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Old 11-10-2011, 07:55 PM   #1
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Default 2.4Ghz Receiver "Brownouts"

Your 2.4Ghz receiver equipped model has flown a number of uneventful flights but on the last and fatal one, you suddenly lost control and crashed. The undamaged RC system worked normally at the crash site.

If you were using a 3 or 4 cell lipo pack, a 2.4Ghz receiver, and 4 or more servos and, your speed control had a built-in "linear-type" battery eliminator circuit, you probably had the linear BEC circuit overload, the receiver "saw" a drop in voltage and the receiver "reset" cutting off all control and you crashed. Some makers of 2.4Ghz systems now admit the need for using high enough amp-rated "switch-mode" BEC's to assure that the receiver always "sees" it's required minimum voltage for reliable operation. When shopping for an add-on switch mode BEC or a speed control with built in switch mode BEC circuit, always read the specs carefully. Some specify that the BEC is rated for 3S only or 3S and 4S lipos, 3 or more servos of different sizes, etc. Best to err on the safe side.

Read the FAQ's etc on Dimension Engineering's website.
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Old 11-11-2011, 03:16 AM   #2
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Nice post. I've experienced a few unexplainable crashes. Thanks for the info!

All of my landings are three point landings if you count the spinner, too
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Old 11-11-2011, 06:52 AM   #3
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Why would this be limited to 2.4GHz systems
Surely if the BEC overload and the voltage drops far enough then whatever frequency the Rx uses it's going to shut down? I cant see how radio frequency is even relevant to this problem?


I had something similar happen recently but the cause in my case was a faulty servo which must have developed an internal short which caused the BEC /Rx to shut down.
I was dead lucky because i was doing a low slow pass at the time and the model (a 3d aerobatic job) simply landed itself with no damage other than the undercarriage screws pulling out. When i recovered the model the surfaces were just twitching and would not respond to Tx commands. I thought it was a bad Rx but investigation showed an aileron servo to be the problem. This was a 2.4GHz Spektrum radio system (though not Spektrum servo) but I would be pretty sure any system would have failed under the circumstances.

Steve

PS.. IMHO at least 75% of 'unexplained' crashes are due to either poor build/set up and/or (and most often) pilot error. In the event of almost any and all crashes the 'brownout' seems to have replaced 'interference' as the standard 'cop-out' to absolve all blame from the guy on the sticks ... Possibly just my cynical view of things
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Old 11-11-2011, 07:31 AM   #4
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PS.. Above post takes nothing away from the very good advice that you always should check specification of your BEC to make sure it's adequate.
This I think should apply whatever frequency of radio you are using.

Steve
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Old 11-11-2011, 07:46 AM   #5
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The basic reason a brownout can cause 2.4 systems the most trouble, is that they have in the receiver, a computer processor, if the voltage goes below operating level, it shuts down.
Then which maybe a split second later, the voltage returns, and the little computer must reboot, ( it takes it far less time than the computer you are reading this on,to reboot, but basically the same thing )

72 band and all other bands do not use a computer chip of this type. They may brownout and return in less time than you can realize, they always know what channel to work on.

For me, if the plane is large enough to carry a receiver battery, that is the single most reliable way to prevent any brownout issues. Or use a separate 10-20 amp bec.

We used to fly with 450-500 mah RX batteries and not think about it, only the large scale planes went with 1100 mah size, now you can have 2000 mah nimh the same size as a 500 was 20 years ago.

I have been flying RC for 35 years, I can not honestly blame any crash ( & i've had plenty) on actual radio system failure. I have had dumb thumbs and a total loss of ideas, but not anything that I did not cause myself. A few times I built a crash into the airplane, but I learned to stop that.

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Old 11-11-2011, 09:02 AM   #6
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Unhappy I Hate Brown Outs

There are a few things you can do to help prevent a 2.4 brown out.

1. Always use a UBEC with 2.4 Period its cheap insurance
2. Always use a Full range 2.4 Receiver Period its cheap insurance
3. Use a Receiver Low voltage Protection Capacitor if your to Cheap to buy a UBEC it will supply voltage for the few seconds that the battery is drawn down to low and prevent a Brown out, a Charged Capacitor is a battery, there has been some debate here on that, But thats Why Spektrum made the darn thing for, to prevent a brown out on rc cars, but it will ALSO work on planes too, it does not know if its in a Plane or a car it will just do its job and supply voltage if it goes down.
4. Dont allow your plane to get bewteen a object and you, like a tree, building etc to prevent a Masking of the radio signal.and a brown out.
5. if your using a non full range 2.4 Receiver, good luck to you, keep your plane in close to you or else, by by plane
6. And thats the Truth

http://www.hobby-lobby.com/voltage_p..._2212_prd1.htm








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Old 11-11-2011, 02:03 PM   #7
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Originally Posted by CHELLIE View Post
There are a few things you can do to help prevent a 2.4 brown out.

3. Use a Receiver Low voltage Protection Capacitor if your to Cheap to buy a UBEC it will supply voltage for the few seconds that the battery is drawn down to low and prevent a Brown out, a Charged Capacitor is a battery, there has been some debate here on that, But thats Why Spektrum made the darn thing for, to prevent a brown out on rc cars, but it will ALSO work on planes too, it does not know if its in a Plane or a car it will just do its job and supply voltage if it goes down.

Sorry
Chellie - this is 100% incorrect.

That tiny cap might help a bit with voltage ripple but it will not provide power for seconds.

Try this test and report back to us. Use a nice 4 cell NiMh or NiCad pack with your Spekky RX and capacitor. Plug in a single servo to a switched channel.

Run the servo back and forth - Use a switch channel to make that easy. While running the servo back and forth power off the battery pack - see how long the RX stays powered and the servo runs with only the capacitor.

I guarantee that servo RX will run less time than you can detect.

The capacity does not prevent brownout. It was developed for the car guys running on carpet with wonky static electricity erratic behavior. The Cap helps with that. It was not a brownout prevention device.

You would have to use a mighty large cap to get even one second of power.

Try the test for yourself and report back your findings....

Sorry to hit you up - but your info is just not correct.

Mike
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Old 11-11-2011, 04:09 PM   #8
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If you want to go the capacitor route, try this one;

http://www.hobbyking.com/hobbyking/s...3uf_3sec_.html

the "brownout caps" I have seen are about 3300-4700 mfd, this new one is 783,333 mfd !

That is 166 - 237 times as big, it may actually help, maybe

I still like a good battery, NO brownouts.

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Old 11-11-2011, 04:56 PM   #9
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I don't know if that huge HK capacitor might actually work (may as well haul a RX battery around, eh?) but Spektrum themselves say that the one they sell is not useful for flight.
I quote:

Overview
Spektrum's new Voltage Protector prevents a DSM™ receiver's voltage from dropping below the proper operating level in lower voltage applications such as 4-cell 1/12 carpet racers. Installation is as simple as plugging it into an open channel slot on the receiver unit.

This Voltage Protector is not intended for Aircraft use.

fly
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Old 11-11-2011, 06:00 PM   #10
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Originally Posted by rcers View Post
Sorry
Chellie - this is 100% incorrect.

That tiny cap might help a bit with voltage ripple but it will not provide power for seconds.

Try this test and report back to us. Use a nice 4 cell NiMh or NiCad pack with your Spekky RX and capacitor. Plug in a single servo to a switched channel.

Run the servo back and forth - Use a switch channel to make that easy. While running the servo back and forth power off the battery pack - see how long the RX stays powered and the servo runs with only the capacitor.

I guarantee that servo RX will run less time than you can detect.

The capacity does not prevent brownout. It was developed for the car guys running on carpet with wonky static electricity erratic behavior. The Cap helps with that. It was not a brownout prevention device.

You would have to use a mighty large cap to get even one second of power.

Try the test for yourself and report back your findings....

Sorry to hit you up - but your info is just not correct.

Mike
Hi Mike Here is what the BIG BOYs are doing to prevent a Brown out With the Spektrum Capacitor, Others might benifite also from using this Capacitor. Also they Explain why you need to keep your keep your Planes Close to you using non full range 2.4 receivers. You can hit me up all you like, But just make sure that you are Right

http://rcfoamfighters.com/blog/?p=499

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Old 11-11-2011, 06:06 PM   #11
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Sooo why cant you use it for Aircraft The capacitor does not know if its in a Plane or a Car, Voltage is Voltage, Come on now people, Take off the Blinders Already

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Old 11-11-2011, 06:14 PM   #12
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Originally Posted by CHELLIE View Post
Sooo why cant you use it for Aircraft The capacitor does not know if its in a Plane or a Car, Voltage is Voltage, Come on now people, Take off the Blinders Already
As stated, it's designed for small carpet racing cars. If it fails...big deal, your car stops or glitches. Oooo

I think you know what happens to aircraft that have an ESC failure.

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Old 11-11-2011, 06:22 PM   #13
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Originally Posted by CHELLIE View Post
Hi Mike Here is what the BIG BOYs are doing to prevent a Brown out With the Spektrum Capacitor, Others might benifite also from using this Capacitor. Also they Explain why you need to keep your keep your Planes Close to you using non full range 2.4 receivers. You can hit me up all you like, But just make sure that you are Right
I am 100% right - guaranteed. Please run the test I asked you too. How long do you get power?

Please just run the test... You will see I am correct.

By the way your "big boys" video is from a post that also has WRONG information like salt water baths for LiPo's. His range studies relate to range - that is also incorrect information. I have tested those park flyer RX's at over a mile. Shadowing is the reason for the parkflyer rating. So just because someone posts a video - does not make it true.

As pointed out above even the manufacturer does NOT recommend them for aircraft use. That is because it helps with voltage ripple on cars racing on carpet.

So please just for grins- run the test before you accuse me.

Mike
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Old 11-11-2011, 06:23 PM   #14
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Originally Posted by flydiver View Post
As stated, it's designed for small carpet racing cars. If it fails...big deal, your car stops or glitches. Oooo

I think you know what happens to aircraft that have an ESC failure.
Sometimes people need to think out side of the Box and benefit from what a related part can do for other Applications

http://www.youtube.com/watch?v=FpPzb...layer_embedded

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Old 11-11-2011, 06:27 PM   #15
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Originally Posted by rcers View Post
I am 100% right - guaranteed. Please run the test I asked you too. How long do you get power?

Please just run the test... You will see I am correct.

Mike
the capacitor is not designed to run servos, its designed to keep the voltage above where the Receiver would kick out at (Brown out) we are talking ma and voltage, to prevent a Brown out. its been tried and tested by a lot of people, it works for aircraft.

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Old 11-11-2011, 06:30 PM   #16
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Originally Posted by Wildflyer View Post
I still like a good battery, NO brownouts.
That is the best solution.
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Old 11-11-2011, 06:37 PM   #17
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COMPARISON OF 2.4 GHZ RADIOS
By: Ron Scott 2-9-2009

The following is a summary of my own experience with 5 different 2.4 GHz radio systems related to flying 42 different model airplanes over the past 2 years. I hope it helps someone out there.

Background: I probably fly more then the average modeler and average 4 to 5 days of flying per week.
I belong to 5 RC flying clubs in the southern California region and have over 200 planes. (Obviously I’m not married) Most of my planes are Glow and Gas powered from size .10” to large 35% Extra 330 with DA 100 or similar engines. I have 62 Electrics from Zagi style flying wings to pattern planes and float planes. Also, numerous gliders from hand launch to slope to large 10 foot wing span thermal gliders. The reason I tell you this is because the point is I fly a lot and believe that this makes a good test bed for trying out new equipment.
Keep in mind for what it’s worth - my write-up is only one man’s opinion. Ask 10 people and you’ll get 10 different answers.

R/C Radios tested:
1) Spectrum DX7 - 7 Channel System
2) Futaba T6EX and T7C – 6 and 7 Channel System
3) Assan (from Hobby City) XR8 Plug in Module to a Hitec Eclipse 7 (or Optic 6) Transmitter.
4) Airtronics RDS 8000 FHSS – 7 Channel System
5) EF Helicopters EF 2401 – 4 channel for helicopters (from Hobby People)

Spectrum DX7 : Cost ~ $300 – 350, I have 12 models (mostly foamies) on this radio system.

Likes: Easy programming & big LCD display showing curves, has 7 channels, model
matching, 20 model memory, 1500 mAh battery. Receivers (AR500 and AR6100
and AR7000) cost between $50-90. More expensive receivers are available.
Dislikes: 1) Charge jack is different from most other manufactures, + is outside and – is
inside connector. (When are they (JR) ever going to convert to match most
other manufacturers chargers i.e. + = center pin and − = outside plug ?)
2) Loss of control – I have had 3 planes lockout (or brownout) for 2-4 seconds
and crash. Later found that if I put a 4,700 fd cap across one of the receivers
output channel + and – pins the problem went away. (Horizon sells a 4,700
fd capacitor that eliminates the lockout potential problem for $6.00 – called a
Voltage Protector”). What actually was happening was a momentary drop in
voltage (+5 to ~3-4 volts) on the ESC power line BEC going into the receiver as
a result of a momentary hi current draw on the battery. There are at least 2 other
ways around this potential problem. One is by providing a separate battery (4-5
cell) to power the receiver only. The other way is to install a separate BEC device
to supply 5 Volt input to the receiver. A company called “Dimension Engineering”
(Dimension Engineering.com on the web) makes a “ParkBEC” and a “Sport BEC”
for $19-$30 to eliminate or reduce the possibility of a brownout condition.
In all fairness, the ESC’s play a major role in the radio’s ability to function
properly. The receiver may be falsely accused of being the problem source – but in
actuality the BEC circuit of the ESC may be limited and not be able to supply a
solid + 5 volts to the receiver. So, check out your specs when you put together your
next Electric plane. Now the question is, why doesn't Spektrum offer a free 4,700
fd capacitor for every radio receiver they sell?

http://www.canyoncrosswinds.com/inde...s-Compared.htm

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Old 11-11-2011, 06:41 PM   #18
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Apr 30, 2010, 12:25 AM #1
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Spektrum AR7000 brownout testing (intentional)

I am currently putting together a new E-flite Pulse XT plane. I use AR6100e receivers in my foamy planes with good results. This plane cost significantly more and will probably suffer more damage in the event of a crash, so I wanted to be a sure as possible that the radio system is solid. That is the reason I'm performing brown out testing on this system, when I haven't with my foamy planes. Also, I have been using Hitec HS-55 servos with my foamy planes also with good results. When I tried the E-flite servos that came on the Pulse XT [I found that they seemed slow, so I wanted some slightly faster servos and found the JR SM22 servos would fill the requirement.]

System components being tested:

Spektrum AR7000 receiver
JR Sport SM22 servos (4)
Spektrum flight logger
Spektrum voltage protector

Also used in the test:
Eneloop battery pack of 4 cells in series [to intentionally under power the system and induce brownouts]
Fluke 863 graphical multimeter
Spektrum DX7 transmitter

So, I connected the four servos to the receiver with the 4S Eneloop AA battery pack for power along with the flight logger and the voltage protector. Then I operated one servo contiuously (with a control arm on it but no load) and took voltage and current reading. Then I repeated the testing with 2 servos operating continuously, then 3, and finally 4. I also performed this testing without the voltage protector to see the difference.

Below are the results. I did get a brownout indication [flashing LED on receiver] only when operating all 4 servos without the voltage protector. With the voltage protector connected I couldn't get a brownout. When I got the brown out, the flight log indicated 16 to 24 antenna fades (about 30 seconds of testing) on the A antenna, but none anywhere else, and no frame losses or holds.
Attached Thumbnails
  • Here are the results. Brownout only occurred with all 4 servos operating and without the voltage protector. 29.8 KB Views: 244
  • Spektrum Flight logger top AR7000 Receiver with satellite Rx 99.3 KB Views: 74
  • Voltage protector on the top (4700F 10V) JR SM22 servo - bottom 78.4 KB Views: 103
  • Close up of SM22 servo label 73.3 KB Views: 67



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Old 11-11-2011, 06:42 PM   #19
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Need i Say More

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Old 11-11-2011, 06:57 PM   #20
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That cap WILL not power your RX for a few seconds as you initially indicated in your post. Running my quick test will show you that.

I hate to see newbies give false information about brownout saving abilities of something not even Spektrum recommends be used in airplanes.

Marginal power supplies for airborne systems are fixed by high quality BEC's or batteries. Plain and simple.

So no - you need not say more.

Mike
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Old 11-11-2011, 07:10 PM   #21
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Originally Posted by rcers View Post
That cap WILL not power your RX for a few seconds as you initially indicated in your post. Running my quick test will show you that.

I hate to see newbies give false information about brownout saving abilities of something not even Spektrum recommends be used in airplanes.

Marginal power supplies for airborne systems are fixed by high quality BEC's or batteries. Plain and simple.

So no - you need not say more.

Mike
Please read it right, i said it will supply Voltage to for a few seconds that the battery is drawn down to low and prevent a brown out

it will supply voltage for the few seconds that the battery is drawn down to low and prevent a Brown out,

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Old 11-11-2011, 07:20 PM   #22
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Originally Posted by CHELLIE View Post
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His test with no load does not PROVE anything other than if you have 4 servos with absolutely no load you might not get a brown out. I don't know about your planes but mine all have a load on the servos while flying. If you look at his own chart as the servo count goes from 2 to 3 and 3 to 4 the voltage get closer to what he had before the cap was installed. Which actually proves that it will NOT maintain a higher voltage at the receiver for 3 seconds

I do not fly Spektrum and have no intention to get this system any time soon but I have my doubts a cap that small is going to save a plane from crashing. If you are worried about a brown out use a separate BEC or receiver battery.

Mike


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Old 11-11-2011, 07:22 PM   #23
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Yes I get what you are saying. What I am saying is if you have marginal power you must fix it not apply a bandaid.

Power is power you either have enough to safely fly or not. The cap does not impact that.

I am super happy you like using the caps. I just know for a fact they won't help marginal power systems and they certainly can't power your system.

Mike
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Old 11-11-2011, 07:28 PM   #24
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Originally Posted by rcers View Post
I am 100% right - guaranteed. Please run the test I asked you too. How long do you get power?
For about a second or two.

Let's say you're pulling constant current. The equation for discharging a capacitor at a constant current is

t = C * (Vstart - Vend) / I

Where C = capacitance
Vstart = Start voltage
Vend = End voltage
I = current (amperes)

You can buy a 3F (3 farad) capacitor at Radio Shack for a few bucks. Let's say you have a start voltage of 5.5V and your RX dies at 3V. Let's say your servos and radio are pulling 2A. We can then write:

t = 3 * 2.5 / 2 = 3.75s.

So, it would take 3.75 seconds before your radio dies if you start at 5.5V, pull 2A out of a 3F capacitor and your RX dies at 3.0V.

I could go out and do the experiment, but my fairly educated guess is you'll get something very close to that.

In real life you probably don't discharge at a constant current, but with a constant resistance, which makes the math a little more complicated (involving logarithms and fun stuff). However, that scenario should give you a slightly longer time.

That being said, i agree with Mike on one point: While a capacitor might be the cheapest solution, it's not the best solution. A drop in voltage is probably caused by a spike in current (amperage), so while a capacitor will help you with short drops in voltage, it's not nearly as good as a redundant power solution...

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Old 11-11-2011, 07:37 PM   #25
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I have run the test - I can barely detect a time difference with our without the cap. Nothing near 2 seconds. That is with one servo and just the receiver. I think the dump voltage for the RX is much closer to 3.6v so that may be a part of it.

I will let you run the test....and see what you get.

Even HK is saying around 2-3 seconds on a 783333uf cap.

Here is there data...on a 3 amp load:

Data on a 3A load spike typically seen when large retracts jam:
Supply 6v with a voltage drop to 4.7v over 0.88sec
Supply 6v with a voltage drop to 3.0v over 3.0sec (3.0v minimum voltage of the OrangeRx 6ch)So again I barely detect an difference with the brownout cap vs not.

Just curious what your results are. Post them when you can... Maybe my cap is bad.

With no servo load it will power the LED on the RX for a bit of time.

Good dialog and fun discussion. I would like to try the HK cap but at almost an ounce I would rather just use a 700mAh LiFe pack. TaDa!

Mike
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