Servo extension & retract servo
 

I am presently attempting to build a "ultra sport 40 plus". I am going to use a Futaba T6XAS and will use S3004 servos.

The booklet of instructions state that if using a computer radio, I will need (2) 6" Servo extensions. (from Tower Hobbies, this is (HCAM2700) I checked this out and the notes from the tech dept. state that these are with JR, Hitec, and Airtronics Z style connecters. No mention of Futaba connectors.

I then went to the list of Futaba connectors and really got even more confused. I have no idea what I should be getting. Would like some advice on which one I need to obtain.

Also, I am going to use these same servos for retracts. A fellow club member who is very knowledgable stated that retracts need a retract servo in order to avoid lots of problems. But when I checked on the price of one of these jewels, I got discouraged. That's a lot of money! Would I be wrong to go ahead and use these standard servos for my retracts? I am planning on installing the Great Planes .40-size Mechanical Retracts.

Would appreciate any help on these two problems. Thank you.

RE: Servo extension & retract servo
 

Retract servos are a different design than standard servos. They really have only 2 positions possible positions, retracted and extended. Normal servos moove over a basically infinite range (not really but close)

Also, the retract servos deadband is greater, so it is less likely to drain the flight pack at the ends of travel. In other words, within reason when it gets to the end of its travel in either the retracted or extended position, the servo motor stops. It would be very hard to get a normal servo to do this, but it is not impossible. Your linkages would have to be really perfect, not easy to do.

Having said this, many will tell you you can use regular servos......you could probabaly drive a car with your feet too, not sure either is a good idea.

Good luck

RE: Servo extension & retract servo
 

You can pick up a Hitec HS-75BB retract servo from Servocity.com for about $29.00. That's not at all out of line.

The JR/Hitec/Aitronics Z connector are all fully compatible with the Futaba connector.

Read up on retract servos in the Comments section at:
http://www2.towerhobbies.com/cgi-bin...?&I=LH4299&P=1

John

RE: Servo extension & retract servo
 

Matt & John....thank you both for the information that you gave to me. I have decided to take your advice and get that Hitec retract servo. I'm new to this building stuff and your advice should certainly help keep me from having more regrets. At least now I know why it is better to put retract servos on the plane instead of regular servos. Man oh man, would I have been really bent out of shape had I found out about this after I tried regular servos instead. Once again, thank you both very much.


Sugarfoot

RE: Servo extension & retract servo
 

Has anyone used the JR Sport RT88 retract servo? I have it in e-flite's at-6 texan, and the rate of travel is way too much. I was told by Horizon, that this servo can't be adjusted. Anybody know of a soultion to this problem?

Thanks

Matt

RE: Servo extension & retract servo
 

It is not a Proportional servo and rotates ~120 deg so you need to make Mechanical Adjustments in order to match your installation. As with all servos, the shorter the servo arm, the more the servo arm has to move to push or pull the pushrod the same distance. I originally used RT88 on my H9 P47-150, but I eventually replaced them with the 791 servo because I needed more horsepower. I am using very short H9 metal servo arms.

RE: Servo extension & retract servo
 

Thanks for the reply, I've never used retracts before, so I'm learning as I go. My RT88 servo moves 180 degrees in both the up and down position, so it won't lock in place. I will try shorting the push rods, and see if I can get it to work properly.

RE: Servo extension & retract servo
 

It is the Servo Arm you need to shorten. Are you using just one servo to operate both Retracts? If so, some people use a Servo Wheel. You drill holes in the Servo Wheel for each pushrod. The closer the holes are to the Servo Arm Screw, the less travel.

RE: Servo extension & retract servo
 

Yeah, there is only 1 servo, the problem I'm having now is when I put the wheels up, they go up part way in the wheel wells and then drop back down, a quarter of the way, at the end of the servo's cycle. So I will try one of the servo wheels, and see what happens.

RE: Servo extension & retract servo
 

If you disconnect each pushrod from the Servo Arm and then Push it and Pull it, does each retract go Up all the way, then Lock, and Down all the way, then Lock?

It could be that the pushrods move further one way than the other. if so, using the Servo Wheel, you can drill the holes for the pushrods so you get some differential.

Are you sure that the pushrods are strong enough and that they are not Flexing? The pushrod wire should be strong enough to move the retract linkages properly. If you take the Servo Arm or Servo Wheel off the servo and twist it by hand, you should be able to tell if the Retracts are moving Up and Down properly and you should be able to tell if the RT88 is strong enough to operate the Retracts properly.

When I used the RT88 servos on my H9 P47-150, there was one servo for each Retract Main. When the plane was upside down, the RT88 could not bring the gear to the Down position fighting against Gravity. I also had a plastic Gear strip in one servo. When I switched to the JR 791 Retract servo, they had plenty of Torque and Metal Gears, as well. My pushrods were only 1" long and Straight. I used 4-40 rod. If your pushrods are Bent or Curved, they may flex.

RE: Servo extension & retract servo
 

Everthing checks out ok, the retracks work fine, even upsidedown and lock in place when down. When they move up, the servo travels to far. With 1 complete rotation of the servo, they go up into the wheel wells and back down part way. I have used different lengths of arms to no avail. I have video's of it, but this forum does'nt seem to allow video uploads. The guys at my local hobby shop are also looking in to this problem.

RE: Servo extension & retract servo
 

Good luck!! Sorry we could not come up with a solution without acutally seeing the install. I have used many mechanical and air retracts over the years. The mechanical ones can be a pain.

RE: Servo extension & retract servo
 

I'm having the same problem with my JR RT88 in my AT-6 Texan as well. I think its ridiculous that E-Flite recommends this servo for the plane and then pretty much lets the user figure it out. I can't adjust the travel with my radio and now I find out that I have to do a "mechanical" adjustment. I did not realize I would have to be screwing around with a servo arm to get my retracts dialed in... What a bunch of CRA***

RE: Servo extension & retract servo
 

No offense, but you're probably going to be screwing with the mechanical retracts for as long as you fly that plane.....unless you're flying off asphalt. I fly several planes with mechanical retracts, and they always seem to need some type of adjustment....but my field is kinda rough. No big deal, just part of the hobby.

RE: Servo extension & retract servo
 

No offense taken, if anything I was a bit hasty with my post about the RT88 in the AT-6... I found out on another site that the RT88 will work fine with the E-Flite AT-6 Texan as long as you set the pushrods up correctly. I gathered up what was left of my patience and went and tried again and was able to manage to get them to work properly, although they still need to be slightly tweaked.

I have two other planes that use retracts,(all my others have fixed gear) and I know what you mean about having to occasionally adjust them. I'm fine with that since my warbirds that have retracts look so much better with the gear up... Its well worth any hassle I have to deal with to get the retracts to operate properly.

RE: Servo extension & retract servo
 

A very good place to start with the set-up would be to measure the total travel the retract "rod" has to move from up to down lock. That's how far apart the links have to be at the servo end.

RE: Servo extension & retract servo
 

Here is my long overdue update, it's just as `p39' put it. I had to do a lot of push rod adjusting until I found the "sweet" spot, for the retracts. But during my frustration I scraped the servo and went with a standard Hitec low profile one. It works a lot better since you can adjust the travel and end points. But like people before me are saying, you just need to find the right length for those rods. Happy flying and many safe landings!:D



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