No.2 : FROJO

Why can't you have a flapping helicopter? This is not done on purpose in real life. Apparently helicopters have hinge pins to allow some flapping due to lift differences between advancing and retreating blades, but they do not actively flap the blades. FROJO (FRed* Or JOe) actively flaps its rotors.

The construction is similar to No.1. A silver soldered wire frame holds the moving bits in relation to each other. A painted cotton covering adds some detail to the model. All the sewing is done using cotton and not wire sometimes. The rotors are covered with parachute silk which was done as a restoration job. Later monsters all make use of parachute silk. There is a beaten copper nose panel for effect, as well as two aluminium side panels with fake rivets. The body is shaped with meshed wire. The wheels are formed from wire with binding to help hold the shape. For the fun of it Fred and Joe have different necks, but both make use of crab claw heads. 

Fred and Joe ended up being desert fighters (maybe South West Africa - yes, pre-Namibia). In their adventures they have sorted out a camel, a sea gull (or maybe pelican), a pair of WWII German aircraft and a pair of AWB mounted combatants. The livestock and bird were accidental. The WWII German aircraft go back to my favourite childhood literature of war comic books, in which a small number of British aircraft sort out many superior German aircraft wanting to overrun their small island. The AWB mounted combatants just added a South African flavour to it as their symbol was 3/4 of a German tail marking and they didn't have aircraft, only horses.

Back to the monster. The fun bit was figgering out how to get the flapping mechanism to work. I knew that it had to have a swash plate, because all helicopter had one. Once this was decided the rest fell into place. A long lever moves the swash plate up and down. By hinging the blade along its edge instead of fixing one side of it, the blade flaps instead of changing pitch (ie. the hinge is rotated 90 degrees to that of a standard helicopter). From the videos reference later you can see that I may have a little too much movement, but that is how I did it then and I don't want to change it now.  The rotor blades are driven by hand cut copper gears which work better than those of No. 1 because they are at right angles to each other. 

To add a bit of visual interest Fred and Joe move in opposite directions and by different amounts. This seems to make them work against each other, which is a common South African trait. A tail rotor driven by a chain was added also for visual effect. This chain came from old photo processing equipment and had to be used. The gears which form part of the chain drive were hand cut from copper (see a theme developing?). The original idea for the monster was to push it along the ground, which would mean that the main rotor and tail rotor would be driven at the same time. For the video I however added a separate motor to the monster mount to drive the tail wheel. This allowed me to get a realistic tail rotor speed, which would not have happened when pushed. (For the video :Youtube Frojo Video)

Sketch showing some principles of the kinetic bits

*FRED : Flapping Rotating Entertaining Device?

This is No. 1

After doing the dragon on a cycle 3D sketches, the next phase involved monsters that could have been derived from aircraft or insects. At this stage I thought it would be a good idea to number them, and this was the first. 

No. 1 approaching?

The numbered monsters have a few characteristics in common. They have wings which flap, are driven by wire wheels, have brazed wire frames and critical moving bits. The wings are covered by cotton cloth and a little painted decoration. The frames are covered with a meshed wire pattern. They all have one or more nodding crab claw "heads", which could be called the pilot(s). I'm not sure though whether it is the pilot or the monsters head. I like the head idea with the flapping structure forming the body. This also works better for the insect derived monsters.

Number 1 is strongly based on a school boys idea of an round engined fighter (https://en.wikipedia.org/wiki/Brewster_F2A_Buffalo) maybe crossed with a Gee Bee Sportster (https://en.wikipedia.org/wiki/Gee_Bee_Model_R). Like all real aircraft it  has round engine  (courtesy of Coca Cola).

This monster retains a little of it's origin in the dragon era by having spines along its back and a scaly paint job on the covered tail surfaces. 

Details showing the scaly tail surfaces paint job

The wings have been made with wire ribs, similar to ultralight aircraft construction. Additional details, such as the covering on the side of the aircraft sewn with fine wire, are to create the impression of a cloth covered aircraft. Details around the cockpit include aluminium panels with false rivets, brass chain mail inserts as well as a copper plate on the nose. These are all for effect and serve no mechanical purpose. The black Eisernes Kreuz (derived from the Cross Pattée) was used on German WWI aircraft before 1918 (and the death of the Red Baron), with this one being closer to the one used between 1916 and 1918. The cross is painted on the wings to create the retro-feeling of an aircraft of 100 years ago (only 70 or so years ago when it was made). The coke bottle cowling was painted red in front with an aluminium plate with bumps representing the bolts on the engine. The aircraft ambiance is rounded off with a copper spinner for the two bladed propeller. 

The mechanical parts of the monster were more challenging. Bearings for the wheel axles, cranks and gear shafts are created by bending wire into a circle. The propeller is driven by hand cut copper gears driven from the wheel axle, and turned through 120 degrees with a bent wire universal joint. The wings and head move via couplings to a crank on the wheel axle. Not everything turns smoothly all the time, but this is why it is a sketch and not a mechanical mechanism (which would imply refinement through iterative designs).

Some mechanical details

The following link is to a longer video which is easier to view than using the bloggers video app : Video of No. 1.

The Starting Blog

This is the first of the actual KR3DS blogs. The purpose of these sketches are to demonstrate some form of movement. This particular one hasn't got a name or originated from any great inspiration, but was purely born out of a "what if ?" moment. 

The basic movement of most of these rotary kinetic sketches is the wheel driving a crank and the crank flapping wings (via one or more push rods). After this there follows many variations of the theme. This particular one has an additional hinge on the end of each wing and an offset fixed point coupled with a push rod. This allows the tips of the wings to swivel and add a little complexity to the basic flapping motion.

Image to give the impression of flapping wings.

The basic movement of the 3D sketch is demonstrated in the following video.

This video shows the sketch (or monster) mounted on stand with a motorized drive for the wheels. The motorized drive is battery powered and drives a large reduction gearbox to provide the necessary torque to turn the mechanism. Originally the intention was to push the monsters on the ground to provide rotary motion via the wheels. Unfortunately the wings generally provide a very unbalanced load, and the wire wheels do not have sufficient grip for smooth motion over the full flap cycle. If you push with enough downward force for a convincing demonstration you end up deforming the monster (wire bends after all). Anyway the motorized drive means that one can have a video without the pusher getting face (or hand) time. There is also the added benefit of not having to be behind the camera as well as in front of the camera at the same time. I prefer it this way.

This monster shows most of the construction techniques employed in the series. 

The frame is constructed using thick wire which is brazed or silver soldered. The overall shape of the sketch is formed with thinner wire, generally woven to create a sturdy structure. Wings are covered with silk in this and the later models. This is stretched and stitched keep it taut. The silk is coated with clear coats of dope, and usually has a pattern painted on the surface.

This particular monster has a cover made of aluminium printers tray with false rivets, for an aeronautical effect. It is attached with brass plates and small pop rivets.  The surface of the wing is painted with red veins to mimic a bats wing with back-lighting from the sun. I don't know why I decided on this paint scheme, but I guess it does fit in with the general theme of "things that could possibly fly".

Here is a link to a longer video showing the basic movement of the 3D Sketch as well as a close up of the mechanism in motion (the crank bits which flap as well as the forward flung hinged wing tips). Youtube video of the starting monster