Personally I agree the launcher needs to be towards the front, say behind the front tire. In the first test when the cable snapped just the front end tapped the boxes, if it had of been pulled around first, it would have been out of the way even with the line snapping. As for the rear end, if you ever have gone to your local race track and seen them race, their rear ends can get way out but they can still handle them and keep them under control, so even if the rear end swung out it would not be impossible to pull it back into control. Also, it appeared that both kinds of cables snapped at its connection to the hook. I believe if you had a loop in the hook adn doubled back the line and connected it where other side was connected on teh car it would solve this problem and give more strength to the cable

Plem is correct on this. The back is where the greatest amount of weight is located and least possiblity of turning. Attempting to turn the car from the back does not make sense. Placing the anchor point closer to the front of the car will help guide it.

It was great to see you guys going above 120 PSI to build the cannon part of this. But PLEASE check out the necessary safety precautions before doing it again! If you are going to use experimental gear that has not been hydraulically tested, then you need to activate everything by remote control from a solid bunker. You need an outdoor test, the very minimum number of personnel possible, and something like a simple trench from which to operate the controls. There was an accident at Scaled Composites a few weeks back that killed three people in a high pressure gas experiment (the tank exploded).
http://www.scaled.com
It is actually not that difficult to dig a small trench and use solenoid valves to operate stuff.
I love the show - don't let this happen to you!

I love this you guys look at problem and try to solve a completly different one that may or not exist. lol

The cable broke, where the cable is rather irrelvant after that since it's dragging on the ground. But at the CG would probably be the best place for it, otherwise it will try to rotate one way or the other.

I think the only way this might work is to use more strands of cable, or as someone else suggested something that was more elastic that could take a greater shock load.

To those that say the Mythbusters should've tried harder, the Mythbusters have these things called shooting schedules which make endlessly trying things kind of hard. Sadly the Mytbusters don't have the time to try every little thing to get these things to work.

That was really not what I wanted to see. I thought the steel cable would work. Maybe if the hook was attached better... somehow....

Anyway... nocturnal sonar using insectivorous mammal man's grappling gun was cool. Too bad the naill fell out of the wall....

"That was really not what I wanted to see."
Me too. I wanted to see it work to, even though I've never heard of Batman doing this.

"I thought the steel cable would work. Maybe if the hook was attached better... somehow...."

Maybe, but it stil looked like the cable itself broke.

"nocturnal sonar using insectivorous mammal man's "

Shessh why couldn't he just say Batman! lol Using actual footage from the Batman shows is one thing but I think the name Batman is pretty much public domain.

But Adam still pulled off a rather difficult thing to do. That was cool.

Ok not that MB is gonna be able to do this, but the ideal conditions for something like this working are to have a more balanced vehicle (read, mid engine), multiple attach points on the vehicle for the cable (at least 2 ,,, fwd and aft of center of gravity), and some kind of bungee mechanism to dampen the initial load (my personal idea involves running the cable through a spring [out of a vehicle suspension ... the bigger the better] , with a stopper on the end of the cable to catch the spring [a high speed shot of that spring compressing would be awesome])

Now seriously, these guys aren't likely to have access to a vehicle which is that well balanced, and it appears that despite the editing they did do their homework before they started the build (although the oversight of newtons 3rd law did make me wonder who was responsible for safety on the set that day). I think with some kind of braking system or bungee that they could have made it work, but they didn't discover that until they went to full scale testing ... and that was probably pretty close to the deadline for completing the project.... overall I think they did an awesome job with the resources available ... I'm not ready to agree that it's busted though.

i think they just need 3 steel cables and three launchers and they will be fine

This one deserves another try. The cable snapped because the car went past the post before the cable tightened. The cable needs to pull at 90 degrees. Batman would need to shoot slightly ahead and then pull in the slack after the grappel caught. Like a seatbelt pre-tensioner. All pretty complicated but they can split it up like they did the assender and the cable shooter. They have already proven the grappel canon works. Part 2: You start with the cabel in place, one end anchored and the other end in a stand with a catch ring. The batmobile has a hook mounted on the side that will catch the ring when it drives by. A shock absorber mounted on the hook may also be needed.

im still sticking by my put the launcher up front idea because it should turn the car rather easily, but the controlability comes into factor. It would make the car skidd violently and they would not line up directly with the street they are turning on but it would do the tirck of making the car turn at high speed. I think that by putting the launcher under the passanger side seat, and through the door, it would allow the car to turn instantly, but it would not let the car completely spin around, as it would do if the launcher was say above the right front tire. also i do agree a cable with more elasticity would work because even though the they say the force being put on the line is 8000lbs, the instant change in the line from slack to taught makes the rope weaker, rather than gradually putting on greater pressure. Kinda like in a tug of war, if everyone starts pulling and they pull harder and harder, everyone can hold on because they were pulling a little more every second, so they can stay standing. If one side pulls when the other side is just standing there, the initial jerk of the rope would pull them to the ground. i know that was a reaaaally bad analogy but anyone get it??

The first rope was plenty strong to rotate the vehicle; it is a matter of getting the force vectors correct. They could do two things. 1. They could place the gun on the front of the car and fire it in the same direction they did in the show, or 2. They could actually place the gun on the back of the vehicle and fire it to a post on the opposite side (outside) of the turn.

This is the same reason that you can steer a car (change its rotation, not its direction of motion) from the front by turning the wheels in the direction of the turn, or you can steer it with the rear wheels by turning them in the opposite direction of the turn. You can't change the rotation of the vehicle if the wheels are at its center of mass.

Unfortunately, rotating the car is different than changing the direction of motion (which requires much more centripetal acceleration, and thus more force), so the car may roll. If it doesn’t roll it will stop very quickly in a side slide and will have to accelerate out of the turn after rotation.

If they want to change the direction of motion and the rotation of the vehicle they should put the cable further in front of the center of mass, but not in the very front. They should be aware that the engine (front) is much more dense when doing this. They could play around with the location of the gun (backward from the front on each trial) to maximize the amount of force on the rope without failure. Ideally they could use two cables. One connected to the front of the vehicle and one connected to the center of the vehicle. If the lengths are correct this would mediate the forces due to changing direction and rotation of the vehicle.

i agree as i said before but BATMAN DIDN'T USE TWO CABLES!!!!!!!!!!!!!!!!!! I went back and looked through my cousin's comic books, huge marvel comic freak, and it doesnt show the placement of the cannon, it covered by a "BANG" sond box. but it did show one rope attaching to a metal support beam of a 6 story building. So two ropes wouldnt be real but i believe the placement of the cannon is key. somewhere between the right front wheel and the middle of the passenger side door should be the right spot to turn quickly without loosing much speed. But making a 90 degree turn without loosing any speed at all is inevitable it just cant happen.

Did any one consider the car itself. I'm sure the bat mobile is not just a car with things attached to it (I know the movie one is but I was referring to the one described in the comics). It indeed had features on it beyond what you find on a conventional vehicle. One feature has to be an improved turning system which probably took most of the force of the turn. The cable would indeed help but would have less force on it than that when used with a regular car. I don't know how to find such a particular vehicle but start with ones which have different wheel drives (either 4 or all).

True, Batman didn't use two cables. Yes, it is possible to take a vehicle turn through a 90 degree arc without slowing down. We do it all the time in our cars as they are, but we just have a larger arc radius. The problem the Mythbusters are facing is that the force of friction on the tires is less then the centripetal force due to turning in a smaller arc. Technically, they could improve the car's turning performance by increasing the road friction. There are few ways to do this. Change the material the tires are made of, or increase the normal force without increasing the mass. You can do this with a large spoiler (upsidedown wing). This will work even at 30 MPH if the wing is large enough.

However, this wouldn't answer the original question because even if the Batmoblie performs better than the car the Mythbusters used, the Mythbusters want to see if a cable improves the turning performance from the baseline performance of the vehicle.

Also, to all those saying that putting the gun further in front, yes this will help initiate the turn. However, it will only rotate the vehicle. Rotating the vehicle is not the same as changing the direction of motion of the vehicle by 90 degrees. By only rotating the vehicle, the car will still rely on road friction to change direction, which is the same no matter where you locate the gun. This means the car will slide and the speed will decrease. The goal of the Mythbusters is to make the car turn in a smaller radius than normal without slowing down. Theoretically it would work to use a cable or rope because the rope takes some of the centripetal force off the tires.

The rope is rated at a much high force than the total centripetal force necessary to turn the vehicle. And, the rope doesn't even have to take all the force of the turn since the wheel friction takes some of the force. The reason the rope is failing is because there is an impulse force when the slack is taken up. This is why I suggested multiple ropes earlier. Not to double the force capacity. I suggested it because a rope on the front of the vehicle will not bear the full weight of the vehicle initially. I will help redirect the vehicle to 90 degrees with the second rope. This will reduce the impulse force. Alternatively, if the rope was coupled with something with more elastic (like really strong bungy) the impulse force would be reduced.

If that doesn't work they could try a pole with a hook, which wouldn't require a gun or accurate timing. This wouldn't be the same as the Batmobile, but it would provide a solution. The Mythbusters normally make it work somehow or another. They are great.

90 degree ARCH RADIUs is possible but batman wasn't turning on a 90 degree arch radius he was turning on a dime from one street to another. a 90 degree ANGLE, not arch. The myth was to see if batman really could do it in real life. with a batmobile that would have to be supped up off of some stock vehicle. In all acuallity the Batmobile is not possible. with supper speed and super handling. But once again he was not turning on an arch. its a two lane street with an L turn no arch is availible. You coulg get a very VERY small arch on the turn but not enough. Lets stay with the myth. Its basically could batman (if real) make a 90 degree L turn with a cable and grapling hook with a car possible to manufacture today. So a super car with super handling is out of the question.

I love you guys, instead of dealing with the problem at hand you find a whole bounch of other problems. lol

A super car might have "super handling" but that doesn't mean it can make that turn. I think the turning ability of the vehicle doesn't have much of a factor here. It's all about the car being spun around on the cable.

I still stand by my point that, the cable broke, nothing else really matters after that. Untill they find a way to keep the cable from snapping all these other things don't really matter.

Also it looked like Grant had done a whole bunch of small scale experiments with that model he was holding. I know I certaintly would! lol They probably would've shown that where the CG was the correct position for the cable. Unfortunatetly they decided not to cut it in, which they should've.

quote:

Originally posted by dread_pirate:
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.

I agree: the chief problem was the high impact force because there was too little stretch. The force is a function of the deceleration distance, which was very small, hence very high force. Use magically strong cord, but if there's insufficient stretch, SOMETHING is going to break -- if not the cord, then the anchor at one end or the other.

I'm guessing that the "high tech rope" was something like Spectra or Kevlar -- these have virtually no stretch. Same for a steel cable. The mount point was rigid, and so was the grappled pivot structure. So "something" needs to be added to give some deceleration distance: a stretchy cord, a big spring, a shock absorber, a brake system, or best would be something to reel back in most of the slack, with a slip clutch to pay it back out during the impact, with resistance tuned below the cord's breaking strength.

Static lines ARE much stronger per unit weight or diameter than dynamic lines, but there's a very good reason that climbers instead choose dynamic ropes for lead climbing: they stretch on the order of 8-10%; static lines, 1-2%. You do the math (Grant), and don't forget there's a bit of trigonometry involved. ;-)

There's also lots of speculation about where the cannon was mounted. That's largely irrelevant; what needs to be near the CG is where the CORD is anchored when it goes taut.

quote:

Originally posted by physics2010:
Too bad the mythbuster don't watch the discovery channel <sic>. They would have learned about the wonders of plasma rope. 1" 12 strand braid 110,000 pound tensile strength, 23 pounds per 100ft or so.

Yes you are right. I saw the show about rope too. Its extremely strong stuff!!! They tried hard and did well but limited themselves to the steel cable. Should have tried rope and chain too.

quote:

Originally posted by gumbync:
This one deserves another try. The cable snapped because the car went past the post before the cable tightened. The cable needs to pull at 90 degrees. Batman would need to shoot slightly ahead and then pull in the slack after the grappel caught. Like a seatbelt pre-tensioner. All pretty complicated but they can split it up like they did the assender and the cable shooter. They have already proven the grappel canon works. Part 2: You start with the cabel in place, one end anchored and the other end in a stand with a catch ring. The batmobile has a hook mounted on the side that will catch the ring when it drives by. A shock absorber mounted on the hook may also be needed.

Nicely Put!!!

For off road recovery we have switched to samson amsteel blue rope. I'm sure there are many others like it. 3/8" steel cable has a breaking strength of 14,400lbs. Amsteel blue 3/8" rope has a break strength of 19,600lbs at half the weight of steel.

The rope is available in sizes well above 2". it seems that this would be a viable option for the superhero car. the 1" amsteel rope has a break strength of 98,100 lbs and weighs about the same as 3/8" cable.

It seems as thought it would be worth a try.

if they stepped up to 1 1/2 inch the break strength would be 228,000 lbs.

This myth cannot be called busted on the premise that strong enough cable isn't available. We now have synthetics that are stronger than steel and not that expensive. The mythbusters should use them.