japes999

My Feedback: (9)

I have a Top Flite .60 size P-51 Mustang. Futaba 7C Tx, Futaba R168DF receiver, new 4.8V battery, Futaba S3004 Servos.

I have the flap servos set up on the 3 position Switch (Switch G), and is using channel 7. I have a Y Harness attached to channel 7 on the receiver and running both servos simultaneously.

The servos will respond, but when the flap is engaged, it seems too easy to push the flap back to the flat position. Like the servos do not have enough torque to hold the flap down. Sometimes there also seems to be a bit of hesitation when the switch is engaged, and the two servos are not always in sync. I have had a few tricky landings where I can’t slow down enough, and suspect the flaps are not fully engaged because of this problem.

Here is where it gets confusing to me, I have tried different servos with a higher torque rating with no improvement, and when I unplug either one of the servos, the problem is improved in the servo that is still plugged in.

Does anyone have any thoughts? I’m all out of ideas.

alan0899

G'day Mate,
I would change to a 6 volt battery, ASAP, LiFe 2 cell is the way to go, if your servos can handle 6 volts of course. The RC world has moved on from 4.8 volts.

japes999

My Feedback: (9)

I like the idea of the LiFe battery, but have a few concerns. The plane is at a remote location where I will not be able to maintain the battery for long periods of time. I suspect if the battery is allowed to go completely dead, they are shot. Am I correct in assuming charge times with LiFe are similar to a LiPo pack?

Bax

My Feedback: (11)

The servos are just not getting enough drive current. You can use the 4.8V battery pack, but you'll need one with more capacity and use heavier-duty wiring so you get less voltage loss. Also, the connectors may not be clean, which also causes operating problems. A better solution is the 5-cell NiCd or NiMH battery pack, or a 2S Lithium if you change to higher-voltage servos. The S3004 servos are intended to be used with a 4-cell or 5-cell NiCd or NiMH battery pack.

japes999

My Feedback: (9)

Thanks Bax. I like the idea of a bigger battery. I currently have the battery shoved into the tail section to balance the plane, and like the idea of the smaller LiFe battery so I can still fit the pack in that location. I am surprised to hear that the S3004s won't work with a 2S Lithium, as the consensus seems to be that they can handle the voltage from a freshly charged 5 cell NiMh pack which could be up to 7.5 volts.

Zeeb

My Feedback: (41)

The self discharge rate of the A123 batteries is virtually non-existent. I would guess that LiFe's are similar since they are the same chemistry but there can be an issue with QA on those batteries. If you go to LiFe's, make sure you get them from a reputable vendor.

All Day Dan

My Feedback: (5)

Here’s a plot of the discharge characteristics of a LiFe battery. Notice that at around 3.1 volts, the voltage of the battery decays rapidly. Using this kind of battery is risky unless you are aware of the battery consumption your model represents and the actual capacity of the battery you are using. You can not depend on measuring the battery voltage at the field because the voltage is so flat before it falls off rapidly. Do what Bax recommends. That is how I have my 50cc powered, 20 pound models set up. Yes I use a four cell NiCad battery pack with no problems. Dan.

Zeeb

My Feedback: (41)

After using A123 batteries for a number of years after Dick Hanson got me started, I have to completely disagree with your reasoning and battery selection.

You are of course, free to choose what you want to use but suggesting a NiCD battery for a situation where the OP may not be able to access the batteries for an extended period of time, is a very poor suggestion. NiCD's do self discharge at a pretty good rate but not as bad as NiMH, nor do they have the false peak charging issues that NiMH batteries have. Li-Ion batteries are similar to NiCD in the self discharge area and take a similar amount of time to charge. LiPo's can be charged at a much faster rate as can A123/LiFe batteries but they cannot be stored at full charge and they will also self discharge but at a slower rate than anything but the A123/LiFe chemistry batteries.

ALL of those chemistries will be junk if allowed to go dead. A123's don't like it but can usually be rejuvenated, I personally would not use such a battery for an rx battery. Now here's where it becomes obvious that the A123/LiFe will be the battery the OP really ought to seriously consider; I've left my A123's without being used for extended periods of time. A while back when I was in the process of moving, my 2.6 Comp-Arf Extra with three 2300mah A123's were not charged nor the plane used for a year. It took less than 100mah's each to charge the batteries and they all still have 90% capacity on discharge testing.

Of course volt checking them is useless as you mentioned, that's why you spend 10 or 20 minutes charging them before you fly and fly by the number of minutes times the per minute average use of a particular model. Most of my A123 equipped models can do about 8 flights before the batteries could use a recharge and I recharge at about 50%.

Bypassing a superior battery chemistry because it cannot be volt checked as you've done in the past, is IMHO, a poor reason for avoiding the use of these newer technology batteries.

kmeyers

+ 1 ZEEB
You are 100% correct in my opinion.

If the OP isn't going to new tech, he should maybe try converting his model to control line (ha ha).

I have regulated 2s batteries in every new glow or gas powered plane. Old equipment that ran on Nicd's that still test above 90% get flown as is. BUT All new battery purchases are Lipo's or Life's (I have many Li-ion's in use as well, but they will be replaced with Life's when they need replacement). Of note I will never use a Nimh again, they are ^%&#.

Bax said "The S3004 servos are intended to be used with a 4-cell or 5-cell NiCd or NiMH battery pack."

But I think it would be better put as 4.8 volts to 6.0 volts, from a technical standpoint. DC voltage doesn't care what chemistry it comes from (as far as I know).

kmeyers

Oops I forgot the last line, any ideas?
Sure:
What is the servo travel volume?
What is the servo dual rate %? three position switch (none, middle =, top =)
What is the length of you servo horn and your control surface horn? center of servo screw to control connection, center of hinge line to control connection.
These questions are to find the mechanical advantage or disadvantage your linkage is set up at.
If you don't use the right setup you limit the torque available.

A very common problem.

All Day Dan

My Feedback: (5)

Good inputs you two. That’s what RCU is for.

1. A battery packs value should always be determined by its discharge characteristics which could lead to lose of control and not its storage characteristics which are basically useless for RC.
2. How are you guys measuring your batteries capacity and the capacity you need for the flights you have taken. Don’t forget, if you are using a cutoff voltage less than 3 or3.1 volts you are already picking up the pieces.
3. The OP is using a servo rated at 6 volts. A LiFe pack voltage is 6.6 volts steady state. Maybe his receiver is also rated at six volts. The over voltage condition could be disastrous. Reducing the voltage by using a regulator would add another single point failure and we already have enough of them.

Dan

BarracudaHockey

My Feedback: (11)

A servo rated for 6V is rated for a fully charged 5 cell Nickel pack, so a 5 cell pack or 2s A123 or LiFe is completely appropriate

Truckracer

My Feedback: (19)

+1

All Day Dan

My Feedback: (5)

I doubt it if Bax would agree with you two. Dan.

BarracudaHockey

My Feedback: (11)

If you read his reply carefully you will that he said the same thing I said.

Zeeb

My Feedback: (41)

Andy is right on this one; five cell NiCD/NiMH packs come off the charger at exactly the same voltage as an two cell A123/LiFe battery but the A123's drop pretty quickly to their nominal voltage which is less than a newly charged five cell of the other two chemistry types.

If you don't believe that, spend a little time on the Futaba support forum to see what Bax has had to say about using the A123/LiFe and Li-Ion/LiPo chemistries.

BarracudaHockey

My Feedback: (11)

He doesn't have to go that far, just read the original reply by Bax.

kmeyers

I don't see why such a focus on the battery for 2 S3004 servos. I bet the linkage and setup is at the heart of this problem.

Zeeb

My Feedback: (41)

That may be true, however the other issue is extended times between when he is able to maintain the batteries. It seems pretty obvious that he needs more power either electrical, mechanical advantage or both. The time between maintenance issue can only be solved by use of the Lithium Iron Phosphate chemistry batteries.