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Gyro and Servo Combinations
Introduction There is a problem
encountered with differing Manufacturer's Gyros and Servos - the Pulse and Frame Rates
differ. This gives compatibility problems. Unfortunately, these are
not quoted on Manufacturer's Literature, which makes it difficult to make recommendations. The best advice is to look
on www.runryder.com or other Forums to see if your combination has been tried
successfully. In an effort to speed up
the Helicopter's Tail response both pulse rate and frame rate have been modified, notably
by Futaba. It's impossible to give all
combinations, so the following has to be a guide only ! Terminology Frame Rate Frame Rate is the number of
pulses (frames) per second that are sent by the Gyro and received by the servo. Frame A Frame is a complete block
of all channel position information sent from the Tx to the Rx and then to the Gyro. The
Gyro controls the frame rate and pulse width sent to the Tail servo. Pulse Width Pulse Width is the length of
the pulse in us (milliseconds). Standard Gyros & Servos These run frame rates between
50-70hz (cyles per second). Normal average is 60hz. Normal pulse width is 1520us. Example Gyros are Futaba GY240
and CSM HLG 200. Normal Servos (analogue or
Digital) have to be rated at 50-70hz also. The problem here is that this
combination is not fast enough to properly hold the tail in either Heading Hold or
backward flying modes and windy conditions. Faster Gyros & Servos These run frame rates
between 270 and 333 hz. Their pulse widths are half
the width at 760us. This is also referred to as "narrow" pulse width. So, they are a) increasing
the frame rate x 4 and also b) reducing the pulse width x 2, both of which speeds up the
Tail response time. Examples are Futaba GY401 /
GY601 / GY611 Digital Servos Note that just because a
servo is digital or coreless does not mean it is compatible with a particular Gyro. But
Digital servos tend to be faster and support faster Gyros. Matching It is important to realise
that Gyros and servos are combinations for the reasons explained above. Any mismatch will
affect and possibly reduce the tail response. Gyros GY401 DS = on - frame rate = 270hz DS = off - frame rate = 70hz pulse width = 1520us Usually used with a fast servo
- 9254 with DS = on. GY601 Can switch to slower servos,
but performance suffers. frame rate = unknown pulse width = 760us Servos BLS251 or 9256 Servos not compatible with
GY401 GY611 Can switch to slower servos,
but performance suffers. frame rate = unknown pulse width = 760us Servos 9256, BLS251 CSM720 Unknown. Known
Examples 1520uSec
/333Hz servos
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