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Old 16th November 2007, 20:16   #1
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Default Building a model car-need help with mechanism

Hi,
As part of my college technical fest,we need to build a small vehicle(max width-36cm and max length-about 20-25cm) which goes UP the slope of a wooden ramp with maximum speed and then goes DOWN the other side with minimum speed.Once set into motion,the vehicle cannot be interfered with i.e the mechanism should be such that it satisfies the above given criteria on its own.The vehicle can be powered by an xternal source.No microcontrollers and sensors can be used.
One of the ideas we discussed involved the use of a roller.The vehicle would have 4 DC motors,one for each wheel.As the vehicle goes up,the roller stays at the back;but as it starts going down the slope,the roller rolls forward(in between a pair of guideways) and hits a switch.This switch in turn makes the two forward motors start rotating in the reverse direction.
Another idea used a very simple principle.We use some sort of a lever that stays up during the upward journey and comes down(due to gravity)during the downward journey and strikes agains the wheels or the rotating shaft,acting as a hinderance.However,this wouldnt get us a lot of marks for creativity.
So now if anyone can help me with these ideas or give their own better ones,I'd be really greatfull!
Specifications of ramp:
Length of upward slope-120cm
Length of flat surface at the top-20cm
Length of downward slope-90cm
Max height-60cm
PS-I hope ive posted this in the right section!
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Old 20th November 2007, 12:35   #2
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Hi JugHead, this is a cool challenge Just curious though, the length of the slope you've mentioned, is this along it's length, or is it along the base ? That is, by 120 cms, do you mean the side of the triangle, or it's base ?

Whichever way though, looks like a nice challenge. The slopes are plenty steep, choice of "wheels" would be critical To have to crawl down the slope as slowly as possible, you could consider an "escape" wheel, like the ones found in clocks. I can think of a pendulum as a means to engage the escape wheel only on the way down.

Would it be possible to post pictures of your entry, as well as the rest of the field - once you're done that is...
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Old 21st November 2007, 01:36   #3
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1 idea stirked in my mind, dont know whether it will work or not.

go with your first idea and read the ending part [edited] of your idea below.

The use of a roller.The vehicle would have 4 DC motors,one for each wheel.As the vehicle goes up,the roller stays at the back;but as it starts going down the slope,the roller rolls forward(in between a pair of guideways) and hits a switch.This switch in turn will activate the two forward motors and deactivate the two rear motors. [this operation should happen at the same time.] Use the gears in it. in this operation while going up only rear motors should work and while coming down only front motors should work.

1.] while going up the hill driving gear should be big and driven gear should be small.

2.] while coming down the hill driving gear should be small and driven gear should be big.

But in this case you will have to use two DC motor [high power and high rpm] for going up
and two DC motors [normal power and low rpm] for coming down.
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