Actually, the only problem I saw with this myth was not the line itself, but the application of it. Using the grappling hook to turn the Mythmobile is entirely possible, even with the nylon rope or the steel braid cable. The strength rating of the line is classified using the total force the rope/cable is capable of holding before snapping. The problem with using it in this situation is that it's not just easing weight onto the line, it's actually a type of collision with instantaneous force being exerted on it.
According to physical properties of collisions, an increase in overall collision time leads to a decrease in force experienced. This is the basic concept behind airbags and padded dashboards. Same overall momentum, but more time for the body to absorb it without breaking. That can be applied to this situation as well. If a high-performance spring were to be included in the line setup, added time would be present to decrease the instantaneous stress on the line, making it less likely to snap.
As for placement of the line, try swinging a pencil on a string. If it's at the front, the back of the pencil swings away from the fixed point. If it's at the back, the front will swing forward. The only place that keeps everything tangent is at the center. They had it just fine.
I hope the mythbusters try it out again, and best of luck if they do!
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He's right. You would need to address the situation from a race car stand point or better yet a go kart standpoint. Assume the rear axle is a spool so one would need to raise or stop the inside wheel while transferring the weight to the outside wheels so it can essentially rail the corner.
So how would you do that? I would set up a triangular system under the car that actually connected to the opposite frame rail, which in turn could be tied in to a roll cage specific to the drivers side that would spread out the force.
I wouldn't use anything that was as static as you were using and although the iron structure was sweet, it might be a little rigid as well, just adding to the tremendous pressure applied which obviously smoked right past the yield point of the cable, clamp, Hook, or whatever. That spike is far too severe.
Webbing or one of the super threads or (silks) I should call them could be used as a buffer to slow the load down so as to reduce the final spike load on the vehicle and hook which just may allow the vehicle to take a stance that would facilitate cornering.
I think "busted" is incorrect. With all due respect.
I think that when the mythbusters were testing the 90 degree turn that when u turn u move into the second lane they only had one lane and therefore it is impossible to make that turn!!!!!!!!!!!!!!!!!!!!!!!!!!!
Originally posted by iceykola: the car needs to be RWD and the cable needs to be attached to the front of the car in order for it to help the front of the car turn and direct it. They did a horrible job of testing this myth. I think it can still be done, if they did it right.
i agree with everyone on the placement of the cannon. more to the front would be abetter place.
as for the cable. the cables or rope they used would have worked if there was a type of spring on the mounting instead of just hard mounted. that would absorb the intial shock and not snap the cable
ok those saying that you have to put the Cannon at the front of the car are very correct, it also has to be LOW on the car, as in hooked to the Frame behind the front wheel, by having past midpoint you are jerking the back end of the car, and forcing the Front End to go the Opposite Direction, also those saying using a bungie type cord, i would say even better is along the Snatch Em Strap, something with some Give to ease the intial shock but not enough stretch to let the car keep going straight
I think everyone is on the right path. I think webbing is the correct material, maybe with a less dynamic core made from something that will limit the range it stretches. You probably could get away with an innter cable if you could just get the firces smoothed out and someone who understands vehicle dynamics.
I disagree with that the placement of the cable was wrong. I think that the major thing would be to keep the the entire car in control. Too far forward would cause the rear to swing out, to far back would cause the front to swing out.It's the same reason that it's easy to fishtail in a RWD car. There has to be control to the rear as well, otherwise the entire car is out of control.
The cable needs to be moved to the front half of the car. Since it is behind the center of the car it will pull the back of the car towards the grappling hook, making the car turn left. If they put it at the front of the car it will turn right and the cable will have a better chance of surviving. This one needs a retest.
if they would have known how to take the turn they would have been able to take the 3rd gen F-body and make a 90 degree turn at 35 tires squealing and a tiny fish tale. I own a 3rd Gen Fbody and I take High speed turns daily and I know those car like the back of my hand. if you watch when they made the turn they hesitate on the turnand nail the throttle to the floor. you cant even do that with a race car. it pushes the front wheels. to top that the ground had a crap load of rocks all over it. they positioned the grappling hook in the wrong place on the Camaro.they put it toward the rear wheels more then the front.to make the car do the turn with the cable the setup needs to put toward the front of the dooror atleast around that area.
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The problem with this segment wasn't the selection of the rope (although that could have been better) but with the design of the experiment, which (as much as I hate to say it) falls squarely on Grant in this case. From what he says in describing the initial selection of the rope, it sounds like he was using an idealized calculation for determining the centripetal force, i.e. a single point mass X, traveling at speed Y, being pulled around a 90 degree turn with a radius of Z. This, and the subsequent experiment design, fail to account for a few things. The first is that the Mythmobile isn't a a single point mass with no outside influances other than the rope. Connecting the rope to where they did on the car may have been fairly close to the center of gravity in that axis, but it fails to account for the affect of the tires. I believe, as others have pointed out, that it would have worked better in this case to tie off to the front right hand corner, which would allow the trailing center of gravity help "swing" the rear of the car around; the question would be how far forward you could go with the tie off point before inducing uncontrollable oversteer. Second, and in my opinion the major reason for the rope/cable break, is that the calculations were assuming a turn that began when the mass had drawn even with the tie point for the grapple and with a cable/rope that was perfectly taught at that point (i.e. that at the moment the car begins the turn the car is still traveling parallel to its original path, the cable running from the solid object to the car tie point is perpendicular to the car's original path, and all slack has been taken out of the cable). Instead, since they were dealing with a fired cable with the slack taken up by the car's foward motion is that the angle between the taught cable and the car's direction of motion was much less than the optimal 90 degrees (90 degrees to original direction of motion providing the most mechanical advantage on the car with the least load on the rope, 0 degrees providing the least/no mechanical advantage and the most loading, which would be like tying the cable to a pole and then driving directly away from it, and I think we know what happens when you do that). If the angle is much less than 90 degrees, the loading, especially the initial shock loading, on the rope/cable is going to go up dramatically. This is one of those experiments where I believe they should have broken out the controlable and non-controlable elements into two parts, then maybe combined them. A better way to test would be the cable being reeled in from the anchor point. As long as the winch (which wouldn't need to be too strong) could take in line at the same speed as the car was traveling, the line should always be taught. As the car drew even with the anchor point, the rate of line takeup would hit zero. Triggering off of that, you could have a hydraulic or pnumatic ram clamp the line, allowing the car to arc through the turn. You could even set it to trigger a quick release or line cutter when the line had arced through 90 degrees. It's really too bad that too many unnecessary variables were introduced into the design, but it's worse that the failures of the design weren't explained after the failed experiment and instead it was busted on the basis of the ropes and cables breaking.
Kudos to Mythbusters for putting on such a great show. Mythbusters is my favorite tv show.
I think calling the 90 degree turn busted is a bit premature. Try utilizing a brake drum to ease the instantaneous load on the cable. After all, a cable-arrest system is used to stop a flying jet on aircraft carriers, which isn't that different of a problem to solve than the 90 degree turn. I'm sure this is, at the very least, plausible.
No cable no mater what the tension could withstand a force of this magnitude.. static weight yes.. but dynamic weight is much different. think of an aircraft carrier.. the cables that stop the plains don't instantly pull all the tension of the aircraft.. it gradually increases tension by paying out cable.. if this type of idea could be replicated on a smaller scale.. is it plausible now?
With regards to the ideal location of the rope on the car:
The pencil analogy is correct, except we are not spinning a pencil, we are spinning a car. The rope should be attached in the place where, if the car were suspended by the rope, it would hang perpendicual to it (i.e. the center of gravity).
This would undoubtedly be closer to the front assuming the engine is responsible for the majority of the weight of the car, but this is supposition.
If they had found the balance point with the car upright (using a log or something), it would be very close to the sideways balance point.
To stop the rope or cable from snaping, the mythbusters should use more then one rope. Like in spiderman 2, spiderman needed to use more then one web to stop the runaway train. With more ropes the stress will be distributed across all of them, instead of all the stress on one. One rope should be mounted in the front, one in the middle, and one in the back. Each rope would have to be a certan legnth so the stress would be even. If the ropes still brake at the hook, the mythbusters could try three hooks from three or more cannons mounted at varius points on the car.
aite this my first post so w/e ya know, for the car you need to use a spectra fiber rope created by Honeywell. It is strongest rope on world for its weight.
Please revisit this, it would have been soooo cool.
Suggestions: - A front-engine car like that needed the tow line probably somewhere between the front seat and the engine. The line needs to point close to the car's center of gravity or else the torque will rotate the car out of control.
- Anything to ease the impact force would have helped the cables from snapping. Other posters have great suggestions... springs, bungees, braking drums, etc.
- The closer you can get the cable to grab when the car is dead even with the structure, the less of the car's momentum that cable will have to fight head on. Work on timing.
- Some other posters suggested doubling up the cable at stress points and using different knots to secure the rope/cable. Reducing the impact force is probably enough but every little bit helps.
- Please be careful! That nitrous cannon could have easily killed you in the shop.
Considering that the car was not at 90 degrees to the car when the chord was tensioned (it was closer to 30 to 45 degrees) the impulse force caused by trying to snap the car around was well over the breaking strength.
At 30 degrees the impulse force in the cable would be about 47000 lbf and at 45 degrees the force would be about 38000 lbf. Either case it is well over the 15000 lbf which the cable used is rated for.
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