Solid State Flippers

 From: pepke@scri.fsu.edu (Eric Pepke)

Subject: Solid State Flippers

Date: Fri, 2 Apr 1993 18:35:55 GMT

This comes up every once in a while.  I'll try to clear it up if I can.

In electronics, the only thing the words "solid state" ever mean is that 

switching or amplification is done by semiconductors, which are made out 

of solids.  A mechanical switch is not a solid state device: it uses the 

insulating properties of air.  Air is a gas, not a solid.  A vacuum tube 

is not a solid state device: it uses the diffusion of electrons in vacuum. 

 Vacuum is not a solid.  Transistors are solid state devices, as are 

silicon controlled rectifiers, triacs, UJT's, etc.

Obviously, it takes less force to keep a flipper up than to get it up 

while pushing a ball.  The best engineering of flippers to date takes this 

into account.  Older flippers used two coils, one for activation and one 

for holding.  A clever mechanism with a switch (either normally open or 

normally closed) switched the current between the coils when the flipper 

got up to the top, using a high-current mechanical switch.

High-current mechanical switches have problems.  When the two pieces of 

metal get close to each other, an arc jumps through the air between them.  

This causes the metal to burn a little every time the switch is used.  

This wouldn't matter, except that the burnt metal is not good at 

conducting current.  So, after a while, the resistance of the switch 

changes, and the behavior of the flipper is effected.  After enough time, 

the flipper fails.  There is no way of eliminating this.

Solid state devices don't have this problem (as long as they are well 

heat-sinked and are operated within their parameters.)  They do have other 

problems, but they can be engineered around.  So, it makes sense to use 

them to switch the current, either by having them switch current between 

two coils, or by using one coil and switching between two voltages.  The 

resulting flipper is far more reliable.

However, this doesn't answer the questions of WHEN to switch the current, 

and this is where DE and Williams flippers differ.  Williams solid state 

flippers are designed to mimic the behavior of the old electromechanical 

ones, with an end-of-travel switch.  DE flippers, on the other hand, don't 

use an end of travel switch.  Instead, they just use a timer, giving the 

flipper a high force first and then lower force after a few fractions of a 

second.

The result of this is that the force curve on a DE flipper coil is always 

going to be the same, no matter whether there are zero, one, two, or three 

balls on the flipper, no matter how fast the balls are going when they 

come into contact with the flipper.  The force curve on a Williams flipper 

varies according to circumstance.

It is this difference, and not the difference between solid state and 

electromechanical, that causes the difference in the feel of Williams and 

DE flippers.

(This information refers to flipper design as of a couple of years ago; 

for all I know they may have changed since then.)

Eric Pepke                                    INTERNET: pepke@scri.fsu.edu

Supercomputer Computations Research Institute MFENET:   pepke@fsu

Florida State University                      SPAN:     scri::pepke

Tallahassee, FL 32306-4052                    BITNET:   pepke@fsu

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