Capt Cash

My Feedback: (1)

I can get 10 of these shipped new in box for $75 each. Never used them before but considering pulling the trigger for this price. They will be going ontwo 25% and 30% 3D-gassers. Somewhat overkill on a 25% I think but the price is right as long as they last a while for me.

I'm going to need 10 servosanyway eventually so I figured I'd get em all at once if I could.

maineflyer

My Feedback: (44)

There are some good threads on them. I have 5 going into a 30% slick. From everything I see they are very similar to the 7955s only with steel gears instead of Titanium. Running them on A123s.

Capt Cash

My Feedback: (1)

Well I've gota bunchof these servos now. I'm going to run 5 on the flight contolsand use a Hitec 5665, also rated at 7.4v, on the throttle. To make things simple I would like to set this up without a power board orregulatoron a Futaba 617 FASSTreceiver.Would this be OK?I've seenthreadsabout others running higher unregulated voltage on theFutaba receivers so I'm not to concerned about it for now but was just wondering if anybody else isrunning a similar setup. The engine ignition will get a 4.8v NiMh battery for now.

I was going to go with the A123 batteries but am now considering the Fromeco Relion 2600's. I've never used the lithium ions and I know this is debated by many, but they seem a little easier in a few respectsthan the A123s. Ialready have a charger rated forli-onsand it appears they do not have to be balanced chargedlike A123s do?You can alsoget an idea of remaining battery capacity through a direct voltage reading right? I would suppose this issimilar to 5 cell NiMhs where you would neverfly below 6.0v, so with the 2 cell li-ion you would never fly below 7.4v.

skyesdad

My Feedback: (1)

I have 6 of these on 6.6 a123 in a new plane 7.4 lith ion will work and fromeco batts are very good so either way you win

Capt Cash

My Feedback: (1)

I figured it would likely be fine too, was just a little nervousabout the highervoltage of the Lith ionbatterieson my receiver though. I wasn't planning on these servos but a got a decent deal on them. Since they are ratedupto 7.4v, I figured why not use the li-ion batteries to take full advantage of them?

wind junkie

My Feedback: (1)

Does anyone know if HV servos (marketed for unregulated lipoly RX packs) have built in regulators?

I really don't like the idea of the servos slowing down as the pack goes from 8.4 to 6V. It's not as noticeable with bare A123s cause the discharge curve is so flat, but lipos don't have that characteristic.

Rafael23cc

My Feedback: (6)

Please let me know which batteries you use that you can continiuosly provide power from 8.4 to 6 volts without having to charge at some point during the day. I do not know of any servos that would have internal regulators.

If talking about the HS-7954SH servo, I doubt a human can detect a difference of 0.06 seconds when swapping from 8.4 volts to 4.8 volts. Never mind that there is no battery capable of operatinng at that wide range of voltage.


Capt Cash: Would you please share with us where can you find such a deal? I am in need of about 15 servos for a 47% aircraft and those servos might fit the bill. Or I might find a deal on alternate servos at the same site.

Rafael

Revy

My Feedback: (1)

I'm running 5 HVs...4x 7950 and 1x7 940 in my S'bach using 2x Spektrum 2000mAh LiPo Rx packs. Average draw from each pack is 350-400mAh per flight. I like the set up performance wise, but the ol' LiPo risk factor is there. I would go A123's next time for the same price just for the safety factor.

Capt Cash

My Feedback: (1)

I bought my servos here: cgi.ebay.com/ws/eBayISAPI.dll
I emailed them that I wanted to buy 10 of them and could they make me a deal? They came back with an offer of 10 servos shipped for $750 so I took it.

I am certainly not a battery expert as that is why I'm asking questions here, but as far as the operating voltage range goes, it's my understanding thatit's good practice tonever operate below the batteries rated voltage.For example withmy 6.0v NiMhs, they come off the charger at about 7.0v and I never go below 6.0v when flying. Theyare usually around 6.2v or so when I recharge.

Except forthe A123s, I'd assume the same principle holdstrue for other types of batteries as well. I've decided I may likelyget the Fromeco 7.4v Lithium Ions and usethem unregulated onmy Hitec 7954servos. These batteries should come off thecharger around 8.2v andyou would never operate below the rated 7.4v correct?

Rafael23cc

My Feedback: (6)

Thanks for sharing that link. I need 15 servos for one airplane and about 8 for another. I have used Hitec servos with 4.8 and 6v battery packs and 6 volts regulated with no problems, I have not used them with straight 2cell lipo or LiIon power yet.

The question about batteries was not directed at you. It was directed at the person that made the comment about the difference in speed between 8.4 and 6 volts.

I have a few Formeco packs on Helis and Airplanes, They get checked with a loaded voltmeter on the 1 amp load setting. If they show 7.0 volts loaded, it is time to re-charge. A properly sized pack could keep you flying for an entire day depending on number of flights. If you limit yourself to the rated voltage of the pack, you would be cutting your flight time too short, and stay way out on the safe side. If you check your packs often, you will notice that they hang around their rated voltage for a long time, then they start to drop.

Rafael

Capt Cash

My Feedback: (1)

Thanks for clarifiying. You mention with the Fromeco 2 cell li-ons, a good time to charge would be when you get a 7.0v reading under a 1 amp load. I assumehowever youwouldalso getan approximate reading of around7.4v under no load? Anyway, I do understand the advantages of load testing your batteries often to get a more true reading of capacity. The load tester I have now is for Nicads and NiMhs so I don't think it will cut it. Looks like Fromeco's 8-ball tester is pretty nice, ahhh everytime I turn around it's another $50 item I need!

Also, I see Fromeco has an onboard 2S battery balancer device. Is this necessary or does it depend on the charger? I assume it would be to keep your batteries in peak condition. Iknow that it's required to balance charge the A123'sand most Liposbut wasn't sure in this application for Lions. Thanks.

Rafael23cc

My Feedback: (6)

I can't remember the reading without a load but I believe it to be closer to 7.1-7.2 depending on the capacity of the pack. The higher the capacity, the closer you can get to 7.0 without a load.

The load tester I have now is for Nicads and NiMhs so I don't think it will cut it. Looks like Fromeco's 8-ball tester is pretty nice, ahhh everytime I turn around it's another $50 item I need![/quote]

If your voltage meter can read 9.0volts accurately, and it has a 1amp load, then it does not matter if it is labeled for NiCds and NiMh. It is a voltage meter in the end. I have the predecessor to the 8-ball and it cycles thru 3 load settings 0.5amp, 1amp and 1.5 amps as well as a resting voltage between 1.0 and 1.5amos and at the end of the cycle. Pretty nifty.

Neither the Fromeco, nor the Duralites need an additional device to charge. They have that on-board circutry to just let you plug to the charger and drive on. There is nothing special about the batteries, I consider them as easy as NiCds when chraging, and using. With the only difference being the voltage readings and since I have failsafe switches, I disconnect the battery at the end of the day. Not like it will drain the battery overnight, but it could, if left connected for long periods of time.

Rafael

wind junkie

My Feedback: (1)

I was referring to the loaded voltage. It's not like flying a foamy which would have a regulated constant 5 or 6V from the ESC. I can definitely tell the difference between 4.8 and 6V unregulated Nicad or NimH packs and was extrapolating this effect to a similar voltage swing which would mimic coming right off charge to the knee in a typical GS lipo pack.

Although I wouldn't personally fly any giant scale planes on lipos approaching 6V UNLOADED, I bet there are many guys who can feel the difference in that 1.5 to 2V swing unless there was a regulator involved which was the source of my question.

Look at it this way: can you tell the power difference of a 2S powered foamy (ie, indoor F3P type) from the beginning to the end of the flight? Of course you can, everyone can. Why wouldn't you also be able to detect a difference in servo speed given a left vs right comparison (all other things being equal). It's largely a theoretical argument, but one I prefer to avoid in practice cause it would 'bug me" just knowing it exists.

Lipos do not have as flat a discharge curve as Nicads did in the old days, and yes, I could tell the difference in servo speed between a freshly charged Nicad pack and one which has a few minutes of use. However, after that few minutes on a Nicad, the voltage stays very flat compared to a lipo. The A123's came to the rescue in this regard and I wouldn't want to revert to unregulated Lipos for this reason and also needing a regulator (another component which could fail).
Joe

Rafael23cc

My Feedback: (6)

There is a big difference between being able to notice the power difference of an electric powered aircraft across the flying capabilities of the battery in question and the ability of noticing servos with a difference of 0.02 sec difference in 1.5 volts. If you can, you should be up there with Andrew Jesky and the XFC gang, I know that for the amateur flyer, it does not matter, because we will never notice it.

On the other hand, We already discussed that most radio pack batteries cannot produce a voltage variance of 2 volts without being damaged or damaging the aircraft. A properly utilized LiIon will have a voltage variance of less than 1.2 volts. Much less than the specified voltage-speed steps on the servo's spec card. I know that LiFe, NiCd, and NiMh have similar requirements. I agree that liPos have a much longer voltage drop curve. I understand the "loaded" speeds of a servo, but how are we going to calculate that? If the load of a servo influences the speed that much, then the servo might be improperly sized for the aircraft in question.

I love your signature line. I am not only an Engineer, but also an RC helicopter pilot where control, speed and precision make the difference between a succesful flight or going home with a bagful of pieces.

Rafael

Capt Cash

My Feedback: (1)

Rafael,

Thanks for the follow up as I am still learning here and moving out of using NiMh batteries on my large scale planes. I have this voltmeter: www3.towerhobbies.com/cgi-bin/wti0001p I'm not sure now if it will suffice or not for the 2S type Lithium Ion batteries like the Fromecos, but I suppose I'll give it a try at least should I go this route with my setup.

This is the balancer that Fromeco sells in whichI was referring to: www.fromeco.org/products/05frc2sbal/ There's not much of an explanation on their site as whether you really need it but as you say, I supposse not.

wind junkie

My Feedback: (1)

I agree I can't distinguish a delta time of 0.02sec/60 deg. However, that is an unloaded sweep speed. If one looks at these specs:

http://www.hitecrcd.com/products/dig...l/not-set.html

One also sees a torque rating change of 333 to 403 oz*in between 6v and 7.4v. This is will certainly be "felt" in practice because it's 17% of the total rating. You don't have to be AJ to take a plane to height, and do some blenders and see how quick it snaps into them. Another test would be to have a plane in the 50cc to 85cc range and a single servo per aileron. On some planes a good test to see if you have enough servo power is to take it to height and roll it while it comes down and see if the roll rate slows down (it should speed UP if the servos are doing their job). A marginal servo (or underpowered) would show this difference in that case, and it just MIGHT be able to be blamed on pack voltage if indeed that 70 oz*in makes the difference.

1.5V is a significant fraction of the overall voltage the servo sees (1.5/7.4 = 20%). It's similar to the 4.8 to 6V swing on which I'm basing my argument (1.2v/6v) of which I know I can feel the difference. I hadn't initially seen the 7954SH spec so my question now seems moot and I realize they aren't using an internal regulator. Again, I must say I think that while most people will fly their packs on the upper part of the lipo discharge curve, for me just knowing the slope of that curve isn't as good as I can get bugs me. If I'm gonna spend that much on my servos, I'm certainly going to spend the bucks to get a better battery choice and sacrifice some overall power for more consistent performance.

We love to argue when we think we're right, don't we? With the proper ego, the worst thing that happens is that we learn something new.

Joe

Rafael23cc

My Feedback: (6)

Capt Cash :

That voltage meter will not provide an adequate "load" on the battery to give you accurate readings. Hangar 9 makes a loaded voltmeter that has options for 0.5 and 1 amp loads. You will notice that it has a red button, and a switch.. The switch is to select the "load' and the red button is to "apply" the load. With the red buttton released, you simply read the unloaded voltage. This is much cheaper than the Froemco 8-Ball and should be sufficient for you.

[link]http://www.horizonhobby.com/Products/Default.aspx?ProdID=HAN171[/link]

I do not know anything about that Balancer. This is the first time I see it. My packs have an internal balancing circuit. I wonder if the newer packs do not have that internal device. I will be in the market to buy new batteries in the near future.

wind junkie:

I agree with all that you are saying, but stand strongly by my statement that the servos you are selecting are not strong enough for the application if you have that much trouble. LiFe batteries will help you here. Their discharge curve is really flat, and you can charge them at 4C safely. That way you will not have trouble re-charging between every flight.

Rafael