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 Post subject: Tail servo temp
PostPosted: Sat Aug 24, 2013 7:10 pm 
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Posts: 40
I have never really monitored the tail servo temp before, maybe because I just never really cared or I did the finger test and it was unremarkable. I noticed here a few weeks ago that both the 9254 on my Protos and BLS251 on the Outrage 550 were coming down pretty hot. Both of these helis just recently converted to flybarless with the 3gx bastard child. The 9254 was coming down at a max of 160F (on the motor end) and the 251 at 140F (evenly spread across the aluminum case) with a 90F ambient.

This all really came to light after I dumb thumbed a landing on the Protos and hit the tail hard enough to break the slider yoke. I had been running the 3k blades and 20t pulley. When I ordered parts, 3k's weren't available so I went for the 72.5 KBDD and got the 18t pulley since I'm running low hs. Not only did this bring the hot servo to light, but it also brought some tail performance issues. I'm not sure that the servo wasn't getting that hot before, but the tail performance was spot on with the 3k's. Its a long story, shouldn't have changed so much at once, and I'm slowly working back to the original setup. Yet to get some more 3k tails. I was able to get the 9254 to run cooler by lowering rudder gain, which with the 3gx servo temp seems to be highly sensitive to rudder gain. Got it down to ~135F, but that still seems excessive. I was also able to get the 251 down to 120 with gain adjustment.

In the mean time, I picked up a new DS655 to try and immediately after just swapping the servo, the temp dropped 20 degrees, but this was on a cooler 75F day. But, the last thing I changed was going back to the 20t pulley and on a 90F day the 655 was coming down 133F three flights in a row.

Mechanically, both tails are smooth. I'll never rule out setup error on my part, but I don't see how this is a mechanical issue. Unless, the tail grip bearings are going out. Hmm, just thought of that. I also know that the relationship between component and ambient doesn't rise linearly with ambient temp. Mechanical and gyro setup aside, I'm curious to hear your all's experience with tail servo temp and what is too hot?? Futaba spec's 140F for the 251.

What about the pulley and the longer tail blades? Can you have too much tail authority and have it negatively effect tail performance? I never really have liked the KBDD's in the past if nothing else due to the annoying buzzzz, so I'm really hoping that's the issue. I found plenty of folks running the stock plastic tail blades without issue, and much less liking the KBDD.


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 Post subject: Re: Tail servo temp
PostPosted: Sun Aug 25, 2013 8:15 pm 
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Joined: Wed Jul 27, 2011 8:13 am
Posts: 1523
Location: Caldwell, TX
Not familiar with the 3gx setup, but I see the 9254 is supposed to have a 333 Hz frequency setup. The BLS251 they say can handle 560 Hz. If they are getting hot, I suggest trying to step them down one notch and see if that helps. Also be sure that you don't have the the ball out too far on the servo horn. That will put excess load on the servo.

Edit: Also should add you can reduce servo temp by also reducing the voltage you supply to them. But who wants to do that?

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Bobby Barr
DT Helis
Graupner USA


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 Post subject: Re: Tail servo temp
PostPosted: Tue Aug 27, 2013 7:27 am 
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Joined: Thu Jun 27, 2013 6:13 pm
Posts: 40
Thanks Bobby. The 3gx doesn't have any functionality to change servo drive freq. Have tried multiple horn lengths, and even went way too short, it still had little impact on the servo temp. I did fail to mention that these are both running on 6v, which Futaba obviously doesn't recommend. However, dropping it down to 5.4 also had very little effect on temp. The Align DS655 is rated for 6V.

So you Texas guys don't see elevated tail servo temps on 90F+ days?

Is it not normal for tail servos to run hotter than cyclic servos?

The only other thing I can think of is a vibe issue that is causing the 3gx to overwork the tail servo????


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 Post subject: Re: Tail servo temp
PostPosted: Wed Aug 28, 2013 12:32 pm 
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Joined: Wed Jul 27, 2011 8:13 am
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Location: Caldwell, TX
We typically don't see our servos much above ambient even on the hot days. With exception of Carter this weekend flying his Goblin 500. That entire helicopter was hot. :face The battery wires and EC5 connectors were warm, and so were the servos. :shock:

Sounds like you have tried all that I can think of. I'll keep thinking.

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Bobby Barr
DT Helis
Graupner USA


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 Post subject: Re: Tail servo temp
PostPosted: Mon Sep 02, 2013 7:13 pm 
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Joined: Thu Jun 27, 2013 6:13 pm
Posts: 40
On the 550, I quit trying to fix the bounce after a hard right piro stop and optimized the rudder gain (tx) and tail lock gain (software). It seems that the 3gx likes the rudder gain just barely high enough to hold the tail in FBF. Got in 4 consecutive flights with a 98F ambient and the 251 was coming down 116-120F after a 6min flight. I can live with that. Switched to the DS655 today, performance was comparable, but it didn't really run any cooler. 87F ambient and it was coming down at 106-110F.

V4.0 is unofficially available on Align's website, but I'm going to wait for a few reviews before I make the jump.


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