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Understanding Other Vehicle Dynamics (Semi's) Is Handy To Know!

Discussion in 'Multimedia' started by joetdm, Dec 1, 2011.

  1. #1 joetdm, Dec 1, 2011
    Last edited by a moderator: Jul 13, 2015
    Yeah I know it's about trucks and not bikes but hell, we come across these monsters thru the spurs and other places often so this is worth a look.

    Bottom line is stay away but think it's important to understand what can happen as they go around.

    EDIT: Should have been in off topic but was thinking multimedia because of it's youtube link... oh well..


  2. OK so I like a good doco and the explanations in this one were quite easy to understand.
    But VicRoads telling people that all will be well if they just slow down is far from surprising, and I'm a bit confused by the "Just 1Kmh..." thing - 1Kmh less than WHAT, exactly?
    If the equation is "x-1=ALIVE", shouldn't they be teaching them how to solve for 'x'?
  3. I enjoyed that but yes, I too found the 1km thing so vague as to be useless, as it was presented here. Do they mean "slow down" - they could just say that. It would have been more helpful to explore the dynamics of tipping loads, corner characteristics and speed.

    I wonder how much enforcement actually happens with respect to schedules putting pressure on drivers, such that as usual it is the actual key worker, who is in effect at the bottom, being pressured to the point that they feel the need to push their speed or be punished?
  4. yeah agree the 1kph thing was the only part I thought kinda silly..

    Lets face it, if you're 1kph over the tipping point then yes it can be the difference.
    But if quite a few k's over, then 1kph is not enough...

    I think they should have spoken more about being under the tipping point rather than a 1kph difference...

    But I found the rest well worth watching..
  5. We've done some research that told us that loading and CoG is the significant cause of truck rollover accidents....but we're going to focus on speeding anyway
  6. Well that right isn't it!
    I don't think truckies go out the first time and immediately tip the darn thing.
    They've probably done the same route so many times at the same speed without incident.
    Then one day a container or load of some sort is put on the trailer with a load which has a very hight CoG and that's when they're caught out.
    In a normal truck, you would feel a lot quicker when loaded with a higher CoG but with a semi, it would be not as obvious in the rear trailer or on the second trailer on a B-double..
    Those videos with the trailers rolling well before the truck starts prove this..

    I learn't a little from watching the video that will keep me a little more vigilent when riding with these monster's around...
    Always good to see/learn things from the other side...
  7. What did you expect? LOL.

    It's always puzzled my why they're allowed to build trucks the way they do.

    Ok, I know why they make them that way - because it's cheap and effective and it works. But at what cost in terms of overall road safety?

    Look up a picture of a pre world war 1 racing car, and you'll see a vehicle with a big engine and a high centre of gravity, primitive suspension design, and driver protection (in the event of an accident) which was so bad they not only didn't wear seatbelts, they actually designed the cockpits with a view to throwing the driver from the seat in the event of a rollover because it was safer than having him trapped in the vehicle. If you look at a picture of a truck from that era, you'll see many of the same features - just scaled up a bit and with a tray on the back.

    Fast forward a hundred years. Show me a racing car with a big engine and a high centre of gravity. There are still a few of those at the drag strip, but they sure as hell don't have primitive suspension or lack for driver protection. And every other sort of competition vehicle has the centre of gravity as low as possible. What about passenger cars? When I was a kid, it wasn't all that hard to tip a lot of passenger cars on their head. Today, there are some 4x4s you could tip over on level ground, but even those are pretty rare. Sedans - impossible. But when you look at large trucks, they haven't changed much in a hundred years. Why? Because it's cheap and it works. Just like the men who drive them.

    You could easily redesign the semi trailer to carry most of the weight near the ground, but it would need to be a little longer to carry the same load, or it would need to carry maybe 25% less load to be the same length. And the loading space would not have a simple flat floor - which would complicate loading and unloading. But in either case, the cost of building the trailer would go from about the $50k ~ $75k area, to about the $150k+. In other words, you're looking at a minimum 10% general increase in the cost of road transport - which would be passed on to all of us.

    Are we ready as a society (not just us Australians - everybody in civilised countries) to pay a bit more for everything, in order to save the lives of a few worthless truck drivers? Because that's the real reason trucks are made just the way they were a hundred years ago - there is no cheaper way to make them.
  8. i'm interested in this part. are you talking flat tops or vans? i'm interested to hear what you think might work.

    you can already spend more than $400k on a B double set so with your figures i assume you're talking about a basic flat top trailer.
  9. I can remember a company that redesigned the logging trailers that used smaller wheels and wider load bars. The result was something like a 1.5 m reduction in the centre of gravity which equates to a much more stable load.

    Unfortunately it cost more to produce, so not all logging companies would buy them. Those that didn't buy them had no additional cost to pass on, so could sell their product cheaper, which gave them a commercial edge.

    So even though we have the technology to make things better / safer, sometimes, unless there is a legislation change it just doesn't get market penetration.
  10. https://docs.google.com/drawings/d/1DGFHBN7bfo-My2P1SBf01laS1aoSATFYyAkE02MKFuc/edit

    I'm trying to embed the image, but ...

    Anyway - the design is similar to what we use as a float for heavy loads now. Either you accept the same vehicle length and a smaller load, or you stretch the vehicle and move the wheels out from under it.

    I would also be interested in developing a system that allowed for a little torsional twist in the turntable for driving over uneven surfaces, but tightened up during cornering to add the stability of the prime mover to the trailer, so at least when the trailer began to tip, the driver would feel it happening early enough to maybe do something about it. Part of the problem, as well illustrated in that clip, is that by the time you feel it begin to happen, it's too late to correct.

    It should also be part of driver training to have a simulator that moved like a full cockpit flight sim. I've been in a semi that was up on its outside wheels, and it's a feeling you never forget, but the action is a strange and jerky one, and not what you'd expect. If you could see what was happening from the outside, it would make sense, but from inside the truck there's this strange series of lurches and twists. It's a side-to-side motion, as well as an up and down wallowing motion, more than a rolling or tipping over motion. It wouldn't be a terrifically hard thing to simulate, but you'd want every driver to know what the beginning of tip over and the beginning of jack-knife feel like - right at the start when you still have a chance to do something.
  11. It's called a step-frame trailer - the trailer frame steps down to enable the load base to be lower than the 5th wheel on the tractor unit. They have been commercially available for years. They just use smaller wheels to retain the same size load platform.

    Ground clearance is a concern on long trailers, so there is a limit to how low you can make the load platform.

  12. Thanks Miraz - that's him.

    Some years ago, BMW and Mercedes started developing active roll bars for their big performance cars. There's a hydraulic system that can 'twist' or pre-load the sway bars to make big heavy soft cars respond quickly and with little or no body roll. The system knows when the car is going to roll and starts tensing up to control it before the body roll gets under way. A system like that on the trailer wheels, and also on the lateral link at the turntable, would transfer the movement of the trailer straight into the prime mover and allow the driver to sense what was going on in real time, rather than a half second or a second behind - when it's often too late.
  13. Wouldn't actually make any significant difference...and creates a whole load of other issues.
  14. Don't let Falcon-Lord watch that video.