MaJ. Woody

My Feedback: (28)

Hi.
I have plan on putting 4 Futaba S3305 servos along with 2 standard servos (Hitec 425BB) in my next plane. I am planning a Hobbico Hydrimax 4.8v 1650 Mah Nimh pack. I use these packs in all my planes but noticed the warning on the Futaba servos regarding high amp draw and the use of Nicd batteries only. How many amps can this battery pack deliver? The plane is a 73" warbird that won't experience high flight loads like an aerobatic bird would. I check my flight pack with a Hobbico volt meter before every flight.
Thanks,
Dom

Bax

My Feedback: (11)

Under a heavy load, these servos can draw in excess of one Amp apiece. If your battery pack can deliver the needed current , then they're OK. The servos came out when NiMH battery packs were notorious for not being able to handle high current loads. You need to make sure the battery pack you use can deliver enough current without becoming damaged.

LSP972

My Feedback: (13)

Maj. Woody,

I'm running two of these on ailerons, along with two 9252 digitals (also power-suckers) on elevators, a 9151 on rudder, and a 3151 on throttle, on an H9 ShowTime. IOW, all servos are so-called 'high-draw'.

My battery is a 2850 mAh NiMH 4.8v with four sub-C cells.

The heli crowd was the first to discover that smaller, AA or AE cell NiMH packs could not produce the necessary grunt to keep up with a bunch of high-draw digitals all being vigorously moved at once- the servos in a heli being flown in hard "3D" are constantly working, ALL of them at the same time, and working hard. The smaller cells could not keep up and would show voltage drops; this was eventually shown to be the cause of the infamous "hard-over" failure mode of the 401 gyro. An otherwise excellent gyro, it had a bad rap for several years through no fault of its own. Those of us who were running bigger-celled batteries had no problems at all, and couldn't understand what was causing it. But the truth finally came out. Yet again, the quest for light weight/high performance showed that there is no free lunch.

That's a long-winded way of saying that if you use a big-nut NiMH battery with so-called "high-draw" servos, you'll do just fine. My X-Cell heli has a 2400 sub-C nicad and five digitals/401 gyro; never had the first hint of trouble. I can fly that ShowTime for four 10-minute flights, with plenty of battery power left.

I'm coming to believe that the 3305 is a real sleeper of a servo. These two replaced a pair of 9252s that were starting to chatter, and the plane flies just as well. You can bet the grocery money that I'll be using these from now on; those digitals are just too expensive, IMO, and I'm not a good enough pilot to miss the improvement in resolution they provide. Note that I DIDN'T say 'power'; the 3305 actually has more torque than the 9252.

JNorton

My Feedback: (2)

The key is buying low internal resistance cells. NoBs batteries has charts on his site and his recommended choice are all low internal resistance packs.
http://www.hangtimes.com/nobsbatteries.html Look at the spec sheets. http://www.hangtimes.com/cell_specs.html
Jogn

MaJ. Woody

My Feedback: (28)

Sounds like the S3305 is a good servo. I still don't know why they call it a car servo and don't list it for airplane use. This servo battery combo is going in a 73" P-40 that will not see the rigors that a 3-D plane would. As such, I don't feel I wil be pushing the 3305's anywhere near their limits (elevator and rudder use only). I will probably be ok with the Hydramax 4.8v 1650 Nimh pack.
Dom

LSP972

My Feedback: (13)

You will. My Goldberg Ultimate has three 9252 digitals, one JR 2721 high-torque analog and one 3001 standard analog, all on a 1650/4.8v NiMH. I've gotten as many as six flights, with power still in reserve. Of course, that was when the battery was new. I haven't flown this particular model in quite some time.

This is a good reminder to charge/cycle the battery. The servos could stand exercising, too. Guess she needs to fly...

tramsay

I purchased 2 6v nimh 2000mah batteries on ebay, and have been using them in my Twist and new Funtana 40. Both are 3D planes and I only have the standard futaba s3004 that came with my TX. I want to upgrade the tail feather servos in the Funtana and was thinking about the S3305's. All that has been said is talking about not being in a 3D application. THese would be.. am i still ok because of the size of the battery and the size of the plane?

...also what is the risk? Are we talking about total failure? or the servo just not delivering what the specs on it says.

Thanks!
~Tip

modeltronics

My Feedback: (27)

The internal resistance on a NiMh battery is higher than a NiCd. On some NiMh it can be much higher. Under load is can cause a significant voltage drop. This can cause problems in the receiver by the voltage drop resetting the decoder.

You can not measure this voltage drop on a meter. A meter is just not fast enough to see the voltage dip and recover. Even if it was fast enough your eyes would never catch it. Here is how I do it, and YES I know not everyone has this kind of equipment at home. I put a storage scope across the power bus inside the receiver. All the servos in the set up must be under load. Then move the sticks on the transmitter. The storage scope is set to trigger at a voltage drop. It is not uncommon to see a drop of a half a volt with a good brand name NiMh right at the receiver. I have seen a drop of 1.35 volt with no name NiMh batteries. Those numbers will go up with increased loads.

I do use NiMh packs for flying, but not in all applications.

Pete

JNorton

My Feedback: (2)

tramsay,
Modeltronics has it right. That's the whole key. If you are going to stress your packs by using them in 3D applications or by using them with digital servos that draw more peak current use brand name packs. If you look at the Sanyo web site you'll see that some NiMh packs have as low an internal resistance as NiCd packs. If you buy off brand Chinese's replacements who knows what you'll be buying. What's you plane worth? Isn't it worth the extra money to buy quality packs?
John

rainedave

My Feedback: (1)

A very interesting discussion. So where does a pack like the Hobbico HydriMax 6.0V 1200mAh Flat 4/5AA U Panasonic fall? At the quality/low resistance/safe to use end of the scale, or at the el-cheapo/high resistance/stay away end? Because I just bought one of these for a 60-size vintage pattern plane I'm building.
http://www2.towerhobbies.com/cgi-bin...?&I=LXLX49&P=0
Thanks.

JNorton

My Feedback: (2)

One other point I would like to make. Everything that has been talked about is what you might call best practices. In other words optimizing the system so you don't have problems.

What can you expect in the real world if you use high internal resistance cells? The buss voltage on the receiver will drop according to the current drawn further than what it would with a lower internal resistance pack. What does this mean? Maybe not much. Depends on the current draw verses the orientation of the aircraft at the time of the draw. But what you might experience is momentary glitching of the servos that magically disappears later on in the flight. Sometimes people think they are getting hit when it's a marginal pack.

The point is it can be really difficult to figure out what causing these problems because on the ground the servos have no air deflection forces on them and so act normally. Using 22 gage wiring with the fewest connectors possible good quality switches and a low internal pack or twin packs will help.

John

modeltronics

My Feedback: (27)

There was some interesting data on the Sanyo site that I got to following the links above. I just looked at one of the cells that was 1650mA/h. At a 3400 mA load there was about 0.1 volt per cell drop over a 340 mA load. This would be a 0.4 volt drop on a 4 cell pack at that load and peak loads can be higher than that for some models. Now to just come up with a way to measure the loads in actual flight.

Pete

rainedave

My Feedback: (1)

Ok, I just read the entire NoBS FAQ on the hangtimes.com site. If you haven't read this, it's very informative and clearly written. And I didn't sense that they were trying to tell me I needed to buy their product or else.

What I basically got out of it is that with 5-cell, 6v packs you have greater headroom if a big voltage drop occurs due to intense servo loads. You are much less likely to drop below 4.4v than with a 4-cell pack. It's easy to get spooked and think you need to run out and replace your batteries and wiring, but unless you're really wringing out a 3D heli or giant scale plane I'm convinced it's probably not necessary. At any rate, something like the Sportsman pattern schedule isn't all too demanding on your planes control surfaces.

Those 3305s are interesting at $35ea. But the coreless BB 9001s for $30 are interesting, too.

JNorton

My Feedback: (2)

In flight data recording. There are a couple more.
http://www.eagletreesystems.com/Plane/plane.html

modeltronics

My Feedback: (27)

Interesting unit but the web site is very vague and lacks a little engineering info so here is what I wrote them. I will post it when I get a reply.

Sir,

I would like to be able to monitor current draw of servos on an RC plane. Can you tell me how many readings per unit of time your system can record? What is the length of time of each reading? During the window it is taking a reading is it averaging or taking a peak?



Thank You,

Pete

rainedave

My Feedback: (1)

The realtime wireless laptop link feature is cool (if I read it correctly).

I looked up the internal impedence of the Panasonic 4/5AA NiMh cells on the Panasonic Industrial web site: 19mΩ Whatever that means! And for what it's worth, Sanyo indicates that its 4/5AA has an internal impedence of 20mΩ

JNorton

My Feedback: (2)

.019 ohms milli = divide by 1000.

More on the Eagle Tree unit. http://www.wattflyer.com/forums/showthread.php?t=3064

John

modeltronics

My Feedback: (27)

from Eagle Tree:

The unit measures at 10 s/s, and averages during each 100 ms period. If you need faster, our pro recorder samples at up to 50 s/s.

BShin

Just bought 5 new Futaba S3305's for a U Can Do .46 Installed the rudder and two elevator servos first, centering them with no load and then attached the servo arm and control rods. Everything seemed fine when I turned the radio on, movement was good, and I made a few ajustments to center the control surfaces. I shut the plane off to work on something else, and when I turned it back on later, one of the elevator servos wouldn't respond. If I continured to hold the elevator stick on the radio (down or up), the servo would SLOWLY move to position, and when I let off, it would SLOWLY return to center. I checked all the leads, the new heavy duty 24" extension I used, and everything looked fine. I disconected the servo from the extension and plugged it directly into the receiver, and it did the same thing.
I've never had a new servo do this before, so I'm assuming it is just defective. Thought I would post this to see if anyone knows of any inherent problems with the 3305's, or if this is just a rare defect. Btw, I am using a 4.8V NiCd receiver battery.

Thanks,

Bshin

TIGITRIGHT

Forget what Futaba says read this link from Greatplains:http://www.greatplanes.com/sellsheet...-sellsheet.pdf
If they weren't for aircraft use then Greatplains would not recommend them for the 27% Cap232.