|Apr 30, 2008, 05:44 AM|
85g/3oz. dc head pusher autogyro - the Nanomum
The Nanomum is a small pusher gyro for flying indoors or outdoors in very calm weather. It's got a dc head and is easy to build and easy to fly - I hope.
AUW 70 g / 2.5 oz.
Rotor diameter: 560 mm / 22"
Motor: 9 g - 2000 kV
Prop: GWS 4.5 x 3
Rx: GWS R4P/JST
Servos: Blue Arrow, 3.5 g
ESC: YGE 4-BL
Battery: AHA 2s-200 mAh
As usual, the plans come in two versions, a jpg-version for looking at and a pdf-version for printing. If you print the pdf-files without any size adjustment, they should print to scale.
Start with the fuselage. Print out the fuselage.pdf file and use the drawing as a template for cutting the outer contour of the fuselage. Use UHU por to glue a 3 x 0.3 mm / 0.12 x 0.025" cf strip around the fuse's outer edge. Then cut out the openings for the motor and servo tray using the same drawing. Use UHU por again to glue a 3 x 0.13 mm / 0.12 x 0.005" cf strip of about 360 mm / 14" lenght to the inside the motor/prop cut-out to reinforce it. Cut the servo tray (parts.pdf) from 0.8 mm / 0.03" ply and glue it to the fuse. Cut the landing gear supports and elevator fins from 3 mm Depron (parts.pdf). Paint everything.
If you are using a motor like mine - and I suppose you will be, because its one of those universal chinese motors that crop up everywhere - use a 20 mm / 0.8" long piece of cf tube with an I.D. of 6 mm and an O.D. of 8 mm to mount the motor. Make a 2 mm / 0.08" deep cut-out around some 40% of the perimeter of the tube at the motor end to protect the leads coming out of the motor, then epoyx the cf tube into the fuse with the cut-out facing downwards. Make a 3 mm / 2.76" hole for the landing gear and glue a 70 mm / 2.76" piece of the ubiquitous outer bowden cable tube into that hole. I've used silicone for that connection to keep it elastic. Use UHU por to glue the landing gear supports and elevator fins to the fuse.
Put a 1.5 mm / 0.06" cf rod of 200 mm / 8" length into the bowden cable tube and secure it with pieces of adhesive tape taped around the rod. The wheels you use should be very light, something about 1 to 2 grams.
Build yourself a Micro Hinge as described here: http://www.rcgroups.com/forums/showthread.php?t=835526
The distance from the lower end of the 2 mm cf rod to the hinge point is 75 mm / 3", the length of the control arms is 35 mm / 1.38" and the angle between the control arms should be around 60°. Glue the Micro hinge to the right side of the fuse with silicone. While you're at it, reinforce the epoxy joints of the motor mount by filling out the notches with some silicone too.
Use double sided adhesive tape to fix the servos to the servo tray. Click mini push rod connectors (Multiplex # 703454, something similar to the Du-Bro RC Mini E/Z Connectors) into the outermost hole of the servo arms. Use two 150 mm / 6" long pieces of 1 mm / 0.04" cf rod as push rods. Slide two 35 mm / 1.38" long pieces of thin heat shirink tube about 15 mm / 0.6" over the ends of the control arms and provisionally shrink thight at the ends of the tube. Stick the push rods into the other end of the heat shrink tube until they connect with the control arms, bend them down and shrink everything tight. Provisionally fix the push rods in the connectors.
Mount the motor with its prop, the Rx and the ESC at the positions shown in the plans. Don't mount the battery yet, we'll use that to adjust the c.g. later.
What's left is the rotor. This is a three-bladed modification of Al Foot's Monotwirl rotor (rotor.pdf). The central part of the hub is a triangle sandwich with a side length of 27 mm / 1.063" , made of 3 mm / 0.118" layers of ply, balsa and ply. The hole in the middle should be large enough to take a ball bearing with an I.D. of 2 mm. Soak the outer surfaces of the triangle with thin ca glue to make them more resistant. Cut the three blades (35 x 270 mm / 1.4 x 10.6") from 3 mm Depron. Reinforce the leading edges with 3 x 3 mm / 0.118 x 0.118" balsa strips and glue the 1 mm balsa triangles to the bottom of the inner corners at the trailing edge. Sand some chamfers to the inner blade edges as shown in the plan. Round off the leading edge. Cut out the two top and bottom circular blade stops from 3 mm Depron and paint the blades and blade stops. Put a small mark on the top of the blades at the inner edge, 6 mm / 0.24" from the leading edge. Put ropes of UHU por diagonally upwards in a clockwise direction across one side of the triangle and on the inner edge of one of the blades. Wait for the glue to get dry, then place the leading edge of another blade against the side of the triangle that is behind the upper end of the UHU por rope. Now take the glue covered blade, put its trailing edge on the 'other' blade and its leading edge on the surface of your workbench, align the mark on top of the blade with the edge of the triangle and push the blade against the hub triangle. Do the same thing with the other two blades - well, nearly the same with the last one. Then gently lift the trailind edges of the blades and put a small drop of UHU por into the blades overlaps, just a small one to hold them together. Now glue the top and bottom blade stops to the top and bottom sides of the triangle - and to the triangle only, not to the blades. Press the ball bearings into the center hub hole and put the rotor on the rotor mast. Add a washer and secure everything with a wheel collar - preferably an aluminium one - or some heat shrink tube.
If you have a good idea how to mount the front wheel, then do it now. My Nanomum has no front wheel yet, I'm still afraid it will simpy get ripped of when I touch down in the relativly high grass at our field. But good ideas for a front wheel mount will be appreciated.
Place a mark on the right hand side of the fuse where the c.g. is supposed to be. Put the flat head of a socket head screw over the mark. Hold the screw between thumb and middle finger and put your forefinger through the prop cut-out on top of the Depron above the screw head. With your other hand you can now push the battery around on the fuse. Lift your forefinger slightly and you can see which direction you should move the battery. When everything is balanced, fix the battery.
Now for the set-up. The movable part of the rotor axis shoiuld be tilted some 10° forward, compared to the fixed part. To obtain a straight descend during autorotation - that is with the motor off - the rotor should be tilted some 14° (fouteen degrees, its true, that's what coning does to you) to the left, seen from behind. At full speed the tilt should be reduced to some 10°.
When you're launching the Nanomum, use only 2/3 of full power. The 9 g motor I'm using is a bit oversized for the Nanomum, and you have to be careful if you apply full power. Do your first flights indoors or in a near dead calm or she will be gone with the wind. Otherwise she's quite a normal gyro to fly, though I've had some crazy situations. Once, after test flying the Nanomum v2 - still very secret -, I forgot to set the Tx set-up back to Nanomum v1. I launched v1 and she turned right over on her back. The rotor stopped, but that did not keep her from flying straight on. After a few meters I decided to put an end to this madness and turned the motor off. Which caused her to gently glide to the ground and land safely on her rotor. Since then I've got the sneaking feeling that we are making some fundamental mistake when we're tryind to get these rotors to rotate properly.
Have fun, nevertheless!
P.S.: Here's the Nanomum video: http://www.rcgroups.com/forums/showp...82&postcount=1
|Jul 27, 2008, 09:32 AM|
By now I've gained quite some experience flying the Nanomum v1, and it's time to incorporate the acquired knowledge into the Nanomum's design.
I've made the fuse a bit stiffer, found a solution for the missing nose wheel, and did some development on the rotor.
To make the fuse stiffer, I've inserted a 0.3 x 3 mm / 0.012" x 0.118" flat cf rod into its front part (see 'Fuselage' drawing). After you've cut out the fuselage and clued the cf strip to its rim, make a cut into the fuse from the top down to the bottom, put some UHU por on both sides of the cf rod and insert it into the cut while the glue is still liquid. Wait an hour or so for the glue to cure before you go on with the cut-out for the prop. I've also lowered the motor position by a few millimeters to have more clearance between the prop and the upper end of the cut-out.
The front landing gear is made out of EPP and looks like something the cat dragged in, but the everything I build from EPP does (see 'NoseWheel' drawing). Cut out the triangle at the top of the drawing 5 times from 3 mm / 0.118" EPP, then trim those triangles down to the correct shape as shown in the drawing. Take a 100 mm / 4" long strip of 0.13 x 3 mm / 0.005" x 0.118" cf and use scotch tape to fix both ends of this strip to the rim of the fuse. Position the front end of the strip some 20 mm / 0.8" below the upper plane of the horizontal stab, the rear end will then be some 20 mm / 0.8" or so before the main landing gear. Using UHU por, glue the center part of the landing gear to the cf strip at the appropiate position. Glue the next two parts - those which have a cut-out for the wheel, too - to the center part, but not to the fuse. Sand two 0.6 x 3 mm / 0.024" x 0.118" flat cf rods down to the shape shown in the drawing and glue them into the slot of the outermost EPP parts. Cut the two cf reinforcements out of 0.25 mm / 0.01" cf and glue them to the inside of the outermost EPP parts, then glue those parts to the rest of the landing gear. Remove the landing gear from the fuse and cut off the protuding parts of the cf strip. Stick three layers of EPP into the opening for the wheel and drill a hole for the axle through everything. Somehow or other (with me and EPP it's mostly other) create a 10 mm / 0.4" wide chamfer at the upper rear end of the landing gear, that's where the battery will go. Paint everything. Stick a strip of double sided adhesive tape to the rim of the fuse, and then two further bits of tape to the sides of the fuse. Hold the landing gear at its front end between your thumb and forefinger, gently press it together, slip it over the fuse and press it down on the double sided adhesive. Mount your axle and wheel.
I've experimented quite a lot with those Depron rotors over the last few months. First thing I did was to change the angle of incidence from -8° to -6° and introduce a delta three flapping hinge with an angle of 15°. This made the rotor run somewhat smoother. There was one thing I still did not like about the hub, and that was the way the blades were joined to it. Every time a blade was ripped off and glued back in place again, I asked myself if the hinge would retain its original flappiness or if it had changed by the re-glueing. Finally I got fed up with this situation and after a lot of unsuccessful tests with other kind of hinges I simply redesigned the inner blade ends. To my big surprise this change not only worked well, but also improved the flying characteristics of the Nanomum. The tendency to swing up and down around the lateral axis when there was a bit of wind or under high load conditions had disappeared. She still flys a bit nose-up, but I tolerate that because she does that real slow, which leaves me more time to react when she's crawling around near the ground. And I can't change the c.g. anyway, I've run out of fuselage or weights to do so.
Make three 35 x 270 mm / 1.38" x 10.6" blades from 3 mm Depron. Cut off the inner ends at an angle of 15°. Make yourself three strips of 3 mm balsa, 5 x 40 mm / 0.2" x 1.6", with the grain running perpendicular to the long side of the strip. Glue these strips to the inner blade ends with UHU por. Sand a semicircular groove with 2 mm / 0.08" diameter down the middle of the balsa strip at the inner blade end. Epoxy a 40 mm long cf rod with an O.D. of 2 mm / 0.08" into this groove, flush with the trailing end. If you want to improve the mechanical stability of your blades, use UHU por to glue a 0.3 x 3 mm / 0.012" x 0.118" strip of cf to the leading edge of the Depron blades. Sand a semicircular groove with 2 mm / 0.08" diameter at an angle of 15° into one end of three 260 mm / 10.3" long 3 x 3 mm / 0.118" x 0.118" balsa strips. Glue these strips to the cf at the leading edge, the groove taking the 2 mm / 0.08" cf rod. Sand down the balsa strips at the inner blade ends so you get a smooth transition from to Depron blades to the cf rods. Cut the top and bottom blade reinforcements out of 0.25 mm / 0.01" cf or gf. Don't use anything thicker, it will change the angle of incidence. Use UHU por to glue the reinforcements to the blades. Sand down the reinforcements so you get a smooth transition to the cf rods. Sand off the cf rods so they are flush with the leading edge, then round off the blades' leading edges and paint everything. Put a mark on the upper blade reinforcements at the inner blade ends, 7 mm distant from the leading edge.
Build the triangular hub from two layers of 2.5 mm / 0.1" plywood with a 2 mm / 0.08"layer of balsa in between. Drill the hole for the ball bearings with an I.D. of 2 mm / 0.08" and then drench the outer surfaces of the hub with thin ca glue. Glue the cf rod at the inner blade ends to the hub using UHU por. Let the blades overlap and adjust the marks on the blade reinforcements with the points of the hub during this process. Make the spacer from 0.8 mm / 0.03" plywood and drench its surfaces with thin ca. Use UHU por to stick the spacer to the upper side of the hub. Why this spacer? If you've got to do some serious repairs on the hub, you can pry the spacer off by inserting a thin knife between the hub and the spacer, without damaging the top hub cover. Cut the top and bottom hub covers from 3 mm / 0.118" Depron, paint them and glue them to the spacer and underside of the hub. Insert the ball bearings into the center of the hub and put the rotor on the Nanomum.
P.S.: The last picture is a preview of the Nanomum v4, 80 g / 2.8 oz., same rotor diameter and RC equipment as the v2. She's already flying, but needs about 40% more power than the v2 to do so. I'm still trying to sort out that problem.
Edit: Changed the thickness of the cf strip at the blades' leading edge from 0.13 mm to 0.3 mm:
Edit: The development of the indoor autogyro Nanomum v2 is discontinued in this thread. For plans of the successor to the Nanomum v2, the Picomum, look here:
|Jul 27, 2008, 11:15 AM|
thank you very much.
I just discovered that I forgot to add the set-up data for the v2. The rotor is now tilted 17° backwards, the movable and fixed part of the rotor spindle are in line. With the motor shut off, the rotor is tilted 6° to the left, seen from behind. At full power the rotor is tilted 3° to the left.
|Jul 27, 2008, 12:11 PM|
New Jersey, USA
Joined May 2003
You're welcome. Can't believe how much good information and creative engineering is packed into only the first page of your thread.
|Aug 16, 2008, 11:50 AM|
It took me some time to get the weather quite right, but at last here's a video of the new Nanomum v2:
|Aug 17, 2008, 12:46 PM|
thank you both. Though it was definitely more a stroke of luck than a stroke of genius that let me build this rotor.
These Depron rotors are very tricky because you've got no appreciable centrifugal force (or 'centripetal force', if you want to be precise, but I don't) to work with. The Nanomum has about half of the disc load of a three-bladed Micromum, but her blades weigh only a fifth of the Micromum blades, the radius of her blade's c.g. is smaller and her rotor is turning slower. That all gives you a centrifugal force that is lower than one tenth of the force that is keeping the Micromum's blades horizontal. That's why the stiffness of the rotor hinges on the Nanomum is so critical and so difficult to get right.
On the other hand, the stiffness of the hinges has a nice side effect: it produces asymmetric lift, which makes the Nanomum lift her nose, slows her down and produces more 'normal' lift by tilting the rotor backwards. The Nanomum's rotor is tilted backwards by 17° in relation to the horizontal stab. I checked the video today and found that the minimum rotor back tilt that I could measure in horizontal flight was about 30° with a maximum back tilt of around 50° while climbing. In other words, without asymmetric lift the Nanomum would hardly be able to fly. Sometimes I feel like Horatio.
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