Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Hello there all,

After a few flights in my new Comp ARF Lightning in which I used 7 x JR DS8911 digital servos I have noticed that the consumption of the batteries was very big. How I noticed that? I am using the Powerbox Royal in the plane where amongst other things the battery consumption is registered.

So after a few flights I noticed that the average consumption per flight was around 1000mAh per battery!!!! This is 2000mAh or 2Ah per flight!!! [sm=confused.gif]Each flight was around 7-8 mins.

Is this normal???

Has anyone else out there used 7xDS8911 servos in a plane and has registered the same consumption?

If yes I think I quickly need to downgrade some servos.

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

You didn't set up your jet with an amp meter.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

What do you mean Sean? The amp meter is in the Powerbox Royal thats how I registered the consumption.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

No it's not, you measured mAH's. The reason you are using so many mAH's is because you have a mechanical bind in the system, most likely the flaps. The reason you have a mechanical bind is because you did not use an AMP meter to setup your control surfaces. The reason I know this, is because I setup my lightning with an AMP meter, and although I'm not using as much juice as you are, while I was setting up my flaps, I decided to really hold them in place electrically, so I'm carrying about a half amp load at idle on flaps, and I designed my electrical system to accommodate a decision I made, having all the information.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Sean is talking about a device like this. http://www.dreamworksrc.com/catalog/...roducts_id=278

It's used on the bench (not in flight) to see which servo is is taking more battery than it should, and it can find a binding servo... Especially 2 servos on 1 control surface.

*EDIT* Sean beat me to it :D

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

You are right there. During my preflight tests I noticed that when I disconnected the FLAPS the consumption reduced quite a alot. I also changed the deflection of the flap servos 1 time. In the beggining the servo arm deflection for 0 degrees flaps was around 45 degrees. Then I set up my linkages so that at 0 degrees flaps the servo arm deflection reduced to around 20 degrees.

But I still don't follow your method. How can one set the control surfaces using an amp meter. Can you please be more specific about your method? Is there a similar thread here in RCU?

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Thanks Mike.

The Powerbox Royal has this feature on it. While setting up all the servos I can see how much current each servo draws. But for the flaps I never noticed more than 1 Amp draw. In this plane also no control surface exists with 2 servos on it.

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

The digital current meter have two leads. You plug the servo to one lead and the other goes to the RX. Then you exercise the servo and fix the linkage until you got the less current draw meassure at the meter. Have to be done to all servos to minimise a big current draw like in your case.

Alex

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Thanks Alex,

Well I'll try that on all my servos to see what's happening. The Royal has incorporated the digital current meter for each servo of each channel and it displays the current draw on the display.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Ideally you want .5 amp draw sitting there at idle. You will not be able to achieve that on the lightning without grinding some material away on your flaps up position, where it binds the flap against the wing. Assuming you have a generation 1 lightning. All my jets with servos at full position carry less than one amp in any direction sans flight loads.

If you have more than that, it really is not safe to fly, because flight loads will double your on the ground amp draw.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

you CAN measure the amps by using the powerbox royal
iut shows you current drawing of amps when programming surfaces
my best guess alo are the flaps
however 8911,s pull about 29 kilo,s at 6 volts.
and they use about 200 Mah each i believe in "rest"

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

As far as I remember I get .5 Amps on the flaps up position. However I will check on that once more. I also know that the 8911 have 25kg torque so at the end of the day the huge consumption I measured could be NORMAL.

I just wondered if anyone else has used 7xDS8911 servos on a plane and has noticed the same thing as I did.

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

I don't use 8911s but my two Hawks use 7 8511s and 8711s,(8911s without the heat sink) my current draws are a tiny fraction of yours. All control surfaces are set up using a Hangar 9 meter. Twin ganged 8711s at rest but pefectly matched using the Weatronics DR, on the stabs are each drawing around .02 amps, (was very surprised at just how low that value is) as indicated on the meter. Even slight mismatch of these two servos can change the current enormously.

I used to think you can set up servos for minimal current draw just be listening to the buzz, WRONG ! The Hangar 9 meter is worth its weight in gold.

It is intersting to note that BVM does NOT recommend using digital servos on flaps, I use ONLY digital servos on flaps and use their accuracy and a Hangar 9 meter to set them up precisely , no binding and smooth operation and, using the H9 meter, work perfectly with never a failure.

The PowerBox Royal is a really excellent and capable device, great for recording total current useage for a flight as you have found, but I dont think it can match the accuracy of the H9 meter for the "set up" phase of the model.

Regards, David Gladwin.

PS I have found that the best way to accurately set up flaps and elevators for minimal current draw is to set them with the wing or tailplane vertical (leading edge up) so that the WEIGHT of the surface is carried by the hinges and not by the servo as is the case when the model is level. Extra time spent setting up all control surfaces to minmise current darw is very well spent. Another trick is to spray all hinges etc with silcone spray as used on nylon curtain tracks. That can work wonders too !

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

That used to be the case David, but now he does recommend 8411's on the flaps of the ARF Bandit, and 8611's on the UB.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Hi Guys,

i´m flying the Lightning with 7x JR 8711 and Powerbox Royal. I have also a high battery consumption from ~ 1300mah each flight on the Powerbox Display.
But when i charge the battery after 4 flys a´8 min, i can max. charge ~ 1000-1300mAh in each battery, which says each flight needs around 600mAh.

After this i talked to Mr. Deutsch and he said me that some Versions need a new adjust for the consumption measure.

So, first charge your battery after the flights and check how much you can charge or discharge both after the flights. So you can really check your consumption.

regards
Jörg

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Hello Jorg,

Can you please pm me the email of Mr Deutsch so I can ask him why could that be?

In fact you are right because after I charged my batteries last night I saw that they took around 1200mAh. Which means around 600mAh per flight.

It could actually be that my Royal is not measuring very well.

Thanks, Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Hello

I am building a CARF lightning with JR8911 servos.
PLease, tpeppas3d, could you tell us the results of you real consumption ?

If your batteries take 1200mAh each ie 600mAh per flight so the Powerbox is wrong to measure current consumption

Thanks
Jean-Philippe :D

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Hello there Jean-Philippe,

After Jorg's post I sent an email to Powerbox. I have to admit they are LIGHTNING fast in their answers and I like the way they support me as they have done many times in the past. This company is FANTASTIC.

Anyway, they asked me to send back the Royal to recalibrate it. It turns out that it could be measuring wrongly. So maybe its FALSE ALARM after all. The fact is that last night when I recharged the batteries they only took around 1200mAh each. So the Royal missed around 1000-1200mAh!

So I could have been mislead from the Powerbox indications after all. Thanks alot for everyone's support. I'll advise you all when I get the Powerbox back from recalibration to see if this was really the case.

Thanks alot,

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Thanks Tassos, this thread is very useful.
I will try the Hangar 9 current meter...It seems to be a very useful device for digital servos. Especially for flaps.

See you
:D:D:D

Jean-Philippe

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Hi, sorry for my ignorance, but what is a JR 8911 servo? I can't find it on their website.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Jeremy, I believe it is the European or Asian version of an 8711. I bought the Comp-Arf prototype Euro at FJ this year and it had "odd" numbered JR servos in it, but they were 8611 and 8711 equivalents.

George

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Guys Remember travel adjust! Set flaps to up position with a little slop. Flying loads will take care of that. Do not stall the servos in the retract/up position.

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

LGM,

Check out these sites for DS8911:

http://www.macgregor.co.uk/jr_propo/DS8911.htm

http://babelfish.yahoo.com/translate...rUrl=Translate

The second site is translated through babelfish.yahoo.com from the Japanese JR site.

25kg of torque is equivalent to approx 350oz/in. Pretty strong servo!

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Dear All,

I've left this thread open and didn't report my findings but here they are and I 'd like your opinion.

These pics were taken a few hours ago after my usual 7min flight with my Ultra Lightning with 7 high torque digital servos and with VERY HIGH CONSUMPION.

These numbers that I'm mentioning here is what I'm reccording more or less during EACH flight.

So from what I read off the Royal Screen the data are these:

Consumption Battery #1: 1018 mAh

Consumption Battery #2: 1009 mAh

Min Voltage: 7.89V

Max Current: 2.7 Amp

So basically 2000mAh for one flight.

Has any of you seen these consumptions in your planes with these servos? There are no binding points cause as you can see the max current measured is 2.7Amp for 7 high torque servos.

IS THIS HEALTHY? IS THIS NORMAL?

Your personal experiences will be highly appreciated.

Tassos

RE: Comp ARF Lightning + 7xDS8911 servos = VERY HIGH BATTERY CONSUMPTION
 

Tassos

This is very high!

I listen to the servos, if they scream they are drawing lots of current. If the sound pitch varies on the ground as you operate the controls something is resisting the servo. The 8911 and 8711 should be the same current, it's just the heat sink case that differs.
As you operate the flaps does the sound from the flap servo change? If it does on the ground something is binding. The Lightning flap does need some cleaning to get a smooth pushrod clearance and the Shut sometimes needs a skim with a BVM scuff board or Permagrit flat sanding plate.

I have always used digital servos on flaps, even when BV said not too. I think the digi servo was designed for applications just like flaps!

My old style Lightning with 7 JR 8711 servos was only using 400mAh per battery per flight.

Dave