About tail rotor servos

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On selecting tail rotor servos

Tail Rotor Servos

There are a class of servos, which we call tail rotor servos. Their pulse range is half as wide (the why is beyond the scope of this article so please just accept that they're different). Anyway, for these servos, instead of neutral being 1520µs, it's half that, or 760µs.

Thing is, they're fast and we've had folks buy them by mistake and have to return them. This is because instead of their range being 1000-2000µs it's about half, or 500-1000µs. Anyway, since their range isn't within the range of the signal sent by the receiver, tail rotor servos require a gyroscope (connected between servo and receiver) to re-interpret the 760µs neutral to 1520µs (so they'll work with a receiver).

The point being, without a gyro, a tail rotor servo won't work with a receiver. And note; while plugging a tail rotor servo directly into a receiver won't work, it also won't hurt it because the receiver doesn't even know it's there! Anyway, we know all this from the specifications for the pulse - see below.


So how do you tell the difference? You look at the specs! Above is a detail from the specs for the DS120BLHV tail rotor servo. There are three lines of special interest right now.

The first is for max travel (depending on the servo, this ranges between 110-125° or 400-1100µs in the case of our tail rotor servo). Max means max, e.g. the very very maximum it can sweep - i.e. if you max out the travel volume of the particular channel on the transmitter by setting it to 125% or 140% each way. Note; this varies by brand of transmitter with Futaba maxing travel at 125% and others like Spektrum maxing at 140% - but - the end result is the max the servo can accept is exactly the same for all brands of transmitters because it's determined by the servo. Anyway, the second line is the normal travel, which is 90°, and the third line is for 0° (neutral, or center).

The take away from all this is 760us is outside the typical range for a receiver and thus, tail rotor servos won't work when plugged directly into a receiver for throttle use. This means you can forget about using a tail rotor servo for the throttle or anything that's connected directly to a receiver because they don't speak the same language and must have a gyro.

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