I've got a Sopwith Pup bi-plane that I would like to replace the aileron servos on. This design uses two servos, one at each wingtip to drive the ailerons. So each servo drives the lower and upper wing ailerons via a pushrod from the lower aileron to the upper aileron.

During crosswind landings, this type of aircraft (slow flying, floater type scale airplane, about 14 pounds) has been known to scrape and/or hit the lower aileron on the runway, causing a jolt to the servo occaisonally.

I'm concerned about damaging nylon servo gears and want to upgrade to metal gears or carbonite. I don't need anything much faster than a standard servo because this is not a fast airplane (WWI Scale). I also don't want a lot of current drain because I'm only using a standard 4.8V pack that came with my reciever, so current drain much higher than a standard servo is not attractive. Can you recommend a servo for this application?

Also, what is your feeling on when I should use a choke, or buffer, or filter on the servo lead lines? This airplane puts about 36" of wire running from the reciever to each aileron on the wing tips. I've seen some jitter occaisonally with my standard servos, but thought that maybe I should just go to a heavy-duty extension to prevent voltage drop. What is the difference between a choke, a "booster", and a buffer/filter? What does Futaba offer in that line?

Thanks!

As far as protecting the servos against a ground strike, your best bet is a small wire loop that keeps the servo from hitting the ground. With impact damage, a metal-geared servo won't necessarily break the metal gears. The force will move down to the nylon gears, and you'll still get gear damage. Protect the gears against impact in the first place.

If you're getting glitching due to long servo leands than you may have to use one of the devices you mentioned to alleviate it.

As far as chokes and such are concerned, Futaba does not make any.

A "choke" is a small coil of wire used to cut down certain types of resonance in its circuit. A buffer is a special type of amplifier between two coonneced devices. The buffer keeps one from influencing the other in an adverse way. A "booster" is an amplifier that increases the strength of the control signal so that the voltage drop of a large line doens't cause the signal to become too weak.

Thanks Bax! I'm planning how best to attach the wire bumper loop on the bottom of the wing, but since my current servo has already taken some hits, I figured on being safe & replacing them prior to failure. Any recommendations from you?

I don't need anything much faster than a standard servo because this is not a fast airplane (WWI Scale). I also don't want a lot of current drain because I'm only using a standard 4.8V pack that came with my reciever, so current drain much higher than a standard servo is not attractive.

For "standard" servos, the Futaba S148 servo is a good buy and is very reliable. It's just about the most plentiful servo in use. If you need more power or other features, please check the servo section of the web page to see which servo might fit your uses.

Thanks Bax. How does the S3003 standard servo compare in terms of design and field reliability? Is it a lighter duty servo?

The two servos are essentially similar, but the S3003 has some lower-cost components in its construction.

If I may add my $.02 here.

I have, at last count, over 100 Futaba servos in current use. I have many 148's, 3003 and 3004. When the 3003/4 first came out I was disappointed that the 148 was being replaced. I bought a 3003 and took it apart to compare it to the 148. Somewhere in the archives I have that report but I don't know where. Anyway, from the fact that the 3003/4 is a little shorter in length than the 148 it is esentially the same servo. It appears to be designed for better automated manufacturing. The 3003/4 will fit where a 148 came out. Now what is the difference between the 3003 and the 3004. The 3004 already has one ball bearing installed on the top of the output shaft. I feel the extra $1 or $2 for the BB is well worth it. It cost more to retrofit the BB than it cost to go ahead and get it initially.

If you need a reversed servo, the 3003/4 can be reversed internally if you can handle desoldering. I have done that for an elevator servo.

Where have I used the servos? In addition to 40 and 60 size planes I have a Ultra Stick 120 with a Saito 150 that is using 3004's for all services, including flaps and rudder. I just put the 10th flight on a GP 1/3 Pitts with an OS FF-320 (4 cylinder). It uses 3004's on all controls except throttle and rudder where I used a Hitec 81 on throttle and a Hitec 605 on the rudder. BTW, the Pitts weights 20.9 pounds.

In my opinion the Futaba 3004 is the best servo available for the money.

Thanks for the input iflyj3.

To you & Bax:

What's the word on toroid-type "noise suppressors" like what Radial RC sells:
http://radicalrc.secure-mall.com/sho...=7&cart=176714

This just looks like a little ferrous ring that you wrap your wire around, doesn't seem to have any circuitry that could fail. Are there any risks to using something like this on long servo leads (36+ inches)? Do these rings stop RF noise like a micro-circuit noise trap would only without the signal amplification?

To add to what Bax has already said on this issue. The ferrite ring you refer to serves as a choke and will filter out very high frequencies if they get on the signal line to the servo and prevent them from getting to either the servo or receiver. You are correct in they are very fail proof in that it is all passive parts.

The one I just saw on Radical R/C was called the "ACE" filter. If it is the one which I am familiar, it is an IC that amplifies the servo signal. In amplifying the signal it will also help block any induced signals of high frequency. I keep saying high frequency because if it blocked the low ones it would not pass the servo signal either.

One must keep in mind that these devices were needed more in the past when the receivers had a marginal drive capability. I had a receiver that had to have a buffer/amplifier in order to drive two servos off the same channel. The receivers made today will drive multiple servos without help. BTW, the servos have also improved and they don't need as much drive from the signal.

Do you need a buffer/amplifier or choke????? My answer is maybe, maybe not. One thing is for sure, using them will not hurt you, unless of course they fail. Will they fix a problem? My answer is maybe, maybe not.
You may have a problem and installing a choke appears to have fixed the problem when all along it was a bad connection of the cable that was replaced by the choke.

My suggestion is to see how things work first hooked up normally. If you have a problem, trouble shoot it and if that fails try a buffer/amp/choke.

I'm sure that my servo jitter was the result of some stray noise, just not sure of the source. It did happen on a freshly charged pack (jittered right when I turned the rx & tx systems on) and I've heard of freshly charged 6v packs causing this kind of jitter. Problem is, I don't have a 6v pack. Only a 4.8v pack. Could the same thing happen on a 4.8v pack? Regardless, it seems like the ring choke is a cheap way to add robustness without adding another failure point in the system. I'm thinking of going with that.

Can you shed some light on this ? I need to do same so any help would be appreciated....

Tnx

This is from memory so use caution.

Remove the four screws that hold the servo together. Remove the top of the servo carefully and try to remember how the gears are installed.

In order to reverse the servo we must reverse the motor and feedback pot.

The motor and the feedback pot are soldered to the PC board (PCB). The motor is soldered on the sides of the board. The feedback pot is on the end where the wires come in. Locate these and use a desoldering tool to desolder the motor and the pot. Carefully remove the board. Remove the motor and turn it 180 degrees and reinstall. Clip the two outer leads of the pot and solder on two short insulated wires. The pot's center wire goes back in the same place. As you replace the PCB criss cross the two pot leads you soldered to the pot (route them opposite to where they originally where). Afre the PCB is back in place finish soldering the pot and the motor leads to the PCB. Reassemble and test. "GOOD LUCK"