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Top Flite 1/7 P-51 Arf retract problem

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Top Flite 1/7 P-51 Arf retract problem

Old 04-08-2010, 12:15 AM
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Fear2722
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Default Top Flite 1/7 P-51 Arf retract problem

This will be my second season for my P-51 with the stock mechanical retracts. When i bought the airplane, I bought a GWS retract servo. That was an epic failure. It cycled the gear several times on the bench with no problem, and the third time to the field, it would not fully retract or extend... result... you guessed it... bellied in landing (looked scale though!)

Second servo was a hitec retract servo... Two flights, same story.

Third servo is a JR Retract Servo.... Haven't flown it yet, sort of afraid to.

I just installed this third servo this week, and I've decided the servos have failed due to a mechanical problem. This is the first bird I've ever had with retracts, so I allowed myself some humility and decided there was too much load on the servo in the retracted position, as there is a click that I never paid attention to before. I fly JR, and the manual for the plane just wants Futaba stuff. Haven't entertained the thought of using a futaba retract servo yet... but it shouldn't be a brand game to get the thing to work correctly.

I've made new pushrods for the retracts, made the adjustments on the kwik links, as well as the white nylon clevis' on the retracts them selves... I get to where it's either no clicking in the retracted position, but clicks in the extended position or vice versa. Something I've learned is that retract servos don't have the ability to adjust EPA... Would a digital retract servo solve this or am I still missing something?

The directions aren't difficult, at least I think, and product support was less than helpful when I called in asking what to do...

I guess if I can't get a servo to solve the problem. I might upgrade to the air system but then I don't know if that's a whole nother headache I've yet to embark upon yet or not.... I just know that I'm tired of looking at the plane suspended from the ceiling!

If you have a solution for me, or advice, or have had a similar problem, please let me know because I feel like I've done everything as far as mechanical adjustments go and have made zero progress.

Thanks a million.

Donivan
Old 04-08-2010, 12:52 PM
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FallDownGoBoom
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Default RE: Top Flite 1/7 P-51 Arf retract problem


Ah, the joys of mechanical retracts...

Your Hitech or JR retract servo should have plenty of torque to push/pull the retracts. (You should be able to pull them open/push them closed by hand without major effort. If that's not happening, then something is binding inside the retract housing, which could lead to your servo problem.)

Assuming there's no binding, then you have to get the correct amount of travel set on the push rod connectors. Unfortunately, you're correct in that there is no end point adjustment on an analog retract servo. It goes 180 degrees in either direction. It sounds like you've got either too much or too little travel adjustment on the EZ connects, and the only way I know of to adjust this is via trial and error.

It sounds like your qwik-connects may be too far out on the servo arm, meaning they push the connecting rods further than they need to travel. This would cause your servo to buzz or click in the open/closed position. (Clicking could also mean you've broken a gear tooth inside the servo.) What I found with my Robarts was that the qwik-connect location didn't correspond to any of the standard holes on a servo arm, so I used a 3/32 piece of aircraft ply and built an arm with the qwik-connects at the right radius from the center, then attached the wooden arm to a standard plastic arm. The way I figured the radius was to measure the linear travel of the actuating arm from closed/locked to open/locked, set half that distance as my radius, then used trial and error to fine tune the adjustment.

You can go to pneumatics, but then you get the joys of tracking down air leaks... as well as spending more $$$.

If you need more ideas/info, I'll try to help.

Fred
Old 04-09-2010, 02:17 PM
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Fear2722
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Default RE: Top Flite 1/7 P-51 Arf retract problem

You could be on to something... THe servo horn I'm using is just a standard straight one from JR, with three holes on each end... I'm using the outer most holes. Should I bring them in closer to the center?
Old 04-09-2010, 06:08 PM
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Default RE: Top Flite 1/7 P-51 Arf retract problem

That would be the easiest first step. You want the actuators to move far enough to engage the retract locking mechanism, but not so far that the servo can't complete it's travel. Moving to one of the inside holes will reduce the linear distance the servo moves the arms. All you need is for the gear to lock in the up/down position. Any further travel than that is wasted, and as you've seen, detrimental to the health of your servos.

If you're using Robart 608HD retracts, the arm travel, at least according to their dimensional drawings, is 1-3/32". Half of this is (like I can really measure this accurately ) 17.5/32", or just a shade under 9/16". I'd measure the distance to each hole on the control horn, and pick one that's close to, but not more than that distance from the center. You might also look at the different styles of arms... JR's got a symetrical cross, a four armed horn with one side longer than the other, and a straight two arm horn you've been using. The other horns might have slightly different hole placement.

Fred



Old 04-09-2010, 07:17 PM
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j.duncker
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Default RE: Top Flite 1/7 P-51 Arf retract problem

I have had the problem with a 180 servo and mechanical retracts where none of the servo arms gave the correct throw.

I took the big round output disk and drilled it to suit the retracts so it gave the correct throw. I was already using ball joints so did not have to cut the disk.

I also always use a separate battery for the retracts.
Old 04-10-2010, 01:04 AM
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Fear2722
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Default RE: Top Flite 1/7 P-51 Arf retract problem

how would you use a separate battery for the retracts? I've got a 2300 or 1700mah 6.0v now... I forget which for sure, probably should check before I fly it this year. I'm leaning towards the 2300 though, due to all the servos!

I went out tonight after work and moved the quick links in to the center holes of the JR arm, no clicking or binding. I've got it on charge now, will check it out again in the AM.

Thanks for your help guys
Old 05-09-2010, 06:16 PM
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TomTreese
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Default RE: Top Flite 1/7 P-51 Arf retract problem

If anyone is haveing a problem with the mechanical retract boxes breaking on a hard landing I have designed a aluminum reinforcement box that will fit the AT-6, P-51 and P-47 models. These boxes have eliminate the breaking and cost $36.00, which is much less expensive than Robarts. I have over 80 landings and over 30 sets in the field on the AT-6 without a failure..

I also use the Hitec retract servo HS-75 and have had no problems

Read more: http://www.rcuniverse.com/forum/m_88...#ixzz0nTdLTXq9
Old 05-10-2010, 12:02 AM
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Fear2722
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Default RE: Top Flite 1/7 P-51 Arf retract problem

Yep I had enough. After much debate, I ordered the Century Jet's. Anything's gotta be better than this junk. Only thing Top Flite could have done better was provide better retracts.

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