Large Model Association Forum

Hi
Just finishing off a Proctor Nieuport 28 and reached the of installing radio gear. Looking at those 1/4 scale servos I concerned as to whether my normal 5 pack pencell Eneloop batteries will cope? I am sure this have been well covered before but being new to large aircraft I would appreciate guidance or advise where I can find the topic covered in the past.
Regards
Edgar

As a start Edgar you will require two battery packs and the most common method is to have these packs with a diode in both positive leads to seperate the supplies. I also favour using a seperate double pole Toggle switch for each battery pack which in effect gives you four switches. You can then have three sets of contacts fail and still have a working power supply.
Slide switches can be prone to failure when used in our models. You may or may not require a power distribution system
depending upon the current demands of your electrical system. If the loading is not too great you could y lead two receiver channels for your two power inputs if you have not enough battery input spares.
Certain types of battery such as a lipo will require a voltage regulator to reduce their higher voltages to a useable level.
Your battery requirements cannot be ascertained without knowing the demands that are going to be placed on them, ie servo
size and types, [Digital servos are great but do need a greater battery capacity] The loading of the servos of course depend on the type and size of aircraft and the way that is going to be flown.
I hope that will help for a start.

Tony

.

go to sub C batteries. Pencells are ok for smaller models.

Edgar, a twin battery set up is a good start, capacity can be from 2500mA up using 5 cells NimH of Sub-C size. You will then easily get 4 flights on that set up dependant upon your type of servo.
Cary

Is this not a little OTT for what is a WW1 quarter scale? Have I got something wrong here? Sub C batteries are good as you will need weight up front, but all this talk of digital servos and dual battery systems seems far too complicated. A (for instance) DB SE5a is fine on standard servos and a single battery. Its hardly a mega model. And four flights from a five cell sub C? I would want to fly all day on one!

I agree with Bob - this is a Proctor kit near museum quality and of light but strong construction,adding unnecessary weight would mar the excellent flying qualities these kits have.
KISS principle is the one to follow - keep it simple - I have flown 1/4 scale WW1 for years on single batteries and never used up any where near the capacity - 2000 to 2500 is ample.
Just my twopennorth
Pete

Hi Bob. Hope you are keeping well.
As Edgar said that he is new to large models I attempted to give him an overall picture, not just for his ww1 model.
I always think that a little bit of knowledge can be dangerous and obviouisly edgar has a bit of a learning curve in front of him.
It's old buggers like us that can help him safely on his way.
Agree with you on sub c batteries, way overkill for his model.

All the best Tony.

Thanks folks heading in the right direction here.
More detail, using Hitec 755MG servos - did not see the point of digital servos on a slow model of this sort.
I like the ideal of two battery packs, any chance of circuit diagram and what diodes to use?
I have used eneloop for some time now very successfully on my normal models as they do not loose charge or sag under heavy load, however they do not make Sub C cells. So would 2 Eneloop packs with Diodes be OK, or if I really need to go to Sub C which are the best?
Although I believe in keeping things as light as possible, I don't think weight is a problem. As I am using a Laser V engine (quite light cf chainsaw type) I am sure I will need nose weight, hence will end up with the batteries inside the cowl.
Appreciate the help. Regards Edgar

Hi Edgar, just a quickie as I am on a tight schedule at the moment.
The Hi-tec 755 servos are way to big and heavy for your model and have a lot of torque - not required at this level.
a more suitable servo would something maybe like Hitec HS-645 MG Ultra Torque 8Kg, smaller lighter and of course easier to
fit in what is a comparatively small model. When I get time I'm only 79 you see I will draw out a circuit diagram
for a twin battery, twin double pole switch , Diode seperation type system with charge points. With two 5 cell battery packs
of around 2500 Mah you will have a total capacity of 5 Amps and only need to use AA cells. Ideal for your model and of course
should one power supply fail, [ has been known ] you aren't going to come down and kill someone.
Must go

Tony.

Edgar,

I have build and flown one of these models Proctor Nieuport 28C and have 20 years experience flying 1/4 scale WW1 on the show circuit. Please call me as I can help you. On absolutely no account use AA batteries with 2.4Ghz in a model like this. Do not use diodes either they will cause even more voltage regulation.
Hi tech servos mentioned are fine. Also I would like to discuss with you your C of G and wing, tail-plane incidences as it is highly likely you will have an un-fly-able model.
The info I can give you is too extensive for this site and will probably save your model. This is an extremely complex model and nothing like conventional Pups, SE5 and DR1 type models to fly. The set up is critical to have any hope of flying it. The plan says 3deg on lower wing incidence and 1.5deg of upper wing incidence with 0deg on tail-plane. This is fine for full size with an airspeed indicator but the rear lower wing will stall first giving nose-up forward centre of lift which equates to an even more rearward c of G than the 37% mean cord on the plan. With the smaller bottom wing the C of G is at more like 43% mean core they get over this by moving the centre of lift back with the high incidence on the rear wing. A model should have more incidence on the top forward wing giving a smooth nose down as the stall is approached. A WW1 model is best at 25 to 26% mean cord C of G with the same incidence on both wings or slightly more on the top wing so it stalls first but doing this moves the centre of lift forward and the centre of lift must NEVER be in front the C of G or you need fly by wire computers to fly the aircraft. I have had to put 2.5lbs of lead around the front of the cowling and have used a DLE40cc petrol twin. I have installation pictures and my 28C was in the Gaydon article in the LMA mag. Please call me.

Regards

Martin 07785-333817

Sorry should have addressed above to Edgar

Martin

Use A123 batteries. They are far better than nickel batteries in self discharge, current capacity and weight.

Well there you go Edgar. You take your pick. Agree with you Rob that A 123 batteries are Excellent.
Otherwise it would seem my 47 years of RC modelling and associated electronic design count for nothing.
My intent was to help you through the important basics not try to confuse and overpower you with information relevant to just one aircraft. This model apparently is doomed from the start without considerable set up and modification.
If you feel that I can help you futher then send me a PM. I will not be posting again on this subject.
Tony.

With a A123 (Life) battery the output voltage is 6.6 volts, which is above the rated voltage for some servos. The solution to this is to add a normal bipolar diode in series which will reduce the voltage to 5.9 volts ( .7 volts drop ).
For a dual battery system the reason for diode isolation is that if you connect a fully charged battery and a flat battery in parallel then one battery charges the other at a current way beyond the safe charging current !
When you want diode isolation without the .7 volts drop then Shockley diodes are the answer which typically have a voltage drop of only .25 of a volt.
Connecting 2 or more diodes in parallel gives the same voltage drop but gives you a backup if one were to fail.

Steve Perry wrote:For a dual battery system the reason for diode isolation is that if you connect a fully charged battery and a flat battery in parallel then one battery charges the other at a current way beyond the safe charging current !

It won't, I've tried!

A year or three back I put my Mythbusters hat on and connected completely flat A123 and NiMh batteries to their fully charged equivalents with a watt meter between them. A bit of current flows, but not a lot, and certainly not enough to either damage anything or flatten the fully charged battery in anything under a week.

A diode will protect against any part of the pack becoming a dead short, but you've got to weigh up the chance of that happening against the chance of a diode stopping working (either open or short circuit).

Don't you mean ammeter Rob?

Nope it was a watts up watt meter, simultaneously measures energy (Wh), charge (Ah), power (W), current (A) and voltage (V)

I bet Edgar is really confused now !!!!
Just goes to show that in this hobby there is often more than one way to solve a problem.
When asking for advice be careful to evaluate all answers, especially those from "forums" and not "mix and match" answers. Pick the train of thought you want to follow and ignore any other answer that offers a different solution.
Edgar, if you are still confused ask Tony Hooper for the name of your nearest LMA Inspector and contact him for advice directly. Inspectors are happy to assist even if your model is under 20kg.

John

Solution, buy a "powersafe" type of receiver that has 2 battery inputs specially designed to handle batteries should 1 fail the other battery is utilised! Simples
Cary

I'm using a single 3300 sub c 5 cell pack on a 1/4 DB Pup at around 15lbs with locking toggle switch. Can get three 15 minute flights and still have 5.2v showing at 2 amps load.
Using Hitec 635HB (non petrol models only) on the 2 ailerons and rudder and a 645MG for the elevator and running a Laser 200v glow engine.

Very little load on the servos as its not a 3D type aircraft. Have been running this set-up for 3 years with no issues. The trick is to load test the battery before, during and after each session or flight.

Anything bigger of heavier I'd run 2 packs.