4x4 / Off-Road TechThis section contains all discussion related to taking the FJ Cruiser in Off-Road situations, 4x4 applications and any armor modifications.
If you FIX the far end of the winch cable to an anchor, and you're ROLLING BACK on the uptake of line over the fairlead, you will have created a simple 2-part "fall", block and tackle system. This increases the force being applied by a factor of 2 since it doubles the amount of line take-up per distance travelled. This means that twice the force of the "pull" is being put on the fairlead.
Not as described here. Still single force pull.
Everything else I agree with. However this is a good idea if nothing else around, and only slightly stuckie... I think that's what was implied. (I know, I get in trouble when I think...)
Everything else I agree with. However this is a good idea if nothing else around, and only slightly stuckie... I think that's what was implied. (I know, I get in trouble when I think...)
I still think that this is correct.
The equivalent would be to tie a rope to the ceiling, put a single pulley on top of a weight, then run the rope UNDER the weight, and lift UP.
This is a simple two part fall. If you lift a foot of rope, you'll lift the load half a foot. It will spread the same force over twice the distance and give a mechanical advantage of 2:1
Remember, the REAL force is being unleashed BEFORE the vehicle goes unstuck and starts to move. If there wasn't a big impediment to movement, the vehicle wouldn't be STUCK in the first place! Once the vehicle starts to roll (or slide) the forces are significantly reduced. Before the vehicle starts to move, all uptake of line is invested in the springiness of the metal parts of the car as they deflect. All you have to do is take ONE FASTENER past the elastic/plastic transition and its over.
The equivalent would be to tie a rope to the ceiling, put a single pulley on top of a weight, then run the rope UNDER the weight, and lift UP.
This is a simple two part fall. If you lift a foot of rope, you'll lift the load half a foot. It will spread the same force over twice the distance and give a mechanical advantage of 2:1
Remember, the REAL force is being unleashed BEFORE the vehicle goes unstuck and starts to move. If there wasn't a big impediment to movement, the vehicle wouldn't be STUCK in the first place! Once the vehicle starts to roll (or slide) the forces are significantly reduced. Before the vehicle starts to move, all uptake of line is invested in the springiness of the metal parts of the car as they deflect. All you have to do is take ONE FASTENER past the elastic/plastic transition and its over.
It isn't correct.
In the example above, the pulley on top of a weight moves relative to the pull, resulting in a 2:1 advantaqge. The fairlead on the FJ bumper is fixed relative to the winch, resulting in a simple 1:1 pull.
The equivalent would be to tie a rope to the ceiling, put a single pulley on top of a weight, then run the rope UNDER the weight, and lift UP.
This is a simple two part fall. If you lift a foot of rope, you'll lift the load half a foot. It will spread the same force over twice the distance and give a mechanical advantage of 2:1
Remember, the REAL force is being unleashed BEFORE the vehicle goes unstuck and starts to move. If there wasn't a big impediment to movement, the vehicle wouldn't be STUCK in the first place! Once the vehicle starts to roll (or slide) the forces are significantly reduced. Before the vehicle starts to move, all uptake of line is invested in the springiness of the metal parts of the car as they deflect. All you have to do is take ONE FASTENER past the elastic/plastic transition and its over.
Agree on the stuck part...
However, NOT a 2:1 leverage advantage. Draw a free body diagram and look at it. Since the anchor is a stationary point, not on the moving body, 12 inches moves it 12 inches. Hold on.. have to go to the store, and downloading Inkscape so I can try to draw... (it ain't gonna be pretty!)
Since we are on the subject Bellydoc whom I respect very much, has always seems to know what physics applies to each circumstances. Yes I did used the rope around my rear tire reverse my self out of the sand where I was stock. Off course because it was sand it was relatively easy to put the loop around the tire without lifting and it worked.
The fairlead on the FJ bumper is fixed relative to the winch, resulting in a simple 1:1 pull.
Agreed (x2). The pulling force that I described of routing the winch cable to the rear (rather than to the conventional forward direction) will still be the same.
Like drbrb said, the winch and fairlead are fixed positions items, and therefore, no line-doubling (or "line-halving") is being introduced. At the very most, some friction may come into play against the skid plate or axle, but the overall work effort of the winch remains 1:1.
Rather than a simple 25 or 30 degree off-axis pull, this one just happens to be 180 degrees off-axis towards the rear.
In the example above, the pulley on top of a weight moves relative to the pull, resulting in a 2:1 advantaqge. The fairlead on the FJ bumper is fixed relative to the winch, resulting in a simple 1:1 pull.
Quote:
5280FJ previously said:
Agree on the stuck part...
However, NOT a 2:1 leverage advantage. Draw a free body diagram and look at it. Since the anchor is a stationary point, not on the moving body, 12 inches moves it 12 inches. Hold on.. have to go to the store, and downloading Inkscape so I can try to draw... (it ain't gonna be pretty!)
I still disagree and you're missing the part where I was talking about the point where the vehicle is moving and not moving.
Once the vehicle is MOVING, the static force of unsticking has been unleashed.
At that point, yes, the winch is moving at the same rate as the line is being taken up.
However, when the REAL force is being applied...
The winch isn't moving
The tree behind isn't moving
However, the FAIRLEAD IS BEING CRUSHED BACK AND DOWN.
The leverage on it at that point is approaches 2:1 what the winch would be doing in straight pull (discounting angles around the bumper, line friction, etc.)
Get it?
Remember... if your winch was only being asked to exert a pulling force equal to the friction of moving your vehicle... you probably wouldn't be stuck!
I still disagree and you're missing the part where I was talking about the point where the vehicle is moving and not moving.
The winch isn't moving
The tree behind isn't moving
I'll try one more time.
The winch *is* moving relative to the tree. It is moving one foot (in this case backward) for every foot of line spooled onto the winch. Therefore the winch is experiencing a 1:1 pull.
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