I agree with Patrick, keep it simple if you can. Until now I have only used shielded cable in my jets, but the one I am building now has some very long leads (1.5 meters+) and I think the time has come for the amplifying and isolating properties that these units provide.

Ron

Martin,
It is possible that if you operate many of those servos under load at once,the voltage across your receiver will drop to the point that it causes an ECU commanded shutdown.So far I have only heard of the issue when deploying flaps,but obviously it could happen otherwise.It is only my opinion,but my only turbine aircraft loss was a direct result of this problem.Good luck,
Erik

Martin
How does the S&M battery backer work? I couldn't get a descent hit on the Google for S&M ! :-) Two switches and two batteries is good but ideally the digital servos should have a separate power supply. As I said before it is only critical when a servo is jammed or for other reasons drawing a high current.
Only dealing with the failure mode of batteries and switches is not taking all risks to account. In fact, the battery failure mode is quite unlikely to happen if the condition and capacity of the batteries is monitored with a modern quick charger on a regular basis.
Minimum safety precausion is a "break out" switch for separate power supply of the servos.

/Johan

You might be interested to see what BVM are suggesting for their Ultra Bandit, 7 JR 8611s plus sundry other servos from ONE battery and ONE JR switch harness. Guess he knows what he is doing BUT no redundancy of any sort and all that power going through the tiny busses in the receiver. Braver man than me, all of my big jets get Powerboxes from now on. Even my little Bobcats get two batteries, switches and regulators.
Regards, David Gladwin.

FWIW, all of my jets have a dual battery system. My F15 has a separate battery allocated to the elevator servos, and just as well, because it seems to cop a hammering each flight judging by the readout from my on board volt logger. All of my new jets have incorporated a powerbox, but I have noticed that power consumption from the batteries seems to be greater than I expected. I guess the powerbox itself consumes a reasonable amount of power to perform its signal amplification and other functions. Anyone else noticed this? David, what have you seen on your systems (I am only using nicads at the moment with mine.)

Craig.

The problem i see with having a battery for power box supplying the servo,s and a seperate
battery for suppling the Rx, you are then having to rely on 2 batteries thus increasing the chance
of battery failure.


Speedbird66 S & M Electronics http://www.smservices.net/

Rgds Martin.

Hi Speedbird,
Whilst I agree with your point that batteries and servos are not the only thing that can fail, statistically they are the weakest link. Short circuits are rare, although someone I know had one. Much more common with both is an open circuit condition. I don't speak about Li Ion or Li po batteries because I don't yet have enough experience of them and real data is scarce too. But the data and experience with Niads and Nimh batteries is extant. A cell can go open circuit without warning, trust me I have had it happen twice in recent years and once many years before. Switches are rather delicate mecahnical devices and can eventually fail to make a good contact. For me, redundancy of this system is of paramount importance in any jet and thus far this approach has served me well.
Erik R
Some of the comments on this thread leave me rather skeptical. When I hear that the Rx dropped out because I put the flaps down I jsut think that does not scan. I tend to use high capacity batteries in my jets specifically to deal with the loads they are put under. These same batteries are used in electric flight scenarios drwing 50 - 100 amps. And yet we do not suffer catastrophic voltage drop in these situations or else these pilots would not be completeing the course let alone winning world championship competions with these batteries. So how come applying flap servos is causing such a voltage drop? Furthermore, How do you know this after the event?
Regards,

John

I was informed several years ago by a JR tech at Horizon that the 900 series RX bus and gold plated pins are designed for a nominal 30 amps with a generous spike safety margin as well...that 180+ watts of dissipation with a 5-cell pack!!!.......not to fret here......copper ribbon has enormous current capabilities at low voltages......upon inspection, I have never seen any sign of deterioration of that part of my RX's in the last 40 yrs......it's getting it out to the servos where the worry for me begins.....In one of my Ham Radio amplifiers, the buss carrying 48 v at 50 amps continous is paper thin and about 5-6mm in width.....you'd be surprised how teenie some of the sub-buss foil wiring was on that behemoth 747 you used to command...

As far as outfitting my UB, it will be as I have done successfully with my heavy Pegasus HP NL/KingCat and my 38 lb P-180 powered Eurosport.......I agree, BV has been amazingly lucky with his 1800 maH packs and single switches all these years in most of his birds, including his heavy iron.....but for me:

---one 5 cell Nicad.....3500maH.....I use SR Brand batteries or Electrodynamics batteries, not because the cells are any better, but because I can special order them with 2 parallel ouput wires of 18 gauge, of any length.....which I can't get from JR......I capacity check the battery biweekly with a nice computer graph of the discharge/recharge curve presented on my computer with my new Orbit Pocketlader Charger.......

---the dual outputs go into 2 HD switches, not only for switch failure protection, but also current carrying capability...even our HD switches are only rated for a about 5 amps before Ohm's Law starts taking a bite, due to smallish internal wiring......of course, if you have the room, you can use (2) 1800-2400 SCR packs rather than (1) big one....weight is about the same......I only use Duralites on my ECU, not on my RX....don't like regulators...they can be a source of RF noise, and are temperature and current limited.....watch out when that bird has been sitting in the sun when ambient is over 90 degrees.....I have used failsafe switches by Smart-Fly with nice 18 gauge input and dual 22 gauge output as well on smaller planes....

---Once again, no regulators

---2 separate sites into the 955 bus, via Y-connector if necessary, in case there is a bad pin on the BAT input......

---output to the servos.....any leads over 24" are done with 18 ga wire, not 22......with 18 ga, negligible voltage drop up to 48" at least.....good for at least 5 amps.....

---proper length servo wires...do not use (2) 18" wires to make one 36" wire, unless absolutely necessary (like in the Kingcat if you want easily removable booms)..... most common failure point in my experience has not been at switches, but at servo wire plugs, wherever they might be located.....each plug introduces another failure point and possible source of increased resistance if there is any defect or corrosion on the plug

---no mixing of servo wire brands.....on careful inspection, I have found not all JR plugs are the same.....some make poor contact when used with competing brands........

----Keep RF generators like pumps away not only from RX/Antenna, but from battery wires....my experience with RC and Ham stuff has been that most interference comes from the input circuit, rather than retrograde from the output, i.e. servo wires....I have never found the right toroids that work for my R/C stuff....too many variables....so I don't use them anymore....

This setup seems to work.....haven't lost a plane to RF link failure of any sort in almost 4 years.....last recorded failsafe was 3 years ago in my Compo Bandit.....cured by going to outside vertical antenna and moving battery leads.....haven't fried any RX or servos, using 5-cell packs without regulators that I know of.....

Nothing new here.....just good ole electricity 101.....sort of like not using 16 gauge wire to distribute house power to your electric stove/oven, but then, by the same token, no need to put in a little substation (PowerBox) between your 200 amp service box and your oven...just grab a little 10 or 12 gauge wire and that steak will broil fine.....

The internal complexity of Opto-Isolators scares me......even with SMT, too many solder points, and the LED optos do fail...once again, watch out for temps.....I think they work best in their original design mode......protecting those big, expensive 100+ amp industrial DC motors from transient spikes......

As mentioned in a prior post, if you need an isolator to fly, you are just masking some underlying problem, IMO.....


Tom

Martin
The Rx is powered by the leads from the PowerBox plugged in to the reciever (5-7 leads depending of model). The Power is taken from the two batteries plugged in to the PowerBox (you don't connect a battery directly to the reciever).
Depending of model and type of batteries in use the PowerBox has voltage regulators for the Rx.
The dual batteries and switches ADD redundancy and safety - not the other way around.
Cheers/Johan

Thanks for your comments John. I haven't had the same experiences of battery failures but I feel more convinced now that a dual battery device is relevant.
The Switches for the PowerBoxes is designed for 20Amps and uses Multiplex connectors equaly capable of 20Amps. Talking about the weakest link: If you plug in the battery (or two batteries with a Y-lead) in to a single slot of the reciever! The standard servo/battery connector is mechanically and electrically very underdimensioned.
Just try to quick charge a 2000mAh battery with a standard servo connector and the charger will start to play up because of the resistance in the tiny connector.

I believe the voltage drop Erik is referring to could be related to the distribution of power in the reciever bus rather than the batteriy failing to deliver the amps.

Cheers/Johan

David and Tom
Please also take to account the dimension of a standard servo/battery connector that is plugged in to the receiver.
This is a weak link. It can not possibly be designed for on a single basis supplying the power for a full set of digital servos etc.
Just compare with any connectors designed for modern electric flight. The standard servo connector is designed to to take a few Amps no more. It wouldn't surprice me if the current drop over that connector affects the servo torque significantly if you have a set up of 4 digital servos and supply the power over a single slot in the receiver.

Cheers/Johan

Craig
I'm pretty sure of that the higher power consumption is mostly related to the servos being propperly powered w/o voltage drop hence being quicker and stronger. Have you noticed the difference of flying the model with and w/o the powerbox? I wouldn't be surpriced if you noticed a difference in control response.
/Johan

During installation on my jets, I always load check the last connector, the one that the servo plugs into, for each channel.....I repeated that on my Kingcat today using 2 Hangar 9 Load Testors set at 2 amps each for a total draw down each elevator servo wire of 2 amps and 4 amps total out of the battery pack.....as noted above, I use only dual 18 gauge wire from the battery, into 2 parallel 18 ga wire HD switches, and then into 2 separate ports on the RX..no regulator..no Y wires are used......18 gauge wires are used out to the servo connection....total length of 40 inches

Measurements with a fully charged 5 cell---3500maH Nicad pack revealed resting voltage of 6.57 volts......after applying 2 amps to each of the servo wires, for a total draw from the pack of 4 amps, the voltage dropped to 6.47 volts at the end of the servo wires......voltage at that time on my on-board IC4 voltmeter, hooked into the RX bus was 6.49volts....a neglible drop, or maybe even calibration error......

I believe a 2 amp load is a good test for an 8611......my resting current/servo with the plane sitting on the ground is about 325-350 ma and with a 3 kilo battery resting on the elevator, which basically stalls the servo, it approaches 2 amps......

I think typical flight current usage, both continuous and transient, is overestimated, which explains why thousands of flights have been completed on jets using only a 5 cell regulated pack and a single switch, using 22 gauge wire from the battery to the servo, including BV on his heavy iron.....

On a typical flight of my KincCat, most of the servos are near idling current when in level, unaccelerated flight....even with a high G turn or pull to vertical, the rudder, and ailerons are in near-streamline trail, with only the 2 elevator surfaces showing significant current draw, and by my estimation, somewhere between 1 and 2 amps/servo, depending on the G-loading in the turn.....even if it hits 5 amps/servo for a few tenths of a second, the voltage drop would still be less than a volt.......still no problem

My experience with full scale aircraft, especially the Pitts Biplane is that only finger tip and toe tip pressures are required on the ailerons and rudder, with the exception of knife edge flight, where the rudder becomes an elevator, controlling AOA and G-load on the airframe.....the only control that really needs a strong arm is the elevator.....

This is reflected in the low total current draw out of the 5 cell, unregulated pack of 400-450maH/12 minute KingCat flight, switch-on to switch-off......with about 1/2 of that representing idling current any time the switch is on.....which, in my experience, is more than adequately handled by a stout 5 cell/3500maH or dual 1800 maH unregulated packs, dual 18 ga BAT wires, dual 18 ga HD switches, dual RX bus inputs, and 18 ga wire to the servos....

I have no problem with the PowerBooster concept, but they all add additional complexity to the install and take up space which is often at a premium, with the unintended consequence of additional potential points of failure.....


Tom

John,
I never said the receiver dropped out.I said the voltage in the receiver dropped to such a low value as to cause the ECU to "think" there was a loss of signal,thus causing an ECU commanded engine shutdown.In my case the aircraft responded to my inputs,but I was in a position to not be able to recover from the loss of energy and ensuing stall.The airplane was dirty,and less than 100ft high.As I started adding power,nothing happened.The previous owner of my cyclone had the engine flameout multiple times when deploying flaps.He was able to successfully deadstick the airplane.Problem solved with powerbox.

Hi Erik,
Ok Got it now. Sorry, I did not read your post properly.
I can't help thinking that there is something abnormal there, for the application of flaps to cause that to happen. I would suspect sticking linkages or even stalling servos. I think that the idea which has been expressed on this forum several times, that we should all check our wiring and servo current draw with a meter, is an excellent one.
Regards,

John

Tom, Craig, Speedbird.

Many thanks for your valuable inputs, they are VERY much appreciated, and what I believe RCU is intended to do.

Firstly, Tom, please substitute 767 for 747, I have never flown the jumbo. However the 767 being the first of the big twins to be cleared for ETOPS had an interesting electrical system, full of backups to ensure total electrical failure was virtually impossible......................until a European 767 lost almost everything, that certainly got Boeing's full and undivided attention.

I had no idea that the rx lands could handle 30 amps, I thought perhaps 10 or 15 but it was not just the current draw that concerned me but the likely voltage drop if large currents were being drawn. It also concerned me that these receivers were designed before the introduction of powerful digital servos and multiple use of such servos but I do wish manufacturers would give us some guidance on these issues.

I see there being two basic issues, one being the security of electrical power, the second being possible Rf pickup and voltage drop in long cables. I am not technically competent to make decisions on a purely technical basis so I have read the opinions of many experts in this matter, my only firm conclusion is there is NO consensus !

On point one, I no longer use a single battery except on a couple of smaller models, but even these use regulators which are dual channel (Mini Hobby) so if one channel should fail then all power is not lost. I do use Duralite 4 cell packs which are series/parallel wired so if a cell should fail only capacity not voltage is decreased so normal operation will continue allowing a safe landing. Never had a problem with RF noise from regulators using JR receivers.

On larger models with several powerful digitals, I use twin Duralites and switches with regulators. Of course there is double the chance of failure but the chance of a simultaneous failure and total loss of power is extremely unlikely. I need larger battery capacity so splitting them makes good sense, to me at least. In flight voltage is monitored by a MAS volt logger and rarley shows a drop of more than one green LED. All batteries get a voltage check before EVERY flight. Both batteries, actually the regulator outputs, are connected directly to the receiver exactly as recommended by the battery expert over on the RCU battery clinic, again never a problem.

For larger models with lots of servos such as my FC Mig 29 (13 8411s on long leads plus many other servos) I use the Power box having read a great deal about it and picked the brains of many other fliers. It offers twin battery redundancy, failsafe switching, signal amplification, opto isolation etc. etc but still keeps a small load on the receiver to retain tuning. Well thats what it says in the manual and I have no reason not to believe it as so many are in very sucessful use. The acid test is that in my Mig 29 range, with everything off (except receiver etc), is the same with both engines running and the hydraulic system running, over 300 feet aerial off. I am using twin batteries and Powerbox Champions on my new AirWorld Hawks which have powerful servos at the end of long leads.

I agree with you wholeheartedly on many of the other points you raised:
I use ONLY heavy duty top quality, extension cables, been using vertical whips, only, since 1999, seperate pumps etc from aerials and power leads. Never found the need to use torroids so RF pickup in long leads seems not to be an issue. Just bought the superb Orbit charger for NiCd, LiPo and NiMh charging and I check and minimise the current drawn in my entire installations by use of the Hangar 9 meter, a VITAL instrument if using ganged servos. (see next RCJI !)


I might also add that I have moved over to JR's new synthesised Tx modules and receivers. The Tx module seems to have greater output power and gives excellent range and has proven to have a completely solid RF link according to my JetCat ECUs and the volt logger which records glitches.

Well thats my approach to electrical power and the proof is it works beautifully AND the use of dual power supplies gives me a comfortabe feeling and THATS important too for my peace of mind.

Regards (and thanks to you all for your valuable input in this excellent debate)

David Gladwin.

PS Just measured the cables to the 4 stab. servos on my Mig 29, almost 2 metres long, but voltage drop even under load is negligible

David Gladwin,
You mentioned a MAS voltage logger. As I remember, they offered several nice electronics items for rc use, and jets in particular. I was considering their fuel shutoff device to use as a backup for turbine shut down.
Are they still in business? I could not find a valid web link for MAS. Do you have a email address or contact?
Thanks.

I am putting a PowerBox into a Boomerang XL. I will be running 8 servos with it with 4 of the servos using almost 6' of extension. Am I correct in assuming that since I am using a PowerBox with dual 2800 LiPos I shouldn't have to worry about an isolator?

Yes , you are correct.

I use the EMCOTEC DPSI RV Mini LDO No.6 for most of my jets. They are very popular in Europe and excellent in terms of size and price. They are sold by DA in the US. More details could be found in the Europian EMCOTEC web site ( do a yahoo search).

regards

I have run into this strange problem while setting up a hotspot.

I am using two DS8231's for rudders. They are in the fuse about 6" from the rudder control horn.
They have a short 6" extension to the receiver (JR950)


When I have the TX (JR10X) antenna fully extended and close to the servos, they will move 0-12 degrees in unison.
dependent upon how close the antenna is placed to the servo location.


Has anyone ever seen this before? It only effects these two servos.

Sorry about that Boeing Blooper....... David....for some reason, I incorrectly associated you with that Qantas 747 that has flown over my house while putting on it's fantastic same-side, loooowwww altitude, 2 engine out performance at EAA Airventure in years past....

I think we are on the same page.......I just haven't found the need yet to place any box, be it an amplifier, isolator, or power booster, or all of the above, as with the PowerBox, between the superbly designed 900 series RX that I have been using exclusively since the first one was shipped to Wisconsin back in 1999, and the servos......it was designed with the first generation digitals, i.e. the 8321 and 8411's in mind, and up to 10 of them, filling all the channels....the 8611's do draw a bit more current, but only when they are stalled does it seem to be significant......they are so darn strong they will often bust a horn off the surface before stalling, as I have found when hooking up a flap channel in reverse...[]

Perhaps 13 is the magic number for switching over, as with your Big Mig......I definitely will be doing a careful voltage/current check while doing the install on the UB when it arrives late June......it will be an Oly NL powered beast wilth lots of 8611's.....the way David Schulman was pulling the G's in his turns at FJ with the P-180 demo bird, I felt maxi-amps moving those elevator servos....At this time I am still planning on using dual 3500 Nicads with dual everything downsteam of the batts using at least 18 ga wire......might try dual RX for a change.....

I have heard that the new synthesized units are performing superbly......Being a radio amateur, I make use of the relatively unbusy 53 Mhz band.....No word that JR will be synthesizing that band.....actually, I have 3 tuned xmtr modules with each one covering 3 of the 6 meter channels with individual xtals.....effectively sythesized when I head for a big meeting....been doing that since back in the Kraft days....

Finally going to get to fly jets this weekend as temps and winds in Wisconsin are tolerable at last.....

Regards...Tom

I have been reading this thread with interest and there are good arguments for both sides. My personal opinion is KISS for those who dont know its (Keep It Simple Stupid) I am involved in electronics on a daily basis. Two way radio, satellite telphones, design and manufacture of many different electronic projects for other companys and also do repairs to radio control and also bandwidth testing for them here. I dont think I have ever had any rf interferance in my leads and I do have some long leads in my models. I always try to keep things simple because the more stuff you put into your model the more chance you have of a failure. Its true electronic devices are extremely reliable nowdays but the more of them in there the more chance you have of having a failure. There are only a few simple things that I always do and it works and has done for 30 years of modelling and the last 6 or 7 years with turbines as well. I only ever use heavy duty servo leads and once they get past 400mm long I make my own from much larger cable. I have the plug housings and pins and use a special wire I get locally which is silcone seathed and looks like miniture welding cable. The key here is VOLTAGE DROP !!!. Most problems are caused by this and its mostly generated in all the leads not in the busbar of the receiver. just measure how long the cable from your battery to your switch to your receiver then out to your servo is....you might be very surprised . The radio manufacturers need to address this problem. They need to supply decent heavier duty leads. The other main issue is batteries. Everyone needs a decent microprocessor based charger to make sure batteries are never overcharged. My rule of thumb is to change my batteries every 2 years regardless this ois not costly and very good insurance. I use nicads because the technology is well proven and can take large current draws and also large current swings just like what we put our servos through in flight. I dont believe that dual batteries are anything but extra weight if needed for balance. I also charge after every flight all batteries but this is only with a good quality charger and I have tried a lot of different chargers and have found some to be lacking or they overcharge the batteries. Its horses for courses I suppose and everyone is entitled to do what ever they think will help protect thier $10,000+ model and if you feel comfortable with all this great technology then thats fine with me...dont get me wrong I dont hate new technology I think its great......but I feel that personally I prefer to keep all my models nice and simple. I have only ever had 1 crash with a jet in 7 years of flying them. That crash was caused by a shoot down and it was basically total destruction...the only thing that was salvaged was the engine and that cost me $700 to repair but all the rest was written off. So for all that written above my last word on the matter is KISS

Regards

Mark Kyle
Simjet Distributor Australia
Kyle Communications Pty Ltd

Good points Mark......I still see folks installing a PowerBox with dual 4000 Liths and then using 22 ga, 48 inch wires downstream to the servos......Also note that Duralite Plus 4000maH RX packs are still shipped with a single 22ga output wire, same dimension as the charging wire which carries no more than 2 amps while charging....should have at least 18 gauge, and preferably 16 ga with something like a Deans Ultra Plug going into the switch and regulator.....preferably using a Perfect Switch setup so all that current doesn't go thru the mechanical switch, most of which develop significant voltage drop after 5 amps is pulled through them, even the HD models

I don't have the exact current limits for point to point wiring with standed copper wire at hand, but for solid conductor 18 ga it is 16 amps, vs 22 gauge is only 7 amps, reflecting a greater than double the resistance in 18 vs. 22 gauge......I agree that manufacturers should be phasing out 22 ga wires for digital servos in favor of 18ga which is a big as I have been able to get into standard JR or Futaba connectors.....and then going to 16 ga from BAT to switch, and then dual 18 ga out of the switch to the RX......would be nice if all RX had 2 separate BAT inputs to the bus......


Your BAT comments are right on.....I have done my voltage drop test as described in one of my prior posts on this thread, using a 1400maH AA Nicad pack, and 1800maH sub-C pack, as well as my newest 3500 maH pack......the results are drastically different, with major voltage drops of over 1.5v with a 4 amp load on the smallest pack right off the charger, with essentially no voltage drop on the 3500 pack until it is discharged to about 50% of it's rated capacity......


Tom

I think most points have been covered in this interesting thread , but I emphatically disagree with Mark on one point, about twin battery setups, they do reduce the risk of total power failure almost to nil. KISS is great, if the simple approach will get the job done !

Tom, we are indeed reading from the same page but to muddy the waters a little I have just received a description of a new Australian product the, "I Switch," from RBA in Perth. This is a device to provide separate servo power, opto isolation and signal amplification in heavy duty applications, and makes the point that it is the plugs and sockets which are the weak link in current use (sorry about the pun) being rated at only 1 amp before voltage drop starts to occur. (I think Speedbird made exactly that point) so anyone who is using lots of high powered digital servos through just one JR deluxe harness, which use standard connectors, may be grossly overloading the switch harness.

On the Duralite cells connecting to my Powerboxes the cable is 16 AWG and the connectors are the heavy duty multiplex type, which match the Powerbox.

In reply to an earlier request , I believe MAS is no longer making the volt logger (or anything else) but try Intairco (www. intairco.net) they may have them, and they are excellent devices.

Tom, glad to hear you are back flying, driving to Oshkosh from Chicago last July, the countyside looked beautiful, green and lush, but I imagine its pretty bleak in winter. Last Sunday here was plus 25 degrees, (C!) light winds with scattered Cu at 3,000 ft., perfect, and a lot of Jet A as burned. Good luck with the Ultra Bandit, it looks superb.

Regards, David Gladwin.

I do believe BV is a bit skimpy on his setup, but he and his men are so meticulous with their pre-flights even before they leave the shop....works for them......

Actually, I have no doubts my straight wire system will work on the UB as I have the identical system on my KingCat #2, as well as KingCat #1 which I sold to my flying buddy, Dave Elsinger, here in Fond du Lac, both with (8) 8411's on #1 and (8) 8611's on my current #2..........between the 2 planes, have over 200 flights without a single glitch.....using 3500maH 5-cell packs without regulators on RX and 4000 ECU Duralite on #1 and a 10 cell 600maH Nicad for #2 with the Pegasus NL AS on board....

As far as Erik's problem with his Bandit with the Duralite......might have been the Duralite.....I just received a pack from one of the vendors that was assembled 8/05........upon the first load test out of the bag at 1 amp, voltage was 4.55v...[].......capacity check was 1200 maH and wouldn't charge right......called up Duralite and got a replacement warranty pack....great service....but even Duralites fail......while you don't have to cycle Lith-Ions, you still have to regularly load check them......David Reid almost lost his Phantom at MAB couple of years ago when his XMTR Duralite took a dump....zero volts while he was just getting ready to shut down.......


Tom