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Old 08-21-2016, 08:24 PM   #1
Planedude
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.46 glow to electric need help


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I need some help,

I know probably nothing about electric engines except they run on electricity. I need some help with a setup or parts list and recommendation for batteries to use.

I would like to replace / build a .46 size glow equivalent with about a 15-20 min run time.

Suggestions?
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Old 08-21-2016, 09:17 PM   #2
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Re: .46 glow to electric need help

need more information such as actual aircraft you are switching, maximum space for the battery for starters. a good start also is to contact a local club member that runs electric aircraft successfully in your size. there is also the need to purchase a charger that is capable of charging lipos. The flying time that you need is possible but a little on the higher side requiring an efficient system. striving for up to 10 minutes might be more realistic
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Old 08-21-2016, 09:33 PM   #3
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Re: .46 glow to electric need help

A .46 two stroke has about 1.2 HP so with 746 watts = 1 HP you will need about a 800 watt motor to replace it. Unfortunately very few motor suppliers list watt ratings anymore so I use Maximum volts X Maximum amps to calculate it.

As for which kv rating to choose - low kv works best for trainers and scale planes and high kv ratings are more suited to faster airframes.

Filght times will depend totally on your style of flying. A 20 minute flight at full throttle will be a bit tough to achieve.

Hope this helps. Merv
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Old 08-22-2016, 07:31 AM   #4
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Re: .46 glow to electric need help

stegl is correct in that more info would help a lot. If you can give specs as to airframe, final weight and type of flying perhaps a better idea of what could get you to where you want to go.

For example, if you use OPRK's numbers you need to know a bit more math.

Along with the total Watts, (power) requirements you have to decide the type of battery, such as the number of cells. That determines some primary factors such as current limits.

Most common are made up of 3S-6S, meaning the first is made from 3 individual cells tied together in series with 6S obviously made from 6.

The 3S will have a nominal voltage of 11.5V, so for 800W you can expect to require in the mid 60 Amp range current feed. Your ESC that runs the motor will need to be at least that capable. I normally try to use 1.5X that so would be looking to install approx 100A.

As you increase the cell count your current needs for the same power drop, but you will be looking at increased battery weight and lower motor Kv to keep the prop speed most efficient. Just like getting a 2 stroke into the peak power band most brushless motors have a "Sweet Spot" RPM/V and lugging them down even a bit drops their efficiency quite a lot. The end result for you is that more of the battery supply turns into heat rather than work for you, with reductions in flight times and perhaps component reliability.

That does not mean you have to look at wildly overrating your power system components , but there are a few other concerns, the most important being cooling airflow. One final test is to check all the components immediately upon landing. If any are too hot to touch or the battery is ballooned you will need to look at more capable bits or better cooling.

Like a lot of this you will be looking at compromises. With nitro you don't see a huge increase in weight with cubes and power. Really the same with brushless motors.

However, this is not so true with the power source for either, especially if you look at capacity. Nitro tank size increase for either longer duration or feeding a powerplant of larger output will increase the weight proportionally. Same with batteries, although you do have some leeway in deciding there. A large capacity yet low output current battery will likely weigh much more than one with high output, yet low total capacity.

This is called "C-Rating" and is a calculation of current output based on total capacity. Think of it as a pail of water. A large hole, (or high C) will supply lots of water, but drain the pail that much quicker. One with lower C will not have as high a C rating, (or total power output) but will last longer and generally place less stress on the battery.

Again, you have compromises. Better cell chemistry and construction can give a much higher C rating for the same size and weight, but you can guarantee the cost will also be higher. Another factor is those batteries should last longer, (meaning number of cycles) than ones of lower quality that will be under more stress from internal resistance, etc.

So, to work with what's posted so far you could expect a total of 800W max power. At partial throttle you may still draw 5-600W. That works out to approx 45A, still a pretty healthy draw. If you look at your minimum 15min flight you would need a very large capacity battery, (getting close to 6000 MAh). That starts to add lots of weight so you have to up the wing area to lower the loading, etc.
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Old 08-22-2016, 08:47 PM   #5
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Re: .46 glow to electric need help

Personally I wouldn't bother with a 3 cell pack on that size plane. Go straight to 4 cell, smaller packs for the same duration.
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Old 08-22-2016, 10:14 PM   #6
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Re: .46 glow to electric need help

Thank you very much Cougar,

I'm in between building a trainer ( Pt-40) or the Goldberg eagle II. Both planes weight in at 5.5-6 lbs. Goldberg has a little better wingloading of around 15oz/sq". With the pT-40 at 18oz/sq".

Flight requirements would be to gently fly around the sky performing the most basic aerobatics while I relearn to fly.
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Old 08-23-2016, 06:06 AM   #7
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Re: .46 glow to electric need help

Invest in a watt meter. It will tell you everything you need to know about keeping all your components within their operating range. Then make sure you have a good selection of props to experiment with.

Taking the time to sort out what prop works best can make or break a project. This is true with any power system and more so with electric. I have seen far too many under performing planes that guys refuse to change props on because "the guy at the hobby store/buddy at the field" said this was the right size!

Maybe it is, maybe it aint...
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Old 08-23-2016, 08:18 AM   #8
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Re: .46 glow to electric need help

Quote:
Taking the time to sort out what prop works best can make or break a project.
How true. Had the same issue with an electric Catalina when I switched it to brushless and I find even Saito can be too aggressive in their prop recommendations.

I too would have recommended a higher cell count for the battery, but was using the 3S for comparisons. Should have stressed that 15-20 minutes MAY be achievable with a good airframe and very moderate power usage. However, think numbers under 10 would be more realistic.

Like anything else the learning curve can be steep at the beginning. With electrics you need to know the characteristics of different motor designs, their advantages and drawbacks, best one for the buck, the ins and outs of ESC selection, (onboard BEC, etc.) and the proper care and feeding of LiPo and LiFE batteries. Even servo selection can be intimidating now.

Like nitro the support equipment list can seem endless, with the recommended wattmeter and a good balance charger high in priority.

planedude, at the beginning I could achieve flights in excess of 20 minutes, (some well over a half hour) in my OS 40 powered Goldberg Eagle. However, it was getting a bit boring by then with not much learning going on with flights that long.

Currently I set my timer for approx 9 minutes regardless of craft and often land earlier.

Like full size the key seems to be to minimize the time between lessons, rather than their length, (with time to relax to absorb between). This means each reinforces the prior lesson, rather than try to relearn what may have been forgotten or grown rusty between sessions.
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Old 08-23-2016, 02:16 PM   #9
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Re: .46 glow to electric need help

http://www.hobbyking.com/hobbyking/s..._46_Glow_.html
The hobby King website is a good place to start in as much as finding combinations of motors, ESCs, props, and batts required for your particular case. You can go elsewhere to find your goodies but this will give you the combinations. By the way, their motors do work very well.
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Old 08-23-2016, 04:09 PM   #10
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Re: .46 glow to electric need help

Quote:
Originally Posted by Planedude View Post
Thank you very much Cougar,

I'm in between building a trainer ( Pt-40) or the Goldberg eagle II. Both planes weight in at 5.5-6 lbs. Goldberg has a little better wingloading of around 15oz/sq". With the pT-40 at 18oz/sq".

Flight requirements would be to gently fly around the sky performing the most basic aerobatics while I relearn to fly.
Dan,

If you want people to offer motor/battery/esc equipment suggestions for specific planes, consider adding the wing area of the plane as this is an essential piece of information needed for using electric plane performance programs such as Ecalc....

A response to previous query of yours recommended Ecalc to you and I very much agree... while you can get a very good understanding of how Ecalc works and its benefits by using its free demo version, the demo version only offers a limited inventory of motors to enter while the subscribed program - only $5 U.S. per year - has almost every motor made in that version.

Such a performance predictor program will give you a "practical" understanding of several key inputs in electric flight: the KV or motor constant specification of each motor, voltage input (the number of lipo cells, eg.3, 4,5, etc.), and propeller diameter and pitch. (As well as many flight performance and
"overload" condition warnings.)
Getting the relationship of these three inputs is an important part of understanding how electric motors typically have a more narrow performance range, even when you adjust the number of cells and prop diameter and pitch than glo/gas engines. For example its much more likely that you could use the typical .46 two stroke engine in a range of planes, from trainer, funfly/aerobatic and even in a pylon speedster just by varying prop diameter and pitch than in electric flight. So understanding this relationship is important in deciding bigger purchase items in electric flight such as motors and the size of battery packs in terms of cells.

I've bought probably 90% of my motors from other individual modelers either on this website or at swap meets, at significantly lower cost than retail, so knowing what a motor's specifications means for flight performance can allow you to react fast when a great used motor pops up for sale.

A good website for information on charging motor batteries and the range of connectors in use is http://www.tjinguytech.com/
I started with an used low power HobbyKing charger and power supply and it was fine and only later bought a more pricey iCharger that was able to provide instant readings on a battery pack's internal resistance, a specification which usefully tracks the declining performance of a lipo pack over the number of power cycles and shelf time.
There range of both main and balance connectors on the battery/esc and charger is frustrating; be prepared to buy adapters.

And do read up on safety issues with lipos; they are more extensive than with glo and gas engines.
Maintenance of lipos - storage voltages and to a lesser extent, temperature - affect longevity, not only the number of power cycles.

When I came back into rc after a break of two decades, and even though I had prior experience in early electrics that used brushed motors and on/off servo controlled motor switches, I found the learning curve for current electric flight to be steep. So be prepared to invest some learning time to gain the benefits and be safe.


good luck
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Last edited by michaely; 08-23-2016 at 04:25 PM.
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