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Old 11-27-2012, 06:02 AM   #1
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Default Piper J3 Conversion and Questions

I am starting a nitro to electric conversion of my Piper J3 Cub. I am not sure exactly what version this one is or who made it as I received it from a friend. I am not exactly sure where to start though. I have weighed it and it weighs in right at 7 pounds. I have seen online that for these type of planes that I should calculate 90watts per pound. So that gives me 630. But not sure where to go from here - Hobbyking has sooooo many choices for motors I am lost.
I already have a couple of 2200mah, 11.1v LiPos so I am hoping I can re-use them here too.

Any suggestions for a setup?


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Old 11-27-2012, 07:03 AM   #2
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Originally Posted by CHSNative View Post
I am starting a nitro to electric conversion of my Piper J3 Cub. I am not sure exactly what version this one is or who made it as I received it from a friend. I am not exactly sure where to start though. I have weighed it and it weighs in right at 7 pounds. I have seen online that for these type of planes that I should calculate 90watts per pound. So that gives me 630. But not sure where to go from here - Hobbyking has sooooo many choices for motors I am lost.
I already have a couple of 2200mah, 11.1v LiPos so I am hoping I can re-use them here too.

Any suggestions for a setup?
What is the wingspan and wing area of your J3 Cub? If this is a real scale model, IMHO, it's not a good idea to go cheap on your motor/esc/battery.

Your value of 90 Watts per pound would be reasonable if you are taking off from very short grass or pavement. If your model takes off from longer grass, more power is always better. Out of curiosity, what engine did you have in this model?

But one issue to worry about is the efficiency of the motor you select. One good source of help is one of those PC model spreadsheets, such as www.motocalc.com.

Very good quality stuff is the Hacker line of motors, and the Castle Creations ICE series of ESC's. More $$$$, but they work and work very well. I've also observed other type motors in my club that have worked out well. But for the most part, these are motors for those foamies and so on. But some of the really el-cheapo motors have been known to have magnets come loose, or worse.

A few club members have motors in the 500 watt range. My Hackers range from an A30, two A40's, three A50's, and two A60's rated for 2500 watts or so.

Below is a little info on models on the order of 1000 watts or so, a little larger than your Cub, but these threads will give a little bit of help in what's involved.

If this is your first electric converstion, be very wary about ESC's with a linear BEC (Battery Elimination Circuit). These linear BEC's can shut down when they get hot, and you loose your model airplane when the BEC also shuts off your receiver/servos. The Castle Creations ICE series of ESC's use what's called a switching power supply type of BEC, that is much more able to handle your receiver/servo loads.

As for electric power, a properly sized electric motor/esc/battery system can easily outperform the glow engine you had installed in your model. The Hacker website shows how their motors perform and what RPM their motors will turn various prop sizes. Methinks a Hacker A40-12S or A40-14S motor would be in the ballpark for your Cub. http://www.aero-model.com/Hacker-Bru...40-Series.aspx I've got three A50's but those motors will haul your Piper Cub straight up out of sight, not a scale type power system for your Cub.

Take a look:
Thread on 70 size glow engine conversion to electric
http://www.wattflyer.com/forums/showthread.php?t=45222

Hacker 6S2P A123 powered Models
http://www.wattflyer.com/forums/showthread.php?t=44686

AEAJR's Site on Electric Power
http://www.wattflyer.com/forums/showthread.php?t=18521

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Old 11-27-2012, 07:18 AM   #3
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Thanks for the info - I'll look at that. The wingspan is 73" and the motor that was installed is a Magnum GPA 40.
I wish there was a nice shopping list.....here are the parts you need....go buy these....
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Old 11-27-2012, 10:55 AM   #4
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I recently did a conversion while building to the 1/6 scale Sig piper cub 71' wing. My all up weight came out a tad over 4.5 lbs.

I contacted Heads Up Rc and went with a 32 outrunner, 60 amp opto esc and a 4s 3300 lipo. The motor is supposed to be 800 watts but I have not propped anywhere near that and most likely will not. May even drop down to a smaller motor in the future after all it's a cub.

Heads Up Rc will recommend a setup for you just send them an email. Shipping is $2 and response is fast.

My .02
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Old 11-27-2012, 05:15 PM   #5
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Originally Posted by Unclebuck21228 View Post
I contacted Heads Up Rc and went with a 32 outrunner, 60 amp opto esc and a 4s 3300 lipo. The motor is supposed to be 800 watts but I have not propped anywhere near that and most likely will not. May even drop down to a smaller motor in the future after all it's a cub.

My .02
Nice thing about these electric motors, if it is putting out to much power, just put a smaller diameter and/or lower pitch prop on it! No need to change to a smaller motor unless you are after saving weight.

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Old 11-27-2012, 05:16 PM   #6
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Originally Posted by CHSNative View Post
Thanks for the info - I'll look at that. The wingspan is 73" and the motor that was installed is a Magnum GPA 40.
I wish there was a nice shopping list.....here are the parts you need....go buy these....
I could provide a list for a $$$$ Hacker + $$$$ Castle Creations ESC setup. This would be around $210 without the Lipo battery.

Let me know.

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Old 12-04-2012, 05:31 AM   #7
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I contacted Heads Up RC and this was their suggestion:
Power Up 60 Sport Outrunner Motor
Hifei 80Amp ESC with Switchmode BEC
APC 13 x 6.5E Prop OR 13 x 6 DFDL Wooden Electric Prop
22.2v 4200mah 35C DBY-Power Lipo Battery.
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Old 12-04-2012, 11:30 AM   #8
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Depending on how many servos you have I would consider an OPTO speed control and a separate BEC. Falls under personal preference.

If you have never ordered from heads up then you are in for a surprise. I've ordered from them multiple times and am always astonished at how fast my orders have arrived for $2 shipping.
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Old 12-04-2012, 01:15 PM   #9
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The power-Up 60 is supposed to be equal to a '60' size glow motor and puts out 1200+Watts.. so its FAR more powerful than you need. While more power isnt a bad thing you do need to watch that you dont end up making the Cub far too heavy.

The Fire Power 46 Sport from heads up would be more than powerful enough using a 4s liPo, and would work out lighter and cheaper: http://www.headsuprc.com/servlet/the...h-07%29/Detail
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Old 12-04-2012, 02:11 PM   #10
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What ESC would you recommend with that motor?
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Old 12-04-2012, 03:57 PM   #11
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Originally Posted by CHSNative View Post
What ESC would you recommend with that motor?
60A is planty, but more wont do any harm. I'm running the FirePower 46 in one of my planes and it's been a good motor so far, despite me driving it well over it's stated limits.
To get the most out of the 46 you would want to spin something like a 14x7 prop, I'd guess you have enough ground clearance to fit that in?

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Old 12-04-2012, 05:40 PM   #12
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Originally Posted by Unclebuck21228 View Post
Depending on how many servos you have I would consider an OPTO speed control and a separate BEC. Falls under personal preference.

.
Agreed:
If your ESC uses a LINEAR BEC (Battery Elimination Circuit) for a model of this size, that can cost you an airplane.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=63779

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Old 12-05-2012, 12:32 AM   #13
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Originally Posted by kyleservicetech View Post
Agreed:
If your ESC uses a LINEAR BEC (Battery Elimination Circuit) for a model of this size, that can cost you an airplane.
True but he did say that the ESC had a switchmode BEC, as do most ESC's of 40A plus these days (and some below)
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Old 12-05-2012, 12:47 AM   #14
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Originally Posted by JetPlaneFlyer View Post
True but he did say that the ESC had a switchmode BEC, as do most ESC's of 40A plus these days (and some below)
I've only been using the Castle Creations ESC's.

Question, do those real cheap China import ESC's also use switchmode BECs?

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Old 12-07-2012, 04:39 PM   #15
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Ok, so I think i have the power system setup correct.........and need to just order the parts. But thinking ahead, I know I will need to build up the firewall a bit in order to have the motor far enough forward to accommodate the cowl. As this is my first balsa model and I got it already built, I am not experienced in the actual building process. What type of wood is needed here....are there mounts available.....what have others done for this? I can be building that now while I wait for the parts.
Here is a photo of the engine mount as it sits now. I just removed the nitro engine so the pushrod and engine mount are still there. And, obviously it needs some major cleaning up.


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Old 12-07-2012, 04:41 PM   #16
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Originally Posted by kyleservicetech View Post
I've only been using the Castle Creations ESC's.

Question, do those real cheap China import ESC's also use switchmode BECs?
Yep, they do, very commonly on ESC's 40A and above and one a few below that too.
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Old 12-07-2012, 04:50 PM   #17
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You could build a motor box from plywood or you can get an adjustable mount: http://www.headsuprc.com/servlet/the...unt/Categories
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Old 12-07-2012, 05:52 PM   #18
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Originally Posted by CHSNative View Post
Ok, so I think i have the power system setup correct.........and need to just order the parts. But thinking ahead, I know I will need to build up the firewall a bit in order to have the motor far enough forward to accommodate the cowl. As this is my first balsa model and I got it already built, I am not experienced in the actual building process. What type of wood is needed here....are there mounts available.....what have others done for this? I can be building that now while I wait for the parts.
Here is a photo of the engine mount as it sits now. I just removed the nitro engine so the pushrod and engine mount are still there. And, obviously it needs some major cleaning up.
Does your motor have a "Firewall" mount where it's simply bolted to the firewall?

If so, take a run to your local hardware store, and look up those nylon spacers in various sizes. Find a bunch of them that extend far enough forward, buy some long screws, some nylon locking nuts, and put the whole thing together.

I've run motors up to 1200 watts this way, with no problems.
The attached photo is of a Hacker A50-12S motor with a 15X10 prop, 1200 watts and 7500 RPM.

(The aluminum bar is placed to allow centering the motor shaft at the prop location. This model has 4 degrees right thrust built into the fuse.)


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Old 12-07-2012, 06:41 PM   #19
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Originally Posted by JetPlaneFlyer View Post
You could build a motor box from plywood or you can get an adjustable mount: http://www.headsuprc.com/servlet/the...unt/Categories
+1....This is exactly what I was looking for. I'll just have to add it to my order. Thanks!
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Old 01-08-2013, 11:57 PM   #20
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Well, the motor mount ended up being too big for what I needed. So, I was able to drill out 4 dowel rods cut to length and used those to mount the motor. Now wouldn't you know, the shaft adapter broke while mounting the prop. While I wait for a replacement I have to figure out where to mount this massive 6s battery.
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Old 01-09-2013, 12:47 AM   #21
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This will be a good one to follow as my dad is starting to fix up an old Nitro 76" wingspan J3.
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Old 01-09-2013, 01:03 AM   #22
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Originally Posted by CHSNative View Post
Well, the motor mount ended up being too big for what I needed. So, I was able to drill out 4 dowel rods cut to length and used those to mount the motor. Now wouldn't you know, the shaft adapter broke while mounting the prop. While I wait for a replacement I have to figure out where to mount this massive 6s battery.
The shaft adapter broke

Would that be the propeller adapter for the motor shaft?

(My Hacker A60 motors use an 8 mm hard steel shaft that is threaded at the propeller end. That prop is going to bust first before hurting that shaft.)

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Old 01-09-2013, 01:09 AM   #23
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Yes, it is a 6mm shaft prop adapter. The collet ends where it tightens around the shaft broke off.
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Old 01-09-2013, 01:26 AM   #24
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Originally Posted by CHSNative View Post
Yes, it is a 6mm shaft prop adapter. The collet ends where it tightens around the shaft broke off.
Interesting.

I've got three of this size $$$$ Hacker motors. Prop adapters have never been a problem. They are made of what looks to be stainless steel.
https://www.aero-model.com/8_69_899/...-12S%20V2.html

The prop can be mounted to either end of this type of motor. Adapters for both front and back mount are included.

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Old 01-09-2013, 01:30 AM   #25
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batteries may need to stay far forward to get cg,possible location is using the bevel balsa bottom just under the firewall and add a hatchthere. since the fuel tank is removed thats the space you have to work with and i build boxs to slide the battery in and secure in place. or remove the wing to locate battery forward but that would make changing batteries a pain.


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