very low tension.
For attachment to the car, try a stiff leg slightly below the wheels but above the cross supports – you can splice or connect the rope at this point.
Don’t worry about rope wear at the bend, as this only has to last a few hours, no pulleys are needed at the mid-span but one might be needed at the “return” pulley for guide issues.
 Bombadier-ropeway.jpg (63.96K)
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All of this is shown in the highly detailed CAD drawing below.
 Float-tramway.jpg (24.76K)
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[JustFloating]

Thanks for the response! The cable was not purchased, I found it lying around our lab. We actually did try rope originally, however it kept derailing at the ends since I think it was too thick for the pulleys I was trying it on. I'll look into trying some rope again, this time with a smaller diameter.

I was planning on using a couple of vertical pulleys to align the rope during the incline. I want to use horizontal pulleys at the two ends, since the cart is going to be running continuously up and down the track. Here's the movement I wanted:

http://i.imgur.com/7KDu8.png

For this reason, I don't think double-wrapping the cable on the drive pulleys would be possible.

I'll try out a low tension system with rope, as you suggested. Thanks for the advice, this was all incredibly helpful!

[Lift Dinosaur]

Where is your power supply going to be? You could locate in mid track, use a capstan pulley and have a motor capable of reversing direction. Attach the rope/cable directly to either end of the car. Limit switch at each end to reverse the motor.
Maybe?
Dino

[Kelly]

Dino has a pretty good idea…Also there is nothing that says the “end pulleys” have to be perfectly vertical or horizontal – you can tip them to compensate for the rope position in the slight curve.
Although not ideal this does occur with ropeways.
 Sheave-Plumb.jpg (13.04K)
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Same would hold true for his idea of drive sheave placement.

[Kicking Horse]

How did this project go for you?