emilem

Hi all,
My new Extra 300 is equipped with four digital servos (two JR DS-811 Fat digital Japan for the ailerons and two JR DS-8201 for the elevator).
The installed battery is 4.8v NiCad 1900mAh and after only two short (10 min) flights the battery checker shows minimum safe. This is my first experience with digital servos and no other pilot around has any experience with digitals. My question is. Is that what I have to expect when using digital servos? Do I have to buy stronger battery? Your comment and help will be highly appreciated.
Emil

mglavin

My Feedback: (31)

The 1900mAh battery should be more than adequate. Have you cycled the battery and verified the capacity? Is it possible you have binding of some sort?

mglavin

My Feedback: (31)

The 1900mAh battery should be more thna adequate. What type of battery is it, NiCad, NiMH? Have you cycled the battery and verified the capacity? Is it possible you have binding of some sort?

rajul

My Feedback: (58)

emilem, what were your charging parameters and which charger are you using ?

Ralphbf

My Feedback: (27)

Have you concidered using 2 batterys with switches?

I have found that servos that need more than usuall current can't get enough from one battery, no matter the size.
It seems the plugs are the limiting factor.

By running 2 batterys there is less voltage drop and less draw on the batterys, even if each is half the size.


Just a thought.

Ralph

emilem

Thank you for your replays gentlemen.
I like the idea 1900mAh is adequate. Yes I did cycle the battery (triple, it is new one)
I will cycle again to see for any improvement.

Charger is Accu Cycle Plus- discharge rate 250mA(93min); charge rate 500mA(120min)

Clevis and servo-arm connections are not sloppy. There are two other things I am not sure how to comprehend.
1. There is some (about 1,5 mm) free movement around central position of the servo arm when the servo is powered.
2. The control surfaces are moving with almost no resistance when the servo is not powered.
Some people say maybe this is typical for digitals. Is it?

Have no idea how to use two batteries. There is enough space for the battery itself but I don’t know where to connect the second battery in the receiver?
Do they have to be the same capacity?

Emil

carrellh

Check out http://rcbatteryclinic.com/ There is an article titled "Parallel Operation - ..........."
The short answer is, you also install a second switch harness and plug in to any open channel on the receiver.

Futaba sells the 7C with 4 digital servos and packages a standard 600mah battery with it. I know that doesn't mean a lot but they could have used a bigger battery and increased the price if they thought it was too small.

rsrogers

My Feedback: (10)

Dude something aint right!! If your cycling a 1900 mAh battery and discharging at 250 mills & it only takes 93 min. what did the compacity come out to?

A 250 - 300 mAh load will give you a very close reading to the batterys specified compacity and (not trying to sound like a know it all) but mAh is milli amp HOURS. So if you discharge a 1900 mAh battery at 250 mAh it should take WAY more than 1:30 to discharge.

One thing you might want to try is cycling the battery using the C10 charge rate of 190 mAh x 16hrs then dischargeat 250. I know this is time consuming but time is cheap compared to airplanes!!

I have a few 2000 mAh batterys & they all take several hours to discharge when I'm cycling to check the capacity at 250 mills.

On another note I know Digitals are said to draw more juice but I have a different opinion. I flew my Funtana 90 for 65 minutes on a 1700 mAh pack (5 Digital servos) , came straight home & discharged it just to see what I had used out of it & it was less than 200 mAh. The pack still had over 1500 mills left in it. I do this with all my planes after the first full day of flying on them to see about what they use & alot of my 40 size planes use more than that.

Just food for thought. Hope everything works out for you.

dirtybird

My Feedback: (5)

Interesting.
I have been running some servo tests and have found I can not get the rated torque for the high torque Futaba servos. For example the 9206 is rated at 133 oz - in. The best that I have been able to get is 100 oz-in. It seems the wiring and plug on the servo is not adaquate. For my tests the servo is wired directly to the battery with no receiver and switch in between. I wonder if you have observed the same?

rajul

My Feedback: (58)

Based on the 500mA charge rate, your charging time should be 1900/500 x 1.4 = 5.3 hours. I would suggest you increase your charge time from 2 hours to 5.5 hours. Your NiCd pack is probably undercharged

dirtybird

My Feedback: (5)

My tests with Futaba coreless digital servos indicate they draw 250ma in the idle condition when subjected to vibration. Four servos would mean a current drain of at least 1 amp. Under flight loads they would probably draw at least twice that. So your 1900 pack should last about 45 minutes.

MO_Radio_Tech

You have probably already ruined your 1900 mAh battery. It is critical to properly "form" Nicad batteries when first used. The first charge when you get the battery should be 1/10 of capacity, that is 190 mA for a 1900 mAh battery. This first charge should be for 24 hours. After the battery is properly "formed" you can Fast charge it occaisoinally if you wish at up to capacity (1.9 amps for a 1900 mAh battery). The optimum charge rate will always be 1/10 capacity.

I would cycle it a couple of times at 190 mA (200 mA would be close enough) and see if it starts performing better. Otherwise, buy a new battery and change you charging habits.

dirtybird

My Feedback: (5)

I have the Sony instructions for using their cells. There is no mention of such a procedure required.

MO_Radio_Tech

That is interesting. Most RC batteries I have seen are Sanyo Cadnica. I wonder if Sony batteries come pre"formed"? I wonder what thier instructions say? Is their a website?

dirtybird

My Feedback: (5)

My mistake- I meant Sanyo not sony. The only instructions I have ever seen on any ni-cd battery is charge it 14 hours at the ten hour rate prior to use.

MO_Radio_Tech

I downloaded and read the actual Sanyo battery instructions once. About thirty pages worth of them. Sanyo Cadnica batteries are indeed supposed to be "formed" at 1/10 capacity for 20-24 hours. It is crucial for the cells so they will have a long life at proper capacity.

I have recently tried to get the instructions again, but the link is dead.

14 hours might be long enough, but I saw 20-24 in the Sanyo manual. Sanyo should know, they designed made the batteries.

rajul

My Feedback: (58)

The forming duration should depend on the rated capacity. Factor of 1.6 should be good enough.

MO_Radio_Tech

www.sanyo.com/batteries

The long technical manuals are all here. Cure for innsomnia, but quite useful and informative. After reading all this the first time, I found out that most of the fast chargers I had were inadequate because they could not charge at 1/10 capacity. The links work, but my old computer can't load them.