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Old Aug 27, 2013, 03:52 AM
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6ft wingspan piper cub glow to electric help

Hi,
I recently purchased a 6ft wingspan piper cub it's quite old and nitro, it's balsa. I'm looking to convert it to electric however I haven't done anything like this before and so would appreciate a little help/advice on what battery and motors to use I would also like to not spend more than £50-75 if possible. This is also my first post so apologies if its not detailed enough.

Thanks,
Jeorgie
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Old Aug 27, 2013, 07:57 AM
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£50-75 just brought a battery and some connectors i would think about it a bit more , a motor for something that big would be expensive.But i am sure someone can help you with it on hear they been doing for me.And very good advise too.

you would need: charger ,battery's , connectors, speed controller, electric motor

,if you don,t already own them.
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Old Aug 27, 2013, 01:29 PM
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Thanks, I've got a 9.6v 1500mah ni-mh battery but I don't think it's big enough and as for motors I was thinking brushless, I've got props/mounts etc but not a brushless speed controller, don't most brushless come with a speed controller anyway? Thanks for the advice ill have to do a bit of research on it

Jeorgie
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Old Aug 28, 2013, 09:06 AM
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Hi J, any idea what size nitro engine it had in it? I have a great planes decathlon with almost the same wingspan, and it has a turnigy 50-55 600kv motor running a 14x10 apc prop and a 4S 4000mah lipo. It has bags of power. I expect your cub would work well with a similar setup, or even something a bit lighter.
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Old Aug 28, 2013, 12:22 PM
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Thanks, not sure as to the engine size because it was far from new when I got it, is it printed somewhere on it or anything. Thanks for the info will deffo look into it, what sort of flight times do you get on average??
Thanks,
Jeorgie
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Old Aug 28, 2013, 03:59 PM
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What is the expected flying weight of the plane?
If the glow engine is still in it, just weigh it as is. The conversions I've done come out just a hair lighter than the original nitro powered version.

Physical size isn't important - it's the weight and desired flying style that you have to look at when figuring out an electric system. With a 6' span on glow (nitro), the plane probably flew on a .46 or .60, but could have been just as easily been powered with a .60 to .90.

Don't use the 9.6 volt battery. It's too small for this application and won't deliver the power you want. You'll be looking at Li-poly batteries and brushless motors.

I've built systems for a number of glow to electric conversions (including a 6' Telemaster, 6' Spitfire, and a 7 pound Great Planes F-14) and the best way I've found is to start with a "battery-first" method that makes sure you get an efficient running and sufficient powered system with enough flight time to not damage your batteries.

It's a faily simple 4-step calculation, but it all starts with the weight and desired flying style.
Let us know so we can help.
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Old Aug 28, 2013, 04:13 PM
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The size of nitro engines is "normally" on the lower side of the engine - one side or the other, just above the mounting flange.

The attached picture isn't the best - but you can make out "25" on the side.
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Old Aug 29, 2013, 10:03 AM
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On the side of the engine it says 40, and as for flying style I would like it to be quite docile and forgiving because I'm still a of a noob and have only flown 2ch and 3ch. Will I need a fast charger or anything for the battery? Should i weigh it as it is with the glow engine still attached??
Really appreciate the help, but am still sitting on the fence at whether to convert or not.
Thanks,
Jeorgie
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Old Aug 29, 2013, 10:17 AM
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If this is your first experience with Li-poly batteries and electric power - it can be a bit overwhelming, but we (I'm by no way THE expert, so keep reading and getting other opinions) can help you through it.

I grew up using glow engines, but am finding electric to be more relaxing to go fly as once you have the system figured out, there's very little to do other than connect the battery and enjoy flying. Less tinkering and mess, but I still enjoy some of that as well.

I've gotten into combat, and in our rounds we have 1.5 minutes to start the engines and get in the air before we lose points. With electric, I find myself waiting at the flight line for @1 minute and finally launching in the last 20-30 seconds while the glow guys are still fiddling with getting started and finding the right needle valve setting. Gravitating more towards electirc all the time.

Weigh the plane as is, with the glow/nitro engine in place.
Most all of my glow to electricconversions have come out a little lighter than the glow powered versions, so the "as is" weight is best to go by.

I usually shoot for 100watts/pound, but with a Cub, you can go lower, or you might find yourself cruising around at 1/2 to 2/3 throttle - but that will only extend your flight time. The calculations I use provides an efficent system while giving you the minimum, full-throttle, flight time without damaging your battery. So far it been a good way to get a sufficient system that you aren't immediately looking to upgrade if you want to do a little "hot-dogging".

I personally charge all my Li-poly batteries at 1C (a 2,000mah pack charges at 2amps) and decent balancing chargers can be found pretty cheap. But you can always find ways to spend as much as you want.
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Old Aug 29, 2013, 12:56 PM
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Just weighed it and It weighs 2332g approx with receiver two servos and speed controller installed. Is there anything else I need to measure??
Thanks,
Jeorgie
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Old Aug 29, 2013, 05:24 PM
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I started running numbers and find that you’re in a good situation option wise; however this presents another set of issues to consider.
The numbers indicate we can build a good power system using a number of battery options. Remember that I’m using a “battery-first” method of selecting parts, so that’s the first thing to consider.

2332 grams = 82.259 ounces = 5.14 pounds

If we shoot for 100-watts/pound, that = 514 watts

At 514 watts… looking at common battery configurations
A 3-cell battery will pull 46.3 amps for a voltage/current ratio of 4.17:1 (an ok ratio)
A 4-cell battery will pull 34.7 amps for a V/C ratio of 2.35:1 (a better ratio)
A 6-cell battery will pull 23.1 amps for a V/C ratio of 1.04:1 (the best of the three)

So…
if you choose to go 3S, you’ll need a 50-60amp (minimum) ESC rated for 11.1 volts.
If you choose to go 4S, you’ll need a 40-50amp (minimum) ESC rated for 14.8 volts.
If you choose to go 6S, you’ll need a 25-30amp (minimum) ESC rated for 22.2 volts.

As for the actual battery size or capacity, it will depend on how long you want your flights to last.
Remember that we don’t want to use more than 80% battery capacity, so as to not damage the battery by draining it too low.

On 3S,
A 2,000mAh battery @46amps will yield a minimum flight time of 2.08 minutes.
A 3,200mAh battery @46amps will yield a minimum flight time of 3.3 minutes,
A 4,000mAh battery @46 amps will yield a minimum flight time of 4.17 minutes,
A 5,000mAh battery @46 amps will yield a minimum flight time of 5.21 minutes.

Remember that these are minimum flight times, or the maximum time you can fly at FULL POWER without damaging the battery packs. Any amount of flight time at lower throttle settings will extend your flight time, but that’s where real-world use and testing will show you what a good time is depending on your “normal” flying style and consumption.

With a Cub on a system as outlines above, you’ll likely be cruising around on ½ to 2/3 power, and can nearly double the above times.

Looking at the 6S system…
A 2,000mAh battery system will have a minimum safe flying time of 4.15 minutes
A 3,200mAh battery will yield 6.6 minutes
A 3,600mAh battery will yield 7.4 minutes
A 4,000mAh battery will yield 8.3 minutes
A 5,000mAh battery will yield 10.3 minutes.

Personally, I’ve avoided going with 4-cell batteries, just for the fact that I can use single 3-cell batteries in smaller planes, or parallel two together for 6S power in bigger/heavier planes.
Clear as mud?
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Old Aug 30, 2013, 03:55 AM
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Right think I've got it, so the best option would be two 3s lipos at 2500mAh each to get a 5,000 mAh. And this would need a 25-30 amp esc rated for 22.2volts But is that going to be the most expensive aswel.
Thanks
Jeorgie
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Old Aug 30, 2013, 09:05 AM
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Two 3S (11.1v) 2500mAh packs in series = 6S (22.2v) 2500mAh
Only the voltage doubles for 6S equivalent power

Two 3S (11.1v) packs in parallel = 3S (11.1v) power 5,000mAh capacity.
Only the capacity doubles

http://www.zbattery.com/Connecting-B...es-or-Parallel

I would try to think into the future, towards what other size planes you are likely to want to fly. On one of my bigger planes, I jumped up to 6S power as it's more efficient, use two 3S 4,000mAh batteries together to get to 6S, and now use the individual 3S 4,000mAh batteries, one at a time, in some smaller planes. I've avoided avoided going to 4S packs as I didn't want to have batteries sitting around just for use in one airplane that might not get flown too often, but if you're likely to have a number of planes to use 4S on, you can do the same thing to get to 8S, but the larger components do cost more individually.

If it were me, and based on the numbers and my personal experience, I'd go with the two 3-cell 4,000mAh packs, and be fairly confident in a 8-10 minute flight time with mixed throttle use. But again I have other planes that will take this battery. If you have (or will have) planes that can use 3S 5,000 packs, you can put two in parallel for 10,000mAh, still get good flight time and possibly buy lower priced components.
Lots of options to explore.
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Old Aug 30, 2013, 11:19 AM
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Will two 3s 2,200mAh lipos be ok for an alright flight time because I'm sort of on a budget, as for future planes I would like a balsa kit cessna 182, power wise i think it would need just one 3s 2,200 mAh pack. I can also save up a bit and buy two more lipos and run one set whilst charging the other. Or even all four together to get 8,800mAh (if that's possible)
Thanks again,
Jeorgie
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Old Aug 30, 2013, 11:28 AM
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Quote:
Originally Posted by J.trickett98 View Post
Or even all four together to get 8,800mAh (if that's possible)
It's certainly possible.

The sky's the limit, but most of us are limited by the budget.
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