Help!!!!! I have a wm Chipmunk-90s and I can't get the retracts to work right.Can anyone who has this kit tell me which retract servo there using.Mine collapsed on the maiden flt T.O. roll.A local hobby store told me I needed a retract servo with a 180 degree throw.The plans call for a 26mm throw.As far as I can tell there's no way this would work.I adjusted the down lock and made 6 flights with the gear down.The plane flys great.The problem I'm having is I don't have enough throw wheels up.If you have this plane can you tell me if you used a retract or regular servo.Any input would be great. Mike

You do need a retract servo, which puts out high torque to raise up those heavy wheels. Always use retract servo with mechanical retracts unless you have a small electric plane with micro retracts. In that case, you can use standard mini servo and adjust the servo throw via your transmitter.

You should verify the throw of your retracts. Pull the retract actuator rod all the way out (wheel down) and mark a spot. Push the retract actuator rod all the way in (wheel up) and mark a spot. Measure the distance between the two spots. This is the distance the two holes on your servo arm must be separated by because the retract servo swings 180° from one side to the other without stopping. 26mm sounds almost right if you are using Hobbico mechanical retracts. In fact, for Hobbico retracts, you need around 27.5mm throw. So if you are not using a retract servo now, you will need to purchase one.

Thanks for the reply.I did buy a hitec retract servo but can't seem to make it work.180 throw is way more then I need.I bought a low profile ailron servo that seems to work fine.Will I wear this servo out?Is the lock pin in the gear enough to keep the gear locked down?Thanks again,Mike

What radio do you have? You may be able to adjust the EPA for the retract servo. I'm pretty sure all Hitecs are 180 degree rotation. To change the amount of throw, you would need to put the EZ connector on a different hole on the servo arm. On all the WM planes I have had, I just set the servo arm so it is parallel to the wing, with the pushrod connector on the side away from the landing gear. Set the gear in the "up" position and attach the pushrod to the EZ connector. Cycle the gear and see if it works. if it does not lock completely in the down position, then move the EZ connector out one hole on the servo arm. If it binds as if it were too much throw, then move it in one hole.

I hope that is not confusing.

Most retract servos, including Hitec, are non proportional. They only rotate from end to end, so I highly doubt that you will be able to adjust the EPA using your radio. Just choose the servo arm with the two opposing holes separated by 26mm. If there isn't one, then drill two new holes.

The problem with using aileron servo is that if the retracts bind or if one of the struts is bent, then the servo will continue draining the battery trying to operate the retracts. On the contrary, the retract servo will just stop once it can no longer move.

Mr Berry- What you need is a set of Pneumatic retracts that comes with a little pump- That way the gear SLAM SHUT!

It was good to see you again at the field- Let me know when you are there on weekends 'cause I need some coaching on the final approach with the flap/down elev.

later,
james

The 'down lock' for WMs retracts does not have to go as far as it can. Same for the 'up lock.' The locking mechanism allows for a little play. Still, for me, I like to have the down & up throws at max.
There is also some length adustment on the retract actuator arm if you cut the rod or it is a little short.
If 180* is too much then your connectors on the servo arm are too far apart.
I just measured the throw on a set of WM retracts. At max travel the actuator arm moved 28mm +- .5mm. It is possible to get away with 23mm given the play in the locking positions. 26mm sounds just right and allows for an extra 1mm in each of the throw's max positions.

Richard L, I like your explanation very well! Why didn't I think of that?

Mike,

I'm in the SD area. If you want we can get togethor and I can help you setup your retracts. I've setup retracts on a P-51 and a Skyraider so I know how to do it. You will need a retract servo for that plane. If you use something else you'll wind up rigging it to work and when it fails you'll have a lot of work to do and will be upset.

Do it right and fly it longer. I know I'd hate to end a good flight with a colapsed gear.

Let me know.

Thanks for all the help guys.We got it all fixed up and it fly's great. I'll be out this sat if it does'nt rain.Happy Flying--Mike

mmm...just a stupid question....if the retract servo was not set up properly...meaning it can only rotate 150 degrees as opposed to the full 180 degrees, wouldn't the servo be stalled and draw excessive current from the battery also, just the same with a normal servo stalling?

Muah,

That's correct. The retract servo was designed to spin 180 and only 180. If it stops short, it will still try to spin the 180 and draw current from the battery. The servo will lock when it hits the 180 which keeps your gear from dropping or folding when you land. Less the 180 on landing could cause a collapse in you gear and that wouldn't be pretty.

I hate to end a good flight with a bad landing.

If you're having probs with your landing gear, get someone that has retract to help you set it up. Take to a LHS if you have to for help.

Let me know if you need more info.

thanks salty...
i don't have problem hooking up retract servos just that i was thinking of using normal high torque servos so that i can use the slow servo function of my multiplex RE to bring the retracts up and down in a scale manner....so what you are saying is that for retract servo, once it is in the lock position it will not draw current when in lock position, as for normal servos, when they are not moving they are still consuming current to resist any movements right? so for example for the throttle servo, the servo moves to the position and stays there but will only draw current if there is another external force acting on the servos, then it will draw current to resist the movement. for retract servo, once it is locked, it stays locked and will not draw current even if an external force is acting on it. if so, what is holding it in that position? a brake?

Not really a brake, as such, but mechanical retracts have an over-center position at each end of their motion. Once the servo moves the retract to either of these extreme positions, the mechanical lock, either up or down, keeps the retract locked until the servo moves again. At either full up or full down, the servo is just idling.

There is some current being drawn by the retract servo at either up or down lock, but it is basically the same current that any servo draws at "idle".

Muah,

Dick is right about the brakeing on the retract servo. Also keep in mind, a normal servo is designed to swing about 120 degrees, and a retract swing is 180. Now a servo used on the throttle will sit where it is, because that is what the radio tells it to do. A normal servo used for retracts is told to go further then it can, in order to hold up or down the wheels. That chatter the servo will be putting out is it trying to keep going; it not only draws more current (eating the juice in your battery) but it also puts wear on the servo and you will have to replace it sooner.

Retract servos are a little more then normal ones but are well worth the money. Once you learn how to set them up you'll see that it isn't really that hard to accomplish.

Hope this helps.

got it...retract servo it is then =)

thanks all...

Richard L.: This may not be the most appropriate place for this but, I am having a problem with my GP Stuka and you seem to know your stuff so, I'm asking my question of you.

More specifically, I am having a problem with the aileron servos. When I set one side to the specs, the other side is way off and when I switch sides and set the other side to the specs, the other side goes out. The servos are connected to a Y-harness. Each servo seems to be capable of performing reliably within the specs but, not together at the same time. I used both new Futaba 3004 servos and I have moved the pushrods on the different hole settings on both the control horns on the servo and the wing to attempt to fix this but, to no avail. I used CA to glue the servos in the wings instead of the servo tape that they supplied otherwise, I would just pull out the servos and check for a servo problem. It seems that no matter what side is out the servo goes way farther up and not enough down to come close to the 3/4 specs reccomended by the manual for low rates. I use a Futaba 9c tx with the new Futaba module installed that allows for channel changing. The receiver is a Futaba 127DF FM receiver. All other servos are also Futaba 3004's.

I have never had this problem on any other plane before. Usually when one aileron servo is correct, they are both ok and if not, simply adjusting the throw in the tx or changing the position of the servo horn and/or pushrod will take care of it. I have not had any problems with the flaps. They each move the same amount when deployed and work well.

Do you think this is a servo problem fixable without removing the servo(s) or maybe a tx programming setting that I may have overlooked?

Thanks,
Bob Proulx

Flieger,

Are your control arms setup the same? Rods the same length and connected in the same hole on the aileron and servo?

You are setting up the amount of travel to be higher up then down? I don't know if you can do that with a Y harness. With the Y one sides up is the other side down. So if you set up the left side to have 3/4 down then the right will have 3/4 up which means when you put the left side at 1 in up the right side will have 1 in down.

I understand you have flaps already setup on ch 6 but is there another channel open that you can put a servo into and connect the two servos seperately?

I had a similar problem on a Midwest AT-6. I spent hours messing with it and finally changed out the servo extension leads with some of better quality and that fixed the problem. I think they were heavier wire and had gold plated contacts.

Bill

Salty25 & Wacoone:
Thanks for your input. I will try different aileron extension leads, y-harness and if that doesn't fix the problem I will run 1 servo on Channel 7.

Bob