What is the opinion on using servo power busses? Like the Electrodynamics Powr Buss or others?
I think they are a good idea but you are adding more parts that can fail as well...

There are always 2 sides to every story and we could go down the PPM/PCM argument!

I have had a jet go down without one and then fitted one and have had no problems since.

I think you need to confirm the following. Are you using digital servos? Do you have long servo leads? Are you running 2 battery packs for your receiver? Do you have more than one servo connected to 1 channel?

If the answer to any of these is yes, then it will be of benefit to you.

Another benefit of these devices is that the receiver will have a constant voltage applied to it. Some of them also do away with "mechanical" switch and incorporate electronics switches.

The down side of it is also as you say, one more thing to go wrong.

The choice is always difficult but you need to feel comfortable using it! Good luck

Zane

I try to keep it as simple as possible and yet have redundant power. I use two batteries with two switches with each switch plugged into it's own battery port in the MPX 12 channel IPD receiver. When using dual 5 cell packs, you can plug into the B1 and B2 ports that are internally isolated in the receiver. Has always worked flawlessly.

I am gearing up a Kingcat and want to keep it simple as well. I was thinking of using two smaller 5 cell packs (1400 each?) with two regulators and two switches, with both plugged directly into the receiver. This would give me around 2800 mah, with some redundancy. Any reason why this won't work ? Opinions ? Thanks-Mike Oberst

Before going to the MPX 12 channels IPD receiver, I flew with that exact unregulated set up for some time and it worked fine. The only aspect that I do not like about it is that the two packs are not isolated from each other. Depending on who you talk to, that can be a problem or not. Most say that if a cell shorts closed on one pack, it will not bring down the whole system. I never had that happen.

There's no reason why that won't work, although if you're running Ni-Cd's you'll be charging a lot. What kind of batteries do you use?

In my 46% Ultimate Bipe, I'm running dual 3600mah batteries with 2 regulators and switches connected into a single receiver. With the Li-Ion's like the Duralite Plus, in this configuration you get both switch/regulator redundancy, and cell redundancy since these packs are wired as a 2 series, 2 parallel configuration. If you lose a cell in your pack, you'll lose capacity, but not voltage.

I would like to stick with nicads for now. One of my main concerns is to get some redundancy with the regulator, if I switch to 5 cells and start using one. I have always used 4 cell packs up to this point, and have considered sticking with the 4 cell nicads (although using a big 2500 mah pack) and not having to use the regulator at all. Any opinions on using a 4 cell nicad with the Kingcat setup, or should I go with the 5 cell / regulator setup ? The jet will have 4 8611 digitals, and 7 other non digital servos, along with two match boxes. Thanks-Mike Oberst

I have always used (before using the 12 channel MPX RX) unregulated 5 cell packs with 22 gage wire in Isobars (roughly the size of KingCat). I figure that the voltage drop over the wire runs helps to compensate for the lack of any voltage regulation. I have never had any issues what so ever due to not having a regulated 5 cell pack. Loose the regulators, just another possible failure point.

P.S. the isolation circuit in the 12 channel receiver is a diode scheme that cuts the voltage down a bit, therefore you have to use a 5 cell pack. No need to regulate.

My main concern, if I were doing a setup like that, would be : what is the voltage is at the furthest away servo - under all conditions (i.e with the RX pack not being totally fresh, with several of the other servos under load, etc. ?

The voltage may drop due to the load from the other servos, and it will drop to some extent over the long distance from the RX to the rudder and elevator servos. If the drop is significant then you not only lose out on power to those servos, you also may reach the point where the servos start hunting, or even stop responding. Using high quality connectors and heavy-duty wiring extensons can mitigate the loss over the long extensions, but using a higher voltage to begin with can help ensure that you still have plenty left at the end of those long leads.

Gordon

I use the electrodynamics power buss on anything that has a high load (mostly on the 4 CCPM servos for the rotorhead on my heavy turbine helis) The electrodynamics bus also optically isolates the rx from the servos. Under heavy load , servos can caus interfearence to the rx also, and the bus prevents that from afecting the RX. The JR match boxes are power buses also if you plug the aux battery in ... The power bus also allows you to run higher voltage to the bussed servos, and run standard voltage on the rest of the electronics ...


I personally love these things ....


Wojtek

This is a good setup IMHO. I use it on everything.

The only downside to this, is that many of the regulators on the market do not have a very high current rating, maybe 7 amps. So if you loose one of the power busses it is not clear the second one can handle the load. I still go with it, cause to do otherwise I would have to design and build a new regulator, or buy a new brand which I am not too keen on doing.

You also have to be careful to check both switches/regulators before flight, if not you could have a latent failure that you would not know about until it was too late. Make sure when you charge you see about an equal amount going into each pack. This can be hard to achieve in practice, sometimes I switch the batteries/regulators around every 20-50 flights or so to help equalize the use of the packs.

Good luck.

The duralite regulators can handle much more than a 7Amp load! Although rated at a continuous load of 10Amps, they will handle at least 20Amps continuous and when the fail....they fail closed! I know of one individual using a duralite regulator on his Ram ECU because he was having voltage issues on startup. The regulator is handling a 25+ amp draw during the startup phase (regulator leads were changed to handle the higher current)! These regulators CAN be used with both NiCad and Li....
Todd

When I built the first DC-10 I was worried about this also...

So I did some testing... I put a volt meter at the servos and also check the current at the battery...

The most current I could pull was ~4 amps only for ~0.3 sec... If I stalled a servo its current draw was
not as high as if the servo was going full speed one way and changed direction. This load was much high
than stalling all the servos.

The big plane had

2 x Big Red Digital 260 oz servos
6 x Red Digital 100 oz servos
3 x standard servos
and the wire length for the many of the servos was around 6 feet.

After testing everything over and over I concluded, with big enough batteries and with 5 cells
there was no need for any thing else....

The current draw was just not high enough, for long enough
that the bus in the receiver could not handle without getting hot.

One thing that helped a lot was using 2 batteries packs. This cut the internal resistance
of the batteries in half and kept the voltage high during load.

For any jet I would recommend 2 x 5cell NiMH 2000 AA... These two packs are all
that is needed for any jet... Each pack cycles at ~1900 mah @ 2 amp load
and will give over 3800 mah tested. I ran the Rig for over 4 hours in the shop
with a pack like this... And remember is only AA cells.

It mostly depends on how many servos you have in your plane...

Now.. I only tested Multiplex servos.. Maybe JR digitals pull more current...

Hope this helps...

Eddie Weeks
http://www.corpcomp.com/weeks1/

Is there any concern for how much draw you are pulling across the receiver boards? (as Eddie alluded to) using a kingcat for and example there are some 10(?) digitals all pulling amperage across the receiver board. That is where I would be most worried.

This statement gets used often like its a fact. It may be but I do not get it. The only way this is possible if Li cells fail open circuit as a rule. If they do they are risky to use. Nicads on the other hand we know to fail closed circuit or open circuit, depending on the failure mode.

We know nicads wired in parrallel will, if one cell fails closed circuit, cause a high inrush (charging current into the shorted cell) causing loss of voltage and capacity.
We also know that when it fails open circuit voltage will be maintained but capacity will halve and internal resistance double.

What do we know of Li packs except for marketing hype and generalisations in our application. Any vendor prepared to state the facts in verifiable scientific terms?

Backup power systems are of course a good thing in principle but they do add to risk of failure. The risk of failure in the case of batteries are however probably higher. Where these units provide an independent regulated and noise filtered RX supply they would be helping quite a bit in a multiple digital servo installation.

Andre Baird

moral of the story is, something can always go wrong, no matter how we try to prevent it ... i had a power bus, and a batery redundancy system on top of that in my turbine bell230 (3 batteries plus ECU battery) .... it crashed anyway .... why ? because the tail rotor shft sheared ... at least my power system held up


Wojtek

I've used Andy's Power Bus on Giant Scale and Jets, including one on my yet to be flown KingCat.....never any problems....solved a few long lead problems on giant scale gassers with electronic ignitions.....use on jets is less well defined, but still amplifies and isolates signals on long leads and keeps most of the servo current out of the RX bus.....Andy states that the unit, like regulators, fails in a neutral pass-thru mode rather than an open circuit, so should be safe in the rare event of a failure, and MTBF is extremely high.......

Re: 4-cell Nicad/NiMH packs and Digi Servos

Interesting article by Tom Wilkinson in latest RCJI, reviewing the West Battery Checker......he found that even at idle(no load applied to the servo) that (4)-8411s suck significant juice, and produced low voltage spikes of 4.24V with a 4 cell 1500 maH pack....dangerously low at idle.....remedied the problem with (2) 4-cell 1500 packs in parallel......then low voltage spike only down to 4.8V, with sustained at 5.0V.....IMO, use of a SINGLE 4.8V Nicad/NiMH pack to power several digi servos should be limited to large, preferably 3000maH or larger packs, with 18 ga leads, and never a single AA pack in the 1500-1700maH range with 22 ga leads, even if your flights are short and you re-charge after every flight.....

Andre:

Good point about failure modes of 18650 Lith-Ion Can cells.....vendors never qualify their "Redundancy" spin with "Even if you have 200 cells in a S/P pack, if one dies dead-shorted, you are done"....... that said, in over 35 years of using NiCads, 10 years of using both re-chargeable and non-rechargeale Liths in cameras and ham radio stuff, and 1 year using Liths in Jets, I have never personally had a dead-short, single-cell meltdown that took out the remainder of the pack.....only ones I have seen in other guy's packs were in NiCads, related to bad wiring of the cells or a serious overcharge of a Nicad(too hot to touch after the overcharge) before the days of peak detecting chargers with cell temp sensors....

Tom

The moral of the story is stop flying that Vario stuff, you break too much of it. I think this is the reason I cant get the parts from Joe that I need. only called him 11 times for one part. [>:] He says he has it but is having a mental malfunction about putting it in the mail to me.

In our KingCat my answer to that concern is the following.

The receiver and the three servos on the radio tray are powered by a 4 cell 1200 Mah nicad. All of the flight control servos are powered by a 5 cell 2200 Mah nicad who's power goes through two parallel switches to a set of 14 gauge wires that run down each boom (gross over kill). Power is taped off at the wing for the aileron and flap, and the rudder and elevator are on the end of each run. Signal and receiver ground go through shielded cable. All the grounds are pulled together at the servo plug. Since there is very little load on the receiver battery it only requires charging once a day, and the voltage to the receiver is very constant. Also when I add the gyro it will be powered by the 4 cell, which is what most gyros seem to need (some don't work on 5 cells). Not sure if it is related to this setup, but the radio has the best range check I have ever gotten, antenna off; 175+ yards.

Steven

Don, thats because i actually fly it


Wojtek

You got to learn how auto rotate that dead weight.

Tam, you ever try autorotating a brick ? i will post that crash video back up .. in 5 min, look at


http://www.voy-tech.net/crash.wmv

i had 12deg max pitch and ram out of rotor disk [] ... i think scale (non symetrical flat bottom) blades, and more pitch (16 deg for bottom of auto ? ) might have saved me ... then again, thinking back, multiple batteries, and a gallon of fuel might not have been such a good idea (



Wojtek

Yeah, autorotations are fun... when you plan them

this is what failed .... you can hear on the video from the onboard cam, the tail clatering itself to death ...


Wojtek

Tail drive shaft coupling?

That sucks!!!

I had that happen to me on a scale Hughes 500 in a park one day. The guy walking the dog loved the chopper until it started spinning 20' up, then he ran faster than I think his dog could keep up when that thing was coming down

that sucks but like you said it happens to everything and everyone.