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Servos stop moving intermittantly- Update...

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Old 09-23-2003, 06:37 PM
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MHawker
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Default Servos stop moving intermittantly- Update...

I have a 25% Extra with a Hitec 5625 Digital servos in the ailerons. Everything has been fine for about 20 -30 flights or so (about 6 months).

This last weekend while doing a range check etc, I noticed the aileron servos stopped working intermittantly while wiggling the stick quickly back and forth. Long story short, one or the other or both would stop. I have them on separate channels of a 149DP RX (see further in the story before thinking it's a PCM thing). And, so far, only the ailerons are affected, although I thought one of the elevators (separate channels too) stopped once.

I originally thought it was the battery. I charged it at the field to make sure it was fully charged. It read 5.3v on a loaded meter. Same thing. I scrapped the flight for that day.

At home I tried another battery (fully charged NiCd pack), another RX, other servos and finally narrowed it down to the servo extensions. I went to the LHS and got another set of Hitec HD extensions. The 24" ext would still cause the same problem and the 12" would not. BUT, some 605bb's that I had laying around would work fine with any extension.

Sooooooo, since I know people have been using longer extensions (including me) with digital servos, why do you think it's the servos? I understand that digi's use more power, but something doesn't make sense. Oh, they have a Mar 02 stamp on them.

Any ideas would be appreciated.
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Old 09-24-2003, 06:04 AM
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Default RE: Servos stop moving intermittantly

Sounds like a power problem, Hitec digitals take alot of current. Does your battery also have a heavy duty lead? Do you have a 6v pack you can try? If so that may help as the Hitec digital don't like too low of voltage from what I have seen, I run 6v on all of my digitals. Also check your switch if it has a lot of resistance you could have much lower voltage at the end of the ext. If you have the hitec programmer or know someone that does hook it up to the end of the ext. on the aileron and see what kind of voltage you are getting, it may be dropping below 4.8 momentarily and that may cause the problem.

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Old 09-24-2003, 10:43 AM
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Default RE: Servos stop moving intermittantly

Thanks Mark. I don't have a 6v pack to try but it wouldn't be hard to make one if it comes to that. I did try using a different pack which was plugged directly into the RX so I could eliminate the switch. Same result.

It sounds like a power problem to me also, but I'm at a loss (no pun intended) as to why it has worked fine up to this point.

Thanks again.
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Old 09-24-2003, 11:18 AM
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Default RE: Servos stop moving intermittantly

It could be a dead spot in the motor. I had some 5625's and some 615's that had similar problems. I talked to the tech at Hitec and was told they had the same motor and it could be the problem. I sent them in and they replaced them.
If a motor has a dead spot in it ( a place where the brushes lose contact) it probably will not fail under the vibration of the engine or under load of operation. It will only be noticeable when you are testing. If it stops , push it with your finger and see if it starts again.
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Old 09-24-2003, 01:46 PM
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Default RE: Servos stop moving intermittantly

Just ditch those servos. With a fully charged battery pack you shouldn't have a problem powering servos with 24" HD extensions. I use 48" HD extensions on my 8411s and they don't have any problems. I'm sorry, but I'm just not a believer in these Hitec servos.
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Old 09-24-2003, 02:59 PM
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Default RE: Servos stop moving intermittantly

Ill second what Flyfalcons said, I have had digital JR8411's on 48" extensions on a jet and a 33% for over a year now on 4.8v with zero problems.. Its not worth losing a model to save a few buck IMO.
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Old 09-24-2003, 04:01 PM
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Default RE: Servos stop moving intermittantly

I'm totally with you guys on this. I'm not about to risk losing a plane or hurting someone, etc which is why I scrapped that flight. Even though the problem only surfaced when I wiggled the stick quickly, that was good enough for me to step back and say, "whoa".

I have had zero issues with these servos so far, but I would be remiss if I didn't question what was happening.

Anyone have any 8411's for sale?
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Old 09-24-2003, 04:04 PM
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Default RE: Servos stop moving intermittantly

Good thinking! I cant remember the place now, but Ryan just got a bunch of servo's from a place that gave a discount for buying a few. Ryan?
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Old 09-24-2003, 04:10 PM
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Default RE: Servos stop moving intermittantly

www.rcsuperstore.com
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Old 09-24-2003, 10:41 PM
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Default RE: Servos stop moving intermittantly

Thanks Ryan.
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Old 10-06-2003, 02:16 PM
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Default RE: Servos stop moving intermittantly

FYI, I sent my servos into Hitec and just received them back with a note that they "upgraded the software".

I'll check them tonight. Great service. I dropped them off last thursday (I work and live about 10 minutes from them) and got them back today.
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Old 10-07-2003, 12:56 AM
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Default RE: Servos stop moving intermittantly

First problem: Why are you performing a range check? You should not be wasting the RX pack with that garbage!

Problem#2: Digital servos- These are like those "computer slot machines" that can create any desired outcome (Crooked) and should not be trusted! Use the Older Hitec 300's for optimum performance..

Lastly: Why you movin' the sticks real fast? Use + expo. like 85% and move them "regular speed"

I am sorry for wasting y'alls time but Mike is so good natured! (Hawker we NEED to have a B-B-Q!)

late
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Old 10-07-2003, 10:58 AM
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Default RE: Servos stop moving intermittantly

Hey Razor!

I'm still laughing!! BBQ sounds good. We'll pick a weekend soon. My mom is coming out from Colorado over the Halloween weekend, so after that would work.

Here are my results.......

Got home and tested my servos......... same thing. Tested the battery and it was low. I charged it overnight and checked it this morning and guess what?........

Same thing. Oh well, back in to Hitec they go. I'm not getting that warm and fuzzy.
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Old 10-07-2003, 02:24 PM
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Default RE: Servos stop moving intermittantly

Another FYI,

I just got off the phone with Hitec Service. They were very quick to call back. They told me I should buy boosted servo extensions as some of their digitals have problems with extensions over 12".

I will be replacing these servos since the answers are just guesses at this point and this problem is too wierd to risk my plane.

Anyone want to buy some ?? 5625's cheap?
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Old 10-07-2003, 03:03 PM
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Default RE: Servos stop moving intermittantly- Update...

You couldn't pay me to take those servos.
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Old 10-07-2003, 03:22 PM
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Default RE: Servos stop moving intermittantly- Update...

This is a voltage issue. Are you using a HD switch harness too?

Flyfalcons- Nice reply for a moderator!

Mike.
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Old 10-07-2003, 04:45 PM
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Default RE: Servos stop moving intermittantly- Update...

Hi Mike,

I agree it's a voltage issue but I can't figure out what it could be. Perhaps I missed something obvious. I am not using an HD switch harness, although in my testing, I did plug the battery pack (a different pack) directly into the RX to bypass and eliminate the switch as a possible cause.

I'll PM you with more details.
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Old 10-07-2003, 05:26 PM
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Default RE: Servos stop moving intermittantly- Update...

Bet it only happens when you move the sticks real fast in both directions as opposed to a stick jam to the corners. Can demo the same thing on one of my planes, even with only two digitals on ailerons. And it only happens on rapid stick movements in both directions after about 2 cycles. This is a problem with too much current draw (due mostly to the reversals) in the system taking the battery voltage below what's needed at the servos or maybe receiver too. You can prove this by plugging in a second batttery pack and trying the same test. I run two packs on the plane in question and can't duplicate the failure any which way.

Do you move the sticks that way in flight???? Probably never.

Fixes: Maybe better switches and extensions will get it but 6 volt packs or 2 x 4.8's will probably get it best.
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Old 10-07-2003, 06:32 PM
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Default RE: Servos stop moving intermittantly- Update...

Thud_Driver,

You're exactly right. I didn't think to try two packs. I can check that tonight.

Nope, I probably wouldn't ever do that in flight (probably being the key word), but since I don't know what causes it, I feel safer not flying. For instance, if it happens because of a load, flying would be detrimental to my wallet, not to mention the chance of hitting someone or something. If it's just when I move the sticks back and forth quickly, then I'm probably fine (again, probably).

Of course, when the analog servos I tried aren't doing it and the Futaba 9252 (digital) I've got on my rudder isn't doing it and the 5925's aren't doing it, you'd be hard pressed to convince me I have to run 6v or two packs v.s. replacing the servos. Sure it'd be cheaper, but I'm afraid it would be masking a problem.

Nice to know I'm not alone, though
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Old 10-07-2003, 07:49 PM
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Default RE: Servos stop moving intermittantly- Update...

Well, for your piece of mind, you'll want to do something. A lot of airplanes aren't going to let you run short leads to all the servos. I don't know if a HD switch and HD extensions will make your particular problem go away. But if it does, fine, but a second battery or higher voltage may improve the margin in your system to a more significant extent.

You didn't mention your Rx battery capacity. Many guys running the bigger airplanes are running upwards of 2400 mah packs. A SCR type Nicad in that range which supports high current spikes better might make all this go away just as easily. On mine, I'm running 1650 mah AA Nimh so heavy current draw capability is an issue (and I knew that going in).
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Old 10-07-2003, 09:20 PM
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Default RE: Servos stop moving intermittantly- Update...

Of course, when the analog servos I tried aren't doing it and the Futaba 9252 (digital) I've got on my rudder isn't doing it and the 5925's aren't doing it, you'd be hard pressed to convince me I have to run 6v or two packs v.s. replacing the servos. Sure it'd be cheaper, but I'm afraid it would be masking a problem.
The problem is a voltage degradation, more than likely. The servos you listed above that are not having the problem are coreless. These servo are more efficient. Some tests were done previously and If I recall the 5600 series were recorded consuming more power. Try 6 volts. What size battery are you using?
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Old 10-08-2003, 04:43 PM
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Default RE: Servos stop moving intermittantly- Update...

OK, here's the last you'll hear of this (famous last words).

I just got back from Hitec. Steve in their service department spent a lot of time with me checking things out. We hooked up a small 6v pack and could not duplicate the problem. As you all (or most) have said, more power may be the best solution in my case.

Although I'm not totally satisfied that I am not able to use a 4.8v pack when the servos are listed as such, I'm not going down the "they should have told me I couldn't run...." road. Luckily I caught this while the plane was on the ground. I am satisfied though, after talking with Steve, that running 6v won't mask a problem but is more appropriate for my set-up.

Thank you all for your input. And many thanks to Steve at Hitec for the time he spent with me.
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Old 10-08-2003, 09:27 PM
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Default RE: Servos stop moving intermittantly- Update...

9252 is a digital servo.
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Old 10-11-2003, 11:10 PM
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Default RE: Servos stop moving intermittantly- Update...

9252 is a digital servo.
Yes, the Futaba 9252 is a Digital servo and it uses a coreless motor.

Digital servos are typically comprised of the same components as there Analog cousins less the servo amplifier (digital or analog).

Some servos which have a 3/5 pole or cored motors again are the same components less the a digital or analog amplifier (Hitec 5600 series, JR 811 and Multiplex).

I mentioned above these servo seem to be somewhat more power hungry and have higher internal resistance.
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Old 10-12-2003, 07:09 PM
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Default RE: Servos stop moving intermittantly- Update...

One thing to note, Futaba suggests using only 4.8 volts on their 9252 servo.
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