afterburner

My Feedback: (18)

I know this has been hashed over before but I'm still not sure what to use. I'm a proponent of the simpler the better. I've used a two battery(5cell)/ 2 switch setup with success on my R54(I know they're over 7.0 volts hot off the charger). That used Hitec servos. I've seen regulators fail before and it's just one more thing that can go wrong IMO. I'm woking on a JL F-15 and have a combination of JR and Futaba digitals. I was specifically interested in the JR 3421's as they don't give any specs on using 6.0volts.. I contacted product support and specifically asked if using 5 cell unregulated is ok and the answer was yes no problem. I didn't ask about the 8611's or the ds168's. I guess I will now. Now I read in the latest issue of RCJI, Dave Wilsheres article about not using 5 cell unregulated batteries on most jr servos [sm=confused.gif] How about some real world reports good and bad on using 5 cell packs unregulated with these servos.

Marty

Shok

My Feedback: (28)

I use unregulated twin 5 cell packs with a mix of JR 8611's and others

Never had a problem

MaJ. Woody

My Feedback: (28)

Both my F-18 and T-45 are setup with two 6V packs and two HD switches and no regulator. Hot of the charger 7.4V and no sign of any weird servo activity. I am using a Futaba PCM RX and a mix of Jr and Futaba digital servos. I also have a few Hitect analog servos in the mix (Flaps, Retracts, Brakes). Niether jet has flown yet (just thawing out in New York) but I have no reservations.

Dom

afterburner

My Feedback: (18)

Thanks guys. I guess most are using regulators or 4 cell packs or just don't want to get into this old discussion.

Marty

rhklenke

My Feedback: (24)

OK, so use a Fromeco regulator and your current consumption will go down, your servos will be quieter, and your responce will be even throughout the flight. With the fail-safe switch, its reliability is probably better than a single switch without the regulator. Not what you asked technically, but that's what I'd do...

Bob

afterburner

My Feedback: (18)

Bob,
I like the redundancy of two batteries. Your suggested setup probably is more reliable than a single switch without a regulator. Even if you check your batteries between every flight(like we know we should), sometimes a cell or pack can weaken/ fail in flight and the regulator won't help. Next thing you know, you have a engine shutdown and maybe have enough altitude, battery juice and talent to have some control to bring her back in one piece

Marty

frothingslosh

My Feedback: (6)

I'm using strictly Hitec digital and analog servos in my new Eurosport (not yet flown) . . . 5955's on elevons, rudder and nosewheel, analogs on everything else. My redundant setup is as follows in case anyone is interested:

2 - 2900 mAh Duralite 7.4 volt 2s/2p batteries.

2 - Duralite 5.1 volt switched regulators with failsafe switches (if a switch fails, it fails in the ON position).
With a full charge and 1 amp load applied, these regulators show almost 5.4 volts output.

The 2 regulators are attached to the receiver with a y-harness.

I should be covered in case of a battery or switch failure, and there should be plenty of battery to prevent a low voltage lockout resulting from heavy servo loads caused by the 5955's and the large Eurosport control surfaces.

Comments welcome . . .

rhklenke

My Feedback: (24)

Froth,

I did some experiments for some folks at NASA that I work with in regards to a setup like your's. Even though Duralite (at least when I checked) doesn't recommend using two of their regulators in parallel, it works perfectly. Invariably, one of the regulators will have a slightly higher output voltage than the other, so that battery will take most of the load during normal operation (you might want to routinely swap the battery-to-regulator connection so that they get equally "exercised), but as soon as the output of that battery/regulator drops below the other one, it will pick up the load. Therefore, ultimately, the total capacity of BOTH batteries is available to provide power. In addition, we tested many different possible failure modes in the regulators and in all cases, the one remaining, working regulator was able to supply the load and maintain the regulated output.

Now what Marty might be refereing to was a dead stick I had in my Eurosport which turned out, was due to the SINGLE Duralite regulator I had on board "crashing" due to excessive current draw. When I landed the plane, the regulator was hot and the output voltage was somewhere around 4.2V. After cooling down, the regulator seemed to be operating normally again, but after that, I switched to the Fromeco regulators with a big heat sink and have not had any such problems since.

Since you are using two Duralite regulators in parallel, you won't have this problem (unless your current draw all of a sudden becomes ridiculous).

I think that two regulators in parallel, with failsafe switches, on 5-cell packs is the ultimate way to go. However, back when I got my first jet, I actually went with two receivers, each controlling different servos and each on a seperate battery. I flew the heck out of that thing and NEVER had a single problem. I've since modified my thinking that, in general, the receivers, regulators, and if you take care of them, the batteries are so reliable, that the cheesy mechanical switch is the weak link, so now I run a single 5-cell battery with a regulator that has a fail-safe switch and I think the reliability is there...

Bob

Alexdu

My Feedback: (3)

I've used, with success or without incident however you wanna look at it, JR servos on unregulated 5 cell Nicad packs. In all ranges from Tams F-16, Kingcat, Eurosport, BVM Mig 15, Composite Lightning. I agree with you a regulator is another link in the chain that can fail. I once ask Tom Wood, who build my Kingcat about using two batteries. His simple answer was: that's just another battery that can go wrong. So in short I only use one unregulated 2400 5 cell Nicads in my planes. I do recharge the battery after every flight, during which time I relax and enjoy the company of my friends.

Regards

Alex

afterburner

My Feedback: (18)

Gee Bob,
I guess I wasn't being vague enough and you got it. Must have been the part about talent that was the giveaway.

Alex,
Good info.
Hopefully some more will mention their experience with Jr servos on 5cell unreg.

Marty
Marty

rhklenke

My Feedback: (24)

Marty,

Thanks, but I think it wasn't talent, it was dumb luck - dumb luck that ran out with the Flash on Sunday

Honestly, I think JR servos will be fine on 5 cells and if that's the way you want to go, you can do so without worry. Its just my personal preference to do it another way. What I will say is that the servo killer is heat and if you go with a 5 cell Pack(s), you must be DOUBLY sure that none of the servos come up against the stops. That is especially true of the flaps in the retracted position if they have hard stops. If they come hard up against the stops, the servo will draw a lot of current and you'll burn it up. That's specifically why BVM doesn't recommend digital servos on the flaps of his planes. With TWO 5-cell packs ready to supply all the current you need, you'll burn up a servo double quick if you stall it...

Now quit screwing around and get back on that thing!

Bob

afterburner

My Feedback: (18)

Gotcha. Just cleared off the bench last night and going to start hinging sufaces tonight.

I know what your talking about on the current. I had a whattmeter on the R54 when checking throws and when trying to get max throw with the flaps down, the current was close to an amp and only three clicks backing off the ATV dropped it to 200ma.

Marty

frothingslosh

My Feedback: (6)

Bob -

I ran an output voltage test on both regulators anf got only a few hundredths of a volt difference. Assume this could have been due to a difference in the amount of charge in the two batteries. Will hook everything up and run the system for a while , then do another check to see if the 2 sides even out as you say. Will post the results later.

Jim Cattanach

Sorry, cannot agree about "just another battery to go wrong".

If you use two 6v packs, each with its own switch, one plugged into the Rx batt socket & the other into a spare channel, with or without voltage regulators, you have built in redundancy if any part of one set up fails.
I would not fly any jet with only one battery pack, be it 4.8 or 6v.

Regards

Jim

Big Tony

USE TWO BATTERIES whats the problem say if its a 1-500 chance of a pack failing the chance of two is 1 in (500 x 500) 250000 so thats that out of the way move onto the regulators - well first off they are apparently more reliable than battries so the chance of two regs on two different battery curcuits will be say 1 in 400000 then look at the chance of a battery on one curcuit and a reg going on the other curcuit ahhhhhhhhhhhhhhh my brain hurts.

don't worry you can drive yourself mad over the how many batteries/switches etc etc etc I can only go on experience and using two batteries DEFINATELY saved my rafale as I had a total battery failure on one side (they were good quality packs).

the powerbox sensor switch is good it has two inputs into two seperate digital switches into two seperate regulator then two outputs into two channels in the reciever both curcuits are completely seperate I can't be arsed to work out all the stats on the chances of this and that but I know they are small.

Some people use the weatronics which I believe has two batteries into two switches but only uses ONE regulator for both (think they feel that regulator are so reliable they only need one) people are using these with no heard of problems so ???? again don't drive yourself mad.

Ant

Dave Wilshere

Jascat

You should not plug two separate batteries/switches into one Rx without a backer

The idea of adding a second switch is Ok to improve switch reliability, but only from one primary battery with two leads.
Only use two batteries that are being split via a battery-backer system.

The reason for this is that you should never connect NiCd batteries in parallel because of their extremely low internal resistance.
NiCd's can have internal resistances as low as 10 milliohms and if the difference in voltage between the two packs is 100 milliVolts-not an unreasonable figure, the current passing between the two packs is 100 over 10 and that is 10 Amps!

That current could be passing down the board on the Rx and through the batterys and wiring.

The only way round this is to have perfectly matched NiCd packs, which is not going to happen.

Dave Wilshere

Jim Cattanach

I can only say, I have never had any problems of this kind in any of my set ups.
I have heard of this objection before, & others who say it is ok.
It works fine for me.

Regards

Jim

Dave Wilshere

Jascat

There are lots of things that work...that really shouldn't. I know of the practise...it's just not a good one

Regards

Dave Wilshere

Big Tony

Hey Dave calm down big man just look back at your history if I recall you told me you have never lost a plane in the zillions of flights you have had due to radio setups - pilot error well I don't think you covered that one.

lucky does at sometime run out its just a matter of time.

Ant

Alexdu

My Feedback: (3)

That is exactly my point. Do what works for you and let other do as they chose. I am quite happy with my setup and NO ONE single failure/loss.

Regards

Alex

Gordon W

FWIW, this morning I took delivery of 4 DS-8411s and one DS-8711 bought from Al's Hobbies. Each of the 8411s had a note enclosed which advised of the high stalled current of the servo which could overload and damage either the motor, amplifier or both, and ended with the following warning which I quote verbatim:

"Please note that JR servos should be used with 4 cell (4.8 volt) NiCad batteries only. 5 cell NiCads MUST NOT be used."

Whether this is an Al's Hobbies add-in, or an official JR notice is not indicated.

The DS-8711 wasn't accompanied by this notice, which is a tad confusing as the more powerful 8711 must draw an even larger stall current and be at even greater risk of failure on 5-cell nicads. Rather annoyingly, having ordered my 8411s, I saw a comment on RCU that 8411s have a habit of dying. So the question now arises as to whether the 8411 amps and motors are underspecified for their job.

As it happens and before I received the servos or read this thread, I had intended using only 4-cell nicads with these servos. Having paid almost £300 for the 5 servos and noted the foregoing discussion, 4.8V is good enough for me!

Gordon

Big Tony

8411 are great have over 20 of them in various models for years NEVER A PROBLEM but obviously they have never been run on an un regulated/reduced 5 cell pack neither has any of my servos for that matter.

Ant

rhklenke

My Feedback: (24)

I agree with Ant. Between my own airplanes and those I have flown for work, I have literaly HUNDREDS of hours operating 8411's and I have NEVER seen a failure. Granted, this has been on 4 cells or a regulator like Ant's experience, but I think they would be OK on 5 cells too AS LONG AS YOU DON"T ALLOW THEM TO STALL. Keep them off the stops and on a free-moving surface and I think they'll be fine...

Bob

Big Tony

Thanks I wish my missus said that but hey never mind

afterburner

My Feedback: (18)

That's pretty interesting. I just went to JR's website and they give specs on the 8411 at 4.8 and 6.0 volts[:-]. I really wish the mfrs would be clearer on the safe voltage range of operation for their servos. They give 6.0volt figures but don't specify regulated and it's naive to think most people would think to use a regulator as opposed to thinking 6.0volts means just using a 5 cell pack.

Dave,
I'm not sure I can agree with current draw between two packs and the Rx. First off, both packs are isolated by the switches until they are switched on. At that point, the load of the servos are drawing the current from the batteries. The voltage difference of each pack would have to be far off to really get some serious current flowing between them with no other loads on them such as servos IMO

Marty