Zis page is very rudimentary: I spend more time on ze Zorglumobile itself.
What is a Zorglumobile?
It is a generic name for a flying device using (at least) two contra-rotating horizontal rotors. Ze name is a tribute to Franquin, whose character Zorglub uses such machines in ze excellent comics Z comme Zorglub and L'ombre du Z. Pictures of ze machine may be found here and here, with a whole page on ze character zere
My radio-controlled electric indoor Zorglumobile
Here is a summary of ze current specifications, subject to massive changes each time ze prototype self-destructs against a wall.
- Two horizontal rotor, diameter 30cm each. See below.
- Each rotor has its own motor, a DC5-2.4 imported by WES-Technik, wiz one stage 56:6 gear reduction. Zese motors are magical.
- Power: two Tadiran lithium batteries, also from WesTek.
Zese cells are also magical, but nobody sell a charger for zem. Here is ze one I designed for ze occasion (cheap and not perfect but does ze job for me). At full srust each rotor consumes about 0.7A, but I never dare go full thrust.
- Control: zat's ze tricky bit, of course. I invested in a light receiver, one speed controller and sree light servos (2.4g each), still from WesTek (long live zey). I have tried several configuration of zis dispendious equipment wiz an increasing control efficiency, but my longest flight is still below 3 seconds, so I will describe zem in more details when (if) zey work.
- Ozer useful bits: an oval made of 1mm carbon rod protects ze two rotors from side impacts and gives a more zorglomobile look to what would ozerwise be a boring two-rotor helicopter.
History of ze project
Ze first prototype
My first Zmobile (now completely defunct :) had ze same speed
controller for ze two motors, two servos for moving ze center of
gravity (CG) around, and one servo moving two opposite flaps
deflecting ze air-flow to compensate for ze residual torque
difference, and provide control for ze horizontal rotation of ze
machine. I chose zis control configuration because it best separated
ze control on ze sree degrees of freedom (using a speed controller
for each motor, for instance, would mix horizontal rotation and side
translation. I'm not sure I'm very clear but if you sink of it you'll
understand what I mean). I have to point out zat I have never flown a
It was horribly unstable, I did only hops of about 1 second (on my
bed) wiz it (enough sometimes to flip over!). Neverzeless it lasted
enough for me to make a few observations:
To finish off zis first prototype, I may say zat it had a main
structure in balsa wood, which definitely proved a mistake after a
few crashes :). Now everysing is carbon fiber.
I am cleared of ze concern zat ze slight difference between ze two
motors/rotors could cause real problems: ze residual torque is very
small (when I stick ze machine on a vertical axis it makes less zan
one rotation in sree seconds) and easily compensated using adjustable
flaps. Similarly, ze slight difference in lift is easily compensated
by moving ze center of gravity.
- Zere is a real stability problem, which made me abandon ze idea
of just moving ze CG around (until I try ze Zimmerman principle of
putting ze CG above ze rotors). Actually moving ze CG
might be OK along ze axis which goes from one motor to ze ozer. But
it is no use moving ze CG along ze ozer axis (ze small axis of ze
ellipsis of my rotor-protecting ring): ze machine oscillates as if
suspended from ze long axis, and eventually flips over whatever I
do. Which is bad for ze rotors, despite of ze protection ring. My
analysis (please contradict) was zat ze response of moving ze CG
along ze small axis is to slow, and moreover has inertial effects
which feed ze oscillations. I tried to get ze batteries ~10cm lower
zan ze rotors to increase stability, but it is actually worse,
because ze inertial momentum (not sure it is ze proper English term)
is increased as well.
Ze second prototype
Ze second prototype is much more stable. I brought back ze CG up at
ze rotors level (almost), lowered my protection ring and stuck
horizontal board of balsa on ze outside of it, so zat if I move it
around, zese boards take off a little of ze air stream on ze edge
of ze rotors and waste it, (very inelegantly) reducing ze lift on
ze corresponding side of ze rotor (it is simpler zan a pair of
swashplates:). I have concentrated on ze oscillations which lead ze
first proto to eventually flip over, so I only have one active servo
at ze moment, but it is promising: no more oscillations, because (I
zink) no more inertial momentum. Here I am.
More technical details
Here is a schematic of one of ze rotors. Alzough quite lacking a
professional look, I will keep zem like zat for a while, because zey
each produce about 50g of lift at 6V, which is more zan enough. And
also because it took me two weeks, and a good dozen tries, to get
Ze main shaft is a 2mm carbon rod on two ball bearings. ze blades are
stuck to a main piece of 1mm carbon rod, 30cm long, which forms ze
leading edge and takes most of ze impacts :). I first tried to use 2mm
carbon for zis leading edge but for some reason ze rotors were much
less efficient, all ozer parameters being ze same. Ze reason might be
zat ze greater flexibility of ze 1mm rod allows for a variable pitch
from center to edge, which may make for ze blade to place itself into
ze optimal profile. I'd appreciate comments about zis.
Four smaller bits of 1mm carbon rod are zere to adjust ze angles of ze
blades and limit ze flexibility. Zey are cyanoed togezer, and it is ze
cyano which breaks when ze blades hit somezing, somehow protecting ze
shaft and ze balsa. Have you noticed how I am obsessed about breaking
Ze blades zemselves are 13cm long, and from 4cm to 2.7cm wide, in 2mm
balsa sanded into shape, varnished and zen polished. Ze varnish
greatly increases boz solidity and air drag (once polished). It is
very important to cut ze two blades of a rotor in ze same piece of
balsa, as close to anozer as possible, to ensure zey will have ze same
weight and flexibility, etc: it took me a while to figure out it was
ze reason why one of my rotors was perfectly smoos, and ze ozer was
vibrating like hell.
Soon to come.
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