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Old Dec 11, 2005, 12:34 PM
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200g/7oz. dc head pusher - the Micromum

Hi all,
here's a little DC head pusher weighing just below 200g/7oz.
I took the basic design of my "Minimum" gyrocopter (see) - 8 tilt back of the rotor mast, neutral motor position and neutral tail fin positions -, put the motor aft of the rotor mast, made everyting a little smaller, tucked the tail unit in under the rotor, and arrived at - the "Micromum".
The gyrocopter is powered by a Potensky 50 outrunner weighing 30g and turning a 7x3.5 GWS prop at 8900 rpms while drawing 2.8A out of a 3s/360 mAh lipo pack. The rotor has a diameter of 700mm/27.5" and is made of 1 1/2" Aerobalsa blades. The rotor hub is cut out of a 0.5mm gf sheet. Two circular servo arms with ball bearings where the servos used to be connect the hub to the rotor axle. The joint between the rotor mast and the rotor axle consists of two 2mm cf rods with rounded ends put against each other and covered by two layers of heat shrink tube. This - unfortunately - is not my own idea, I got it from StephanB - thank you, Stephan. The lower cf rod of the joint is fixed to the rotor mast by means of an end piece used for balsa push rods. The head is controlled by two 6g servos with metal gears. The airframe is made of 8x8mm balsa rods, the sides of which are reinforced by 6x0.6mm cf strips. The tail fins are 3mm Depron with the leading edges strengthend by 3mm cf strips. Hang angle is -8 with the vertical cg about 30mm below the motor axle.
Rather surprisingly, the first prototype flew right off the drawing board. The second - and at the moment - final version was made a bit sturdier and better looking. Flew it this afternoon and it worked as well.
Jochen
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Last edited by JochenK; Dec 20, 2006 at 02:46 AM. Reason: title change
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Old Dec 11, 2005, 02:24 PM
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I am a similar pusher. How does it repond without rudder control?

Wahid
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Old Dec 11, 2005, 02:50 PM
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Wahid,

like an airplane with ailerons and elevator and no rudder. You bank it with roll, pull nick to get it around the turn and keep the flightpath level with throttle.

Forgot to add the reference for the "Minimum" in my post. It's
http://www.rcgroups.com/forums/showthread.php?t=392919

Jochen
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Old Dec 11, 2005, 03:06 PM
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I understand the ailerons and elevator controls. I have a very good experience with autogyros. Please see my website:

http://home.comcast.net/~wahid17a/Autogyro.htm

I built a pusher without rudder control, but the turns were not very responsive.

Wahid
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Old Dec 11, 2005, 03:07 PM
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Can you please post close ups of the model?

Wahid
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Old Dec 11, 2005, 04:42 PM
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Wahid,

you have to use a lot of throw on roll to get a good response. I'm using about 15 up and down and in tight turn I bank the gyro up to 60 to 75.

What parts of the model are you interested in?

Jochen
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Old Dec 11, 2005, 04:56 PM
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Jochen,
that's very nice. I'am proud, that the hinge works. To say the trueth, this kind of hinge is not my idea. This is Karel Pustkas idea. He died a year or so ago and i feel the loss.
I'am not working on autogyro right now. Indoor season....
Will be back in autogyros, when sun comes back in spring. Ever thought about InterEx, next year in Netherlands...
Stephan
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Old Dec 11, 2005, 04:57 PM
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I like to see some close up pics of the head. I like to come up with some innovative ways to make the heads. See my link below:

http://www.rcgroups.com/forums/showt...light=traxxas+

Wahid
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Old Dec 11, 2005, 04:58 PM
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Have to tried this model without the horizontal stabalizer?

Wahid
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Old Dec 12, 2005, 03:20 AM
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Wahid,

here are some close-ups of the head without the rotor. Though you have to mix your nick and roll signals in the Tx, I prefer this 'forward V' configuration of the servo links to the normal 'L' configuration, because due to the drag of the rotor you get an automatic pull-pull situation for both servos.


Stephan,

when I designed the 'Micromum' I actually had indoor flying in mind. Now, after the outdoor tests, I still think it's possible to fly it indoors, though not with me as a pilot. InterEx in the Netherlands, where and when?

Jochen
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Old Dec 12, 2005, 03:56 AM
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Wahid,

no, I haven't tried it without the horizontal stabilizer. I'm not sure that it will work.

Jochen
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Old Dec 12, 2005, 03:27 PM
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Stephan,

when I designed the 'Micromum' I actually had indoor flying in mind. Now, after the outdoor tests, I still think it's possible to fly it indoors, though not with me as a pilot. InterEx in the Netherlands, where and when?

Jochen[/QUOTE]

Jochen,
it's in Nederweert, a weekend in september 2006.
Nice community, big fun.
http://www.inter-ex.com/
http://mcb.ssy.free.fr/ (2005 event near Paris/France)

Stephan
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Old Dec 13, 2005, 04:27 PM
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Stephan,

mmmh, let's see what I'll be flying next September.

Jochen
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Old Dec 16, 2005, 03:34 AM
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Finally got around to completing the plans for the Micromum and writing a few words of explanation, and here they are.

When I print out the first three drawings on my printer, they print out in a scale of 1:2. The rest of the drawings are scale. I've added scales to the drawings, so you can adjust the printout to get the correct size.

First a word of warning: waiting for the glue and paint to dry takes longer than the actual building of the Micromum.

We start with the airframe.
Glue the balsa pieces of the airframe together and see that the rotor mast is tilted 8 backwards. I've used PVA glue for that. Shape the 8 x 8 mm top end of the mast to fit into the 6 x 6 mm push rod end piece. Drill a 2 mm hole 12 mm deep into the top of the rotor mast to take the bottom part of the rotor axle. Enlarge the 1.5 mm hole in the push rod end piece to 2 mm and glue the bottom part of the rotor axle into the end piece, so that its visible part is about 10 mm long. Epoxy the 6 x 0.6 mm cf strips to the sides of the airframe. Put the push rod end piece on the top of the mast and drill a 2 mm hole through the cf strips, the push rod end piece and the rotor mast at the lower end of the end piece. Use a 2 mm screw to hold everyting together. Epoxy the diagonal parts of the landing gear on top of the part perpendicular to the tail boom. Epoxy pieces of Bowden cable tube to the bottom of the perpendicular part to take the landing gear axle. Epoxy everything to the bottom of the tail boom. Use epoxy soaked cf rovings to tape the joints of the landing gear and the joints of the landing gear with the tail boom as well as the joint between the mast and the tail boom. Use a 2mm cf rod as an axle for the landing gear and secure it with heat shrink tube. Use light wheels to your own liking. Make the mast support/servo holder out of 3 mm balsa and glue it to the front of the rotor mast. Watch for the direction of the balsa fibres given in the plan. Glue the motor mount to the rotor mast: two pieces of balsa on the sides of the mast and a piece of plywood behind it. The axle of the motor should be parallel to the tail boom. Make a little pod for the battery by glueing an upright piece of 8 x 8 mm balsa to the front end of the tail boom. Glue 1 mm strips of balsa to the front sides of the tail boom and upright balsa piece and then glue on the plywood sides of the pod. You may want to leave buliding this pod until you have finished the RC installation, in fact it might be a good idea to make the front end of the tail boom some centimeters longer than in the plan and cut it off to your needs after you have set everything to get the correct hang angle.

Round off the top of the rotor axle sticking out of the push rod end piece and round off the bottom end of the upper part of the rotor axle. Take two pieces of 22 mm long heat shrink tube, one that just fits over the bottom part of the rotor axle and one that fits snugly over the first tube. Put a thin layer of PVA glue on both parts of the rotor axle, but stay off the rounded ends. Put the smaller piece of heat shrink tube over the bottom part of the rotor axle and insert the top part of the axle into the heat shrink tube until the rounded ends of the cf rods touch. Shrink. Put the larger tube over the small one and shrink again. A wheel collar with an inner diameter of 3.2 mm should now fit over both heat shrink tubes, if it doesn't, enlarge the hole in the wheel collar. Drill a 2.5 mm hole through the wall of the wheel collar, opposite the hole for the grub screw, using the grub screw hole as a guidance. Enlarge the 2.5 mm hole to 3 mm from the other side. Exoxy a piece of 3 mm cf rod of 20 mm length into the wheel collar. Take two 46 mm long strips of 6 x 0.6 cf and glue them together. Drill a 3 mm hole through the middle and drill 2 mm holes 36 mm apart. Epoxy this strip to the 3 mm rod, about 4 mm from its end. Use epoxy soaked cf rovings to tape the strip/rod connection and the outer ends of the strip, to keep the strip from splitting up. Screw the balls of a ball link servo connection into the 2 mm holes. Put everything on the upper part of the rotor axle, just below the upper end of the heat shrink tubes.

Cut the tail fins out of 3 mm Depron. Glue 3 x 0.3 mm strips of cf to the leading edges of the horizontal and bottom part of the vertical stab. Glue the horizontal stab to the bottom part of the vertical stab and stabilize the connection with 1 mm cf rods from the outer ends of the horizontal stab to the bottom of the vertical stab. Leave enough free space on the vertical stab, so you can still push it into the end of the tail boom. Glue the top part of the vertical stab on top of the horizontal stab. You can glue the tail unit into the tail boom or just fix it with two 2 mm screws.

Print out the drawing of the rotor hub - check the size of the printout against the scales on the drawing - and cut it out. Glue the cutout to a piece of 0.5 mm thick gf sheet and use it as a template to drill the holes and cut the gf sheet to its proper dimensions. Use a 2 mm drill for all holes except the central one. Drill the central hole to the size of the central hole in the servo arms you'll be using in the next step. Remove the paper from the gf sheet.

Take two circular servo arms that can take a 5.9 mm servo cone and have a diameter of about 35 mm. Enlarge the cone holes to 6 mm without drilling through the servo arm. Use a screw to put one of these arms into a drill and sand it down to a diameter of 25 mm. Screw the the gf hub to the top of the larger servo arm - watch out for the direction of spin - and use the hub as a template for drilling three 2 mm holes at angles of 120 into the servo arm. Repeat for the smaller servo arm, but screw this one to the other side of the hub. Finally use 2 mm screws to bolt the servo arms together with the gf hub in between. Put two 2 mm ball bearings into the openings of the servo arms. Using some washers, put the hub on the rotor axle, add some washers again and finish everything with a wheel collar.

Take three Aerobalsa rotor blades of 340 mm length. Cover the inner 40 mm of the blades with pieces of 0.6 mm plywood and drill 3 mm holes at the appropiate places. Glue small pieces of Bowden cable tube into the 3 mm holes and cut them off flush with the surface of the plywood. Make a 2.5 mm thick balsa wedge and glue it to the bottom of the plywood. Drill 2 mm holes into the wedges. Cut off the inner ends of the blades according to the plan and mount them on the hub with 2 mm screws. Balance the rotor. If you are using the RotorBlade Airfoils from Aerobalsa adding additional lead is not neccessary.

Install your motor, battery and RC equipment and adjust the battery position to get a hang angle of -8. Use a delta mixer in your Tx to distrbute the nick and roll signals to both servos. Personally, I use 15 for roll and about 8 for nick with 60% exponential mixed in on both. Additionally I have mixed throttle onto roll, so I get a further 5 tilt to starboard when going full throttle to compensate for motor torque.

If you want to equip the gyro with a pilot, cut three pilot figures out of 3 mm Depron, two full figures and one having only head and body and no parachute. Glue the figures together, the maimed on in the middle. The rotor mast support will go into the slot between the two parachutes and the legs of the pilot go outside the battery pod. You can secure the pilot by putting a small strip of double sided velcro through the opening between the arms and legs and fastening it below the tail boom.

Now take everything apart again and apply some colour. Reassemble, and you're ready for your first flight.

Do your first flight on a day with just enough wind to keep your rotor spinning after you have given it a push with the gyro tilted 90 backwards. Walk a few steps and see the rotor spinning up. Walk a bit faster and put the gyro in a nearly horizontal position. Turn on the motor and give enough throttle to feel the push of the prop. Add a little throttle and jog a few steps. When rotor lift and motor push seem o.k. release the gyro into the air with a gentle shove, and it will fly away.

Have fun, Jochen
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Old Dec 16, 2005, 08:12 AM
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Great presentation Jochen. Really like the creative head control assembly.

David
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