All details and functions of the original 42113 have been perfectly replicated in this mini model. The mini model uses only the parts that are available from other sets. The fuselage of the original model is 9 studs wide and 9 studs tall. I chose the shrunk factor is 2/3, so the fuselage of the mini model is 6 studs tall and 5 studs wide. Certain parts are scaled around the real Osprey rather than the 42113 set to ensure realistic appearances.

Functions:

- Retractable landing gears
- Movable 2-piece ramp
- Spinnable blades
- Tiltable nacelles
- Movable flaps

 

 

This mini 42113 has 1016 pieces. The only rare parts are the micro panels in orange, only available from 42196, and tapered panels 5x11 in DBG, only available from 42146. But even then, according to Rebrickable total part cost is around 200$, which is pretty manageable.

Instruction: https://rebrickable.com/mocs/MOC-182759/nguyengiangoc/mini-42113-bell-boeing-v-22-osprey

 

Edited August 10, 2024Aug 10 by Ngoc Nguyen

Nice work and well presented.

1 hour ago, Paul B Technic said:

Nice work and well presented.

Thanks a lot for the support!!

I like this, all the micro panels work quite well for this model, nice shrinkage!

On 5/6/2024 at 3:50 AM, gyenesvi said:

I like this, all the micro panels work quite well for this model, nice shrinkage!

Thanks for the compliment!

I finally got the pieces and did a demonstration video! Everything works flawlessly!!! Development story is coming later.

 

Words or photos or my phone can't really show how cool this thing looks in real life. I have it on my work desk and it's a real head turner.

This is a cross section of the model to show you the inner working. As you can see, there is barely any unused space. Everything about this model is difficult, and I'm very very happy that it is finally functional.

 

The root of the challenges in the design process is the width of the fuselage. The original 42113 has a fuselage that is 9 studs wide and 9 studs tall. I decided to shrink by 2/3, so that the mini fuselage has a height of 6 studs, but the width has to be an odd number, so it can only be 5 studs. Since the walls already take up 2 studs, the space I have for all the gears and functions have to be squeezed in a space of 3 studs width. 

 

 

The landing gear function uses different gear ratios for the front and for the rear wheels, because when folded, the rear wheels only need to move by 90 degrees, while the front wheel, due to being placed further front, needs to move by a larger degree. The front 20z gear also presents a convenient chance for me to use a worm gear to ensure the positions are locked. The rubber piece is used because the swing arm (4L thin liftarm) together with the block is actually longer than 4 studs, which means it will collide with the front column when it rotates up. Fortunately, the rubber piece can bend backward slightly so that the thin liftarm can do a full swing smoothly.

 

 

The opposite movements of the two pieces of the rear ramp are achieved through simple linkages. When the knob is turned clockwise, the 2x3 quarter liftarm will push the bottom piece down.

 

 

The highlight of the design is the arrangement of the rotor and the tilt function. Both of them have to go to the wings at an angle, but the wing only can only accommodate one axle in the middle, so that axle will be for the rotor. The tilting is achieved through a meshing of 8z-28z gears at the turntable at the end of the wings.

 

Because the width is only 3 studs and the axle has to be attached to two universal joints on two ends, there is no space for perpendicular transmission. That's why the transmission for the rotors go by a combo of 4 horizontal spur gears. It's very fortunate that the 16z gears fit perfectly under the slot in the middle of a 3x7 panel, so I can cover the middle part with that panel. 

The tilting transmission has a worm gear driving a 12z gear. Originally I used a worm gear with a 8z gear, but that doesn't generate enough force, and 12z gear is the only bigger gear that fits into that place. To mesh a worm gear with 1 12z gear, the worm gear was put at a 0.5 offset, which means it needs universal joints to be taken back to grid. In the back the transmission has to be geared down twice further.

The final gear ratio from handle to nacell is (12/20) x (12/20) x (1/12) x (8/28) = 0.0085 which is 0.8% reduction. That means the tilting nacelle works very slowly, but it is only through such heavy gearing down that the knob can provide enough force to tilt the nacelle. Anything larger will cause the gears to skip. 

Edited August 11, 2024Aug 11 by Ngoc Nguyen

Thanks for showing pictures of the inside! That does look like it was quite a challenge to compact it that much!

6 minutes ago, 2GodBDGlory said:

Thanks for showing pictures of the inside! That does look like it was quite a challenge to compact it that much!

The real compactness challenge is when the rear wheels are folded up.

 

The transmission for the tilting nacelle, which drives the worm gear, has to be routed to the back. But at the same time, there's a 20z gear on top and the landing gear mechanism in the bottom. The linkage for the wheel needs a midline block to prevent the wheels from collapsing on itself, hence the existence of the 2L axle hole-pin hole liftarm. The pin hole has a 1/2 pin that serves as a block, so when it is fully retracted, in theory the 1/2 pin will collide with the CV joint.

 

But thanks to the magic of flex, in real life, the CV joints and the universal joints are slightly bent to the right while still capable of rotating smoothly, and since the CV joint has a frictionless axle holder it has a small sideway wiggle room.

Big Osprey and small Osprey in maiden flight color scheme! Photos by dan1992002.