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Christo's Speed280 Page
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The humble Speed 280 Motor
The story of my Speed280 Gearbox
During the second half of
1999 I've decided to design a gearbox
for the Speed 280 motor and
what a success it has turned out
to be. It has totally revolutionized my electric
flying experience.
Obviously, it has to be
used in a very light plane like a park flyer, but
that doesn't mean that it has to fly like a trainer or a Piper Cub.
No sir! Put it in something with a decent wing (ailerons and a
semi-symmetrical section) and you have one mean little machine
capable of some very respectable aerobatics. I humbly predict that
this kind of flying is going to take off like nothing we've seen before.
With this particular
(1:2.6 ratio) gearbox it produces about 200 grams
(7 oz) of static thrust on 8 Ni-Cad cells and 8x4 Graupner Slim Prop
while drawing only 2.2 Amps.
You may think that that is not much thrust, but compare it to 230
grams (8 oz) for a direct drive Speed400 motor drawing 10 Amps.
It is a lot more (400%) efficient than the bigger motor. OK, so you
say that's not fair - compare it with a S400 with a gearbox. Well,
I've
tested that configuration as well. The Graupner FG1.85 6V (1:1.85)
gearbox and motor combination with the recommended 9x5 Slim Prop
delivers 430 grams (15 oz) at 10-11 Amps. The S280 is still 216%
more efficient.
My latest development is
to use 700mA/h Ni-MH cells. They weigh
only slightly more than the 300mA/h Ni-Cads I've used previously
and obviously the duration has increased (from 8 minutes with
the Ni-Cads) to 15-18 minutes with Ni-MHs.
I've also started using 9 cell Ni-MH packs and this resulted in a
power increase of an estimated 30%. Now the performance
is really something while the duration is not that much less.
12-14 minute full power flights is the norm.
Someone who recently saw me flying, commented:
"Looks like you land when you get tired of
flying and not when the battery runs flat..."
Here are some pictures of
the 2nd prototype gearbox. It has a 3.2mm shaft
and 1:1.88 ratio, but the sketch below (and the downloadable plan)
shows the one I'm flying with: 4mm shaft for using Graupner 4mm
prop adaptors and the tried and tested 1:2.6 ratio servo gears.
Click pictures to zoom in
If you decide to build the
gearbox or the Tadpole plane,
please e-mail me at skylar@mweb.co.za
and tell me about it...
The Tadpole
The model shown below is
the plane I've designed
specially for testing the gearbox and there seems to be
enough thrust for the 430g, 1020
wingspan plane.
Click pictures to zoom in
A Tadpole derivative
(foreground) was built by Arthur Langley.
It flies slightly better - probably due to a sheeted leading edge.
Please send all comments to: skylar@mweb.co.za
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