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Curare - install electric system

Old 03-09-2013, 08:35 PM
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solentlife
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Default Curare - install electric system

64" span pattern aerobatics classic of Prettner ... made for 61 Glow power.

Attached plans ... my proposal is balsa / foam sandwich construction with electric power ...

Based on Hobby King gear ... suggestions of motor / prop / ESC / battery combo please ?

I'm hoping that I can keep in a 3S LiPo, 11 x 7 or 12 x 6 prop arena...

Nigel
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mk_curare.pdf (1.47 MB, 466 views)
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Old 03-09-2013, 09:59 PM
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So far looking at :

http://www.hobbyking.com/hobbyking/s...0KV_1295W.html

and

http://www.hobbyking.com/hobbyking/s..._60_Glow_.html

The 42-48 appears to be best as prop size is better suited ...

But LiPo - that needs to up to a decent 4S or best at 5S it seems. Luckily I have a couple of 5S 3000's - so that's not a problem.

Will have to have a look at weights ... see what differences I get.

Original :

61 Glow motor
Tuned Pipe
350ml fuel tank
4.8v Rx pack

replaced by :

BL motor
70A ESC
5A BEC
5S 3000 LiPo

Nigel
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Old 03-09-2013, 10:26 PM
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kyleservicetech
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Originally Posted by solentlife View Post
So far looking at :

http://www.hobbyking.com/hobbyking/s...0KV_1295W.html

and

http://www.hobbyking.com/hobbyking/s..._60_Glow_.html

The 42-48 appears to be best as prop size is better suited ...

But LiPo - that needs to up to a decent 4S or best at 5S it seems. Luckily I have a couple of 5S 3000's - so that's not a problem.

Will have to have a look at weights ... see what differences I get.

Original :

61 Glow motor
Tuned Pipe
350ml fuel tank
4.8v Rx pack

replaced by :

BL motor
70A ESC
5A BEC
5S 3000 LiPo

Nigel
As others have indicated, for real good performance, you'd want about 150 watts per pound of airplane. That put's the motor and battery in the 5 or 6 cell LiPo range.

Per www.motocalc.com, these Turnigy motors have pretty decent efficiency ratings, on the order of the high 80% range.

I'd go for the G60 motor, but that requires 6S or 7S Lipos.
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Old 03-09-2013, 11:14 PM
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rcers
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You will need 6s unless you can get it a good deal lighter than glow. Forget the HK ratings they are bunk but if you take a 3w/g that is about max. For larger stuff like this I really think spending a bit more on a Hacker, Scorpion/Hyperon are worth it. Those motors are a more efficient and you can likely get 4w/g out of those pretty safely.

But they are real money - no question. I think the second motor you show is likely in the power range needed around 1,000 watts. Can you keep it at 6 lbs (2.7kg) or so?

Mike
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Old 03-10-2013, 12:05 AM
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kyleservicetech
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Originally Posted by rcers View Post
You will need 6s unless you can get it a good deal lighter than glow. Forget the HK ratings they are bunk but if you take a 3w/g that is about max. For larger stuff like this I really think spending a bit more on a Hacker, Scorpion/Hyperon are worth it. Those motors are a more efficient and you can likely get 4w/g out of those pretty safely.

But they are real money - no question. I think the second motor you show is likely in the power range needed around 1,000 watts. Can you keep it at 6 lbs (2.7kg) or so?

Mike
From personal experience with my 8 Hacker motors, you really can't go wrong with them.

Here is a lot of reading info on models of this size:

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

Hangar 9 Kantana Model
http://www.wattflyer.com/forums/showthread.php?t=68844

AEAJR's Site on Electric Power
http://www.wattflyer.com/forums/showthread.php?t=18521
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Old 03-10-2013, 10:24 AM
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mmmmmmmmmmm 6S ... somthing I'm trying to avoid if possible.

I may even scale down the Curare a few % to suit better the 5S ...

I also have the Mini Curare20 plans ... which a 38xx motor would fly well.

The problem is really budget ..... I have so many projects on the go that costs are governing ...

I'm not intending to enter Pattern comps - just fancy having one again ... as a sport / fun machine - they do surprisingly well. So scaling up or down won't hurt at all.

The other option of course (RCGroups fuel section is on that ...) is to scale up a touch and fit my RCGF 15CC gasoline engine ... that's still in its box on the shelf.

Nigel
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Old 03-10-2013, 07:24 PM
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Look up the AXi 4120-18. on 6S it will pull about 45-50 amps with the correct prop.

Don't pick the motor by trying to match the glow power prop size it will be wrong for electric. You may need to go to a 3-blade for ground clearance.

I used a 4120/18 in a "60-90" size pattern ship with good results. I plan to put that power system into a King Kobra.

Use 2X 3S packs in series. You can then use the 3S for other planes too. I commonly fly planes that call for 3S 2200 mah with 3S 5000 mah packs. Just makes tjhem handle wind a little better :p

***************

Note: I have had very bad results with Turnigy motors... they get up to about 140F and the magnets come unglued.
Very bad when using a 5000 watt power system and a 22 inch prop

The AXi is fine at 150F
The E-Flite power 160 (same KV, same size, same weight) has no trouble with the same prop, esc and batteries as what destroyed the Turnigy motors.
You do get what you pay for...
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Old 03-11-2013, 01:27 AM
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Originally Posted by fhhuber View Post
Look up the AXi 4120-18. on 6S it will pull about 45-50 amps with the correct prop.

Don't pick the motor by trying to match the glow power prop size it will be wrong for electric. You may need to go to a 3-blade for ground clearance.

I used a 4120/18 in a "60-90" size pattern ship with good results. I plan to put that power system into a King Kobra.

Use 2X 3S packs in series. You can then use the 3S for other planes too. I commonly fly planes that call for 3S 2200 mah with 3S 5000 mah packs. Just makes tjhem handle wind a little better :p

***************

Note: I have had very bad results with Turnigy motors... they get up to about 140F and the magnets come unglued.
Very bad when using a 5000 watt power system and a 22 inch prop

The AXi is fine at 150F
The E-Flite power 160 (same KV, same size, same weight) has no trouble with the same prop, esc and batteries as what destroyed the Turnigy motors.
You do get what you pay for...
IMHO, when your motors get into the multi-thousand watt range, you've really got to watch the motor's efficiency ratings. A program such as www.motocalc.com will give approximate info on this. The quality motors in this power range are running around 90% efficiency. Even so, with a 5000 watt motor, that is 500 watts of power lost in the motor itself. No matter what motor you are using, that motor had better have a lot of cooling air.

My opinion, especially with these larger motors, is, if the supplier does not furnish their motors winding resistance, go look elsewhere for a motor supplier. The winding resistance is critical with regards to motor efficiency, and it is quite easy to measure. (http://www.wattflyer.com/forums/showthread.php?t=50740)

A fairly safe rule on these larger motors is to run them at no more than 100 watts per ounce of motor weight. That would put the 5000 watt motor at around 50 ounces. Any mfg'r that claims 5000 watts with a motor that weighs 30 ounces is likely to have problems if the user actually runs their motor at the specified power level.
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Old 03-11-2013, 02:38 AM
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Getting kind of sidetracked... but the E-Flite motor is hitting the same temp as the Turnigy did. (Eagletree V3) The thing that killed the Turnigys was inferior glue... apparently they put the magnets in with low temp "hot melt glue" and the E-Flite used high temp epoxy.

What should be the critical factor for temperature is the magnets. Rare Earth magnets start to be degraded about 180 F. The insulation comes next somewhere above 220F (if they use good stuff) The 140 to 150 my setup gets to should be just fine if the motor is made right.
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Old 03-11-2013, 11:15 AM
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Why would I need a 5000Watt motor for this ?? C'mon guys ... back to the reality of the Curare.

This baby will fly on significantly less than that ... in fact a fraction of it !

Nigel
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Old 03-11-2013, 05:33 PM
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What was meant as a note about quality of Turnigy motors got sidetracked..

I just don't like motors held together with a glue that melts long before anything else in the motor will be affected by the heat. They saved less than $0.01 per motor by using cheap glue and it makes the motors unreliable.

The Axi 4120-18 is about equal to a .70 glow engine in power. Swings a considerably bigger prop though, thus the note about potentially needing to go 3-blade for ground clearance.
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Old 03-11-2013, 09:17 PM
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Originally Posted by fhhuber View Post

The Axi 4120-18 is about equal to a .70 glow engine in power. Swings a considerably bigger prop though, thus the note about potentially needing to go 3-blade for ground clearance.

Good point.
For the newbies, these electric motors, especially the higher powered units swing a much bigger diameter prop than the equivalent horsepower glow engines.

As an example, my Hacker A50-12S motor is similar or perhaps a little more powerful than a 70 size glow four stroker. But the A50 easily swings a 16X8 prop at 7500 RPM on the ground and 8000 RPM in the air, all while running on a 6S2P A123 battery pack.
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Old 03-11-2013, 09:26 PM
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Larger props turning lower rpm are more efficient.
The higher the multiple of airspeed your prop tip speed is, the more power you are just wasting. (especially if the prop tip is approaching Mach 1)

Full scale aircraft use reduction gearing to convert the engine RPM to something more appropriate for the prop.

We can tune the e-power systems far better than any glow or gasoline power system to get the most useful thrust for the lowest energy input. I like to call my E-flite Power-32 a 32 that thinks its a 46. It has that much useful thrust.
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Old 03-11-2013, 10:17 PM
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Originally Posted by fhhuber View Post
Full scale aircraft use reduction gearing to convert the engine RPM to something more appropriate for the prop.
Some do - some don't. All the jet turbine powered stuff obviously does, but many of old school general aviation piston aircraft are direct drive.

Most of the WW2 piston aircraft did use a transmission for shaft reduction so, as you point out, spin much larger propellers or multiple blade props more slowly and efficiently.

Our electrics are MUCH better at turning slower but we still spin stuff much faster than our full scale counterparts do.

Mike
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Old 03-12-2013, 12:48 AM
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Originally Posted by fhhuber View Post
Larger props turning lower rpm are more efficient.
The higher the multiple of airspeed your prop tip speed is, the more power you are just wasting. (especially if the prop tip is approaching Mach 1)

Full scale aircraft use reduction gearing to convert the engine RPM to something more appropriate for the prop.

We can tune the e-power systems far better than any glow or gasoline power system to get the most useful thrust for the lowest energy input. I like to call my E-flite Power-32 a 32 that thinks its a 46. It has that much useful thrust.
Nice thing about some motors such as the Hacker line that come in a wide variety of different "Winds" for the same motor frame. This allows the user to select a big diameter slow turning prop, or a smaller diameter fast turning prop while using the same motor frame size.
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Old 03-12-2013, 04:11 PM
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I have Turnigy and other Ebay motors that have survived all sorts of mistreatment by me. The worst treatment is my Need for Speed where I'm pushing heli motors way past specs ...

I have only 2 motors that have failed because of over-powering ........ and both are same Inrunner 4890kv motors ... the end bearing retaining ring on the shaft fell apart ! But they were turning 2x recc'd rpm in an EDF.

My 2830's ... 38xx's .... EDF's etc etc. all performing magnificently. In fact I've only had one motor throw magnet .. and that was a Westor High power 3700kv Heli motor. Replaced with Turnigy that has outlasted the Westor... at less than half the price.

I'm not posting against better motors ... just remarking that so far my motors have all performed well - that includes RCTimer's.

Nigel
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