RE: A question of Weight. [TANKS]

["Steve Tyng" <STyng-at-ACPTrust.com>]

Aahz wrote:

> Is it getting bent from engine torque or rough terrain?

From running into things like minivans and trees.  The idler and drive
wheel shafts are susceptible to impact damage.  Makes sense since these
wheels are sitting at the four corners of the tank.

The front and rear road wheel shafts in an solid suspension design are
susceptible to getting bent just from running around on rough terrain.
On the T34 I had to occasionally bend them back into alignment.  

Bent shafting is all about physics.  A 120 pound tank running at 5mph
has quite a bit of inertia.  Lets say said tank impacts a large rock on
it's left front drive wheel while attempting to evade the Cromwell.  The
rock is set in well compacted soil so the rock isn't moving anywhere.
This tank is a solid suspension design so the force of the impact will
not be absorbed by a spring or shock absorber.  The force of the impact
has to go somewhere so IF the road wheel, shafting, shaft mounting, and
the hull are robust enough, the force of the impact is transferred to
the entire vehicle as it is pushed up and over the rock.  Lets assume
this is not the case.  The builder did not heed the advice of other
builders or suggestions on the mailing list and skimped on shafting by
using 3/8" all-thread rod (pretty weak stuff). This tanks front left
road wheel shaft is not rigid enough to transfer the majority of the
impact force to the hull of the vehicle so it is absorbed by bending 1"
up and to the rear.  This is bad enough in itself but it gets better
(for the Cromwell that is ;-).  Since this tank is still trying to do
5mph with the left front road wheel out of whack, lo and behold - the
left track has just flown off the tank!  This results in the tank
skewing to the left and giving an easy broadside to the Cromwell that
has just stopped outside the 5' no fire exclusion area and is letting
loose with a volley into the hapless victim.

The morel of the story is don't skimp on material strength.  Think of
the point impact areas on your tank and ask yourself how they would fair
if you dropped your tank from a 1' height onto those impact points.
Don't forget items inside your tank like those big and heavy SLA's that
should be blocked in place and securely strapped down.


Steve "We Don't Battle on a Golf Course" Tyng