[TC25] 42145 Airbus H175 Rescue Helicopter

[Ngoc Nguyen]

The general impression towards the original 42145, or at least my impression, is that it is an excellent Technic model in terms of functions and building experience, but not a really good replica of a real H175. Take the name away and it's hardly recognizable.

Hence I've been working on a smaller 42145 that aims to capture the accurate proportion. The original model I worked on is motorized, and that's the source of the fun.

 

The design challenge involve fitting a battery box + a motor + a two-function gearbox in a very tight place and building a form locked structure around them. It was very challenging and very satisfying to have arrived at a satisfactory solution.

But TC25's rule does not allow electronics, and faithfulness in terms of color to the original model is one of the scoring factors. So I hollowed out its inside and changed it to this.

 

At the moment I'm not sure of which color scheme I should go with. 42145's original color scheme is not very inspiring to me, and the color scheme I originally used is based on this, which is much cooler to me.

 

 

Another thing is that without the gearbox and electronics the model is very boring inside. The winch is already manual. Now I only need to add a driving crank to the landing gear mechanism and the rotating blades. I guess in the end I'll just have to roll with it.

 

 

[Ngoc Nguyen]

Since the inside is hollowed out I do feel like putting a function or some mechanism in, but I cant think of any. Even simple collective pitch wont fit in this scale.

[Jundis]

18 minutes ago, Ngoc Nguyen said:

Since the inside is hollowed out I do feel like putting a function or some mechanism in, but I cant think of any. Even simple collective pitch wont fit in this scale.

From the looks, it's great. But without a function it's rather strange... sure there is not enough space for collective pitch? Small turntable with inner axle should do the job or not?

[howitzer]

I briefly considered 42145 as well, but the main attraction for the set is the collective and cyclic pitch control, which are really hard if not impossible at reduced scale so I decided against it. I don't think this is a good candidate for this contest, as dropping the most important functionality reduces it to a generic helicopter with not much to show off.

[Ngoc Nguyen]

4 hours ago, howitzer said:

I briefly considered 42145 as well, but the main attraction for the set is the collective and cyclic pitch control, which are really hard if not impossible at reduced scale so I decided against it. I don't think this is a good candidate for this contest, as dropping the most important functionality reduces it to a generic helicopter with not much to show off.

I have another shrunk model in progress but given my summer schedule and the fact that the contest only lasts for 2 months I decided against using it, sadly.

[Ngoc Nguyen]

8 hours ago, Jundis said:

Small turntable with inner axle should do the job or not?

How exactly would you design that?

[Ngoc Nguyen]

This is how the motorized version looks inside. Very dense and challenging build.

[Alex Ilea]

This was the set I originally wanted to build for the competition, but found another meanwhile. I believe that, if you want to have an interesting personal challenge, and potentially win the contest, you should add the variable pitch, and the trigger to power the blades. 

Yes it will be difficult (borderline impossible) but it doesn't  need to be perfect, and it would be really cool to see.

Good luck friend on this project!

[Ngoc Nguyen]

At this scale the model can only be 9 stud wide.

 

The original area for the rotor is only 4 studs wide if it's to be accurate to scale. There's also a fence around the rotor hole. The new swashplate is 5x5 and with tow ball pins attached it will be 7 stud wide. So theoretically it might fit if I remove everything between the two walls.

 

24 minutes ago, Alex Ilea said:

you should add the variable pitch

I think there is only space for a collective pitch if I put the swashplate lower in the body. 

[Thirdwigg]

Great work already, and I like the set you have chosen.

But I think you have to do some collective control or something for the main rotor. Maybe switch to four rotor blades. This would keep the feel of the set still and allow for a simpler and smaller design.

[Ngoc Nguyen]

I have decided that I will keep the 5 blade structure and add a collective pitch function.

I have hollowed out a 5x5 square below the rotor for this.

[Ngoc Nguyen]

This is the temporary placement of the swashplate.

 

It was quite a struggle to find a proper place. The whole model is 9 stud wide, and I wanna keep a wall of 2 studs to have space for structural reinforcement, so the rotor hole can only be 5x5. The problem is that the swashplate itself is already 5x5, so the liftarms that connect it to the blades must be directly above it.

That means I need another one stud going outside to connect the 5 holes to the 5 liftarms, causing the structure to have a 7x7x2 space. And because the collective pitch is supposed to go up and down, the actual required space is 7x7x3. To complicate matters further, I need a liftarm that connects the landing gears in the front and in the back. So I put it in the seating area where there is enough space, and that means the 28z turntable has to be on the floor. 

And that means I'll have to find a way to connect the turntable to the rear rotor. That's a whole different problem..

If things dont work out and I get desperate I'll hollow out a full 7x7 column.

 

[SaperPL]

@Ngoc Nguyen pro tip: WIN+SHIFT+S and select only portion of the screen through windows snipping tool instead of wasting real estate of your screenshots on the UI of bricklink studio and windows taskbar :)

[Ngoc Nguyen]

11 minutes ago, SaperPL said:

@Ngoc Nguyen pro tip: WIN+SHIFT+S and select only portion of the screen through windows snipping tool instead of wasting real estate of your screenshots on the UI of bricklink studio and windows taskbar :)

I know I'm just lazy. Aint nobody got taim for aligning the snipping tool precisely on the model.

Edited July 2, 2023 by Ngoc Nguyen

[HydroWorld Outlook]

Nice work so far! I can't wait to see how the final version looks.

Also, I have a suggestion for how you could accomplish blade pitch. Maybe if you attach each of the five rotor blades to 12-tooth single bevel gears (using 2 of this part, 2 of this part, and 1 of this part on each rotor blade), with a 20-tooth single bevel gear in the center, you could achieve adjustable pitch on all blades in a compact space. Building the rotor hub should not be that much of challenge using the new starfish piece, which I see you have already done in the pictures posted above. Because you would be using the axle to control blade pitch, you would need to mount the entire rotor assembly on a 28-tooth turntable in order to drive it, which could be accomplished by connecting one arm of the starfish piece directly to the turntable's upper toothed half. Doing all this would enlarge the whole rotor a bit but only slightly.

Normally I would not recommend this method for variable-pitch propellers on LEGO Technic models because centrifugal force would easily rip all the blades out while the propulsion motor is spinning them, but because there are no electric motors allowed in this competition, and all functions must be manually-operated, centrifugal force should not factor here. Additionally, if you would like to simulate the collective and cyclic pitch functions of the larger model in your scaled-down version, you could connect the blade pitch control axle (the axle rotating the central 20-tooth gear) to a universal joint so that it can be tilted while rotating. 

Hopefully these ideas help.

Edited July 2, 2023 by HydroWorld Outlook

[Ngoc Nguyen]

On 7/3/2023 at 3:29 AM, HydroWorld Outlook said:

Maybe if you attach each of the five rotor blades to 12-tooth single bevel gears (using 2 of this part, 2 of this part, and 1 of this part on each rotor blade), with a 20-tooth single bevel gear in the center, you could achieve adjustable pitch on all blades in a compact space.

I gave this a thought but I don't really understand how it will work. If all blades are attached to 12-tooth single bevel gears, and they all mesh with a 20-tooth single bevel gear in the middle, when the blades rotate, the 20 tooth bevel gear must rotate too, which means the vertical axle that it's on rotates too. Then how would collective pitch be achieved? 

[JoKo]

6 hours ago, Ngoc Nguyen said:

I gave this a thought but I don't really understand how it will work. If all blades are attached to 12-tooth single bevel gears, and they all mesh with a 20-tooth single bevel gear in the middle, when the blades rotate, the 20 tooth bevel gear must rotate too, which means the vertical axle that it's on rotates too. Then how would collective pitch be achieved? 

I'm not sure what @HydroWorld Outlook means, maybe he can show it with a picture.

Anyway there is a way to make variable pitch propeller with bevel gears but you'll need a complex mechanism including two differentials in a substractor.

There is an exemple on my Napier Lion airplane engine:

I tried with 2, 3, 4 and 6 blades but should be possible with 5 with the new starfish piece

Let me know if you have any question about the mechanism I used.

[Ngoc Nguyen]

4 hours ago, JoKo said:

a complex mechanism including two differentials in a substractor.

Subtractor only works if the drive is motorized doesnt it

[Thirdwigg]

This is a great project, and I love what you have so far. I hate to suggest to simplify the build and rotor mechanism, but by going to three or four blades for the helicopter might help a lot. Plus, if you only keep the collective, and not the cyclic, you'll pick up a lot of extra room.

Edited July 7, 2023 by Thirdwigg
clarity

[Ngoc Nguyen]

40 minutes ago, Thirdwigg said:

Plus, if you only keep the collective, and not the cyclic, 

I have never intended to do the cyclic 

40 minutes ago, Thirdwigg said:

by going to three or four blades for the helicopter might help a lot

We can never know for sure if I dont try it first

[JoKo]

1 hour ago, Ngoc Nguyen said:

Subtractor only works if the drive is motorized doesnt it

It will work with manual knob to drive the rotor but will behave weird if you push a blade with your finger to rotate the rotor.

I' not sure that it can be more compact than the original collective mechanism though 🤔

 

[Ngoc Nguyen]

I think I'll drop this entry and drop out of the contest. It just doesn't feel right to remove hub and motor to make a manual model. That's not what I started the designed for, and that's not how I want it to end up being. It feels like butchering my creation. And the contest is about fun. I don't really feel the fun in making a manual version out of what I initially started. Also I spent my creative juice on the 42157 B model already; my workload is also heavier for the upcoming month.