I want to buy a Great Planes RV 4 60 ARF and a Futuba 6 channel radio to go with it. The instructions for the plane call for (6) 54 oz-inch servos and (1) 30 oz-inch servo. The 6 Channel radio comes with 44 oz-inch servos. Looking at all the available servos, their ratings are either way above 54 oz-inch (like 74 oz-inch) or under such as 44 oz-inch. Would it be OK to go with the 44 oz-inch servos? Does it really matter if the servos are 10 oz-inch off? Thanks! <! / message >

Are those rating's based on 4.8v and if so what would they be on 6.0v?

The ratings are based on 4.8v. At 6.0v the rating is 57 oz-inch. Now, I'm electronically challenged, how do you get to 6.0v?

Your radio probably did not come with a flight battery so you will have to buy one. So get a 6.0v.

4.8v is a 4 cell, 1.2v per nicad. 6.0v is a 5 cell, and they're pretty easy to get cheap off ebay.

Do they make the 6.0v as a NiCAD or are they NiMH? I only see NiMH on the Tower Hobbies site.  I'm back into the hobby again after a 23 year hiatis, all the new battery stuff is kind of blowing me away! I used only NiCAD's back when I flew last, not even sure if the other types were available. I'm trying to piece together a radio for a new plane but need 6 out of 7 servos to be 54 oz-inch. I'm a "buy as a package" guy, so, I'm looking for everything I need to be in one package (TX, RX, Servos, TX batt, RX batt, charger). There are several of these available at Tower, but the servos are below the 54 oz-inch rating I need. With my lack of knowlede, it's difficult to "piece" it all together.

You can get 6 v Ni Cad but there are better batteries out there now..Ones that hold charge longer and work better..I dont know much about batteries either but if I were you I would check out the Life batts Nicads gradually lose there charge over time where as some of the new ones do not...I took a few yrs off too and the changes are amazing espially in the radio area..Radios and ARFs...One thing you need to be aware of is that different batteries need different chargers...The wrong charger can destroy the battery and on certain batteries cause fires I believe..

TPL33

I presume you are fairly new to the hobby. There is a lot to learn and it will come with time. Though very good, I dont suggest you go for LiFe(PO4) batteries just yet as they have a different charging system to NiMH. Best to get good NiMH batteries- look for Sanyo Eneloop. These are rechargable batteries so each is 1.2V. With a 5C pack you will get redundancy (if one cell suddenly fails you can still continue flying) and you get higher servo torque (except for specifically marked servos, all servos will operate at both 4.8v and 6v and you will get more torque at 6V). If you cant make a battery pack, get a club member to help you with the soldering part. These batteries are fairly safe and will stand up to any abuse you end up metting out to them. Your charger (that came with the Tx) will have the connector to trickle charge them (charge them at a low rate).

Just look at the servo model number, Futaba will come with basic 3003 or 3004 servos. These are fairly good. One of them is a ball bearing servo which will last a bit longer and you are using them on a 60 size airplane. Otherwise you are sorted

If you want to try LiFe, go with Hobbico's set. Select around 2100mAh for good number of flights. Unlike NiMh, these have a flat discharge curve, so voltage will drop off suddenly at the end. Unlike NiMH, they cant be reliably monitored with a Voltwatch. But unlike NiMH, these dont have to be cycled in the off season. You can charge today and go fly after a year if you want (dont test that!). They are still far safer than LiPo but as a beginner I would stay away

Ameyam

I'll second the suggestion that you get back in using NiMH 6v packs.

That should give you the torque you'll need. Just remember to size your packs LARGER than what you would have used with 4.8v packs.

Ameyan's suggestion of 2100mAh packs is a good one.

I've used the OUTRAGEOUSLY EXPENSIVE ( 12.00 each!!! ) 2100mAh LiFe packs from Turnigy. [link=http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=28650]LiFe Packs[/link]

They are light enough that I can afford to use redundant packs in .40-.60 size planes.

They do require a LiFe charger however.

Thanks for all the helpful replies. To sum it up, is it still OK to go with Nicads? From what I've read, the Lipo and niMH give you longer flight times and last longer than Nicads. I just feel that I'm too inexperienced to take on the new types just yet. If I get the correct torque servos for  4.8V, nicads for the TX and RX, will I be OK flying the RV 4 1/4 scale aircraft?

The nicads will be fine! Size for size, they're actually capable of supplying more amperage than the NiMh.

When I got back in after being gone for a long time I ask the same question. It was suggested I go NiMh, so I did! My newest nicads were over 10 years old at the time, and though many would still cycle, I didn't trust them on some of the stuff I was flying. I repowered everything with NiMh (4 planes and 2 transmitters). Won't go into all the details, but the short story is I'm not happy with them.

Go with what you know for now, just don't go overboard like I did. When you get time, look into A123 or LiFE. They're the same technology, are awesome, but everything you know about the care and feeding of nicads aren't going to do you much good. You'll need to take some time to come up to speed with this new stuff. When you do, pretty sure you'll like them. -Al

Thanks.

TPL33,

technologh primer: NiCd and NiMH are basically nickel derivative batteries. Both are good for decent flying, safe to use and give good life. However, they have a low discharge rate (sometimes also called C rate). You will struggle to find anything over 2500mAh. Thats a technology limitation. They are both 1.2V nominal. Make a note that when fully charged, they will show a higher voltage. For example, NiMH 6V pack when fully charged may show 6.5V or so. That will drop quickly when load is applied. They can be plugged direct into the RX. One queer thing to remember is that they suffer from "charge memory" i.e. if you keep them fully charged and do not discharge for long time like in the off-season, they will slowly lose charge. This is because they have high internal resistance. In this condition if you check them in, they will show a full charge but discharge almost immediately. For this reason, they need to be kept charged and discharged or regular basis. This is called cycling. You could do it by puttinh your battery under load (even moving your servos around in the airplane), letting it discharge fully and then charging. Many chargers do this automatically for you. The adapter you got with your TX is not one of those, you will need to but one seperately. NiMh chargers typically send a small current through the battery to charge it, nothing complicated. But as the battery charges, the internal voltage increases. As current flow is inversely proportional to voltage, as the voltage increases, the current flow into the battery drops. The battery stops charging when the charger voltage and battery voltage is equal. Since, during discharge, battery current varies as voltage, these can be monitored with a voltwatch

Lithim Polymer or LiPo batteries are more advanced than NiMH / NiCd. These have to be charged by the constant current constant voltage method. They also have to be thermally monitored because there is a risk of fire if they get too hot. LiPo chargers come with all these features and therefore are expensive. The batteries cant take any abuse at all. As a rule, anything high performange spoils faster. If case of LiPo, the internal chemistry generates hydrogen making them explode sometimes. You will see this clearly- the rectangular battery will become a barrel. The resulting lithum fire burns at a high temperature and does not extinguish easily. Thats what makes the battery risky to use. I have seen a LiPo battery start to burn on its own in a heli and the owner took the risk and threw the battery onto the ground. Inspite of using a fire extinguisher, it burned most of the day in the corner of the field. Hence not recommended unless you know what you are doing!. They are high performance though and 5000mAh and 50C is not uncommon. Each cell is 3.7v nominal, so they are 7.4 and 14.4V though, so you will need a regulator. They have a flat discharge curve (current and voltage remain constant as the charge drops) so cannot be monitored with a standard voltwatch. There is no charge memory problem. Due to their voltages, they are mostly used on electric airplanes where the voltages are designed to use these batteries

Lithiun Iron Phosphate (LiFePO4) are much more stabe than LiPo. They also need to be cc/cv charged, so a dedicated charger is required but can take a standard charger (dont test that claim!). Like LiPo they are available in high capacities. They also have a flat discharge curve with a sharp drop at the end. Again a voltwatch cant be used but some monitors can count the total mAh use and thet can be used to monitor. These are 3.3V nominal per cell, so 2S is 6.6V, meaning direct plug into Rx. Though more stable that LiPo, you have to remember that these are lithium batteries, so more care has to be taken and the battery shouldnt get hot (over 65Deg C). Since the electric models are used to the LiPos LiFes can be used there

My recommendation of a 2100mAh was based on pricing. In Hobbico, 1900 / 1800 / 1300 are priced similar as they geared to small airplanes, transmitter use etc. 3200 is fairly priced but very heavy and I believe 2200 is priced similarly. 2100 lies in the sweet spot.

As a corollary, I have some NiCds, specifically one from my 9CAP, which though only 800mAh, is unbelievely resilient. When I got the 9C, I replaced the low capacity 800mAh stock with a Hydrimax 2900mAh. I didnt use the 800 at all for over a year. Then expecting it to be a gonner, I still tried it with a electric pump and it had full capacity after charging. These original batteries are good. My 2200mAh and 1800mAh battries I had purchased for my 6c conked off in under a year. Just FYI

Ameyam

Nope not hydrogen... It's nitrogen. What makes them puff up is inert.

It's been tested and documented.

The fire is the result of the lithium combustion along with the plastic sheeting.

Ok, I stand corrected.

I hpe the OP has got a good insight though

Ameyam

My two cents.
NiCads do have a more significant voltage falloff with load and charge state.
NMIH's have a flatter falloff curve, as do many of the other newer battery types.

After some testing - -
NMIH batteries rated at 2000mah or so may not be able to supply the current and the voltage needed
for 6 standard or digital servos, based on Sanyo's charts.
I did some testing, and found out that some of the common digital servos can draw up to about 1-1/2A when exercised
with a servo tester at a high sweep rate.
A "quality" NMIH 2000Mah battery can provide about 2A when it's fully charged, but at say 50% charge, the voltage drop may not be acceptable.

That said, 5A current capability seems to be adequate for six digital servos in "normal" operation.
Just make sure that they don't "stall" due to linkage, control surface travel limits, or servo stop limits.

The old 600ma NiCad receiver packs common just a few years ago on 72mhz systems with analog servos don't get the job done these days!
I'm beginning to think that 6 to 10A switching BEC's, powered by 7.4 to 14V or so are really a better way to go.

Wish this information (which duplicates my experiences using anything bigger than "standard" servos) was more commonly available. You darn sure aren't going to see it browsing through a Tower Hobby's catalog....

In their defense, you can run 2 of these packs in parallel without issue. Add a second switch, and you have a redundant system that's pretty bullet proof.

His observation is correct on all counts, however NiCD's and NiMH packs tolerate the drain well and do not exhibit instant voltage drops which help avert brownouts.

I found this out the hard way when I attempted to use an 8A regulator with 3S LiPo packs on my 50cc Ultimate.

The plane uses nine servos, of which 7 are high torque standard sized analog servos that have 1.8A ( I tested ) stall current.
Since the servos should NEVER approach full stall current, and normal operating current under load was measured to be around 800mA, I thought that 8A was enough.

I started connecting servos one at a time, then turning on the plane after each connection. Everything was great until I got to the fifth or six servo. After that the servos would budge slightly when I turned on the plane and everything would freeze.

I double checked the vendor's specs on the regulator. I discovered that the 8A rating was really for max draw and that the regulator was really rated for 5A continuous... but even then it would seem that would be enough right?

Well it turns out that during power up or during simultaneous arm movement to extremes, the servos can draw almost full current for a brief fraction of a second. That is enough drain the small on board capacitors and trip the switching transistors in the regulators causing them to STOP SWITCHING, e.g. producing no more voltage!

I've used an equal number of identical servos with 3200mAh NiMH packs and/or 3000mAh NiCD packs without problems. I can see the momentary drain on a meter particularly during power up, but the older technology packs fare much better than the regulators.

Due to the availability of cheap LiFe packs ( $12.00 for 2100mAH 30C+ packs!! ) I switched the plane over to redundant LiFe's. This is lighter and cheaper than the NiCD/NiMH packs while still providing more than enough current e.g. 4200mA @ 30c+.