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Porsche Trebuchet

Kinetic energy is good energy.
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I have been thinking of trebuchets again after watching one built on Junkyard Wars. I am struck by several things. It seems to me that it is hard to hoist a heavy weight up and hold it there. I do not have a good feel for how a trigger for such a device would be made; I do not think I could make one. Another thing is that devices which store potential energy in a thing which then releases it with a conformational or positional change (weight, spring, pneumatic pressure etc) are dangerous!

Much potential energy can be developed by a moving vehicle, and technology to control this energy is very mature and cheap. I think a car could be used to provide the kinetic energy to fire a trebuchet. As opposed to potential energy stored in a counterweight and released, the short arm of the treb would be tied thru a fulcrum at the ground and from there to a car. The car (here a Porsche because of rapid acceleration and so shorter tether, as well as snappy name) would race away and on reaching the end of the tether, transfer the acceleration into the short arm. Much more energy would be transfered than with a falling weight. Steel construction would be necessary to withstand the forces transferred.

Thinking about practical matters, this would be tough on the car frame and the treb. Also if the year is 1560 there may not be cars available or you may want to conserve the one you have.

Modifications: 1. Instead of direct to car, treb is hooked to wagon / trailer load pulled by car. Before tether ends, shorter subtether pulls pin and releases car from load. Car continues on to get clear. 2. Treb short arm releases tether at maximum excursion, so machine to not pulled over by remaing force in load. Load may have some sort of drag brakes. 3. If cars in short supply, loaded wagon pulled by horses may be substituted for car.

Punking Chunkin rules do not seem to prohibit use of a car. For simplicity and because this contest takes place in a field, one could use an old truck or offroad vehicle capable of speed, where frame integrity was not a great concern.

bungston, Jun 21 2010

Pumpkin Chunkin rules. http://www.punkinch...chunkinrulesv10.pdf
[bungston, Jun 21 2010]

Jeremy Clarkson http://www.streetfi...gly-cars_150806.htm
in action..... [xenzag, Jun 21 2010]

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       Yeah, a 600hp engine probably would come in handy.
rcarty, Jun 21 2010

       Pulleys might be used here to avoid a ridiculously long throwing arm / tall tower.
bungston, Jun 21 2010

       [neutral] I was hoping for a Trebuchet that threw a Porsche. :)
goldbb, Jun 21 2010

       Thinking about war machines again, it might be more practical to have the loaded wagon travel at a right angle to your trebuchet - otherwise the wagon is travelling towards your target and assuming you have pulled your device as close as you safely can to your target, your horse and rider will get closer than is safe.
bungston, Sep 26 2011

       Why not use a rocket?
pocmloc, Sep 26 2011

       Or drive the Porsche up a steep see-saw, then release the see-saw when the Porsche is at the top, thereby lowering said Porsche and lofting the projectile.
MaxwellBuchanan, Sep 26 2011

       Thinking that using a motor vehicle or complex arrangement of horse/cart, ropes pulleys etc is simpler or easier than just making a simple sear trigger is very halfbaked indeed.   

       I have made several small trebs and I can tell you the trigger is probably the most simple component. In the middle ages they simply used a rope they cut. I used a rigging device (can't remember what it's called, works like a release aid for archery where a release sear is built in and it's designed to release under load with minimal sear force) - simple cheap and reliable.   

       Anyhoo, if you want to use a car, I'd advise against going from standstill - that means you need max HP as it's a limited stroke. I'd use a snatch strap and extension. This is basically a very strong elastic band used for 4wd recovery. Give the car a bit of runup so the snatch comes tight at a moderate speed and the strap will do the work. May want to build in a load release so that you don't haul the car back into the treb.   

       Now I'm thinking using a light truck or 4wd as an energy source for a trebuchet. Very dodgy indeed.
Custardguts, Sep 26 2011

       Would it maybe easier to just drive the Porsche at whatever it was you wanted to trebuche?
MaxwellBuchanan, Sep 26 2011


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