Hawk Pro/AR7000 - flight battery question

[DeadTom]

I have all the parts to put the Hawk Pro together finally but I have a couple of questions;

1) What size battery is good for the flight pack?

2) I have picked up a GY401 and a Fut 9452 servo, the servo is rated for 6v NiCd only, the question is should I run a BEC?

The Fut 9452 is a high speed, high torque, digital, metal geared monster......it was the only thing close to what I was looking for at the LHS. Will this servo be alright?

Thanks for any help,

Tom

[RAV50]

I have used the following relatively inexpensive 4Cell/4.8V battery packs:

1500 mah NiCd, 2400mah Sub C Nicad, 3000mah Sub C NiMH,

All worked well with the best from the 2400 mah Sub-C Nicads

If you are using the GY401 then I would see if I could exchange the 9452 for the 9254 that it is usually packaged with - the 9452 will work at 4.8V but with less speed - the 9452 is a bit overkill for the purpose you want.

What other servos do you plan on using? If they are Futaba digitals, you may be better to use one of them with the GY401, and use the 9452 on the collective.

[DeadTom]

Thanks Rav, I like your suggestion on using the monster on the collective. I will be in Las Vegas again tommorrow so I will stop by one of the hobby shops and pick up one of the 9254 servos for use with the 401.

[JustPlaneChris]

I'm using a Castle BEC (5 volt setting) powered by a 2100 mah 2 cell lipo in my Hawk. Based on recharge data, I can get at least 12 flights per charge with this configuration. I have it plumbed into a regular receiver switch in such a way that the battery is disconnected from the BEC when the switch is off (rather than the BEC being disconnected from the receiver). Works great so far!

[RAV50]

I get 10 on the 2400 NiCds using the inexpensive Futaba S3151 digital servos with the hi-torque S9252 on the collective.

Chris,

I use a similar set-up on my Swift 550 - the CNE400 Century BEC with a 2S1P/1500 Lipo...but that is because of the higher drain of the eCCPM servo layout...almost double that of the Hawk.

[DeadTom]

Chris and Rav,

Thanks for the good information, I see I will now have to pick up a new bigger batt.
Next week my wife and I will be going to the Washougal Wa. area to a scale RC heli meet so I will not have much time to get the Hawk ready to go. I might take the Dragonus with me just to have something to fly.

Tom

[RAV50]

What battery pack do you have? It may work well, but you just may have to charge it more often.

I recharge the 1500 I have in mine now, every 4 flights or so.

[DeadTom]

I have the Spektrum 4.8v 1100mah NiCd that came with my DX7 a little small for any long term flying.
I stopped by a local shop on my way home and picked up not only a new 12v gel cell for my old flight box but a 2700mah 6v Ni-MH 5-cell Rx batt. Any thoughts on my new purchase?
I will try that one first and see what transpires.

[JustPlaneChris]

Just be aware that if you swap out the servos and use a 9254 on the tail, it won't be happy with the voltage from that 5 cell pack. Right off the charger, it'll be over 7 volts and that's a no-no with that servo.

[GyroAl]

What is the physical size of your 2700 NiMh pack. If they are the AA size then they are the high internal resistance type (marginal current capacity - specially if you are ever using all digital servos)....If they are the bigger, sub-C size, then they would be the low internal resistance type and better at handling the current draw rquired with digitals.

It is due to the higher internal resistance of the NiMh technology that I do not use NiMh's anymore.

[DeadTom]

Chris and AL,

Both very good points and yes they are the AA size batteries. Looks like this pack will be used with one of the airplanes instead of the Hawk. I will be in Las Vegas again for the next few days so I will try one of those shops for a better battery.

Thx,
T

[soegeng.patrick]

Sorry it's bit of the topic... Why modeller still use NiCd Instate NiMh wich have more Amp and lest weight..

Thank's


Best Regards,
Patrick R. Soegeng

[GyroAl]

In a nutshell, it is not just the mah rating and voltage rating of a battery that is important - NiCd or NiMh - but the current (amperage) they can provide without dropping their voltage output too far. Think of it as the size of the tap, on a barrel of water, that limits how fast the barrel can be emptied.

When we look at Lipo batteries, we find they give the three ratings - Voltage, Mah and C rating - not so on the NiCd or NiMh battery packs or cells. e.g. a lipo rating may be 14.8V/3700mah/20C. So the battery can deliver an amout of power (Watts) that can easily be calculated. 14.8V x 3.7amps (3700 ah) x 20c = 1095 watts for a reasonable erid of time before the voltage output will drop significantly under such a demand.

One can have two 4.8 Volt (4 Cell) 2700 mah NiMh batteries but they can provide power in very different ways. One has a higher internal resistance then the other. This means that it cannot only be charged as quickly as the other, but it also means it cannot be discharged at as high a rate.

Both may take one hour to discharge if the power required is only 13 watts or so (14.8 x 2.7 amps). But if one needs 24 watts (4.8V x 5) then the one with the higher internal resistance, may drop drastically in output voltage causing the failsafe in the RX to kick in or worst, for the RX to go into a "brown out" (as in some Spectrum RX's). Yet when tested with your battery tester that just loads it with only 1/5th of an amp, they will read as good!

On the other hand, the low resistance pack may be able to do so easily. Of course it would discharge in much less then an hour but it would not cause premature failsafe or brown-out.

In the same physical size, you will generally find that NiCds are much more comfortable operating in a high current environment, then can a NiMh cell of the same physical size. That is why the NiCd, of the same size, will be heavier (denser).

In the past, when we were using analoque servos (that demand much lower power input) rather then the high power requirements of the digital servos we use now, and before we pushed our helis at the high rotor speeds and through the high G maneuvers we do now, it was not much of an issue, as seldom did we need power delivery that required more the 2 amps - not so today.

[DeadTom]

Wow Al,

Thanks for the explanation, that was qutie a mouth full. All great information.

[GyroAl]

Glad you appreciated it. When the AA size 2700 NiMh first came out, a good number of us who have been around awhile thought "Wow. small size yet great mah" so we treied them and learned of their weakness the hard way. Personally that meant two hi-cost crashes!!! :o

So I am just trying to keep others from being sucked in by the numbers.:)

[DeadTom]

I went to one of the LHS arounf the are today and he was telling me that Horizon Hobby recommends not using the 4-cell batteries at all with their system.........? My Dx7 shipped with a small 4 cell rx pack? I looked on theier website and found nothing regarding this constraint. He also said that he would have to order any bigger batteries and that will take a week or so.
I think I will just go with the 2 cell lipo like Chris and also get a BEC and set that on the 5v setting.
I did not think this was going to be such a trial to get a rx battery.

[JustPlaneChris]

They don't really come out and say it, but this article points out the importance of adequate power:

http://www.spektrumrc.com/Articles/Article.aspx?ArticleID=1683

[DeadTom]

Chris,

The CC BEC that you have is that the one that has 10amp peak on the front of it?

[JustPlaneChris]

Yessir, as far as I know CC only makes one version of the BEC. Mine is an early model that will cause the Spektrum receivers to go into bind mode when plugged into the battery port. I get around it by just pulling the signal wire from the connector after programming, but I believe new ones have been modified to avoid this behavior. Here's what they have to say about it:
http://www.castlecreations.com/support/faq/faq-ccbec.html#ccbec8

[DeadTom]

Thanks Chris,

I have just ordered the CC BEC and the CC Link along with an EVO flight 7.4v 2100mah lipo from my LHS, and since I live in Reno, Tower Hobbies has a big warehouse here so the LHSs can call and get products from them and sell them locally and not to mention faster than normal. I can probably pick this order up this afternoon or tommorrow...very nice indeed.

T

[JustPlaneChris]

Sweet! Sounds like a perfect setup. Oh wait, it's like my setup. :smokin:

[DeadTom]

Alright Chris,
I have all the aforementioned items and also you eluded to the perfect little setup with the BEC, RX and batt? Would you be willing to give a quick pic or a little diagram of said setup? That would be most appreciated as I am at that point in my build.

Tom

[JustPlaneChris]

Oh. Hmm.... it's all buried in the frame. Basically I soldered the BEC into the standard radio switch, in the lead that goes to the receiver. The lead from the switch that ordinarily goes to the nicad battery now goes to the lipo. That way when the switch is off, the lipo is not connected to the BEC so there's no power drain. Switch on, the power flows from lipo, through the switch, to the BEC then to the receiver.

Make sense?

[DeadTom]

Yes, I believe I have it. When I get home today I will put it together and take a pic and post it and when you get a chance have a look at it and let me know if I understood correctly.
Thanks again,
Tom

[eddo22]

Oh. Hmm.... it's all buried in the frame. Basically I soldered the BEC into the standard radio switch, in the lead that goes to the receiver. The lead from the switch that ordinarily goes to the nicad battery now goes to the lipo. That way when the switch is off, the lipo is not connected to the BEC so there's no power drain. Switch on, the power flows from lipo, through the switch, to the BEC then to the receiver.
Make sense?
man, i wish i would seen this before i lost a tp1320 to the power drain...dangit!