Dec 12, 2012, 09:26 PM
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Aeroplayin's Avatar
That looks like a better option. AV8TOR...

And that makes more sense, Bryan. Thanks.
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Dec 12, 2012, 09:38 PM
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Ohio AV8TOR's Avatar
Originally Posted by Aeroplayin View Post

Also, you don't need an external U-BEC for this setup IMO for two reasons. First, you are creating another failure point, and second, no one I know has yet to have an issue with running the 2S lipo right into the Rx, unregulated.
Funny you mentioned this as tonight I soldered up a female JST connector to a short Futaba servo extension to do just that. It seemed like a nice simple way to do this.
Dec 12, 2012, 09:59 PM
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Aeroplayin's Avatar
The batteries I have for the AR7000 Rx has two standard Rx connectors for JR and Futaba, and a balance tap... $15 for a 2100mAh at only 3.5 oz.
Dec 13, 2012, 03:20 AM
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Hey guys,

So i'm looking to pick up a EF 78" extra in the new year and i've got a Motrolfly 5320 here that I burnt up the stator on (due to my poor KV selection, live and learn), so i've got a new stator coming I just need to pick a KV wind to go with. From what i've seen a 10s setup is probably most ideal and I currently use 10s 4500mah Zippy compact packs (2x 5s in series) in another model so it would avoid having to buy more packs if I stick with 10s. Problem I'm now faced with is picking the prop and hence KV to go with, 20" seems to be the most popular choice but i've seen a few guys running 22" props. My thought process would be to go with 220kv-230kv for a 20" prop and about 190kv-200kv for 22" prop use. So what's the consensus guys 20" or 22"?

As for flying style i'm probably more a sport to 3D ish flyer, I typically don't do real low and slow stuff my skill and nerves aren't really up to it, lol. I generally stick to hovering, harriers, snaps, tumbles, and general sport aerobatics. So the ability to handle higher throttle settings for longer may be more suited to my style.
Dec 13, 2012, 03:40 AM
Registered User
I've also got a Torque F3A Silver Bullet here, but I was going to put that into the model the Motrolfly came out of, since getting a new stator was going to take a month or so, so was just going to use the Torque instead and save the motrolfly for the Extra.
Dec 13, 2012, 04:40 AM
bryansifsof44's Avatar
There is a gentleman that is running a 20x10 wood prop on a 5320-230kv... Although ken doesn't recommend anything bigger then a 19" prop on 8s and a 20" prop on 6s. The 4330 will handle a 22x10 prop on 8s to 2700 watts with a 255kv. Which works out to about 205kv on 10s to spin the prop the same RPM.
Dec 13, 2012, 08:09 AM
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Aeroplayin's Avatar
The 78 is a superb airplane and IMO, anyone who understands how great EF planes are should have one eventually. It has a 76 inch fuse so it presents like a 50cc airplane, but it still fits in my SUV with the stabs on. We all know that Donatas Pauzuolis flew the plane on 6S in order to keep the weight under the FAI restrictions, so it can do a lot within a wide envelop of power systems. With that said, I am also a big fan of Motrolfly and bought seven of their motors, and have nothing but great results as far as power, efficiency, and endurance.

Considering all of this, every one of us has to make a decision on how they want to fly any of their individual planes. We are all different, but what we do have in common is the fact that we eventually set up the planes we have to the power systems we like. If I look at the planes I set up for myself and for my son, who is far more advanced than I am, the common denominator is a propeller that is 27 to 29 percent of the wingspan to obtain as much torque throughout the full throttle range, a 240 to 280 Watts per pound power-to-weight ratio in order to achieve a high level of momentum quickly, and for all but one IMAC airplane, a wing loading under 27 so the wings continue to fly at low alpha and lower speeds when we want them to.

For this reason, we use a 14x7 prop to 850W on a 48 with a DM2820-683, a 16x8 to 1500W on the 60 Edge with a DM4315-480, and a 22x10 to 3700W on the 78 with a Hacker A60-16M.

According to the Subsonic motor page, the 5320 is a 6 or 8 cell motor at the 330 to 300 Kv wind (22x10 on 6S and 20x10 on 8S) and limits to 2800 Watts. Doing the math, 6S on a 330Kv with a 22x10 at 6020 RPMs means 2540 Watts and 111 Amps at 3.8v per cell. This is about 196 Watts per pound and a 4 minute flight time using the throttle conservatively.

8S on a 300Kv with a 20x10 at 7750 RPMs means 3080 Watts and 100 Amps at 3.8v per cell. This is about 235 Watts per pound and a little over 5 minutes flight time using the same 40% average throttle setting with a 4400mAh setup.

If 2800 to 3000 Watts and 110 Amps is the power limit for this motor, and a 20 inch prop to 7750 RPMs and a 22 inch prop to 6020 RPMs is an acceptable angular momentum (precession), then the 10 cell options are limited to no more than a 20x8 prop on a 250 wind, which would produce 2800 Watts and 74 Amps at 7600 RPMs. I’m not sure if a 250 wind is realistic, but at 255Kv, you would get around 2960 Watts and 78A at 7750 RPMs at 3.8v per cell, if this voltage can be maintained. This is also about 6.5 minutes of flight time at the same throttle settings, and almost 230 Watts per pound.

Realistically, you may get a bigger voltage sag and on the low side, it will deliver 2625 Watts and 72A at 7445 RPMs. This is back to 200 Watts per pound.

I did go with the Hacker A60-16M on Tom's plane because it generates 3700 Watts on a 22x10 prop on 10S and flies for an easy 6 minutes.
Dec 13, 2012, 10:23 AM
bryansifsof44's Avatar
Those are good numbers for the hacker... What is the all up weight? What is the cost?
Dec 13, 2012, 12:08 PM
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Aeroplayin's Avatar
Here's the weigh breakdown...

The 78 with all hardware out of the box, but with the CF LG, was 106.4 oz, or 3014g.

The motor was 27.68 oz all soldered up, the A60-MM mount is 4.96oz, the Castle HV120 is 6.24 oz, the Rx, Rx battery, and one Rx switch is 4.64 oz, the 5x Savox SC-1267SG servos, all the servo hardware, extensions and connector clips comes to 14.08 oz, the Mejzlik 22x10E is 3.52 oz and the CF Lite spinner with hardware is 1.76 oz.

Total weight is 213.44 oz or 6046g. That's 13 pounds 5.44 oz.

You can find the prices here...

Motor Mount:

Considering the stuff I had in the parts draw, and some coupons from Castle, it cost me about $1,310 to put the plane in the air. You can also use a 22x10 Xoar PJN instead... $25.16:
Dec 13, 2012, 12:16 PM
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Aeroplayin's Avatar
A side note to the A60-MM... IMO, it will need some minor reinforcement with the 22x10 on 10S because the precession is 1.88 Kg-m2. A simple aluminum strap to reinforce the starboard side before bolting it together should do it.
Dec 14, 2012, 01:38 AM
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Well I previously had a 260KV wind on 10s spinning a 20x10 xoar and burnt the motor up after 5 flights. I was pushing around 3500w, which as it turns out was just too much. I've been looking around and a few guys are doing 2700w on 10s with a 230kv wind spinning a 20x10 prop. So I think i'll go with a 220-230kv wind and just play around with prop sizes till I get something I'm happy with. I guess i'm confident the motor will fly it with authority, it may not be quite as insane as your 3700w setup, but should fall within the EF recommended range.
Dec 14, 2012, 08:55 AM
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Aeroplayin's Avatar
One of the main issues with motors and big props is the fact that the faster they spin, the more precession is produced. This force at 90 degrees to the shaft line can get so high as to pull the rotor to the point where the magnets impact the stator. The A60-MM cage mount has a rear bearing, and the motor has large concentric bearings, so that the shaft is held in place better than most motors, or motor setups I've seen.

Motrolfly and Hacker (Q series and V2 in the A series) have also made some design changes that reducing the length of the motor and beefs up these bearing so that the shaft radius is reduced. This makes impact less probable as the shaft torques the same distance. It's simple geometry, actually, but a great solution.

The other thing is that there are few motors out there built to spin a 20x10 Xoar to 3500 Watts-in because you need to spin that prop to 7600 RPM to get there. The 22x10 only needs to spin 6850 RPMs to get there using the same current of about 96 to 100 Amps. I used an HV 120A in the 78 setup because I like to leave a lot of headroom for the ESC.
Dec 15, 2012, 08:36 AM
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Aeroplayin's Avatar
I just saw this ad for 15% off Savox Servos through Jan 10th with coupon code 3DFLY...
Dec 15, 2012, 01:28 PM
stgdz's Avatar
Originally Posted by Aeroplayin View Post
I just saw this ad for 15% off Savox Servos through Jan 10th with coupon code 3DFLY...
oh what the heck, going with 3 257's and 2 255's. I all ready have a 257 so I can finally outfit my mxs and yak or laser with the digital servos.
Dec 15, 2012, 02:14 PM
It's gone...
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