Re: Suspension Springs

[Frank Pittelli <frank-at-rctankcombat.com>]

DBone-at-comcast.net wrote:

> How do you figure out what size and type of springs to use on a tank
> suspension.

A good question indeed.  As I see it, there are two things that need to 
be considered:

1) The springs on each of the roadwheels need to be stiff enough to hold
up the weight of the vehicle in normal operations and to withstand the
dynamic force of the vehicle hitting the ground hard.  In the first
case, divide the total weight of the vehicle by the number of road
wheels to determine the force-per-spring required.  Then, get a spring
that moves about an 1/2 inch for that amount of force (that's how
springs are rated).  If you give yourself an inch of total travel for
each spring, when the vehicle is resting, each spring will be
depressed/extended (depending on the type of spring used) 1/2 inch. That
lets the wheel move up or down as it goes over terrain.  When the 
vehicle hits the ground hard, the spring can still move another 1/2 inch 
to absorb the shock.  (Depending on the suspension arm assembly, the 
wheel itself may move much further than 1/2 inch, but the force 
calculations are unchanged ... I think ;-)

2) When the road-wheels move, the track will slacken (regardless of the
type of track), so you may need to take up the slack with another
spring.  The strength of that spring should be chosen so that in normal
conditions, it exerts the most tension on the track.  That way, when the
road wheels move, the track tension spring can take up the slack.  On
the Tiger, I plan on adding a tension spring to my rear idler wheel
assembly.  You could also place tension springs on the small idler
wheels that some tanks have above the road wheels to hold up the track.

Did I leave out anything important?

        Frank "Now Where Did I Put That Physics Book?" Pittelli