Radio Gear Issue - RC Groups
Shop our Airplanes Products Drone Products Sales
Thread Tools
Mar 05, 2017, 02:46 PM
Registered User
Backyard's Avatar

Radio Gear Issue

The sail winch servo on my Victor Stars & Stripes that I built way back in the 1900's has finally given out. It's an Airtronics Sail Winch Servo 94581 that is no longer available. I want to use the sheets and asymmetric arm that is the original setup. To operate properly it requires nearly 180 degree rotation so I chose the HS-815BB.

When connected to the other semi-antique AM radio gear it rotates only a total of approximately 60 degrees. I guess this is due to the character of the signal (pulse width etc.) that the old receiver puts out. I have present day computer radios but I would rather use as much of the original gear as possible.

So, I wonder if anyone here has a suggestion short of the obvious renovation and upgrade?

Thanks for any comment.
Sign up now
to remove ads between posts
Mar 05, 2017, 06:59 PM
Registered User

Servo rotation range modifications

Hey Backyard

There are several forum threads about modifying a servo rotation range ...

There are commercially available "Servo Stretcher" modules that expand the range of servo rotation

There are other MORE COMPLEX ways ... that are more aggressive and require some tinkering skills ... to open n modified the servo. That requires some basic skills of FINE SOLDIERING to disconnect n add / modify resistors inside the servo

In some cases ... depending on the servo ... may also require removal of a portion of the servo "Gear Stop - Rotation Tabs" that limit the servo rotation travel.

modifying the resistors would end up burning out servo if trying to drive servo against the servo gear rotation stops/tabs

Do some more homework before doing servo modifications

FYI ... I still have Victor Soiling with EXACTLY SAME Airtronics servo (still works) that you have to replace 🤓
Mar 05, 2017, 10:32 PM
Registered User
Hey Backyard

I did a forum search

Here is a link that describes how to modify servo to increase rotation from 90-degrees to approx 180-degrees

Hope this helps - or - at least gives you AN idea what is needed AND how to make the servo mods ... especially warnings AND hints
Last edited by slo.ca6; Mar 06, 2017 at 02:39 AM.
Mar 05, 2017, 10:44 PM
a.k.a. Bob Parks
Old guy here - what is with all the n's?
Mar 06, 2017, 12:21 AM
Registered User
Hum interesting, I have that servo in my ODOM and it rotates about 140 plus degrees with my futaba 7c radio. I would hook it up to a different radio and try that to see if it works better.
Mar 06, 2017, 01:17 AM
Registered User
Servo stretcher is the cheap way forward here.

The benefits of 2.4GHz are no interference, the ability to put model specific limits and trims in the radio (including a 120% stretch) and useing modes like exponential so the rudder is fine control around center and then a barn door at the ends. You can also use switches to do magic like dump 10% if you see a wind gust. The problem though is you still want a transmitter for each person so if you want to sail a boat with a friend you still need a pair. I like the spectrum with the orange reciever but it appears that alternates are flooding the market.

Is that attack a mode 2 where the sail stick does not have a spring?
Mar 06, 2017, 07:49 AM
Registered User
Backyard's Avatar
Thanks guys.

The Attack has springs in both sticks.

Curious that the specs. say 140 degrees and 200 degrees rotation "out of the box", whatever that means.

Dimensions 2.59" x 1.18"x 1.26" (66 x 30 x 57.6mm)
Product Weight 5.6 oz. (152g)
Output Shaft Style 15 tooth (D1) spline
Voltage Range 4.8V - 6.0V
No-Load Speed (4.8V) 0.48sec/140
No-Load Speed (6.0V) 0.38sec/140
Stall Torque (4.8V) 274.96 oz/in. (
Stall Torque (6.0V) 343.01 oz/in. (
Max PWM Signal Range (Standard) 920-2105μsec
Travel per s (out of box) .169/μsec
Max Travel (out of box) 200
Pulse Amplitude 3-5V
Operating Temperature -20C to +60C
Current Drain - idle (4.8V) 8mA
Current Drain - idle (6.0V) 8.7mA
Current Drain - no-load (4.8V) 700mA
Current Drain - no-load (6V) 830mA
Continuous Rotation Modifiable Yes
Direction w/ Increasing PWM Signal Clockwise
Deadband Width 8s
Motor Type 3 Pole Ferrite
Potentiometer Drive Indirect Drive
Feedback Style 5KΩ Potentiometer
Output Shaft Support Dual Ball Bearings
Gear Type Straight Cut Spur
Gear Material Nylon
Wire Length 11.81" (300mm)
Wire Gauge 22AWG

Not sure I'm up to the surgery.

I'll look into the stretcher. I wonder if it modifies the pulse width or something like that.

Maybe HiTec has an answer, or Servocity.

Thanks again for the ideas.
Mar 06, 2017, 10:48 AM
Registered User
Hey Backyard

Regarding the sticks both having springs ... as you described above ... see the following suggestion.

Most folks that use this radio for Sailboats open the transmitter and remove centering springs on left stick. This way the sail position stays were you leave it (vs constantly having to fight the centering springs on the stick wanting to return the stick to CTR position). NOTE: Others also do this when left stick is used for "Throttle" and wanting to hold constant throttle stick position (and not fight the centering springs).

Also ... in some versions - but - not all transmitters ... when you open transmitter to modify the left stick as noted above - there is a metal strip that can be installed after springs removed ... which helps keep stick in position since the stick has ribs (like a gear) that interacts with the added metal strip NOTE: remember that not all versions have this option metal strip - or - loose or don't know what this part is in the transmitter box and end up tossing out this part with the transmitter packaging.
Mar 06, 2017, 11:03 AM
Registered User
Backyard's Avatar
Thanks slo.ca6. That will be a big help. Hope my transmitter has this feature.
Mar 06, 2017, 11:10 AM
The wind is free, go sailing!
Scratchy101's Avatar
I have the HS815-BB in my IOM.
Using a Flysky FS-T6, I get 140 rotation.
I used the endpoint adjustment to get a full 180 rotation.
Mar 06, 2017, 11:38 AM
Don't lie to my dog.
Gregg28's Avatar
It is relatively east to lengthen the throw of the servo. You would need to solder two resistors in line with the two outside leads on the servo pot. I am not sure of the actual value, IIRC it is in the 1k to 10k range. If you soldered small 10k pots in there you could then adjust the throw and then close it up. If they do not fit you could just replace the pots with resistors of the final value and then close it up.
Mar 06, 2017, 12:02 PM
Registered User
As Gregg28 noted above (as well as other links to other forum threads - provided above) adding resistors to a servo is not that hard

Just to help and be more clear ...
TWO (2) resisters of equal value are ADDED to each respective leg (either side of existing pot - potentiometer).

Each resister can be either FIXED VALUE (ranging from 1.8K Ohms to 2.2K Ohms) ... or ... separate 10K ohm potentiometers.

NOTE: as described above by Gregg28 - using 10K potentiometers vs fixed resistor allows fine adjudtment / trimming for each direction from CTR position. Because the sailboat winch is large internal space - the 10K ohm potentiometer is nice option (which is what I have done ... and works great)
Mar 06, 2017, 12:29 PM
Don't lie to my dog.
Gregg28's Avatar
Thanks for clarifying.
Mar 06, 2017, 05:51 PM
Registered User
Originally Posted by Backyard
I'll look into the stretcher. I wonder if it modifies the pulse width or something like that.

Maybe HiTec has an answer, or Servocity.

Thanks again for the ideas.
Yes, the servo city stretcher is inline and intercepts, modifies, and resends the width of the electrical pulse. The 200* means that there is a mechanical stop that needs to be modified for more travel.

The pulse width is the "go to" command and the potentiometer is the "you are here" signal.
Mar 06, 2017, 06:32 PM
Registered User
If as you say you already own a modern computer radio it would be so much easier to use the new equipment. There is no collector or other value in a twenty plus year old Futaba attack radio. A new system shoukd also be much more reliable.
Last edited by Tom Corbett; Mar 06, 2017 at 08:53 PM.

Thread Tools