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Old Jun 23, 2012, 09:44 AM
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Mark Anderson's Avatar
United States, WA, Tumwater
Joined May 2010
260 Posts
Mini-HowTo
My twist on electric Bird of Time

I decided to electrify my BOT, but did not like the look of the oval shaped fuse at the spinner. I came up with this method to make it match the spinner. First cut off the nose just forward of where it measured 40 mm wide. Then the nose weight was broken out with a screw driver and hammer, and The forward servo tray is removed. Mark the fuse across the bottom 12 inches back from the new nose and cut across the bottom up to the factory stripe. Then cut along the stripe on both sides and remove the bottom of the fuse. The cutting is done with a pull saw. A razor saw would work. Then mark the fuse to remove a wedge of material from both sides. The wedge is 16mm wide at the front and tapers to nothing at the back. A little sanding to clean up the edges of the fuse and bottom piece so they set together with minimum gaps. Sand the inside of both pieces with coarse paper an inch back from the edges all around.Tack the bottom back on with a few spots of CA then tape the seams on the outside. I made my firewall from 1/8 inch G10 sheet. It was cut with a harbor freight adjustable circle cutter so it had a nice bevel on the edge. I also cut a 40mm hole in a piece of 1/16 ply. The firewall is pushed into the nose and aligned with the bevel toward the front. I used no right thrust and just a little down thrust. I made no measurment, just eye balled it. The others that I have done since were matched to the original and all fly well. The plywood with the hole in it is pushed over the outside if the fuse to hold the fuse round and tight against the firewall. Use thickened epoxy laminating resin to make a small fillet in front of the firewall. smear some of the thickened resin into the seams of the cut out with your finger tip. Fiberglass is applied over all the seams with unthickened resin. I used fiberglass tape, but strips cut from glass will work, they will be harder to work with then the tape. I like to wet out the strips on a piece of cardboard rather then wetting them out in place, then put them in the fuse and brush them down. After the resin cures sand the front edge smooth. I just applied trim tape over the seam on the side of the fuse and did not worry about the line across the bottom. I have now built 5 of these for myself and friends. They fly great.
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Old Jun 23, 2012, 11:41 AM
Gasbags & Gussets
jswain's Avatar
Riverside, Ca
Joined Feb 2009
1,196 Posts
thank you

thank you for the write up.
i have a arf bot in a box and
with the knowledge from the other recent BOT electricification specs post and your info it is enough to pull a new project together.

js
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Old Jun 23, 2012, 06:43 PM
volare est vivere
ray foley's Avatar
United States, OH, Toledo
Joined Jan 2005
2,004 Posts
hi there fromToledo

That is a nice and fairly straight forward modification. Well thought out.

On a similar note about ten years ago I saw a magazine article where a modeler rounded the eliptical nose section of a fiberglass fuselage for a folder prop by making a round motor mount and exterior form like you did. The motor mount was screwed to a wooden dowel which allowed easy insertion and thrust angle alignment.

He then heated the fiberglass fuselage's nose with a heat gun and put the outer form in place mostly rounding the fuselage. He then inserted the epoxy coated motor mount into the epoxy coated inside of the nose, completing the rounding of the fuselage. After aligning the down and right thrust with the dowel, the epoxy set up over night.

The dowel and outer former were then removed and the screw hole was enlarged to become the clearance hole for the motor shaft. Some sanding tidied everything up nicely. The spinner and folder prop fit quite nicely and the sailplane flew well electrically.

ciao -rjf
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Last edited by ray foley; Jun 23, 2012 at 07:29 PM.
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Old Jun 24, 2012, 12:47 AM
doo
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doo's Avatar
United States, WA, Raymond
Joined Dec 2002
72 Posts
Very nice. I like it!
I will mod my BoT this way.

Thanks for the write up and pics.
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Old Oct 09, 2012, 04:40 AM
Registered User
Romania, Dolj, Craiova
Joined Sep 2007
14,649 Posts
Can't you simply make the oval opening round by pressure ?
The motor firewall should be enough to keep it round, I guess...
Attached is a picture of another fuselage that was round natively and I make it oval only with fingers pressure. Why not the reverse ?
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Old Oct 09, 2012, 08:44 PM
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Mark Anderson's Avatar
United States, WA, Tumwater
Joined May 2010
260 Posts
Probably could. I just showed how I chose to do it.
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Old Oct 10, 2012, 07:39 AM
Full Scale Piper Cub Driver
Piper J3's Avatar
Hinckley, Ohio
Joined Nov 2008
2,417 Posts
No problem... I have cut the nose off of a couple of fiberglass fuselages that were oval and installed a round motor mount. The fuse will confiorm nicely to the round shape.
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Old Oct 10, 2012, 07:54 AM
FPV Desert Beta Test Center
Mesa, Arizona
Joined Nov 2006
2,422 Posts
My method is to first epoxy in a G10 motor mount with the motor and spinner installed. The motor mount holes in the mount are drilled offset to provide the desired down and right thrust. It is positioned in the fuse so that the spinner aligns with the upper half of the fuse. This then shows you exactly how much epoxy/microballoon is required to fill the bottom half of the fuse. After filling the spinner again shows you exactly how far to cut down the fuse to match.
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Old Oct 10, 2012, 10:15 AM
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Romania, Dolj, Craiova
Joined Sep 2007
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Btw, what would be the recommended down-right trust angles, or offsets for a 40mm spinner ?
Motor a Grapuner 460W 3642 1200kv 12x6 prop.
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Old Oct 10, 2012, 10:55 AM
FPV Desert Beta Test Center
Mesa, Arizona
Joined Nov 2006
2,422 Posts
Quote:
Originally Posted by RENATOA View Post
Btw, what would be the recommended down-right trust angles, or offsets for a 40mm spinner ?
Motor a Grapuner 460W 3642 1200kv 12x6 prop.
3 - 5 degrees is the norm. You can determine the amount of offset needed with a drawing. Just extend a line from center at the degrees your after and measure the differance at the prop. Then with the motor installed to the mount and the spinner taped in place the mount is correctly positioned for epoxying.
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Old Oct 10, 2012, 02:11 PM
Registered User
Romania, Dolj, Craiova
Joined Sep 2007
14,649 Posts
Got it.
Also, remember from multikopter, the special washer used to lean motors by 3 degrees, the slope is 0.5mm for 1cm width. I can use these numbers to calculate for 19mm of motor screws, or 40mm of firewall diameter.
http://mikrokopter.altigator.com/mot...pter-p-99.html
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