A friend of mine finished a 28% plane the other day. when I looked in it I'd swear I was looking at the inside of the space shuttle! I am constantly flabergasted at the money I see people spending on boxes, isolators,do-dads of various types in the electronic chain. Hundreds of dollars.

I have been flying a couple of 35% planes for a couple of years now with all digital servos, one receiver, two 6v nimah batteries and two MPI type HD combination charge/on/off switches on the receiver side; and a single 4.8v battery and switch on the ignition side. No regulators, no boxes, no isolators or other do-dads. I do use the GEM2000 system on both receiver and ignition systems, use high quality extensions and check voltages and functioning often. Thats it.

I would be interested in comments that would indicate how many of you follow the same "simple is best" philosophy. Or give me an indication I'm living on barrowed time.

Mr. Scott was quite correct when he opined that 'the tricker they make the plumbing, the easier it is to stop up the drains!'.

KISS works for me.

Besides, when all is said and done in defense of 'redundant receivers' and other attempts at making an in-flight model absolutely fool-proof, the fact remains that there is no such thing as a redundant R/C receiver, period. Having half a model on one receiver and the other half on a second receiver is not redundant, it's just two receivers each controlling half a model.

If we ever actually see redundant receivers, where there is a third logic box to switch the model's controls between receivers, I'll be the first to snag one. Until then about all we can really do is use heavy duty wiring and switches, and the most bullet-proof receivers available.

One would hope that any future redundant receivers are also capable of frequency hopping in some fashion, to avoid plain old shoot-downs.

As it stands, no amount of extra trickery in the model will counter a dolt switching on a second Tx while your model is at exactly the wrong altitude and attitude.

The third logic box already exist in the Emcotec DPSI Twin [link]http://www.rc-electronic.com/html/englisch/unten/dpsi/dpsi_twin/dpsi_twin.html[/link]


Agreed

28% planes, one receiver, 1 4800 mah li-ion, 1 2400 mah li-ion (ign) Fromeco regulators with reliaswitch's, 1 smartfly fibreoptic cut off switch, coupled with failsafe programmed into JR 9303
35% same thing only 2 receiver batts
All my planes are using JR 8611 and or 8411 with PCM recievers and a few matchboxes here and there.
I think you will find that making the move to a li-ion or li-poly battery system will give longer stays at the field and much better peace of mind, they also contribute to some of the doo dads that you refer too.
Oh and by the way nothing is much easier to setup than this and it also exceeds safety rules by tha AMA and Imaa

longer time at the field is not relevant. I have a Sirius Quad charger. I can recharge the whole mess in just a few minutes.

Well you just answered one point that i tried to make and that is if you go lithium you would not have to recharge the whole mess in just a few minutes. Is it keeping simple or keeping it cheap? what is a few extra $'s in relation to the cost of our planes, i dragged myself into the lithium age and have not regretted it but then when I spend appx 250 hours building a plane it is worth it to me.

I use one receiver....

On warbirds most of the time two battery packs and two stitches. (Mostly for balancing weight)

I also use the super switches that plug one battery into two slots on the receiver.

No Li-ion. (My field chargers work well for charging is I need to be at the field all day. (I use 2 Dymond chargers. One for the RX pack and one for the Ign.)

Simplicity is the key for me.

I guess I should stay out of this, according to most, my planes shouldn't fly.

Darrin R cash

This has been re-hashed to death. Do a search for all the arguments.

I fly dual rxs on all my research planes (20+) valued from $5K to $15K. I have survived all types of component failure with dual rxs without losing the plane. For me, it is a no-brainer . . . . .

You can either carefully prepare your plane and fly carefully and hope your single rx does not fail

Or

You can plan for failure by carefully preparing your plane with dual rxs. The probability of total failure is a power of 10 less with dual rxs.

Elson

Bugman, I have done all the searching and read so much stuff it gave me a headache. What I was after here was how many people, if any - do what I do and fly simply with two switches and two batteries on one receiver without doo-dads. Didn't really want to hear from the multi-do-dad crowd. Maybe should have said that.

But, to contradict myself; lately, I have been having second thoughts. I would ask a question. Do you have a link, by chance, to a nice article or site that comprehensively deals with a dual receiver setup.

Sounds to me that you don't know what you want. You do know that dual receivers are going to move you closer to the LIGHT don't you?. I think you are going to find a split decision on dual receivers at this time a lot of the BIG boys are only using singles. Of the people that do use dual's most split the plane to left and right, I have seen some that set it up ,left aileron, right ele, etc it is very simple to do,however their is an opinion that dual JR's will give you limited range based on facts of course and the fact that most of us have trouble landing a good plane let alone a plane with only one side functioning.A lot of the bigger planes are being flown with one receiver and power boxes with redundant batt's of course, but then we get back into DOO DADS which we know you don't like,so maybe just keep it SIMPLE and let the rest of us deal with this awfull thing called modern technology to try and lengthen the lives of our planes. Seriously though I think once you start looking at this stuff you are going to find it simple to set up, use and maintain. Good luck with your decision.

(THE "KISS" CROWD IS SHRINKING)

I like to keep things simple too, but I also like a system that works correctly. Yes one RX will work on 35% and bigger planes without any of the do-dads, but is it working properly?
I think not. The RX will only carry a certain amount of power through it. Once you have more than 10 or so servos on a plane, you're system is going to be calling for more power than a single RX can handle at times. When you use only one RX, you are now limiting the power to your servos and they will not be performing as they should. You may get blow-back. You may not get full throw. If this is O.K. with you, then keep using just one RX.
I personally will be using some do-dad or a second RX to make sure my system works the way it should and gets enough power to my servos when they need it. I will keep my system as simple as possible, but not to the point where I am sacrificing on performance.

As for redundancy or whatever you wish to call it, there are many people right here on RCU that will tell you having a 2nd RX saved their plane. One RX failed and they landed the plane with the other RX working 1/2 the plane. How can you argue with that?
It's just like purchasing insurance. If you don't want to spend an extra $100 to $150 that might save your $5,000 plus plane, then don't do it. It's your plane and it's your risk.
I'll gladly spend $100 to $150 more on a second RX as "insurance".


Jim

Jim

I have not decided I want to start adding do-dads into the electronic chain. I think they are just another element (link) that can fail. The dual receiver setup got me to thinking though, because the single receiver is the week link in the keep it simple approach. But it seems that I read someplace as you have alluded to, that dual receivers can cause their own problems. I just haven't found a place that clearly discussed a dual receiver setup.

How many 1,000's of guys are using dual RX's right now (and have been for several years)?
Where is this supposed problem you speak of?
You've got to start paying a little less attention to talk and a little more attention to what is proven to work.

As for the tired out arguement of do-dads being "just another element (link) that can fail", I think that is ridiculous. Every part or piece you put on your plane is "just another element (link) that can fail". If you use that reasoning, you shouldn't build the plane to begin with.

There is risk every time we take off in this hobby. This is the case if you have one RX or two. This is the case if you have a do-dad or not. All we can do is possibly minimize the risk by choosing quality components and using a properly designed system.

So we have to use some common sense and figure out how we can reduce the risk. We then have to decide if it is reasonable financially (and this will be a personal decision). We all have our own tolerances for risk vs money.

When you use just one RX in large planes, you are overstressing your RX and servos (you've admitted this already). This greatly increases your risk because a system under stress is more likely to fail. By using a 2nd RX or a do-dad, your system will now work the way it is supposed to and will not be over stressed. The risk of failure has now been lessened in my opinion because things are working properly and are not over stressed.
So using a do-dad or 2nd RX actually decreases your chance of failure in my opinion.


Jim

I could not agree more Hammbone, nicely put.

Jim, At what amperage levels are the recievers over loaded? Are these amperage levels dependent on the reciever used (JR vs Futaba vs Hitec etc etc)? Is this imformation documented by the manufactuers as well as expected servo currents so we can determine when we are overstressing our recievers based on our planes configuration? I would like to know if I am overstressing my receiver in my Comp Arf Extra with JR digital 8611 servos?

Thanks for your help,

I am no electronic expert and will not pretend to be. I was just stating a more "common sense" general type of view.

I don't think that RX manufacturers have done testing like this for us. I have seen individuals here on RCU that have done their own testing though, and it seems the consensus is that if you are going to have 10 or more servos on a plane you may be exceededing the capabilities of the RX bus and you need to use either a second RX or some kind of power distribution do-dad in order to get enough power to the servos.

Maybe someone else with more knowledge than me can chime in here and give their test results or opinion.

Each individual set-up is going to have a little different loads and requirements depending on many different factors. I'd rather play it safe and know my servos are getting the power they need. If there is any question in my mind I will go ahead and get the 2nd RX or do-dad. For me personally, anything over 30% scale will get a 2nd RX or do-dad, but as I said earlier, this is a personal decision each of us has to make depending on our own tolerance of risk vs. money.

Jim

First I want to state that I am also not an electrical engineer but my job does involve working with electrical systems, wiring and large electric motors so this subject is not foreign to me.

The problem is not with the receiver, it's with the power distribution system as a whole. The receiver provides the bus that all of the components connect through. If you consider that a servo draws a given amount of current under a given load then X number of servos multiply that load, across the receivers bus. All those little motors in your servos draw a given amount of amperage at a certain voltage, allow that voltage to drop and the amp draw goes up accordingly. When the amp draw rises so does the temperature of ALL of the components in the system, especially any point of connection. As temp goes up on electrical wiring systems so does the internal resistance which compounds the problem even further as it's also reduces the voltage and causes the amp draw to rise more. It's a vicious circle that can add up quickly and have undesirable results. This is the whole reason it's highly desirable to use HD extensions with gold plated ends and heavier wire in the first place, to keep the voltage constant as much as possible, preventing an unusually high amp draw for the system as a whole.

While two batteries operating through 2 separate switches are great for redundancy in the event of a switch failure, they are also provide double the capacity on the bus, an added and highly desirable benefit.

Also something to bear in mind is that Li-ion batteries that have a high voltage rating are regulated down will hold the voltage at a constant level much better than Ni-cad or Nimh. Remember that the nickel batteries start out at a lower voltage and go down from there so as your batteries deplete the amp draw rises accordingly. On smaller planes this is a non issue but on larger models it can actually be felt in the control response of the model by a highly experienced pilot.

It's really a no brainer that once you get over 30% scale that Li-ion becomes the battery of choice for the reasons presented above, on smaller models with fewer servos it's not as critical to the performance of the system.

Are you sure about this? Two batteries on one RX bus increases the capacity of the bus? How is that?
I thought of the RX bus like a wire. A certain size wire can only handle so much current. Putting two batteries on a wire does not make the wire carry more current.
What am I missing?

Jim

Scott, also considering that I am just now starting to look into Li batteries, a couple of questions. I'm assuming that all Li batteries require the use of a voltage regular. What is generally considered the least complex way to accomplish this regulation. thanks.

Jim,
If you use a single pack your system is drawing ALL of it's power through the two wire lead that comes off of that pack and delivers the power to the receiver bus. Adding a second pack adds another set of leads that feed the bus and thus each lead, from each pack respectively, only sees half the amp draw, reducing the possibility of a voltage sag. Of course this assumes the packs are of similar capacity and voltage.

Spias,
There is nothing special about li-ions. The 2-cell flight packs are nominal rated at 7.4 volts per pack which is too high for most radio equipment. This necessitates the use of a regulator to knock the voltage down to around 5.5 to keep the gear happy. All you need to use them would be a regulator per pack and a switch per pack, assuming you run redundant packs. There are 4 sell packs but they are nothing more than two 2 cell packs in the same warpper that are wired in parallel, you get higher capacity but the same voltage.

Yes, I understand that the leads (or wires) coming from the batteries have their own limitations, and that by having two batteries you can double the amount of power going to the RX bus.
This has nothing to do with the amount of current that the RX bus can carry though. The RX bus still has it's limitations seperate from the battery leads. You can hook up 10 batteries to the RX bus if you want, but the RX bus is only going to pass so much current because it is only capable of passing so much current (Just like the battery lead can only pass so much current.).

This is the whole reason they've developed power distribution systems. In order to get enough power to the servos we need to bypass the RX bus and its limitations.

By using 2 batteries, you are getting rid of one weak point in the system, but the RX bus is another weak point.

One company I know of that has done some testing is Fromeco. Check out their website if you haven't:

http://www.fromeco.org/

Lots of good info on this subject there and lots of good products that solve the problem of limited capacity in our systems.


Jim

Do you have any data that support this statement??

People can make very general statements such as with "10 or more servos"... Servos can draw different power with the airplane at differetn speeds. Different servos even demand different power requirements. Plus- are all the servos drawing max power at the same time?

Generalizations can be difficult to understand and still be believable. There's lots and lots of variables.

I have always been a KISS proponent.

I have however recently been using the Powerbox on large planes (35%+) . While on the surface it looks like an expensive "do-dad" it simplifies a lot of the rats nest wiring in the plane and combines several functions into one. I only use Li-Ion power and would never even consider anything else.. Li-Ion power is THAT GOOD. So by using the powerbox I combine battery load sharing, comprehensive battery monitoring, power fail safe / redundancy, servo output ampification, RFI reduction on long leads and receiver isolation. It is a complete power redundancy system and it is all controlled by one solid-state switch with nothing to vibrate loose or create RFI. It weighs less than the regulators and wiring it replaces!

Yes, its pricey $350 but I only need to buy it once, and it truly has made life simple. Its a waste on anything less than 35% though.

In this case I believe more is less. The cleanliness of my equipment installs is as good as it gets and I have plenty of clean power all around.
My engine off vs. engine on ground range has improved dramatically as well.

DP