ZIPLINE PROJECT, make object travel 7.4 meters and back on a horizontal zipline

[ziplinegirls]

HELP PLEASE!

I have to create an object that will travel a straight, horizontal zipline of 7.4 meters, and then travel back .4 meters to the starting point.. The object has to be all mechanical (no electric power source) and can't weigh more than 2 kg. It also has to be pretty cheap ($50) to make/acquire. I don't have many ideas at the moment, except maybe using a balloon to propel it for one way. I don't know how I can make sure the object travels back to the starting point. I was thinking of using a spring to make it bounce back when it hits the wall after the 7.4 meter mark, but I don't think the spring will provide enough force for it to come all the way back. The object also has to be able to carry a set amount of weight on it for maximum points achieved.
Any help, ideas will be much appreciated! Thanks in advance.

:)

 

[iceworm]

HELP PLEASE!

I have to create an object that will travel a straight, horizontal zipline of 7.4 meters, and then travel back .4 meters to the starting point.. The object has to be all mechanical (no electric power source) and can't weigh more than 2 kg. It also has to be pretty cheap ($50) to make/acquire. I don't have many ideas at the moment, except maybe using a balloon to propel it for one way. I don't know how I can make sure the object travels back to the starting point. I was thinking of using a spring to make it bounce back when it hits the wall after the 7.4 meter mark, but I don't think the spring will provide enough force for it to come all the way back. The object also has to be able to carry a set amount of weight on it for maximum points achieved.
Any help, ideas will be much appreciated! Thanks in advance.

:)

4.5 lbs and $50 is a pretty tight budget. Let's see what you have to work with.

"a straight, horizontal zip-line ...and then travel back ...to the starting point" - so you don't get to trade any verticle heigth for energy.

The operation will require an energy source - both directions. Electric is not available. Is stored mechanical energy available? Clockwork spring, linear compressed sprng, compressed air bottle, little CO2 cartridges, dropping weight - anything like these?. Do you get to launch it? Or do you just set is on the zip-line and turn it on?

ice

 

[ziplinegirls]

hey , yea we can use springs, compressed air bottles, idk about CO2 cartirdges, probably not though. we can use pulleys, wieghts too.

 

[iceworm]

Now you will need a trigger. When the Rube Goldberg hits the end-of-the line - a trigger switches over to the driving the other direction. Hummm ... still sounds expensive.

How about two model rocket motors? Fuse the second one long enough to not light until after the contraption hits the end-of-line - a several second delay wouldn't hurt anything.

ice

 

[Xilor]

How about this system on a table using weights? Seems easy enough, start it by knocking the weight on one end off, and balance the weight on the other end of the table so a slight push will knock it off.

http://imgur.com/3EFtO

 

[ziplinegirls]

no we cannot use motors or the table mass system

 

[Zula110100100]

What is the extra mass it must carry and is there a time limit?