For a production of Blythe Spirit, Klaus Holm, Technical Director at Wilkes College, needed a way of toppling a chair on a thrust stage. As the chair had to move from one location to another during the play, wires could not be used. Instead, Klaus converted a small section of a platform beneath the chair leg into a small trapdoor — a “flipper” — which would open and close quickly, tipping the chair over in the process.

FIGURE 1: SYSTEM SCHEMATIC AND FLIPPER HINGING DETAIL

Figure 1 illustrates the essential parts of the chair-tipping mechanism: an offstage control lever, a connecting rod, a swing arm, and the flipper, and details the flipper/swing arm hinge connection. When the operator pulls the control lever back (or pushes it forward) quickly, the flipper pops up momentarily and then reseats itself.

FIGURE 2: FLIPPER OPERATION

CONSTRUCTION NOTES

1. The connecting rod must be secured to the floor in such a way that it can slide back and forth easily without lifting off the floor.

2. The transverse arm shown in Figure 1 was useful in gaining speed because it let us join the connecting rod to the control lever farther away from the lever’s pivot. Some deck and connecting rod hardware designs will permit direct connection between the control lever and the connecting rod — and some will need no separate control lever at all.

Most of the components in this system can be replaced with alternatives which may better suit other applications. The hinges shown bolted together in Figure 2, for instance, could be replaced by a double-swing hinge. Similarly, neither the control lever nor any part of the linkage need be made of lumber, and a solenoid-controlled pneumatic cylinder could be used at the flipper. In our case, however, Klaus decided to use lumber and hardware already on hand in order to save money and time in both the shop and the theatre.