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Aug 29, 2019, 09:50 PM
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Build Log

Great Planes Revolver Sport Aerobatic GP/EP ARF 70"


I searched RCGroups for previous posts on this model, and could not find any recent posts. There are two other of these Revolvers in my RC club, both powered by a 20 cc gasser. Mine is going to be powered by a Hacker A60-5XS motor, 17X10 APC-E prop and a 7S2P 5000 mah A123 battery pack.

That 5000 Mah pack is a full 15 1/2 ounce over one of my 4500 Mah 6S LiPo battery packs, which puts the model weight at 158 ounces. This is a bit strange, with the motor and ESC installed, the model balances exactly right on the required CG location. So, adding a battery pack in the usual location will require 1/3 pound of lead in the tail. I've found that splitting the A123 pack with a 4S2P pack behind the wing tube, and a 3S2P pack in front of the wing tube places the CG at the proper location.

I checked with my club members with their 20cc gassers, both of them required around 6 ounces of lead in the tail. It would have been great if the design had placed the rudder and elevator servos in the tail. Problem is, the elevator is split, and tail located servos would have required two servos.

It is built, ready to go at this time. I've just finished building up the A123 battery pack, and have to wire it up. Hope to fly it this Sunday if the weather cooperates. Photos of the installation along with flight comments will be posted at that time.

The motocalc numbers for A123 are:
Power 174 Watts per pound
Rate of climb 3200 feet per minute at 90 degrees
83 Amps at 20.1 Volts for 1680 Watts, verified with actual measurements.


The motocalc numbers for the 6S LiPo are:
Power 203 Watts per pound
Rate of climb 3690 Feet per minute at 90 Degrees
87 Amps at 20.9 Volts for 1788 Watts.
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Aug 30, 2019, 07:42 PM
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Power Test Results


I just ran up the Hacker A60-5XS motor with my new 7S2P A123 battery pack. Here are the results.

70.5 Amps at 22.04 Volts for 1540 Watts. The motor turned the 17x10 prop at 7400 RPM.

Compare that to my existing 6S LiPo battery pack that was tested under the storage voltage condition.

66 Amps at 20.61 Volts for 1360 Watts. The motor turned the 17X10 prop at 7290 RPM.

So, if the LiPo test were to be tested at full charge, it would be fairly close in performance to the 7S LiPo. Problem is, the A123 pack is about 16 ounces more weight. (I can live with that)

Our field is closed on Saturdays, but Sunday weather prediction is for a bit of rain. Hopefully, that will clear up during the day.

As previously indicated, this Revolver model has a severe tendency of being nose heavy, so I had to split the battery pack with eight A123 cells located behind the wing tube, with the remaining six A123 cells located in front of the wing tube. On checking the CG with a 4500 Mah 6S LiPo battery pack, the LiPo pack would have required about 5 ounces of lead in the tail to balance the model.

Out of curiosity, I checked the Battery IR values with my BattIR project. It showed the LiPo battery pack at 4.92 MilliOhms per cell at the storage voltage. Doing the calculations that predicts a voltage drop of 1.94 Volts at a 66 Amp load. The actual voltage drop came out to 2.19 Volts, which can be accounted for on the voltage drop across the LiPo battery packs #12 lead wires.
Last edited by vollrathd; Aug 30, 2019 at 07:56 PM.
Sep 02, 2019, 07:29 PM
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Flight Tests


I put two flights on my new Revolver today. I moved the forward battery pack toward the motor two inches, but did not do any acrobatics since I did not have any tie wraps at the flying field to secure the battery pack to the Velcro.

The model flew very well even at the heavy weight. Vertical performance was straight up out of sight, but probably not enough for those that do 3D. (I don't) Landings were a non-event in dead air, with no tendencies to suddenly drop a wing if the landing speed got to slow.

This model is a keeper, and will be getting a lot of flights in the future. The photos show how the A123 battery pack was split to handle the CG issues.
Sep 08, 2019, 12:30 AM
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Seems like the Lipo will give you more performance at a lower all up weight?. correct? if so, what is the benefit of using the 123 batts, I like to understand.
Sep 08, 2019, 12:45 AM
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Quote:
Originally Posted by Sam Ehab
Seems like the Lipo will give you more performance at a lower all up weight?. correct? if so, what is the benefit of using the 123 batts, I like to understand.
The 7S A123 battery pack matches the performance of the 6S 4500 Mah LiPos I also have for this same motor.

What are the A123 advantages?
They can be left at full charge indefinitely, holding 95% of their charge after a full year on the shelf. No storage issues.

They can not become flaming blowtorches if severely abused. (IE Crash!)

They are designed to be fully charged in the model in 15 minutes with a high powered charger. I permanently install the A123 packs in their respective models.

These cells have nearly identical characteristics, little variation between cells I bought last week, and cells that are 5 years old with 500 flights on them.

These cells are closely matched in performance. Compare that to LiPos where you can have very good mfg, and some cheap LiPos that are not worth the box they came in.

They have flat voltage discharge characteristics, with little drop off in RPM between the start and the end of the flight.
They have aluminum housings, compared to the plastic baggies used on the LiPo packs.

Their aluminum housings, along with their larger physical size allows better cooling in the model. They don't run hot like a LiPo can.
They are rated to be used at minus 30 degrees F.

My model collection has over 200 A123 cells installed, with the largest pack consisting of 36 Cells in a 12S3P configuration. It powers a Rimfire 50 cc electric motor, pulling 130 Amps at 4500 Watts. Smallest is a 4S1P 2500 Mah A123 pack running a Tower Hobbies Slow Ride model at about 400 Watts.

I also have three models that are powered by my four 6S 4500 Mah LiPo battery packs. they don't get much flying time.

I see you are in California. I've seen several model crashes with the electric motor powered by LiPo batteries. The models LiPo battery pack became a flaming blowtorch for many minutes. A123's don't do that, can't do that. In California, that might be an advantage.

A123 disadvantages, they have larger physical volume than a similar LiPo, and with the Revolver model airplane, they add about 8% more weight to the model. They are pretty much limited to around 40 Amps maximum per cell, putting out 2.9 Volts DC per cell at 40 Amps.
Last edited by vollrathd; Sep 08, 2019 at 01:04 AM.
Sep 10, 2019, 06:23 PM
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Thx, good to know.

Are the prices and availability comparable?
Sep 10, 2019, 06:41 PM
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Quote:
Originally Posted by Sam Ehab
Thx, good to know.

Are the prices and availability comparable?

I build my own A123 battery packs, and purchase the individual cells from here:
http://a123batteries.com/anr26650m1-...phate-battery/

I've got drawings and photos on how to build your own packs. One critical requirement is the purchase of a high powered temperature regulated soldering iron. The one I use is the Weller 100 Watt iron with its 3/8 inch diameter iron plated tip. I also have a half dozen other irons, even my 60 Watt iron isn't anywhere near capable of soldering to these cells. It goes for around $60.00, and with a variety of tips from 1/8 to 3/8 inch wide, you can solder just about anything model related with it.
Weller Iron Mouser (Weller is just one supplier of this iron)
https://www.mouser.com/Search/Refine...Keyword=w100pg

You can also buy custom built A123 battery packs from here, but I don't know what they use for the interconnection between the cells. And, they are very expensive. They want $90 for a single 4S1P 2500 Mah A123 battery pack. The 7S2P (14 cell) A123 pack I just built up from A123batteries cost me around $110.00.

https://www.radicalrc.com/category/A...ells-Packs-199
SKU Number: RRC#S2500
Last edited by vollrathd; Sep 10, 2019 at 06:48 PM.
Sep 11, 2019, 11:09 AM
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This is great info, I do have a good soldering gun. If I need a battery for a sport/scale model that is not too sensitive to a little extra weight, this will be a great option. Thx for taking the time to respond.
Sep 11, 2019, 11:11 AM
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BTW, I have been waiting for Tower to get the 70" Revolver in stock....
Sep 11, 2019, 12:57 PM
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Quote:
Originally Posted by Sam Ehab
This is great info, I do have a good soldering gun. If I need a battery for a sport/scale model that is not too sensitive to a little extra weight, this will be a great option. Thx for taking the time to respond.
FYI, a soldering gun will not work. I have two of them.
Sep 17, 2019, 12:32 AM
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Revolver Landing Gear Support


My Revolver now has 37 flights on it, very nice flying model that is easy to land. Until now.

The last flight was a perfect "greaser" landing until I hit the rudder while the model had slowed down to around 10 MPH. And, the landing gear flipped out of the fuse. The LG wheel pants put the usual dents into the bottom of the wing.

The photos show how the LG was supported in the fuselage. There was little adhesion between the small ply plate and the bulk heads in the fuselage. There was absolutely no adhesive binding between the laser cutting on the LG plate and the fuselage. Didn't take long to repair the mount per the second photo.

This isn't an unusual problem, seems many of those mfg's over you know where don't consider how these models can pull their rather inadequate LG mount loose when landing on a grass field.
Sep 17, 2019, 09:56 AM
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This seems to be a common problem with many ARF's, even the Great Planes ones. My GP Escapade LG looked like it was not well glues/supported, Luckily I decided to add a CF cloth with some thin CA to re-inforce that area. So far it has been solid. Since then, I pretty much check/re-inforce any ARF LG/retract area as see fit.

I am still looking for this ARF....Good thing you got your fixed!
Sep 23, 2019, 08:24 AM
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That landing gear failure is known weak point in these planes. Should be modded out of the box but looks like yours is fine and fixed.

I've been a "fuel or bust" guy forever but seeing most of the ppl at my field fly electric and how much performance you get... I think I'm going to sell off and make either this Revolver or my Valiant my first electric besides my EDF/glider.

Great write up on the batteries, I can definitely solder and a $60 good quality iron is a good investment IMO. Do you have any links to write ups on how you do it?

To the person who was saying they are waiting on the Rev70 to come back in stock on Tower... it might be a while if ever... GP and the factory that produced the models went under. If Tower can find a new manufacturer then maybe we'll get them again but I dunno. I do know that I'm happy I got legit one of the last ones they had because it went out of stock about a week after mine arrived...
Sep 23, 2019, 11:37 AM
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I did notice that many GP ARF's are "not available"

Are the news that the factory that does them GP planes is gone under confirmed? reliable sources?
Sep 24, 2019, 02:03 AM
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Yes its a reliable source, its been on here and other places a few times. Searched the OP's name on google and found his how-tos on these A123 batteries. Very cool stuff. I already use LiFe batteries in all my planes for RX packs but I might have to switch.

Gonna start on the Rev70 this week and look into ordering A123s here, they are pretty cheap in Europe.

Would love to see an update on this Rev70 in the thread and what sort of high voltage charging setup is used. I fly at a field that doesn't have power so I'd need something that can be used on a car converter or a 12v battery directly. These A123s can be charged at 4C correct? So that would be what like 20 amps for a 5000mah pack?
Last edited by scottydsntknow; Sep 24, 2019 at 07:11 AM.


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