The 
KST DS315MG has a hardened steel drive train and a coreless motor capable of running from 4.8V to 8.4V (4 cell NiMH to 2S LiPo) meaning these servos will deliver the power and reliability you need. They are super high speed with pretty good torque.
The accessories include 3 standard output arms and 2 red strong output arms. 
KST DS315MG Features
- Compact and strong design
- Excellent speed with good torque
- Wide 4cell NiMH to 2S LiPo voltage range
- Excellent heat dissipation
- 7075 Alloy casing
- Hardened Steel gears
| KST DS315MG Servo Servo Specifications | 
|---|
| Body dimensions | 23.0 mm wide x 12.0 mm thick x 26.5 mm high | 0.91" wide x 0.47" thick x 1.04" high | 
| Max dimensions | 32.0 mm wide x 12.0 mm thick x 33.0 mm high | 1.26" wide x 0.47" thick x 1.30" high | 
| Stall torque (4.8V) | 2.8 Kg.cm | 39 oz.in | 
| Stall torque (7.4V) | 4.3 Kg.cm | 60 oz.in | 
| Stall torque (8.4V) | 4.8 Kg.cm | 67 oz.in | 
| Weight | 20.5 g | 0.72 oz | 
| Lead length | 21 cm | 8.3 in | 
| Operating speed (4.8V) | 0.1 sec/60° | 
| Operating speed (7.4V) | 0.08 sec/60° | 
| Operating speed (8.4V) | 0.07 sec/60° | 
| Operating voltage | 4.8V to 8.4V | 
| Operating temperature | 0 - 50 °C | 
| Bearings | 2 ball bearings | 
| Gear material | Hardened Steel | 
| Case material | 7075 aluminium alloy | 
| Motor type | Coreless DC motor | 
| Working frequency | 333 Hz | 
| Dead band/resolution | 2 µs | 
| Pulse width for ± 60º | 900us-2100us µs | 
| Digital | Yes | 
| Programmable | No | 
| Position feedback | Potentiometer | 
| Supplied accessories | 3 standard output arms, 2 red strong output arms, 2 arm retaining screws, mounting screws | 
| Optional accessories |  |