Servo
Servos are electronic actuators designed to operate mechanical linkages to perform actions such as steering, controlling throttle and controlling brakes. Servos come in a wide range of prices and specifications.
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Specifications
Dimensions
Standard dimensions for use in the savage are approximately 40mm/1.6" long, 20mm/0.8" wide, 38mm/1.5" high.
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Spline Count
The output of a servo is a shaft with a series of splines designed to mate with a servo horn. Different manufacturers may use different spline counts. It is worth noting that manufacturers that do use the same spline counts are still not guaranteed to have compatible splines - some are deeper than others.
| Manufacturers | Spline Count |
|---|---|
| JR, Sanwa(Airtronics), Acoms, KO, Spektrum | 23 |
| Hitec | 24 |
| Futaba | 25 |
| Ace(Thunder Tiger), Bluebird, Supertec | 25 (smaller spline) |
Performance
Torque is measured in oz in or kg cm, higher values being better. Speed is measured in seconds per 60° arc (ie the time it takes for the output to rotate through 60°), lower values being better.
Suitable steering servos should have at least 90 oz in (6.5 kg cm) but preferably 120 oz in (8.6 kg cm) or higher. Speed is not as important but lower than .20 seconds is preferable. Racers may prefer faster servos (.15 seconds or lower).
For nitro Savages, suitable throttle servos should have at least 33 oz in (2.4 kg cm) but preferably 90 oz in (6.5 kg cm) or higher. Higher torque is useful for increased braking strength. Speed is generally more important for a throttle servo, especially for racers.
When buying your first replacement steering servo, it is beneficial to replace the stock throttle servo (SF-1) with the old steering servo.
Digital/Analog
Analog servos use simple analog circuitry to process the control signal for the servo. Digital servos use a microprocessor to process the signal. This can allow for higher resolution and speed but generally at the cost of higher power usage and expense.
Motor Type
Low cost servos use 3 pole brushed motors. Higher end models may utilise coreless or brushless motors. Coreless motors are similar to brushed but have no heavy core in the rotor allowing for fast acceleration. Brushless motors have no brushes, allowing for very high power and less chance of failure.
Suitable steering servos
| Name | Manufacturer | Torque (oz-in @6v) | Speed (sec/60° @6v) | Typical price (USD) | Gears | Bearings | Motor | Digital/Analog | Water/Dust resistant |
|---|---|---|---|---|---|---|---|---|---|
| S3010 (HPI SF-2) | Futaba | 90 | 0.16 | $25 | Plastic | No | 3 Pole | Analog | No |
| SF-3 | HPI | 90 | ? | ? | Metal | Yes | 3 Pole | Analog | No |
| SF-4 | HPI | 90 | ? | ? | Metal | Yes | 3 Pole | Analog | Yes |
| S3305 (HPI SF-5) | Futaba | 124 | 0.20 | $35 | Metal | Yes | 3 Pole | Analog | ? |
| HS-645mg | Hitec | 133.31 | 0.20 | $36 | Metal | Yes | 3 Pole | Analog | ? |
| HS-5645mg | Hitec | 164.2 | 0.18 | $55 | Metal | Yes | Coreless | Digital | Yes |
| DS1313 | Thunder Tiger | 173.6 | 0.13 | $78 | Metal | Yes | Coreless | Digital | Yes |
| DS8411 | JR | 188 | 0.15 | $115 | Metal | Yes | Coreless | Digital | No |
| DS1015 | Thunder Tiger | 201.4 | 0.108 | $90 | Metal | Yes | Coreless | Digital | Yes |
| HS-5955tg | Hitec | 333 | 0.15 | $115 (Discontinued) | Titanium | Yes | Coreless | Digital | Yes |
| HS-7955tg | Hitec | 333.29 | 0.15 | $120 | Titanium | Yes | Coreless | Digital | Yes |
| Z9100T | JR | 370 | 0.15 | $140 | Metal | Yes | Coreless | Digital | Yes |
| DS8711 | JR | 403 | 0.15 | $140 | Metal | Yes | Coreless | Digital | Yes |
