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5945 mg servo inaccurate?

Old 07-21-2005, 09:49 AM
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Default 5945 mg servo inaccurate?

I bought 4 of these servos 1 yr ago. I have about 15 normal flights on them, I cannot 3d. I have on the control surfaces a 3/8 play out of all these servos. I trace it down right to the servo. no linkage play at all. This is on a 28% plane. It makes setting up dual elevators and accuracy impossible. When I contated hitec through e-mail they told me ya its gear slop. Thats it so now what. I remember them being this way from new. Gear slop so now what i am stuck with servos that won't center properly won't always travel the same and give on pressure. So fly them this way???? do I really trust this??? I guess my next choice will be with jr equipment Maybe they give me what I payed for. [:@] Brenden
Old 07-21-2005, 11:44 AM
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Default RE: 5945 mg servo inaccurate junk

Have you tried to reprogram them?
Old 07-21-2005, 12:31 PM
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Default RE: 5945 mg servo inaccurate junk

as far as what? I set centers and end points. I have not set nor checked deadband. Hitec told me that would solve my concern. But you move the elevators three four times they don't line back up. same with max throws. keep the stick position there and push the play out of the flaps and you can line them up. I JUST CAN'T BELIEVE these are worn out already that just isn't possible. they haven't been used that much. And all of them to be pretty much the same. elevators and ailerons??/?/ I don't know
Old 07-22-2005, 03:35 PM
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Default RE: 5945 mg servo inaccurate?

It's very unlikely that the gears would be worn after 15 flights or that the gears had slop when brand new. What horns are you using? There must be another explaination here... the 5945's are well accepted in the industry as top of the line and offer excellent centering, resolution and gear wear.

Be aware that the 5945's are comparable to the JR 8411's which are well know for premature gear wear. The Hitecs have a much better reputation here so to say that swiching to JR will be better is not necessarily true. The new 8611's are better but they compare to the Titanium geared 5955's where Hitec has the advantage here too.

Mike.
Old 07-22-2005, 04:30 PM
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Default RE: 5945 mg servo inaccurate?

Mike,
let me say that first I think the support I received from the hitec websight was terrible. The only answer I received is it's gear slop. Boy what help they were.
Anyway, I am trying to trace this down. I had factory 1.5 in. heavy duty hitec horns on the servo. I now have replaced them with aluminum. still the same. I am now going to replace the only other option which will be the hanger nine ball links that are attached to the control horn. Brenden
Old 07-22-2005, 05:42 PM
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Default RE: 5945 mg servo inaccurate?

To clarify, you can move the servo horn 3/8" back and fourth at the output shaft? Are you sure there is not slop somewhere other than the servo gear-train?

I have hundreds of flights on these servos with very little gear-train wear fitted in 40% models.

The link below is a two year old 5945 removed from Josh's 2004 XFC Competition Extra. As you'll note, these servos center very accurately. The only deviation is yours truly man handling the DV camera.

[link=http://mglavincom.temp.powweb.com/45.wmv]Servo Resolution link[/link]
Old 07-22-2005, 07:26 PM
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Default RE: 5945 mg servo inaccurate?

I will post some picks of the play I have at the control surface. I replaced the hitec arms with aluminum ones. I also replaced the ball links . It is the exact same. Before I do anything else I am checking the deadband. TRUST me I cannot believe the amount of play out of these servos. By the time it reaches the elevator it is alot. I don't trust this much movement in a 3000.00 plane. I am not a wild 3d pilot. these have been flown fairly gingerly. As far as the video goes thats great but that don't help my problem. I believe there good servos thats why I bought them. I just cannot believe this. Brenden
Old 07-22-2005, 07:43 PM
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Default RE: 5945 mg servo inaccurate?

Changing the deadband will have no effect on slop realized, be it gear-train wear, linkage or surface induced. The "slop" is a mechanical thing shortcoming.

Remove the linakge from the servo and see if the 3/8" slop you note is present. I'd be surprised if it was.
Old 07-22-2005, 08:41 PM
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Default RE: 5945 mg servo inaccurate?

I have the servo arm only on the servo. I have some small movement. Exceptable???? I think. Now I have replaced the horns on the elevator and it cut the play I would say in half. Would you except some play in the elevator?????????????? the deadband as you said had zero effect.
Old 07-22-2005, 09:36 PM
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Default RE: 5945 mg servo inaccurate?

A small amount of play is normal with metal-geared servos.

Any slop is amplified, from every source with the linkage in play. Longer linkage arms and offsets reveal or amplify the original slop. Please post picture of your setup. What length are the control arms, measure from the hinge centerline to the control link pivot point. What length servo arms? What type or brand elevator control arms and linkage components are utilized?
Old 07-24-2005, 09:10 PM
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Default RE: 5945 mg servo inaccurate?

Micheal here are some pics of my changed set up. I cut down the play by half to maybe an exceptable 1/8 play at the elevator it self. the last pics are of some components I changed. I didn't see play in them but changing them wound up making a difference.
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Old 07-24-2005, 09:11 PM
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Default RE: 5945 mg servo inaccurate?

the third pic above I tried changing to that style end but didn't like how the nut for the screw spun. So in the trash
Old 07-24-2005, 09:13 PM
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Default RE: 5945 mg servo inaccurate?

here is the part I changed that seemed to make the biggest change.
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Old 07-24-2005, 10:04 PM
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Default RE: 5945 mg servo inaccurate?

Looks good.

What length is the servo arm and what is the distance between the hinge line and control arm pivot point centerlines?
Old 07-25-2005, 09:06 PM
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Default RE: 5945 mg servo inaccurate?

I will try to answer this the best I can. The servo arm is 1 1/8 from the center screw to the center of the ball link.
From hinge line to pivot on the elevator horn is 1/2 inch(meaning my pivot is not on the hinge line)
An last 7/8 from the hinge centerline to the actual bolt that comes down from the elevator
Anything else I missed let me know?

So I guess the 1/8 play out at the elevator is ok, (normal)??
Old 07-25-2005, 09:34 PM
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Default RE: 5945 mg servo inaccurate?

Measure the distance between the control arm pivot piont and the hinge center line. Sounds like the control arm pivot point is behind the hinge line 1/2".

1/8" is not unsual. Where is the play? Can you hold the servo arm and move the surface and realize the play?
Old 07-25-2005, 10:27 PM
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Default RE: 5945 mg servo inaccurate?

No, I have no play by holding the servo arm at the elevator. I can move the servo arm and get that.
Old 07-25-2005, 11:44 PM
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Default RE: 5945 mg servo inaccurate?

I'm confused... How can you hold the servo arm at the elevator?

Hold the servo arm at the servo firmly and move the elevator slightly back and fourth, is any play present? If not the play is in the servo. Now do the inverse, hold the elevator and try and move the servo arm...
Old 07-26-2005, 12:20 AM
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Default RE: 5945 mg servo inaccurate?

I always assumed the push rod should be (at least close) to 90 degrees to the servo arm and elevator horn, your set up seems to have a fairly large angle. I also thought the connection at the push rod and elevator control horn had to be in line with the hinge line, otherwise you get different elevator movements from up to down (I think), and the elevator hinge has a different pivot point than what the mechanical linkage and they work against each other by causing a bind and excessive drag. Sometimes too much drag in the linkage can prevent the servo from centering. Disconnect the elevator and see if the servo centers with no load. Try to make the distance from the elevator hinge to push rod connection the same ,or at least closer, to the distance from servo arm screw to the push rod connection point. My guess is that you have a combination of problems that add up to amplify the gear slop and provide poor control.
Old 07-26-2005, 01:09 AM
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Default RE: 5945 mg servo inaccurate?

Spad

You're onto something....

Ideally the control arm pivot should be centered over the hinge line. The offset that exists does create unequal travels arcs either side of center, but binding is generally not an issue until extreme throw is realized. One can compensate for the offset at the hinge line by rotating the servo arm from perpendicular or 90 degrees from the case and obtain linear throw again. You’re also right in assuming the angles, offsets and such exasperate the play.

Granted the depicted setup is not ideal. b-mccor8 have you tried to install the servo arm 180 degrees from the present location? This would be much better IMO. If you can provide accurate dimensions for the setup I can extrapolate the best case set-up for you.

I'll draw something that shows what dimensions are needed; I suspect it will be easier to show you than explain. Give me a little time.
Old 07-26-2005, 05:08 AM
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Default RE: 5945 mg servo inaccurate?

thanks
Old 07-26-2005, 11:01 AM
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Default RE: 5945 mg servo inaccurate?


ORIGINAL: mglavin



Granted the depicted setup is not ideal. b-mccor8 have you tried to install the servo arm 180 degrees from the present location? This would be much better IMO. If you can provide accurate dimensions for the setup I can extrapolate the best case set-up for you.

That is the way I had it originally. But I had the play problems so By eliminating certain ends I had to go back to the setup that is on the bottom end what you seen now. I have flown it this way it it seems fine. I have my throws where I wanted them at 50 degrees and it doesn't seem to ever move the servo arm BUT REALLY I AM OPEN TO BETTER SETUPS. I am here for help.

And your other question. If I hold the servo arm i can not move the elevator. If I hold the elevator you can get movement out of the linkage all the way back to the servo arm that you can see it move. I hope I explained a little better that time
Old 07-26-2005, 05:54 PM
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Default RE: 5945 mg servo inaccurate?

Ok, sounds like you have removed all the slop in the linkage.

After doing some work in ACAD and on my Excel spread sheet I realized the resultant behavior is a little different than I believed with your servo-linkage configuration. It turns out the servo arm pivot point “-“or below the control arm pivot is best. With the pivot point below the servo axis the deflection ratio is more linear and the power required either side of neutral is too. In either case the total throw was not a factor.

Any-who provide the dimensions as noted on the drawing below and I’ll give you the best case set-up for your elevators.
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