The rotary spark gap triumphs over many of the short come of the static gap. Making use of moving electrodes instead of fixed ones is the key. A rotary spark gap fires when the electrodes are aligned. A simple rotary spark gap consists of a pair of fixed electrodes and a pair of moving electrodes mounted on a spinning disc. If a motor turns the disc, then the electrodes will align frequently. Every time an alignment occurs, the spark gap fires. General a rotary spark gap is preferable to a static gap for serious Tesla coil work because the firing times are regular, making operation smoother, and sparks more repeatable. The power handling capability of the rotary spark gap is greater than a static gap because the electrodes are dynamically separated after firing.  The rotor gap below is using a Magnetec 90 VDC/1/3 hp/3000 rpm/3-amp motor. Below the motor is a full wave rectifier. To vary the speed, a 3 amp/110 VAC variac is used. Tab on pics to enlarge  
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