Mark Vandervelden

Hi all
I'm not far from a maiden with a 40lb 1/4 scale jet airframe . Normally I'm very conservative especially with primary control surfaces and stay with what I know, which in this case would be the JR8711 delivering 25kg at 4.8v. On this particular airframe the tails are quit large at 16"x22" each! and after first fitting two 8711 servos I had second thoughts as I felt that I would be close if not beyond the 8711 servos ability. I have now opted for the 26.3kg @ 4.8 up to 40.6kg at 7.4v spec of the MP82Twv servos, running them at 5.9v. This would be delivered from my PB SRS unit hoping to achieve around 30-35Kg. I have no practical experience of these servos other than on the bench and know of no one locally that's using them. I would appreciate any reports of "actual experience" of some one that's "actually" using them in successfully or not there airframes. Its a big world out there so JR must have sold more than the two that I've bought .
Looking forward to your replies, Mark V

HarryC

My Feedback: (1)

A related issue - a properly designed all moving tailplane of symmetrical section should have zero aerodynamic force trying to move it back to centre. In reality it won't be designed or built absolutely perfectly, and so for safety's sake should be designed deliberately slightly on the stable side so some small blow-back force will exist but it should be less than the blow-back force of a normal hinged elevator. Therefore the servo should only be having to start and stop the momentum, and hold up any mass imbalance, but have very little aerodynamic blow-back to deal with. The sheer size of all moving tailplanes leads us to believe they must have a huge blow-back force trying to centre them, but if done properly there is actually very little blow-back force.

Mark Vandervelden

Hi Harry
I'm in full agreement with you and in an ideal world all our all moving tail planes would be designed with this principle in mind thus requiring only the minimum of force to actuate and be aerodynamically stable at all speeds.
However we are not living in an ideal world and our model airframes all moving tail plans are at best are a compromise between scale outline and practicality.
In this particular case and drawing from my own experience having too powerful a servo is not usaly bad thing .
In any case its not actually the power of the servos in this application I'm asking about that would be for another thread.
I'm really asking about its there reliability as there failer would result in the loss of the airframe, but thank you for your comments.
Regards Mark V

Dave Wilshere

OK. Million and once time. There is NO such voltage as 4.8v in relation to servo operation. Its a 4 cell Ni cell designation for the servo. When you charge a 4 cell Ni pack (flat at 4.8v) good ones settle at 5.9v, operate at 5.6-5.7v...the ACTUAL voltage JR test all their (4.8v) servos at Its a regulated power supply running around the building.
So 25kg 8711's are just a smidge over 25kg at PB 5.9v. Same for your WV 82's so you are seeing 28kg maybe.

Yes, sold a few and longest have been operating for nearly 2 years

Dw

Mark Vandervelden

Hi Dave

Again I agree and do know that we don't run servos at 4.8v and would not dream of trying to do so, its not me that gives the specs them its JR that still use a obsolete voltage.
I realise that the 8711 will give a little more than 25kg from a regulated PB unit and the MP 82T a little more than that at the same voltage hopefully not working as hard.

I respect your "Yes, sold a few and longest have been operating for nearly 2 years" and always value your advice as a fellow modeller and a JR stalwart but are you using them in any airframes your self?

This thread was to ask "I would appreciate any reports of "actual experience" of some one that's "actually" using them in successfully or not there airframes."

Thank you for your reply, Regards Mark V

Mark Vandervelden

With refrance to voltages deliverd by rx packs and there use with servos.

4 cell Nim packs give as DW says 5.6-5.7v in use, JR know this and state a 4cell pack nominal vtage to avoid us using a 5 cell pack rated at 6v but delivering in use 7-7.1v

2 cell Lipo packs give 8.4v and stay above 8v for quite a long wile so the same situation applies with servos rated at only 7.4v.

Now 2 cell Life/A123 packs are often used direct on none HV servos and there users insist there only 6.6v "but there not"
These packs are in use over 7v and stay there for more than half there usable charge.

"just saying"

HarryC

My Feedback: (1)

Can't disagree with that Mark! Though hopefully the model is well enough designed, and built closely enough to the design, that the 8711 should be massive overkill.

TWOOD

hi Mark
I have these servos on the stabs of my twin turbine yellow f-18.
I have 15 flights on the airplane and they have been flawless.
They are the best centering servos I have ever used, and they have very little slop around center.
hope this helps.
T Wood

LA jetguy

Mark... I have JR8911HV on all surfaces in my BVM Ultra Bandit with a Jetcat P300RX... IMOH they are the best on the market for holding torque...

I'm assuming you are using a Jeti system.. Those servos on a Jeti CB200 and two Lipo's are a great combination...

Dave Wilshere

#

As I said JR don't use or expect servos to be used at 4.8v. Its a carry over from only having Nicads. If they had said 6v was OK, people would have used 5 cell packs. I spent ages getting JR Japan to confirm actual voltages and also get MacGregor (UK JR distributor) to remove that miss informing sheet of paper saying 4.8v

No one uses 4.8v as an actual voltage. Its a nothing figure.

No,I have not used wide voltage servos in my models, because I have never seen a call to use them. The guy using them for near two years is a close friend, flys at the club I fly at and I have flown his model a few times. Its all the info I need, that and other sales and no negative feed back.

Dave

rrembert

Mark,

I am operating them in a 2.5m Futura. So far at 41 flights or so, they have been great. It does take a couple of cycles to get used to the "slow start" characteristics. If the surface attached to the servo is not neutral, it will slowly move to the neutral position when powering up the system. During this short time stick inputs do nothing to that surface. I am currently "building" a CARF J10 and have them installed on everything except the NWS. Hope this answers your question..

Bob

Mark Vandervelden

Hi Dave

I had not considered wide voltage servos my self until now. I had completed this particular airframe using a PB SRS set to std voltage and JR 8711 all round but once built had second thoughts regarding there authority over the all moving stabs. JR as far as I know do not offer in std voltage a more powerful servo than the 25kg 8711 so that was not an option.
I posed the question to Steve at JR UK and he suggested fitting two of these wide voltage servos to the stabs allowed me to retain the regulated power supply and still have a tork increase, plus the soft start on the large stabs is a welcome bonus.

Thanks for letting me know you have first hand knowledge of someone your trust has had good and more importantly reliable use of them.

Not having negative feed back is also good to know "bad news travels fast" so if they were anything but 100% I'm sure you would have had your ear bent by now.

With Thanks, Mark V

Mark Vandervelden

Hi Bob

This is just what I was hoping to hear, there nothing like first hand experience as hearsay is notoriously unreliable.
The soft start to centre is a very welcome feature and IMHO should be std on all servos.
Enjoy your J10 build and keep us all posted with your progress


Regards Mark V

Mark Vandervelden

Thank You T Wood

Very encouraging, the large swept stabs on the F-18 need a desant amont of power to stay in check, what voltage are you running them at?

Mark V

Mark Vandervelden

Hi

The Ultra Bandit is a big beast and with a Jetcat P300RX no slouch

Yes I looked at the 8911HV servos for my stabs but would have had to change all eight servos to accommodate the step up to 7.4v, easy to say but still a $1,200 upgrade!

Yes I am now using my Jeti but until the CB400 is realised at the moment still need a regulated power supply so will stay with the PB SRS unit for now.

I also considered direct voltage to the stab servos by splitting there signal wire, and staying with regulated voltage to the rest of the aircraft.
This may still be an option with my wide voltage servos and the SRS unit, I will run it past Richard at PB.
When the CB400 becomes available I will prop ask you the same question but know already it will cause issues with the servo overload protection.

Good to here from you, Regards Mark V

LA jetguy

Hi Mark...

The CB400 should be available later this year (was told before the end of the year)... It's a great choice. Based on the current info available to us the regulation on the CB400 is for all 24 pins. We were hoping to have adjustable regulation for voltage for each pin. This way you can have a mixture of servos ( HV and non-HV) in an air frame...

Things may change until the product is released...

Enjoy......

Mark Vandervelden

I ran the question past Richard at PB and got the usual quick and concise reply.

I can run HV directly to the two stab servos by splitting the servo leads, neg and signal to the PB SRS unit and + and - to the servos
I've also now had it confirmed by Richard I can use a Powerbox 12 battery backer and take the power from the same two packs as used for the SRS unit.
This would give my duel voltage and have full battery redundancy for all the servos .

This way I would get the full 40.6Kg from the stab servos, don't think there will be a lack of elevator authority then !




On the next build and if its a biggy I think I use the MP82Twv all round from the get go, it would be more straight forward

TWOOD

I have dual a123 with a spectrum 12120 power safe receiver unregulated.
I am using the airwild dual control arms also. Very strong.