>> ^juliovega914:

This type of gear is commonly used so that you can have a gear ratio (mechanical advantage) that is a variable as a function of angle of rotation of the gear. Its difficult to tell just from this video if that is happening in this case (as oppose to simply having a z-constrained contact point, not unlike a helical gear). If the contact point moves from left to right in the x direction (perpendicular to the axles, in the direction from gear center to gear center) the leverage changes and so you can have a regularly variable gear ratio, which is useful for certain applications such as periodic motion generators.
One thing I am sure many of you didn't notice is that the gear on the far right is not touching the center drive gear at all, despite it only being slightly more distant from the drive gear. Indeed it is spinning in the opposite direction while still not interfering with the drive gear. It would take an extremely small axial motion for the drive gear to transfer its torque to the right gear and away from the left, and would likely result in extremely minimal galling and gear damage since the gear is pretty much kept in proper shape. In a standard spur gear, this would require the use of huge numbers of extremely tiny teeth, which anyone who knows their solid mechanics would tell you that they are very weak compared to something like this.


I came back just to upvote your comment, I almost forgot

This type of gear is commonly used so that you can have a gear ratio (mechanical advantage) that is a variable as a function of angle of rotation of the gear. Its difficult to tell just from this video if that is happening in this case (as oppose to simply having a z-constrained contact point, not unlike a helical gear). If the contact point moves from left to right in the x direction (perpendicular to the axles, in the direction from gear center to gear center) the leverage changes and so you can have a regularly variable gear ratio, which is useful for certain applications such as periodic motion generators.

One thing I am sure many of you didn't notice is that the gear on the far right is not touching the center drive gear at all, despite it only being slightly more distant from the drive gear. Indeed it is spinning in the opposite direction while still not interfering with the drive gear. It would take an extremely small axial motion for the drive gear to transfer its torque to the right gear and away from the left, and would likely result in extremely minimal galling and gear damage since the gear is pretty much kept in proper shape. In a standard spur gear, this would require the use of huge numbers of extremely tiny teeth, which anyone who knows their solid mechanics would tell you that they are very weak compared to something like this.

she sounds strikingly similar to Axl Rose (or Layne Staley)

Electric cars would really benefit from getting rid of the axle drive train and using two or four independent motors to up the efficiency.

I can't compete with you on the number of people I know who have been injured/died, but I do know one guy who has a similar hard luck story to your first one.

A Warrant Officer I used to work with was known as "Hard Luck Henderson" because he just couldn't get a break. While in Afghanistan, the LAV he was in was blown up. He survived with a concussion.

Shortly thereafter he was blown up again and received a concussion on top of his concussion.

A few weeks later, during a patrol through some fields of tall grass, he felt some pain in his foot and thought he had kicked something sharp. They get out of the grass and see that he has been bitten by a poisonous snake. So he gets flown to a hospital where the pump him full of anti-venom because they have no idea what kind of snake it was.

A few months later, at home in Canada, he is driving a truck down to an army exercise and he hits a coyote with his truck. This is normally not a big deal, but this coyote gets wrapped around the axle of the truck. Henderson gets out, begins to unwrap the coyote, and it bites him on the arm and wont let go. He had to strangle it with his bare hands.

So he gets to the exercise (where he has quite an important job to do) and refuses to see a doctor. The next morning his arm looks like a balloon so he is ordered to get it checked out and it is decided he needs to undergo the full rabies treatment (which is about as horrible as any medical treatment gets). He was alright in the end, but had one hell of a year.

Surprisingly, he's a pretty positive guy, hehe.

>> ^Morganth:

In special cases like this, would it help if the rear wheels could have independent turning?


Like a long fire truck? I think that would help, but the load itself would have to be on a free-rotating platform above both the front and rear axles, since it is a single long straight piece that cannot be bent.

On the other hand, without that it just becomes an exercise in taking the turn nearly as wide as possible, and going very slow with the help of spotters to make sure that you have clearance everywhere -- which isn't particularly unusual for a CDL semi driver. So it is a special case, but I'm sure they did the math to make sure that it could fit through the turn and had plenty of law enforcement and spotter escorts to check clearance.

>> ^spawnflagger:

this is why the towing vehicle should weigh more than the load...


Umm... no. That idea falls apart looking at any semi-trailer. The weight of the tow vehicle doesn't matter nearly as much as the trailer or the load placement. If a vehicle is rated for carrying the weight, it can be use to tow.

This is why people, who otherwise can drive just fine, need training to tow trailers. A huge proportion of trailer-related accidents are due to inexperience.

1) Improper trailer. Car carriers need to be as low to the ground as possible. The trailer in the vid is a flatdeck for carrying construction materials or styrofoam blocks. The center of gravity there allows the load to sway, causing the trailer to turn, not unlike a skateboard. That sway takes on a harmonic imbalance, ultimately causing the jacknife.

2) Improperly placed load. The load should, for the most part, be forward of the axles. Placing it that far back actually pulls UP the rear end of the tow vehicle, reducing tire traction, helping the harmonic sway.

3) Improper tow vehicle. Just because your car can accellerate that much weight, doesn't mean the suspension can handle it. If the load HAD been centered properly, the front end of that car would have been off the ground if the rear end hadn't collapsed first.

4) Improper speed. Just because your car can accellerate that much weight to that speed doesn't mean it's stable. The faster you go, the longer it takes to make any changes and the less time you have to do them.

I don't understand how the brakes can have any effect on the pitch while he's in the air.


They stop the wheels turning.

Imagine instead that there was just an axle and two wheels. If you hit the brakes, what would happen? The axle would start turning along with the wheels. The axle can't exert a force on the wheels without "feeling" it.

A car won't start spinning (its momentum is larger in proportion to the wheels) but it will get some rotational velocity going. As you see, though, the rotation will dissipate quickly because of other forces at play (there's a lot of aerodynamic silliness going on).

Accelerating is more complicated because it's not just wheels - there's an engine (which could be mounted in different ways) and in some cases a large flywheel involved. In some cases, accelerating could end up rotating your vehicle sideways in the air (probably not good).

I don't have a CDL license, but I used to drive semi trucks on back roads for my family farm, so I'll take a stab at a couple of the question/comments here.
>> ^sadicious:

How does it turn at an intersection?
This is a fair bit different from the trucks and trailers I've seen, but I've personally been at the wheel of a double trailer and seen quite a few triple trailers. In either case, I was quite surprised at how well the successive trailers track the path of the semi cab itself and the trailer in front of it. I could actually take corners sharper in a double trailer than with a standard long single trailer. So, I bet that this thing can take a fairly standard wide semi-turn and each trailer will follow almost exactly the same track as the one in front of it.

Backing up would be pretty much impossible, although I felt that way about the double trailer I drove and some of the more seasoned hands than mine could back it through a course around obstacles with seemingly relative ease. I've even seen veterans do the same with triple trailers, which just blows my mind.
>> ^mxxcon:

i'm surprised that wimpy truck could pull so many
Note that all of the trailers were empty! A standard semi with a single grain hopper trailer like my family farm used would weigh about 23-25,000 pounds empty, with a bit higher empty weight for a double/triple trailer. The limit on total weight for any such a rig in the US is around 82,000 pounds (with some more specific regulations on weight per axle, etc.) so you can legally haul a bit under 60,000 pounds of cargo. On back dirt roads with very very rare vehicle inspection, sometimes we would try to cram a trailer full and ignore the weight limits.

Most of our hopper trailers could get up to around 92,000 lbs for semi plus trailer if we did that, but the double trailer I drove on occasion could sometimes top 105,000 lbs.

My guess is that the truck in the video is hauling about all the weight that it can handle in empty trailers, and once they get loaded with sugarcane (I think?, from the tags) the 10 trailers get divvied up between either 5 or 10 trucks. They might not have weight limit regulations, or they might not be enforced. Without any weight limit laws, or lax enforcement, people will tend to load to the maximum their trucks can handle.

From Wikipedia-

Tractor pulling, also known as power pulling, is a motorsport competition, popular in America, Europe and Australia, which requires modified tractors to pull a heavy sledge (sled) along a 100 metre track, with the winner being the tractor that pulls the sledge farthest. The sport is known as the worlds most powerful motorsport, due to the multi engined modified tractor pullers.

All tractors, in their respective classes, pull a set weight in the sledge. When a tractor gets to the end of the 100 metre (300 feet) track this is known as a “full pull”. When more than one tractor completes the course, more weight is added to the sledge, and the winner is the one who can pull the sledge the farthest.

The sledge is known as a weight transfer sledge. This means that as it is pulled down the track, the weight is transferred (linked with gears to the sledge’s wheels) from over the rear axles and towards the front of the sledge. In front of the rear wheels, there is a ‘pan’. This is essentially a metal plate and as the weight moves over this the resistance builds. The further the tractor pulls the sledge, the harder it gets.

The most powerful tractors, such as those in the 4.5 modified class in Europe, can produce over 10,000 bhp.

http://en.wikipedia.org/wiki/Tractor_pull

Reminds me of something my dad did back when he drove 18-wheelers. On one particular delivery he had two tires blow out on the same side of one axle within ~5 minutes of each other. Being around 20 miles from the nearest town and no way to replace the tires he ended up using a chain attached to the trailer frame to elevate that side of the axle until he could stop somewhere to have it fixed.

It wasn't as cool as using a tree limb, but it must have looked nearly as odd driving down the road.

If a solution is posted on the internet and everyone calls you an idiot, is it still a solution?

Rick figured that although a nut traveling DDWFTTW might be the simplest form of such a device, replacing the threaded rod with a wheeled vehicle would be more compelling – and possibly even less intuitive. He conceptualized replacing the device’s keel nut with gearing from a drive axle to a propeller shaft that would replicate the kinematic constraint perfectly. With the problem solved as far as he was concerned, he posed the new brainteaser on two internet forums, one for radio controlled helicopter pilots, the other for kitesurfers. Given the solution, Rick imagined people would find this clever.

Instead they considered him an idiot for ever imagining such a thing to be possible.

This is where the pointless brainteaser took on a life of its own. Science, physics and aerodynamics forums exploded. Sailing forums exploded. Flying-related forums exploded. It was silliness traveling at the speed of electrons. Turns out it’s serious business when someone is wrong on the internet, and boy did the internet ever believe Rick was wrong.

One interesting factoid emerged from the chaos. We learned that a Michigan University student posed this same non-problem – and a solution identical to Rick’s — in the 1940s. The student’s paper surfaced at Douglas Aircraft in the 1960s. Apollo M.O. Smith, the company’s chief aerodynamics engineer, and wind tunnel engineer Dr. Andrew Bauer went at it like Rick vs. the Internet. Bauer said it would work. Smith wasn’t convinced. Bauer bet Smith a dollar and went to work.

Read More http://www.wired.com/autopia/2010/08/ddwfttw/all/1#ixzz0y2H81thY

I'm giving him a 10 for the double axle split, followed by a quadruple flip and a successful dismount.

I actually thought the fat shirtless guy was going to BE axl rose.

I'm sure that after years of putting up with Axl Rose, shit like that is easy to handle.