How to Modify a Futaba S-148
for 180 Degree Operation

Text and Photos by:
Dave McDonald
AMA 40128

Did you ever need a servo that rotated 180 degrees to run a cheap pair of mechanical retracts?  And did you cringe at the thought of spending twice as much money just for that retract servo.....than you paid for your retracts themselves?


Did you ever wish you had a fully proportional servo that rotated 180 degrees to operate your flaps?......but you couldn't find one any price?

I think I owe Airtronics an apology here!  It has been brought to my attention that the Airtronics 94739 is a 170 degree proportional double ball bearing servo that is similar in size to the Futaba S-148, but with nearly twice the torque.
The Airtronics 94739 servo lists for about 100 dollars with a street price of about 70 dollars.
Thank you Jack Albrecht for bringing this to my attention!

This procedure will explain how to easily modify a standard Futaba S-148 into a servo that travels 180 degrees instead of the usual 60 degrees.  But unlike a dedicated retract servo, this modified S-148 will still be fully proportional.

Modifying the electronic circuit only requires adding 2 new resistors to the
S-148 circuitry.  It isn't diffiult to do.....BUT......because of the very limited space inside the S-148 servo, and the small size of the S-148 circuit board, I don't recommend that you try this unless you are experienced at soldering and desoldering small electronic circuits.

And now that the disclaimer is out of the way,
here's how I did it:   :-)

Materials needed:

You'll only need a total of 2 new resistors for this project.
One is a 1.2k resistor, 1/4 watt.  (brown, red, red)
The other is a 2.7k resistor, 1/4 watt.  (red, violet, red)

Disassembling the Futaba S-148 Servo:



Modifying the Futaba S-148 Servo
for 180 Degree Rotation:




Do NOT allow the modified servo to try to rotate beyond the mechanical limits of the geartrain!!!

If necessary, adjust your transmitter's ATV to avoid over driving the servo!!!

Please let me know how your 180 degree modification project worked out!

Just click on one of these links and
Send your comments to:

Thanks Dave!
My 180 Degree Futaba S-148 Works Perfectly!


Dave, I've Got a Problem with My 180 Degree S-148!


Dave, you S.O.B.!!!!
You Made Me Ruin a Perfectly Good S-148!

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