42179 Planet Earth and Moon in Orbit

[R0Sch]

18 hours ago, aeh5040 said:

Oh yes, well spotted! Although I wonder whether that is a 20t or 36t (or even a turntable again).

It is looking very much as if all the gears are horizontal, so really the task is to connect the 20t that turns the big turntable with the central vertical axle, with the correct spacing and ratio ...

I've kind of got obsessed with this!

EUREKA!
36:12 * 36:12 * 16:16 * 36:8 * 60:20 = 121.5:1 gear ratio and with a 3 day period results in pretty much a year (364.5 days to be precise).
After many trial and errors I realized the base frame is not comprised of 2x 7x11, but instead one large 11x15 frame. This opened up the possibility of fitting another row of gears underneath the 16T ones. And with the enhanced image from yesterday it's clear that this is the way.

Edited December 15, 2023 by R0Sch

[Zerobricks]

Bravo to everyone for reverse engineering! Can someone count the number fo gears? I'm curious.

[R0Sch]

4 minutes ago, Zerobricks said:

Bravo to everyone for reverse engineering! Can someone count the number fo gears? I'm curious.

Thank you! Actually not so many only 25 gears + 4 turn-tables + 4 banana gears.

[Davidz90]

45 minutes ago, R0Sch said:

36:12 * 36:12 * 16:16 * 36:8 * 60:20 = 121.5:1 gear ratio and with a 3 day period results in pretty much a year (364.5 days to be precise).

Whoa, that is way more accurate than I expected. Also, great reverse-engineering!

[R0Sch]

15 minutes ago, Davidz90 said:

Whoa, that is way more accurate than I expected. Also, great reverse-engineering!

Yes, that is a great feat from the Designer(s).
Here's the link to the Studio file (only missing 20 pieces, most likely pins): 42179.io

[Zerobricks]

I think there are small train wheels used instead of 2x2 dishes inside the small ring foor support.

Edited December 15, 2023 by Zerobricks

[R0Sch]

10 minutes ago, Zerobricks said:

I think there are small train wheels used instead of 2x2 dishes inside the small ring foor support.

Yes, you are right. They act like roller bearings to keep the middle centered.  Fixed it!

[aeh5040]

5 hours ago, R0Sch said:

EUREKA!

Wow! Brilliant! This is clearly it. I am quite surprised and impressed that they got it so accurate, and even more impressed with your powers of deduction. I had actually started to ponder the possibilities of 8t-36t, but I don't think I would ever have got it.

Edited December 15, 2023 by aeh5040

[R0Sch]

Thanks to all who helped with tips and the required ratios! It was a really fun challenge.

Too bad it looks so crude and the colors are all over the place. I also noticed in the pictures that despite the robust construction and roller support, the arm hangs quite a bit.

[CP5670]

This is a really nice set. It's the kind of thing we used to only see in universal sets and idea books back in the day. It's pricey but I'll probably get one.

[aeh5040]

17 hours ago, R0Sch said:

Thanks to all who helped with tips and the required ratios! It was a really fun challenge.

Too bad it looks so crude and the colors are all over the place. I also noticed in the pictures that despite the robust construction and roller support, the arm hangs quite a bit.

Yeah I agree. I like the look of many parts of it - the rings, the core structures etc. But the base is just a mess. I guess some of it is colour coding to help with the build - the unsecured 3L blue liftarm matches the exposed blue axle pin (which I think should be 1/2 a unit lower btw), and there is probably a red one on the other side. But it would be so easy to tidy these things up at the end. 

Still, let's not lose sight of the many positives. It's a very clever piece of engineering, and completely unexpected as a set. We can hope that it heralds a new era of interesting mechanisms.

Edited December 16, 2023 by aeh5040

[Davidz90]

I was curious if the 364.5 is optimal since it is so accurate with limited number of gear ratios. So I've written a computer program and the results are:

up to 4 gear ratios
1/16*1/16*28/40=1/365.7143
1/28*1/28*28/60=1/365.867
1/36*8/36*16/36=1/364.500

up to 4 gear ratios, with differential
1/60*(1/20+16/140)=1/365.2174
1/140*(1/12+12/40)=1/365.2174
1/140*(8/24+1/20)=1/365.2174

I selected only few best ones  because the output contained several hundred redundant solutions, like 1:3 done in several ways, the same gear ratios in different order etc. The 364.5 is, indeed, the best option with 3 or 4 gear ratios and no differential.

Ideally, we want 365.2425 days; differential options are really close to that (error of 36 minutes)

Edited December 16, 2023 by Davidz90

[R0Sch]

1 hour ago, Davidz90 said:

I was curious if the 364.5 is optimal since it is so accurate with limited number of gear ratios. So I've written a computer program and the results are:

up to 4 gear ratios
1/16*1/16*28/40=1/365.7143
1/28*1/28*28/60=1/365.867
1/36*8/36*16/36=1/364.500

up to 4 gear ratios, with differential
1/60*(1/20+16/140)=1/365.2174
1/140*(1/12+12/40)=1/365.2174
1/140*(8/24+1/20)=1/365.2174

I selected only few best ones  because the output contained several hundred redundant solutions, like 1:3 done in several ways, the same gear ratios in different order etc. The 364.5 is, indeed, the best option with 3 or 4 gear ratios and no differential.

Ideally, we want 365.2425 days; differential options are really close to that (error of 36 minutes) 

Interesting. And let's not forget no worm gear was used either. All your combinations need at least one worm gear. How about the sun and earth rotation speeds, do they match well enough as well?

[Davidz90]

3 minutes ago, R0Sch said:

How about the sun and earth rotation speeds, do they match well enough as well?

Sun is not solid and it's rotation period depends on latitude; 24.47 days on equator, 34 near the poles. Basically anything between 1:24 and 1:34 is ok, so 1:27 used here is fine.

[howitzer]

Not using differential to get the gear ratios more accurate is a kind of missed opportunity here. I'm sure many people have familiarity with the usual gear systems but using a differential to get different ratios is probably something that most people don't know about and this set would've been a perfect opportunity to introduce such a mechanism.

[gyenesvi]

3 hours ago, howitzer said:

Not using differential to get the gear ratios more accurate is a kind of missed opportunity here. I'm sure many people have familiarity with the usual gear systems but using a differential to get different ratios is probably something that most people don't know about and this set would've been a perfect opportunity to introduce such a mechanism.

What ratio is achievable with a differential? I was wondering about that recently, but could not really find out how to calculate that..

[Davidz90]

12 minutes ago, gyenesvi said:

What ratio is achievable with a differential? I was wondering about that recently, but could not really find out how to calculate that..

It's in my earlier post. Some of the many, many options:

1/60*(1/20+16/140)=1/365.2174
1/140*(1/12+12/40)=1/365.2174
1/140*(8/24+1/20)=1/365.2174

in general, differential output is average speed of inputs. So, for example, if we have two inputs, both geared down so for 1 rotation of input we have:

A: 1/3 rotations

B: 1/2 rotations

then the differential output is

(A+B)/2 = (1/3+1/2)/2 = (2/6+3/6)/2=(5/6)/2=5/12

By gearing output 2:1, we get a simple sum (A+B) instead of an average. If inputs rotate in opposite directions, we have a difference (A-B).

Edited December 17, 2023 by Davidz90

[gyenesvi]

2 hours ago, Davidz90 said:

in general, differential output is average speed of inputs.

Oh thanks, I meant in general. Silly me, I knew that it averages, I just didn't think it is used that way for gearing :)

But what I was actually wondering the other day, is that if it has two inputs, and only one is driven temporarily, it essentially halves the speed, but does that double the torque at the same time? I guess it should, as in total, power should not be lost (not counting loss in friction), right? So if I have two motors driving the two sides of a diff, and I stop one (brake it) then the speed will become half, but the torque will be the same (only one motor, but torque doubled), is that right?

[Davidz90]

56 minutes ago, gyenesvi said:

But what I was actually wondering the other day, is that if it has two inputs, and only one is driven temporarily, it essentially halves the speed, but does that double the torque at the same time? I guess it should, as in total, power should not be lost (not counting loss in friction), right? So if I have two motors driving the two sides of a diff, and I stop one (brake it) then the speed will become half, but the torque will be the same (only one motor, but torque doubled), is that right?

Yes, with one powered input and one locked input, the differential casing has half speed and double torque.

[zoo]

1 hour ago, gyenesvi said:

So if I have two motors driving the two sides of a diff, and I stop one (brake it) then the speed will become half, but the torque will be the same (only one motor, but torque doubled), is that right?

Not sure how the two motors work together in this application but in essence, if input torque is halved while input speed is the same, you need to gear down output speed to half in order to maintain initial output torque.

Edited December 17, 2023 by zoo

[gyenesvi]

1 hour ago, Davidz90 said:

Yes, with one powered input and one locked input, the differential casing has half speed and double torque.

Thanks!

1 hour ago, zoo said:

Not sure how the two motors work together in this application but in essence, if input torque is halved while input speed is the same, you need to gear down output speed to half in order to maintain initial output torque.

And that's exactly what the diff casing does if you drive its two sides (normally the outputs).

[SNIPE]

Bravo on reverse engineering this set, I havn't seen those 36 tooth gears in a technic set ever since 42100.

Edited December 18, 2023 by SNIPE

[allanp]

The accuracy of the gear ratios is very impressive, I'm liking this thing more and more! Does anyone know what the white parts on the base are for? Are they to indicate something or can just be swapped out with black or something?

[howitzer]

16 hours ago, SNIPE said:

Bravo on reverse engineering this set, I havn't seen those 36 tooth gears in a technic set ever since 42100.

It was actually in the Top Gear rally car, Concrete mixer truck and in Mini Claas Xerion in 2020 and in the Off Road Buggy in 2021. Still, it is along with the 40T gear surprisingly rare among Technic sets, at least compared to most other gear sizes.

[Zerobricks]

Don't forget if the gear ratio is 364,5 the Earth does one additional revolution going around, so the end gear ratio is actually 365,5.

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