B. NEG'ATORŪ CONSTANT TORQUE SPRING MOTORS
1.0 INTRODUCTION
The NEG'ATOR Constant Torque Spring Motor is a sophisticated, compact device which consists of a take-up drum (a) and usually a larger diameter output drum (b) mounted on two separate axes as illustrated in Figure 1. The motor spring itself is mounted on the storage drum which is free to rotate; its other end is attached to the output drum. The spring coil is pulled straight in zone S and then wound onto the output drum by bending it against its natural curvature, thereby storing energy in the spring. Only the material passing through zone S changes stress (Figure 2).
When the output drum (b) is released, the spring returns to its preset form, rewinding itself on the storage drum, and rotating the output drum imparting moment (M). The near constant torque generated results from the spring, which has been stressed sequentially during back-bending onto the output drum, releasing energy as it returns to the storage drum. 

Because of these unique characteristics, the constant-torque motor spring offers a number of advantages over the conventional power spring:
1. An absence of inter-coil friction and resultant high hysteresis that is inherent in  
   a power spring.
2. Higher permissible material working stresses of constant torque motors result in
   higher energy storage.
3. Rotary motion can be taken directly from the output drum shaft. Linear
   displacement can be developed by means of a cable reel on the output drum
   shaft.
4. Light duty escapements or governors can be used because the peak torque
   developed by a power spring is not present.

The difference between a NEG'ATOR spring motor and a conventional power spring is illustrated in Figure 3.