Servo Control Unit V2.3

Servo Control Unit v2.3
Version 2 of the Servo Sweeper makes the setting
up of the unit much easier:
• Each servo can be set independently for
three sweep positions.
• Theoretical resolution of 0.04°.
• Fine servo positioning (+/-1.3°) using
trimpot during set-up.
• Trimpot controls servo transition speed
(up to 30 seconds).
• Optional oversweep position.
• Transport sweep-lock mode.
• Excellent spurious signal rejection.
• Hold Last Position failsafe.
Connect the two servos to the appropriate outputs of the unit (marked Servo 1 and Servo 2). Connect
the desired control channel from you receiver to the input of the unit (this must me a rotary control on
the transmitter during set-up, but can be a rotary or three-position switch after set-up is complete).
Power to the unit and servos is supplied by the receiver connection. It is perfectly feasible to power the
servos from another supply (say 6V). However, the voltage to the unit must not exceed 5.5V.
For descriptive purpose, a rotary flap control on the transmitter is used in this document.
Set-up Mode
The method of entry into the set-up mode will determine the number of sweep positions available
(three or four). Setting the unit for three positions is shown in normal text. Setting the unit for four
positions is shown in (italicised parentheses). The factory setting for all sweep positions is mid-sweep.
To change these settings, turn the lock switch off; switch the receiver on; and toggle the lock switch
on/off twice (three times) within 3 seconds. The unit will respond by flashing the LED at
approximately 1-second intervals. If the LED flashes rapidly, turn the lock switch off within 5 seconds
or the unit will reset (see Factory Reset).
Six (eight) settings can be stored in the unit. These correspond to servo positions for three (four) sweep
settings for each of the two servos: unswept, mid-sweep, fully swept (and oversweep). Each setting is
indicated on the unit by a flashing sequence on the LED: 1 flash for setting 1, 2 flashes for setting 2,
and so on.
Setting/Flashes Description
For each of the six
(eight) settings, use the
Servo 1 setting for the unswept position.
flap control to set the
Servo 2 setting for the unswept position.
coarse position of the
appropriate servo, and
Servo 1 setting for the mid-sweep position.
fine tune (if required)
Servo 2 setting for the mid-sweep position.
using the trimpot. The
Servo 1 setting for the fully swept position.
speed of the servos is
Servo 2 setting for the fully swept position.
slowed down to a fixed
(Servo 1 setting for the oversweep position.)
(Servo 2 setting for the oversweep position.)
Toggle the lock switch
on/off once to store the setting (the LED will stay on for 1 second to indicate success) and move on to
the next setting. If you do not wish to change the setting, do not move the flap control. After 5
sequences, the servo will return to the stored setting, and the next setting will be selected
automatically. After setting 6 (8), the unit will loop back to setting 1. To exit set-up, switch the receiver
Factory Reset
To reset the unit to factory settings (mid-sweep for all positions), turn the lock switch on; switch the
receiver on; and toggle the lock switch off/on twice (three times) within 3 seconds. The unit will
respond by flashing the LED rapidly. After 5 seconds, the LED will stay on for 2 seconds and the unit
will then reset. The LED will start flashing rapidly again, starting the sequence again. To exit this
mode, turn the lock switch off or switch the receiver off. If the lock switch is turned off, the unit will
enter set-up mode (see above). If this mode is exited before the LED stops flashing, the unit will not
Normal/Lock Mode
To enter normal or lock mode, turn the lock switch off or on respectively, and switch the receiver on.
The LED will be off and the servos will move to the sweep position selected by the transmitter. After 3
seconds, the unit will enter the selected mode.
Normal Mode
With the lock switch off, the LED will be on and the three main sweep positions can be selected using
the flap control. Fully anti-clockwise will select unswept, mid position will select mid-sweep, and fully
clockwise will select full sweep. You can reverse this selection order by simply reversing the flap
channel on the transmitter. Adjusting the trimpot will set the transition speed between sweep settings.
Fully clockwise will slow the servos down to about 30 seconds end-to-end travel. Fully anti-clockwise
will give near normal servo speed (about 0.1s), and a mid-position will give about 1 second. To enter
Lock/Transportation Mode, turn the lock switch on (see below).
Lock/Transportation Mode
With the lock switch on, the LED will blink off once approximately every second and the fully swept
(oversweep) setting will be selected. The unit will ignore the flap control whilst this switch is on,
effectively locking the wings. To set Normal Mode turn the lock switch off (see above).
Signal Loss and Signal Rejection
In normal operation, pulses are received approximately every 20ms. If no pulse is received within
33ms, the unit will replace the missing pulse with the last good pulse, effectively acting as a hold last
position mode. If no signal is being received at all, the LED will flash twice per second. To reduce
glitches, acceptable pulses are greater than 0.74ms, and for the unit to accept a new pulse it must have
received five pulses in sequence with values within 0.05ms (about 3%) of each other. If these
conditions are not met, the invalid pulse is dropped and replaced with the last good pulse, effectively
acting as a hold last position mode.
Specifications are subject to change without notice.
The author shall have no liability or responsibility to the customer or any other person or entity with
respect to any liability, loss or damage, caused or alleged to be caused, directly or indirectly, for
equipment sold or furnished by the author. Notwithstanding these limitations, the author’s liability for
damages incurred by customers or others shall not exceed the amount paid by the customer for the
particular equipment involved. Neither the author nor this document makes any expressed or implied
warranty, including, but not limited to the implied warranties of merchantability, quality or fitness for
a particular purpose.
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