BaldEagel

aerobatx

The Hitec 5955TG's are supposedly OK at 7.4volts its the fully charged state of a LiPo that concerns me at 8.4volts, but thanks for the information on the Rx.

Mike

arobatx

Exactly....so I would regulate to your safe level at 7.4v

Bob Pastorello

My Feedback: (198)

Perhaps this is why my "all 5955" setups are working well. I'm using dual pack NiMh's, 5 cell, through all HD (20ga) harnesses.
My earlier post was based on my reading of that other thread. It seems that the "low reset" point of 4.7v stated would be pretty risky in an un-regulated, digital servo environment with a *four* cell pack.

Guess that's what is rattling folks, and it would me, also.

Maybe 4.8v inline "regulators" are needed when doing 4 cell setups???

BaldEagel

Or don't use 4cells, I don't have a single plane without a minimum 5 cell Nimh at 2500Mah AA size, I change all my batteries at the most every other year.

Mike

arobatx

I've never seen a problem with the voltage of a freshly charged 4.8v pack, which is usually around 5.5-5.7v, depending on the quality of charger used. Why not run one or two good 5 cell packs, regulated to 5.7?

BaldEagel

I have a Medusa Regulator to step up too 45V down to 6V I think thats the way to go as I have it already. Fresh off the charger my 5cell packs are at 7volts they drop down too 6.5 pretty quickly after that, the 3300Mah unit that I use has a double lead out of it from either end of the pack to two switches to provide a bit of redundency, but I am very loath to go the full double redundency route with everything, its the KISS principle.

Mike

pilotpete2

The use of 5 cells packs is great, but since most modern servos are rated for use with 5 cell packs there is no need for a regulator, why add complexity where it's not needed?
Pete

arobatx

I have felt the same way about total redundency....I prefer to grab a good quality, low internal impedence 5 cell pack like SR, high quality leads, connectors and switches. Money well spent I would only regulate the system if the servos aren't happy.

BaldEagel

pilotpete

Its a weight issue with Nimh v LiPo and getting the capacity with that light weight also, trying to keep the wing loading down as low as possible for good 3D performance.

This total redundancy kick that everyone seems to be on in Giant Aircraft is I belive driven by the manufacturers of the redundancy equipment, with good maintenance you should not need it, in 45years of flying RC I have never had a failiure of my equipment that a doubling up of my on board equipment would have saved.

Mike

rmh

I have been using the new A123 cells (two of em)-2300ma- as well as 5 cell NIMH of very low impedance.
In actual practice - the voltage is about the same - --in mid 6 volt range under some mild loading
Under really heavy loading - the lower amp rated A123 -- will deliver power as well as a 4300ma NiMH-- but obviously not for as long ( less ma)
either pack can easily be fast charged
the A123 can be fast charged at 8 amps-at the field -no cooling off required -don't try that with the NIMH
so - I just check and allow a battery recharge as I am refilling the gas tank.
also no reg needed (or wanted).
a pair of cells is 5.5 ounces as pack and is jut fine for 33% models
a 40% model - two pair and two switches is a good idea.
one note of warning -- if your servo setup is binding or servos are undersized -- you can burn up stalled servos as the 123 cells don't simply loose voltage under high loading . Many batteries -including LiIon with regs simply drop voltage under high loads ( measure it if you doubt it) and may save the servos if they are stalled due to undersizing for air loads which stall the servos .

Mitsu1

My Feedback: (13)

This has probably been discussed in this looonnggg thread, but I need the concensus opinion. I just read on RCGroups that on some page in the manual, it states that if the receiver ever sees 4.7 volts that a receiver reboot will occur, and this can take as much as several seconds. Over at the other site several are claiming to have experienced this mid-flight reboot, withone person saying he lost 2 brand new airplanes to this while flying his DX7 & AR7000 combo. I'm depressed about this, because I sold my new Futaba 9C radio, and I have a brand new 50cc Katana S that I'm ready to put in the air, ... and am now scared. I am running a single 2700mah 6 Volt NiMh battery. I don't want any regulators or other complexity in this setup. I usually fly 4 -5 10 minute flights in an outing. I feel like I jumped out of the frying pan .... right into the skillet

rmh

ask the Horizon guy Danny - - you apparantly have a lot of bad info.
there is nothing to be frightened about.
use your field tester and see that your battery stays above 6 volts - check each flight till yo u get a feel for battery usage

the low threshhold of the Spktrum is closer to 3.7 v.

V2PLUS10

I have a EF Yak 54, with and OS 160 glow engine. Same battery pack, a 5 cell 2700 nimh and I've had many excellent flights so far without a glitch. Four HS-5645 digital servos, one HS-5985 digital servo and a HS-85 std servo on throttle. I've read the same thread that you refered to and it concerns me. But, the fellow was on his fourth flight, which could represent anywhere from 40 minutes to an hour of "on" time for the airborne pack, so he may have simply depleted the battery pack. I wonder at the fact that he then took this same receiver, which had been through an evidently severe crash, installed it in another airplane and then crashed on the first takeoff. I personally would have had the rx looked at by a service tech. All that being said, I'm still concerned. I may set up the Yak in the garage and turn the radio system on and sit there and wiggle the controls untill the rx battery is depleted. Not at all scientific, but I may still learn something. Also, could the tx programming be at fault? If you do not inhibit the flap switch when using two aileron servos in the flaperon mode, can accidentally selecting the flap switch to "on" command a turn? I know I've done this during the programming phase of aircraft setup, but I'll need to look into it and see if i can duplicate it......It will be interesting to see how this works out.

The fellow on the RCgroups site posted that he had installed one of the capacitors that Spektrum offers to see if that solves the problem. Do you suppose he'll use the same receiver?

randy

V2PLUS10

One more thing....be certain to cycle your new nimh battery pack a couple of times. After the first full charge my pack had about 25% capacity, but after a couple of overnight trickle charges and subsequent discharges with a Sirius Supertest, it came up to full capacity....

Just check the flight pack between flights, and charge if needed...

Randy

jlkonn

My Feedback: (1)

I'm building a new Focus II for this season.
I just went out and plugged an old, old 700 mah, 4 cell NiCd in to the Jaccio regulator.
The battery with no load showed 4.9 volts on my Hobbico battery tester...remember...no load and I haven't messed with charging this battery ( I use it for bench purposes) in weeks.
I was too lazy to get the wings out of their covers and plug everything in so I am only using the servos that are in the fuse:
2 Futaba 9650 digital servos, one on each elevator halve
1 Airtonics 94758 digital on rudder
1 old, old Futaba S133 on throttle...I know, I know...[&o]
I turned everything on and wiggled the sticks as hard as I could and got a glimpse of a reading in the 4.4 volt range a couple of times.
No receiver reboot on the 7000 rx.
So...Dick may be right...it drops out in the 3.7 volt range.
I am going to continue to run the battery down and see if anything weird happens.
JLK

Mitsu1

My Feedback: (13)

I don't have the RCGroups thread before me, nor the manual, but If I remember correctly the posters said that it clearly reads on (page 107???) of the manual, that it would reboot if the receiver ever sees 4.7 volts. Several others confirmed that this was in the manual also. Dick, .. or anyone else, .. are you saying they put 4.7 in there as a safety buffer, and that reboot actually occurs more in the 3.7 volt range?

rmh

I think it's time to start over--
I am not a tech rep for jr/Spektrum--
the 4.8 v batt is below operating levels at 4.7. --that is what the tech was trying to tell you . so if it is below operating voltage --any load will depress it quickly.and could easily go to 3.5v -which is minimum on DX2 6100rx and I presume- the 7000rx. I said 3.7- which is a bit high, according to specs on 6100 rx.
the important point tho--is that it is the owners responsibility to keep the cells at correct operating levels . a 4.8v batt is below useful levels at 4.7.
Now -in real life - a simple 4 channel model weighing 5-6 pounds with 4 servos total - is a decent match USUALLY for the 1100 ma 4,8 nimh/nicad cells - but -you must monitor the battery!!!
the new high power servos (as came with the set) can easily flatten a battery if they are stalled or oveloaded from a lousy installation.
Properly installed in a model which is not a performance setup - it all works fine - but you still must monitor the batt.

Uh-Oh!

In the "General Information" section, on page 102 in my manual, is written that we shouldn't fly with a Tx voltage lower than 9.0V and the Rx should be no lower than 4.7V. That being said, this entire section of the manual looks like it was "borrowed" out of a 72 Mhz set up. They are giving contradictory info on range checks, frequency procedure which are all quite correct for a 72 Mhz transmitter.

This low voltage thing concerns me. Not overly so that I'm afraid of it. I don't ever let the voltage get below 4.7 before a flight. Quick charging doesn't take so long as to risk an airplane. I have adopted 6V Rx packs and do not intend to fly the 7000 without one.

What does concern me is low voltage drops during some hard manuvers. Would 5 DS 821's and an old Futaba S3001 potentially cause a drop to the reboot point using a Hydrimax 6V 1650 Mah NiMh battery? Am I possibly being paranoid? Probably...

Maudib

My Feedback: (51)

The statement is correct. Page 102

It says: "Check the battery voltage on both the transmitter and the receiver battery packs. Do not fly below 9.0V on the transmitter or below 4.7V on the receiver. To do so can crash your aircraft."

This is the TEST voltage on the ground, not the voltage at which the receiver will reset. ABove 4.7 you may fly, below you may not.

Without a load or with a small load, low batteries can still maintian voltage, butif the current demands increase the voltage drop can be significant... espeically on cheaper/smaller nimh (like the AAA/AA size which seem so popular for midsized glow planes)

The point is that if you BEGIN a flight with a battery that is less than 4.7 volts, the you are taking a GREAT risk that the voltage under current will drop enough to reset the receiver.

It's always a good idea to check the voltage of the pack with a 1 amp load prior to flying...

Maudib

My Feedback: (51)

If you have a wattmeter, you cann connect the pack in question to it and an electric aircraft... runt he throttle up to get say 5-10 amps and see what the voltage odes...

rmh

It very well may--if one of the older Hydrimax is being used
I have measured these under load and the voltage drops like a tu-- from a tall cow.
FWIW
older design cells have high impedance - ALL of em --and NIMH were the worst.
high impedance reduces current flow upon demand
buy, beg, borrow or steal a Whattmeter and watch the voltage drop under load . then you will understand the need for new cells in proper charge - if you are using performance models having higher power servos.
the run of the mill stuff just a couple of years back -is NOT up to present needs.
remember-- when any component pulls down the voltage --all the components see the change.

Uh-Oh!

Good idea! I knew I kept the Himax on my old mini Funtana for a reason...

Thanks...

Uh-Oh!

It's a fairly new unit but, I have a Whattmeter and will definately check it out. I just didn't think about using the Whattmeter. Old age is creeping on me quickly....

Thanks

Pile-O-Wood

People do not understand what 4.7 vdc means on nicad or nimh batteries. Please do a google on nicad discharge curve and you will see why they say don't fly below 4.7 vdc.

jlkonn

My Feedback: (1)

I believe the caution in the manual to not fly below 4.8v is standard practice for a 4 cell pack.
I did leave my DX7 tx and 7000 rx on most of the afternoon.
Got the old 4 cell NiCd pack to drop below 3.7 volts while I wiggled the sticks.
Nothing happened...
No dropout...
No "reboot"...
Is it safe to fly this low?
I wouldn't.
What did I prove?
Not much...
I just satisfied my own personal curiosity with a not very scientific experiment.
What't the saying...?
"Inquiring minds want to know"!

Good Luck!
JLK