Isaac F

Hello Guys, I remember long time ago a web that show you how to convert a regular Futaba 148 servo to retrac servo. I remember that the web show you how to put 2 resistor on the potentiometer inside the 148 servo to make the servo horn to have more travel like a retrac servo.

Can somebody help me???

I have a lots of F-148 servos but none retrac servos and I want to use them on my new Hangar-9 T-34. I am pretty sure the 148 weight less than does $28.00 retrac servos

Dave McDonald

My Feedback: (19)

Try here:
http://mypage.yhti.net/~dmcdnld

Isaac F

Hey Dave, Thank You

pt19 flyer

My Feedback: (1)

hi isaac f

I have converted several 148 for myself and other club members. It does involve installing two resistors, one in each motor lead. I will try to find values and get back to you on this.

Joe

there is an article on this in Model Aviation Nov. 98 page 50 giving instruction on conversion. Case for 180 degree servo. If you do not have this magazine I think I still do...I will try to find it and if you need it I can email it to you as an attachment.

let me know

joe

Isaac F

Hey Joe, whats up? I dont have that magazine. In fact, you will not belive this but I am not keeping old RC magazines anymore[X(] I use to keep all my RC magazines until I develop some kind of allergic reaction to the dust (dust mite) on the old magazines. I suffer from a rash in my hands and all kind of allergic things[&o] So I just keep them for around a year and then goodbye.

About the retrac article you mention. Is this similar to the one on http://mypage.yhti.net/~dmcdnld ??

Also, do you know if I can use different servos like:

OLD FUTABA
FP-S28
FP-S148
FP-S121

Hi-tec 422

Thanks for your help and coments

Isaac

FHHuber

The Hobbico retract servo is relatively inexpensive, and already made for the 180 deg rotation. and has the neat little battery saver circuit in case the retract binds. (your conversion will NOT have that circuit. and that can cost you an airplane.)

pt19 flyer

My Feedback: (1)

hi

I think you could use the 28 don't know about the other, just try it and see what happens.

you can go to ama digital archives and down load the article and print it out
think the location is http://206.246.138.100/resultsimage_article.htm four pages to the article I think, quite extensive on conversion.

will look at location you suggest.
it was a how to do it article in magazine. try the digital archives locataion in the members only section of modelaircraft.org website

good luck

joe

Dave McDonald

My Feedback: (19)

Issac,
The 180 mod can be done to any servo, as long as it's a proportional servo, and as long as the servo is mechanically capable of rotating at least 180 degrees. The only difference will be the resistor values needed to achieve the 180 travel.

The easiest way to find the correct values is to temporarily wire in a couple of variable resistors (potentiometers). Each variable resistor is placed in series with each of the outer legs of the servo's feedback pot. Plug the servo into the receiver and use the transmitter to operate the servo while adjusting the variable resistors until you get the desired 180 degree travel....WITHOUT hitting either of the mechanical stops. Then disconnect and measure the adjusted resistor values with an ohm meter and substitute the closest fixed resistor that you can find.

This is exactly the method I used to determine the resistor values needed to modify the S-148. In most cases, a 5K variable resistor will give you plenty of adjustment range, but some servos might require using a 10K variable resistor to find the correct values.

Just remember the goal is to achieve 180 degrees of total throw, WITHOUT hitting any of the mechanical stops in the servo geartrain, or overdriving the mechanical limits of the feedback pot. This is the reason that the S-148 servo requires two different resistor values.

FYI: The Hobbico retract servo is not a proportional servo. In fact, Airtronics is the only company I'm aware of that makes a proportional retract servo.


Joe,
Thanks for the info about the MA article! I may have to link that article to my 180 servo web page.

FHHuber

The link to the AMA archives is not too useful... Something about the way the archive is set up is preventing that link from predictably hitting any article.

1st try got me the archive sign-in page.

2nd got me some article about setting up a control line contest

3rd got me an article on setting a durration record. (Maynard Hill was at it again. )

Again... the converted servos won't have a safety circuit. Retracts binding can leave the servo draining your battery. I've seen a plane go in on total loss of control (servos would not move) which we suspected had that as the cause... but there wasn't enough left to prove it.

***************8

And... you are sitting there working to make a retract servo (by the thread origin...) out of a standard servo... with the goal of flipping a switch to get 180 deg travel... so why worry about the suggested retract servo not being proportional to begin with?

***************

The Hobbico retract servo is virtually the same weight as the S-148... a tiny bit wider. a bit shorter. (fits in the wing better)

**************

The FACTORY MADE retract servo WILL work.

The conversion MIGHT still function if you manage to do the soldering job correctly...

You are being penny-wise and pound foolish to do the conversion. It is NOT worth the risk to try to save $15 (the difference in servo cost....) and a couple of grams.

Dave McDonald

My Feedback: (19)

The Hobbico retract servo is actually slightly lighter than a Futaba S-148.
The Hobbico retract servo will have nearly twice the torque of a Futaba S-148.
The Hobbico retract servo will have a stronger geartrain than a Futaba S-148.

It's true that a stalled retract servo may end up crashing your plane. FHHuber may be right, but I've never seen any technical data on either Hitec's or Tower's web sites indicating that the Hobbico retract servo has a built in safety circuit to protect against high current draw during a stalled condition.

The 180 modified S-148 in my Ultra Sport 40 ARF has accumulated several hundred flights over the last ten years with no problems....except once I stripped the geartrain by waiting too long to lower the gear. In this particular plane, the S-148 is running two Hobbico retract units, with very light wheels, so it doesn't take much force to operate the retracts.

While it's true I originally modified a S-148 to run the retracts in my Ultra Sport 40 ARF, I mainly use these 180 modified servos for flaps since they are fully proportional, and they can provide a positive mechanical lock in the fully retracted, and fully extended positions.

I just went to the Hangar 9 web site to have a look at your T-34. Since it has a trike gear, you would need to use at least two 180 S-148 servos to handle the load......one for the nose gear.....and one for both main gears. If the wheels aren't light enough, or if the gear legs are too long, the 180 S-148 might not have enough torque to raise the gear. On the other hand, a single Hobbico retract servo should easily handle all three retracts.

IMHO, operating the retracts on a 40 sized T-34 will be near the upper limit of the capabilities of a 180 modified S-148. If you've had previous experience with setting up mechanical retract systems, then a couple of 180 S-148 servos can be easily made to operate the retracts reliably. But if this is your first experience with mechanical retracts, then I'd recommend starting off with a dedicated retract servo.