Re: [GZG] AFV ground pressure ( was Re: New to the list, and 2 questions: lift/jump infantry)

On Mon, Jan 12, 2009 at 4:33 PM, Damo <damosan@gmail.com> wrote:
>
> On Jan 12, 2009, at 3:57 PM, Tom B wrote:
>
>>
>> OTOH, when my car takes a corner, the wheels turn all the way
>> around. I don't lock one track and spin the other, which probably
>> has some deleterious effects on road surfaces.
>>
>
> The M-109 didn't lock a track per se -- it simply applied small bits
> of break to cause the turn so both tracks would still turn but at
> differing rates.  Unless you cranked the wheel all the way over and
> hit the gas.
>
> Don't most modern AFVs work in this fashion?
>
Forget modern, the french Char B1 had this in the 1930's.  It is not a
brake.	It is a funky application of epicyclic gearing that allows an
auxillary hydraulic motor to run the tracks in opposite directions, or
the steer the vehicle if the engine is driving the tracks.  If you can
picture an epicyclic gear set, there is a sun gear in the center,
smaller planet gears on a carrier that circle the sun, and a ring gear
that encircles the planet gears.  If the track is connected to the
planet carrier, its movement is a summation of the movements of the
sun gear and ring gear.  The Char B1 combined this with a hydrostatic
transmission that was continuously variable and allowed the driver to
aim the bow-mounted cannon.  The swedish S-tank added hydraulic rams
to the suspension to provide elevation, so the gun could be rigidly
mounted to the vehicle.

For fun, I built a tracked vehicle with a similar powertrain using two
lego differential gear sets, the lego Power Functions bits from the
Creature Creator set, and the track links off of the lego Jawa Sand
Crawler.  The lego XL motor had enough torque to pop one of the gear
shafts off, if it slammed into a wall (probably a good thing, so when
I rebuild it, it will retain that feature).  It was an 'Amaze your
friends' toy, as it was not obvious why it the gearing did not lock
solid.

Because the tracks have a non-zero length contact patch, there will
still be scuffing at the extreme ends.	Tight radius turns will have
scuffing along nearly the entire length.  For heavy vehicles, replace
"scuff" with "tearing up of the pavement".

The air pressure in your tires is the ground pressure of your vehicle,
if the tires are soft rubber slicks.  If they have any tread pattern,
the ground pressure is higher.	High pressure is better for fuel
economy, as deforming the tire takes work, and that work is
proportional to the size of the contact patch [ob. useless trivia,
there is a maximum speed at which the contact patch can be moved along
the tire.  Exceed that speed and the car has effectively left the
road]

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