Acoms AS17 Technical Note
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Timpdon Electronics Tel 0161 - 980 7804 Issue 1 – April 2014Web www.timpdon.co.ukEMail electronics@timpdon.co.uk Page 1IntroductionAll RC Servos include a bi-directional speed controlled motor, driving an output shaft via a highreduction gearbox.Coupled to the output shaft is a feedback potentiometer, measuring the position of the shaft,which is used within the servo to control the motor speed and direction, such that the positionof the potentiometer, and hence the shaft, always matches a reference position determined bythe joystick setting of the transmitter channel in use.If the coupling between the output shaft and potentiometer is removed, the motor willattempt to rotate continuously either clockwise or anti-clockwise depending on whether thetransmitter joystick setting is greater or less than the fixed position of the uncoupledpotentiometer.If the transmitter setting is equal to the position of the potentiometer, the motor will stop.On most servos, there are mechanical end stops which prevent the output shaft from rotatingmore than approximately 180 degrees, but these can easily be removed, permitting continuousrotation of the shaft and, in conjunction with a centre neutral transmitter joystick channel, bi-direction speed control of the servo as a motor gearbox.The resulting maximum rotation speed of the output shaft can be easily determined from thepublished maximum rotation rate of the servo. For example, if the servo is quoted with a slewtime of 0.2 seconds for 60 degrees rotation, this corresponds to 1.2 seconds per revolution, or50 rev/min, maximum.This speed is almost ideal for direct drive of anchor and similar winches.Conversion ProcedureThis conversion procedure involves mechanical modifications only. All of the original electroniccontrol circuits are retained, and used to provide bi-directional motor power in the convertedversion.The description below uses an ACOMS AS17 servo, but most standard servos will be similar inconstruction.Please note, however, that you embark on these modifications at your own risk. No warranty isgiven that this procedure will work on all servos. Also some dexterity is required. Do notattempt this modification unless you are confident in your ability to achieve success.Also, carefully read and understand all of the procedures outlined below before starting.TimpdonElectronicsTechnical Note - No. 16How to Convert a Standard RC Servoto a Bi-directional RC ControlledLow Speed Motor Gearbox |
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