Propeller and shaft for rubber

 23 September 2021

Ideas for material of the propeller, shaft and bearing for small rubber models:

• malleable wire from a small paperclip for shaft, shaft bearing,
• plastic tubes from cotton buds or ball point pen for propeller hub, shaft bearing
• balsa for propeller hub and blades,
• other wood (bamboo, bass, chopstick) for propeller hub,
• cardboard for paddle blades,
• foam or plastic cup for propeller blades,
• ??

I think it is ok if the propeller hub is strong and heavy, plenty of hits and noseweight usually needed anyway. A malleable shaft means it will be easier to adjust it straight again, spring steel is too difficult to make and to correct. A jig is needed to check symmetry, for sanding angle flats and gluing blades. 

No such problems if capacitor powered.

Sniffi, review of a balsa glider

Gone (22 Sept 2021)

Lost over fence of adjacent condo last Sunday. That's the end of it.

Needed up substantial up elevator and left rudder, flies too fast. Doesn't recover well, seems the dihedral and rudder are too small. Definitely not roll off the top model.  Would prefer catapult launches.

Do it again? nah.... wasn't forgiving and flight times quite short even on occasional good launches.

Last point: don't use UHU APG for this, bendy joints.

Before flying (14 Sept 2021)

This Ikea plastic laptop table worked as a work bench for this model. 

I used double-sided tape on the edges to hold the balsa parts for planing and sanding. 

It is still available from Ikea, Klipsk bed tray at $13.90.

I planed too much off the port wing tip. Having the balsa grain going outwards is not a sure fix.

I don't have 'resin glue' at hand, so I used UHU All Purpose. Result: the joints remained flexible for a few days after gluing. The fin was glued ok, it stiffened the quickest because it was so easy to sand the edges square. The polyhedral joints do not have matching joints, it wasn't easy to sand at approximate angle, so more glue filled the gap and it takes a longer time to stiffen, currently, 3 days has lapsed and I think it may be ok for launching. To play it safe, I am giving it a few more days.

The decorative strips cut out from the plan were glued with white glue to the sanded model. I didn't have glue stick at hand and tried successfully with white glue on the small logos of 'Aero-naut' to the fin. However, the rest of the decoration wrinkled, white glue is not suitable, I might have had better success with UHU All-Purpose Glue (UHU APG).

The tail jig set the horizontal stabiliser square and the fuselage vertically to receive the wings. The dihedral jigs were spot glued to the wings' underside, and then the wings were joined to the fuselage. The mini-plane rested over the dihedral joint to keep both wings pressed against the mounting area. I left it jigged like that for 2 days to allow the UHU APG time to harden.

After UHU APG has stiffened enough (feeling a bit springy at the dihedral joint with light finger pressure), I did "bed-glides" by launching the model over my bed towards my pillow. The diving glides indicated that the single lead piece provided in the kit is enough. That is good news. It is not time to give it up-elevator yet, during the bed-glides, I noticed it was turning to the right. Slight bend at the fin seems to straighten the glides but the starboard wing hung low. Putting the model on the floor had the starboard wing down on the floor. Balancing the model inverted on my fingers confirmed that the starboard wing is heavier, the CG is to the right side of the fuselage. This is probably due to the different balsa density between the two wings. Since my port wing and tail have their tips planed off, I think I will glue a paper wing tip to the port wing to reduce the mass offset but I will leave the port tail alone.

I may remove the wrinkled decorations, it would be easy, just moisten with water and perhaps a few passes with a sanding block after the model is dried. I want to try with it on first.

At the beginning (6 Sept 2021)

This is my ongoing review of Sniffi. I got Sniffi from Rotor. It seemed simple enough, but I over-estimated myself and had to pick up lessons along the way. It has been a long while.

The kit was die-cut, everything seemed to be there except that I only found a small piece of lead, the larger piece indicated on the pictorial instruction was not found. I don't think that will be enough but since that was what I received, and the lead weight is to be concealed, I am trying it out with just one small lead weight and didn't source from my collection.

A curious warning on the instruction pamphlet says to use resin glue and not wood glue for the fuselage pieces. Perhaps the concern is warpage? Since this Sniffi appears to be a German Kit, I am going to use UHU General Purpose.

The CG indicated in pictorial instructions is confusing, I hope it is 20mm in front of the trailing edge? This would be the first time I will have a glider with such a rearward CG.

The balsa pieces were cut through, the pieces were crushed on the entry side but thankful that the exit side was clean.  The wings and tail is only of 1/16" thick sheets. Mine had hard balsa for the wings and soft balsa for the tail and fuselage. I think the wings ought to be of lighter balsa and the fuselage pieces would require heavier balsa. I suppose the heavier wing is ok because the CG seems to be near the wing's trailing edge.

I wanted to use the clean cut edges for the bottom of airfoil because I figured that some sanding on the crushed top side will make it look alright. But this is not possible for the port wing because of how the pieces are laid out on the balsa sheet.

I wanted the tail to be of lifting section, with the fin lifting to yaw the plane to circle left. I also thinned the tips to reduce the tail's weight further. Thin trailing edges allow for future adjustments, there will be a gap between the fin and elevator, better for adjustment I hope. 

I wanted the wing to have a sharper leading edge and thin trailing edge. I wanted the tips to be thinned outwards. 

Lessons learned:

• One elevator tip was cut too deeply. Only plane in the direction where the wood grain will throw out the planer, that way, it will not dig in. Even if it meant that I am planing towards myself. 
• Use new sandpaper. I was using old sanding blocks and it doesn't cut the balsa.

Positioner for small objects

 16 September 2021

Idea 1

Material: 2 ice-cream sticks, 3mm thick scrap piece, one rubber band.

Make it:

1. Glue or tape 3mm thick scrap piece to one end of a ice-cream stick.
2. Place 2nd ice-cream stick over the 1st.
3. Loop rubber band over the ice-cream sticks in the middle.

It becomes a flat pincer for holding upto 3mm thick objects.

Constant grip/clamping force.

Idea 2

Material: 1 ice-cream stick, double sided tape.

Make it:

1. Lay double sided tape to one end of ice-cream stick.

It becomes an extension arm of the small object stuck to the sticky end.

Delicate grip, easily removable when small object is secured by rocking it off. 

Receiving a receiver today

16 September 2021 (latest)

I received the receiver. It is too small to fit in the connecting pins, the spacing looks to be around 1mm.

I wonder how to solder.

The holes are small, I don't think my wires are that small. Maybe I have to solder the wires to small diameter pins and then solder the pins to the receiver. I wonder if a staple pin is small enough to fit in the holes and if it can be soldered. 

I also remembered I have magnet wire, un-used in a coil that I purchased a long time ago. It looks like lacquered single strand copper wire, maybe I can use that?

But do I really want to cut off the servos' connectors?

10 September 2021 (earlier)

AEORC RX346/T 2.4GHz 6CH Mini RC Receiver with Telemetry Integrates 2CH Electromagnetic Servo Controller and 1S 5A Brushed ESC Support FlySky for RC Drone - Without Telemetry

I am going to receive this receiver today!

Brand Name: AEORC

Item Name: RX346/T Receiver

Model: RX346/RX346-T (with Telemetry)

Weight: 0.5g

Size: 16*10*2.5 MM

Working Voltage : 3.0V-4.2V

Automatically match frquency

Integrated 2CH Electromagnetic Servo Controller and 1S 5A brushed ESC

Support FlySky Transmitter

I already have something like this:

The ones I had, have grooves in the female housing as well, similar to the male pins. I think it meant I can break it into the number of channels that I want.

If it fits into the holes in the receiver, I wonder if I can use them to connect the battery and the power supply to the servos.

The obvious drawback to using these connectors is the size, weight and maybe I lack the ability to do it nicely. The manufacturer have designed it for direct soldering and I am complicating things for myself.

How do I wire it up? For use as a 3-Channel receiver maybe I would disregard the Magnet servos and Ch1, Ch5 and Ch 6. Ch1 is disregarded because it is on the other side of the receiver whereas Ch 2 and Ch 4 are adjacent to each other.

Soldered at receiver: 

A) 3 male prongs for GND-, 3.0-4.2V VIN+, CH1 (PWM OUT); (solder CH1 just in case) 

B) 2 male prongs for GND- MTR, VOUT+ MTR;

C) 2 male prongs for CH2 (PWM OUT), CH4 (PWM OUT).

Soldered at each of the 2 servos: 

Signal is female pinned to plug into C,

GND-, VIN+ are male pins to connect to busbar adapter.

Soldered at the motor:

2 female. These plugs into B of the receive.

Busbar Adapter for 1s Cell 

The 1S cell will have a pair of female connectors (right in the photo below) to plug into a pair of matching male connectors (left).

In the photo above, the battery (1S cell) will come with the female connector as shown on the right. The male connector as shown on the left is usually directly soldered to the receiver. For our purpose, strip the ends of the 2 wires of the pair of male battery connectors to solder to a pair of busbar adapter.

The busbar adapter block is a pair of 3 female pins.

The wires are soldered across 3 female pins.

These female pins will supply power to receiver and 2 servos.

 

How to plug them together?

• Plug power leads of the servos to the busbar (check polarity).
• Plug busbar to the receiver (check polarity).
• Plug motor to the receiver (check polarity).
• Plug signal wires of the servos to the receiver.
• Mount the receiver on model (because the connections will increase the height by a lot).
• Plug 1s Cell to the busbar.

Footprint of receiver (UNCERTAIN)

Getting every connector on top of receiver

It will not be possible to plug the busbar over the receiver because the servos' power leads will be in the way.

Bending the legs of the GND- and VIN+ inwards over the receiver may not be feasible.

Getting connectors to cross over the receiver

Bend legs of the GND- and VIN+ outwards, legs of the PWM in the same direction (both will be alongside the GND- and VIN+).

Do the MTR connectors interfere? Solder on the other side of the receiver?

2mm depron glider

 13 September 2021

I still have a few sheets of 2mm extruded polystyrene (can't buy it here now) and I could spare one to make a few chuck glider. The main advantage is it is light.

There is grain to the polystryene, cut wing in one piece, cut horizontal tail and vertical fin. Maybe can use Sniffi as a template.

For polyhedral, don't cut the wing, bend it. It will be floppy but it might be enough. At least I will not be adding weak points and weight. Either bend it over a straight edge and it might be too floppy, then I guess I can try to stiffen it by applying 2 strips of paper to both sides. Or, over a round dowel and heat applied to the foam to help it go round.

hmm, maybe a piece of tape on the bottom and a paper strip on top is good. I'd rather the foam compressed than having it cracked.

Shape a short strip of balsa and glue it to a long strip to give it more strength at the wing's leading and trailing edges. Shape and sand smooth the fuselage and add nose weigh and catapult hook. Be generous with the catapult hook because it is located at the nose and weight is useful there. 

Osprey 1

13 September 2021

I placed my order for another Dart 280 last month. Shipment was delayed to 12 September 2021 and I had received other items I ordered on that day. I checked the status today and shipment date was indicated as 21 September 2021, and I have the option for a refund.

19 July 2021

Some days before 17 July 2021, I trimmed the pylon down to the motor because it looks better. I also checked that all controls are working.

On 17 July 2021, I placed the 1s cell in the side pocket and just infront of the servos, the CG seems ok and I tried a test glide. It glided well enough and I didn't need more test glides. I didn't have to do any adjustments for my test flights. And then, surprise surprise, the motor didn't start even though the rudder and elevator servos were working. Quite a dampener

Perhaps the Dart 280's receiver isn't too durable. What shall I do now? Buy another Dart 280 just for the receiver, servos and motor? I recall that the Dart 280's servos didn't plug into my other micro receiver. 

5 July 2021

Ready for test flight and trimming on 17 July 2021.

I had to use bamboo to stiffen left-right distortion.

I used old carbon pushrods but they were too short, so I pulled the z-bends out and fabricated longer z-bends. Hopeful that it will hold up until trimmed.

I used Dart 280's receiver, servos, motor and cell. The receiver's battery plug's housing will pull out from wires if not careful. The motor lead wires were short, at one time I connected an extension lead, but after realising the CG was too forward, I used a smaller 1s battery and used double-sided tape to mount the receiver and motor on the pylon. 

If I need to adjust up/down thrust, hopeful that double-sided tape allows this flexibility and will hold until trimmed.

Hoping it is light enough for indoor flying in Kembangan CC.

16 June 2021

After the servos were glued, interest dwindled and the project stalled.

I still need to:

1. Hinge the elevator (horn already glued in)
2. Make the slot in the fin and glue the horizontal tail (I have to decide how much decalage)
3. Hinge the rudder to the fin (horn already glued in)
4. Fabricate and connect the pushrods
5. Make the slot in the pylon for the pusher (I have to decide the thrustline height and downthrust)
6. Make a hole in the wing for the motor plug
7. Pass the wing through the pylon and glue
8. Glue the motor (motor wire may be too short, I have to decide the side thrust)
9. Glue the motor doubler
10. Connect up and test

22 February 2021

10 minutes just to clear a workspace, finding stuff and tape the plans together.

40 minutes to mark out and cut out the blanks for the wings (grooved) and fuselage.

 

2 February 2021

Osprey 1 is a homebuilt type of seaplane that seats one and it had the engine on a pylon turning a pusher propeller. There is a plan on outerzone for a CO2 power free flight model and it is at 18" wing span. 

I wanted a slow indoor flier that uses the motor prop, receiver and servos and perhaps 150-400mah 1s cell. The electronics are from: Jumper W280 Dart 280mm Wingspan Indoor Park Flyer Mini Paper RC Airplane BNF for Trainer Beginner. I didn't get my Dart to fly reliably before it was damaged and didn't want to put in further effort. This is because the dart has a lot of drag, the planes are at 2 angles the wing portion at one angle and the fuselage portion at another. I don't like the waste of thrust and the model is not efficient.

I don't want to follow the outerzone plane faithfully. I will probably run out of steam. My desired construction is:

1. Profile 3mm foam fuselage with integral pylon, fin and rudder. Left side pretty, right side all the stuff and pushrods etc. Use a bit of weight at the left wingtip to counter balance.
2. Flat plate cranked wing of 3mm foam. It slots through the fuselage's pylon. 

So here goes, starting with the wing (because the wing seating on the fuselage has to match the airfoil shape (cranked flat plate)) :

1. Mark out the wing blank: 1) at the bottom, the slot, the polyhedral joint, 40% chord line for cranking; 2) at the top, the tip panels' polyhedral joint. (15 mins)
2. Cut the wing blank, the slot. (5 mins)
3. Groove the underside, raise the trailing edge (upside down), hot glue to set the crank. (5 mins)
4. Cut from bottom the polyhedral joint line. (2 mins)
5. Flip tip panels top side up, cut at angle the polyhedral joint line. (3 mins)
6. Flip mid section wing top side up, set the two tip panels to the right angle, glue together. (10 mins)
7. Sand the whole wing, matching up the polyhedral joints and rounding the edges. (15 mins)
8. Apply thin vinyl tape to reinforce the polyhedral joints and leading edge of wing. (15 mins)

70 mins

Now that the wing crank is set, it can be measured and transfer to the fuselage profile. I wouldn't use the raked fin and rudder on the Osprey 1, because I prefer to have the pushrod more perpendicular to the hinge line. 

A slow flying model at low throttle means the wing has to be big but this is not possible because I have to maintain the planform shape and size. To increase lift, I am using the cranked airfoil and presenting the wing at a positive angle of incidence. To maintain the angle of attack of the wing I have to use the stabiliser, so I must present the wing/stabiliser at a slightly greater decalage. I will take the stabiliser at zero degrees to the direction of flight. I will present my wing at 3 degrees. The propeller is mounted above the wing and will have a strong nose down moment. I will present my motor at at positive 6 degrees to the stabiliser.

1. Mark out the fuselage blank. (10 mins)
2. Cut the fuselage blank, separate rudder and cut slot for motor. (10 mins)
3. Sand the fuselage and rudder blanks. (10 mins)
4. Mark out the stabiliser blank. (5 mins)
5. Cut the stabiliser, seperate the elevators. (5 mins)
6. Joiner to the elevator. (5 mins)
7. Hinge the elevator to the stabiliser. (5 mins)
8. Apply thin vinyl tape to left side of fuselage, fin and top side of stabiliser. (10 mins)

70 mins plus 60 mins.

Follow by:

1. Glue the horizontal stabiliser to the fin. (5 mins)
2. Glue the wing through the fuselage pylon. (5 mins)
3. Mark and cut the engine blank. (5 mins)
4. Glue the motor to engine blank. (5 mins)
5. Sand the engine blank. (5 mins)
6. Glue the engine blank assembly to top of pylon. (5 mins)
7. File slot so that the motor connector can pass through right side of wing. (5 mins)
8. Apply thin vinyl to pylon to hide the motor wires. (5 mins)

130 mins plus 40 mins.

Finally, glue receiver, servos, horns, making up pushrods etc. (60 mins)

Total time will take 170 mins plus 60 mins = 230 mins or 3 hours 50 mins. Can be built in about 4 sessions.

Motor mounting for geared coreless motors

10 September 2021

I read through some articles on constructing Peter Rake's mini RC models on outerzone and found that he designed the motor mount either vertically with a hole to fit the motor or horizontally with a slot to receive the motor and one builder used Goop so that the thrust line can be adjusted.

Maybe I can use UHU or epoxy to glue the motor cylinder to my mount.

What a simple idea and I didn't think of it.

29 March 2021

The cheapest geared coreless motor unit does not have a horizontal flange to mount the on the model. I have a few ideas to mount the geared coreless motors:

• Bulkhead
• aluminium bracket
• square section rod

Bulkhead

Make a hole in a thick slab of foam or 2 pieces of ply to fit the nylon housing. Enlarge hole to clear propeller bearing. 

If the block shall also be the nose block, such as is possible with blue foam slab, then the hole will be at 2 angles and not perpendicular to the block, to cater for side-thrust and nose-thrust. The big propeller gear will be exposed. The motor unit slips in from the front with the propeller already pressed fitted.

If the bulkhead shall only be to mount the motor unit, then the hole can either be perpendicular with the sides of the block bulkhead sanded to the thrust line or in 2 bulkheads system, by positioning the holes differently or as per the first option of single slab bulkhead, to have the sides squared and the hole at the tilted angles. The motor unit slips in from the front.

Either way, the motor unit is glued to the bulkhead/s.

Aluminium bracket

Cut strip of aluminium from an aluminium can. Coil strip around diameter of nylon housing then bend 2 tabs so it is a half bracket.

Internal flat bulkhead to support bracket will be needed.

Since the aluminium is so pliable, it can be twisted to the thrust line many times by hands.

The aluminium half bracket will be glued to the nylon housing. Roughening the contact surfaces may also allow hot glue to be used.

Square section rod

Each housing has a small 2x2 or 2.5x2.5mm square hole.

If I can find a stiff enough square rod, then I could have this as a single beam across 2 perpendicular bulkheads.

There will be minimal contact area at the bulkheads, so an alternative is to glue it to a horizontal bulkhead.

If the square rod can be bent by hands, then it can be bent to the thrust line many times too.

A further option is to glue the square rod to a flat strip and use that instead. 

Sanding Tools

 2 September 2021

Sanding jig (1) for square balsa strips

1. Base piece from ice-cream stick, 2 cm long
2. Pressure piece from ice-cream stick, 2 cm long
3. 2 scrap balsa thickness spacer
4. Sand paper 150grit, 250 grit  
5. Double-sided tape

Lay double side tape to 1.

Lay sand paper stick to 1.

Lay double side tape to edges of sand paper stick.

Lay 3 to edges of sand paper stick.

Lay 2 over 3.

Squaring balsa stick/s

Pinch jig to grip balsa stick slightly

Pull stick

Reverse edge.

Sanding jig (2) for square balsa strips

1. Sanding block with sand paper 150 grit, 250 grit
2. 2 scrap balsa thickness spacer
3. Double-sided tape

Lay double side tape to 1.

Lay 2 on tape.

Squaring balsa stick/s

Lay double side tape on table.

Lay sticks on tape.

Lay jig over sticks.

Slide jig over sticks.

Lift sticks and reverse edge.

Sanding jig for balsa ends and edges

1. Rectangular piece of ply (harder than balsa), 1 side straight edged
2. Square piece of ply, each side is the width of the rectangular ply piece
3. 45-90-45 triangular ply piece
4. Base piece with length same as item 1 and width is 2cm wider than item 1
5. Sanding blocks, 150grit, 250 grit  
6. Double-sided tape

Glue 1 on 4.

Glue 2 on 1.

Lay double side tape to 1.

Sand balsa stick/s

Item 3 sticks on double side tape to hold balsa stick/s at the angle.

Lay balsa stick/s on double side tape between 2 and 3.

Slide 5 along 1.

Sand balsa formers straight

Lay balsa former blank over item 1's straight edge.

Slide 5 along 1. 

Sand balsa/foam discs

Pin blank at set distance from edge of 1.

Slide 5 along 1.

Repeatedly lift and rotate blank and slide 5 along 1.

Sanding around coins and other round object

1. coin or other round object (harder than balsa)
2. double side tape

Lay 2 on 1.

Sand discs

Lay balsa/foam on 2.

Slide 5 around 1.