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Old Oct 11, 2013, 07:34 PM
joe_crash's Avatar
United States, MD, Gaithersburg
Joined Oct 2010
488 Posts
10lbs sugar in a 5lb sack?

Hello -
I'm fairly new to building - I've built a few ARFs, 2 kits (short kits) and a few scratch foamies.
I got this 2m sailplane from R2 hobbies, for a very decent price - under $100, with flaps and ailerons, (built up) and a fairly nice for the price fiberglass fuse. I was going to power it with a Hacker A20, but there is only one way to mount that motor, and it's with the 3 wires coming out on the firewall side.
My problem is it won't fit! The end of my fuse is 30mm, while the Hacker, taking into account, is 35mm.
Should I take the fairly drastic (for me - I know it wouldn't even be a speedbump for most of you guys) step of cutting it back from the fuse end by a few mm? I don't have any other motors, excepting one, that will fit, and it's from a heli, with a Kv of 3500 - which I think would be way too much turning an 11" prop (or even an 8") without high current draw. I've thought of planetary gearboxes, but haven't seemed to be able to find one.

Any advise you can give me would be very much appreciated!

(even if I bend the 3 wires to the max it's 32mm, and the wires would be against the motor housing, and I think that would burn through them in a very short amount of time.)
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Last edited by joe_crash; Jan 13, 2015 at 09:49 PM.
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Old Oct 11, 2013, 08:13 PM
Registered User
United States, MA, Waltham
Joined Dec 2001
7,137 Posts
Does the motor sit behind the firewall with the prop shaft coming through?

Check the balance by taping all the components on the fuselage at the same distance from c.g. that they would be installed at. If it looks like you wouldn't need much additional weight on the nose, you might consider cutting the nose back a little. You'd need a larger spinner to match. If the balance is right, you're better off with a shorter nose anyway.

BP Hobbies carries some planetary gears.

You could also just make a little streamlined blister for the wires.

Turning the motor around is a possibility, if it makes things easier and doesn't mess up the c.g.

Brushless motors are pretty cheap and you might try that too.

Depending on the climb you need, you could consider a 7 or even 6 inch prop. THe original Allegro Lite climbed ok with a brushed ferrite speed 400 (!) and a Graupner 6 inch folder (modified slightly). Not fast enough for ALES, but fast enough to have fun. Maybe it would take a minute or two to get to 200 meters instead of 30 seconds.
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Old Oct 12, 2013, 01:53 AM
If it flies - I want one!
Petem's Avatar
Werribee, Victoria, Australia
Joined Jul 2008
1,131 Posts
Wires out and back?

The simplest way (if the body of the motor will fit) is to bring the wires out through a new hole just behind the firewall, then back in to the fuselage a little further back - might finish up being a longish slot rather than two holes.
As Lincoln suggested, you could turn that into a blister fairing for cosmetics if required.
Wires and plugs are the curse of electronic installations - everything always looks as if it will fit until it comes to stuffing the wires and plugs into the available space!
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Old Oct 13, 2013, 12:07 PM
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Canada, BC, Kelowna
Joined Aug 2010
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I have extended the shaft by about 1cm to overcome this problem. I replace the shaft with a longer one and the "wheel collar" that comes with the motor makes a superior replacement for that wimpy ( and now bent out of shape) circlip. This method does not give a lot of extra room but it does help a little. The only advantage I can see vs. cutting the nose and using a bigger spinner is a bit better streamlining and maintaining the original profile. The Motor mass is moved back just as far so CG considerations are similar.
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Old Oct 13, 2013, 04:30 PM
joe_crash's Avatar
United States, MD, Gaithersburg
Joined Oct 2010
488 Posts
Hey, thanks everyone for the great suggestions! I'm definitely not going to cut the nose shorter - I'm not that great a builder, and that sounds like the best way to make the fuse worse - I like the suggestion about the blisters covering a slot for the wires, that doesn't sound too bad, and I've even got something I think would work from a different project. What I think I'm going to try first though is finding a 380 e-flight and putting some 6 inch props on the spinner - I even have them, so I won't have to buy anything new. I was disappointed that the Hacker won't fit w/o changing the fuse - but oh well - and I'm not a competitive flyer at any rate, so getting to 200m in 30 seconds sounds pretty fast to me, lol.
Thanks again everyone.
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Old Oct 13, 2013, 10:54 PM
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Joensuu, Finland
Joined Mar 2002
1,609 Posts
+1 on running the wires outside of the fuselage. If you need cooling air, the blister could do double duty as an air intake scoop. I know, draggy. But if you need the air, it will be draggy anyways.
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Old Oct 13, 2013, 11:01 PM
Silly n00b
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United States, NC, Charlotte
Joined Sep 2011
815 Posts
The Turnigy GliderDrive motors have the bullets on the rear of the motor. Makes for an elegant solution to a narrow nose.

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Old Oct 16, 2013, 03:27 PM
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United States, CA, San Jose
Joined Mar 2012
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I've been wondering how you were progressing on your build. You were right when you said it would take a long time!
For what it's worth, in my Passer (almost the same) I regret not putting the servos all the way to the front/bateery behind it, as the 850ma battery is too heavy and too far forward...but that may not even be an issue for yours (or too late). My buddy got the same plane as you, but hasn't touched it yet, so I've yet to see it.

I'm unfamiliar with the Hacker motor, but I had to take the motor apart a bit to flip the shaft around so that it mounts inside the fuse with only the shaft sticking out/wires out the back.
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Old Oct 17, 2013, 06:50 PM
joe_crash's Avatar
United States, MD, Gaithersburg
Joined Oct 2010
488 Posts
it's been a while!

When I said it was going to take a while, I didn't think it would be this long!! I got side tracked with multi rotor/quad/ stuff - I would have finished this plane ages ago if it weren't for that. I'm dividing my attention between the 2 now - I got tired of seeing the nice blue glass fuse leaning in the corner, and am slowly getting it together.

I normally just flip the shaft also - but on this motor, that won't work; it only has mounting holes on the one side. I actually did manage to stuff that Hacker in - I haven't powered it up yet to test whether or not the wires are going to rub on the spinning case of the motor, but it looks as though it will just barely clear it. If that doesn't work, I have a Keda short shaft motor which is described as a Hacker 20 clone, but with slightly different dimensions - it may even fit better. If the Hacker's wires rub, I'll try the Keda, if that doesn't work, then I'll get out the dremel and start cutting (something I'm always leery of doing - it's so easy to remove material, but so damn hard to put it back!)

I still think it's a bargain at just under $100 - the wings are built up balsa, and they are really nicely done; I've bought planes in the past that costed a lot more, and had worse finishes. Thanks for the tip on the servos - I have them zip tied in to the servo tray the way it came, so if it doesn't balance right I can easily move them forward. I need to figure out where the COG is on this; the kit was pretty complete as far as hardware, but zero documentation.

Hopefully I'll get this in the air sooner than later, and when it does happen, I'm going to definitely post my 1st video of the maiden flight!
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