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History of the Dynaspot Moveable Mass Racket

by Marv Sassler, Inventor of the Dynamic Sweet Spot racket

The Moveable Mass Racket was developed as a result of an injury. I went for one of those spectacular overhead slams and unfortunately caught the ball on the edge of the racket. The twisting force almost tore the racket from my hands. In a few moments my elbow started to ache and by the end of the game I was in real pain. I had developed a severe case of “Tennis Elbow”. Perhaps the injury was coming on gradually and the overhead smash was just the event that precipitated it, but the result was the same. The only good thing about the episode was that it stood out so clearly in my mind. It was the sudden tremendous twisting force that caused the injury.

In the long recovery period that followed I had time to think about the twisting force and ways to reduce it. Being an engineer, and analytical by nature, I started computing the forces involved and was astounded by their magnitude. Then one day I woke up with the answer.

Make the racket head a gyroscope that inherently resists twisting forces. This could be accomplished by allowing part of the material making up the racket head to move. Thus the Moveable Mass Racket. Implementation of the idea would take the better part of a year and even then resulted in models so crude that they were relatively ineffective. The first model was a wooden racket whose head was shaved down to make it lighter. A plastic tube partially filled with mercury was bound to the racket head. Better models were needed to prove that the idea worked. Metal frame rackets, and finally graphite fiber frames were used to make models that clearly showed the validity of the idea. Mercury was replaced by safer materials.

Ultimately, it would require either high-speed photography or a computer simulation to evaluate the effectiveness of the moveable mass racket in reducing the twisting force caused by an off-center-hit. Since the cost of high-speed photographic equipment was prohibitive, a computer simulation was implemented. The results indicated significant reductions in twist due to off-center-hits. These results were later confirmed by high-speed photography performed by the noted tennis coach Vic Braden and sports psychologist Gideon Ariel of the Coto Research Center.

Dynaspot (a contraction of Dynamic Sweet Spot) was incorporated to produce and market the Moveable Mass Racket in 1982. Patents applications for the device were later submitted and granted.

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