Help needed for an assembly

[bj51]

Hello !

I'm trying to find a solution to a problem i'm having. I'm building a lattice crane and one of the sections needs 9.5L liftarms... I've come up with this :

But it's a little too bulky, compared to other lattice sections with just liftarms. This particular assembly fits like this in the section :

Anyone have an idea for a less bulky 9.5L liftarm ?

It needs :

• to be 9.5L long,
• to be put between plates at both ends, so the 2 first holes at each end should remain free,
• to resist length-wise efforts in traction (you should be able to pull at both ends and it wouldn't break), so an axle/axle joiner/axle connector solution won't work.

Thanks for reading !

Edited January 7, 2020 by bj51
typo

[Gray Gear]

Dont change the liftarms, change the whole assembly to use normal full length liftarms. It will look better and be more stable as well.

[bj51]

Yeah, i thought of that. I looked for a long time before settling on this dimension. The problem is there are 8 different sizes of lattices in the crane : 2 sizes of boom, with each 2 sizes of lattice (they're rectangular in section, not square). On top of that, you have 2 lengths of each section, 6m (with 3 arms per lattice) and 12m (with 5 arms per lattice), so you've got 8 different combinations (6 in fact, the small side of the larger boom is the same as the big side of the smaller boom). Here's a family picture :

From left to right : Large 6m boom, large 12m boom, small 6m boom, small 12m boom.

All other lattice lengths are integer-lengths of liftarms, except for the one on the small 12m boom. So you see everything has to fit together, so it's hard to change the size of just that section.

[Jundis]

Do you need to use liftarms? Maybe you can go with the 5.5L crossaxle and axle connectors?

EDIT: I should read through the post before answering....

Edited January 7, 2020 by Jundis

[Filipe128]

2 hours ago, bj51 said:

 

• to resist length-wise efforts in traction (you should be able to pull at both ends and it wouldn't break), so an axle/axle joiner/axle connector solution won't work.

 

Maybe there's a way to use axles and connectors but also be resistant to traction and compression forces applied along the axis?

[bj51]

Just now, Filipe128 said:

Maybe there's a way to use axles and connectors but also be resistant to traction and compression forces applied along the axis? 

I don't think so, unless you use the old 10L threaded axles, but that's not really an option. If a normal axle is positionned length-wise, there will be sliding at one end or the other.

[Filipe128]

Do you need the first 2 holes at each end to remain free or just the first one?

[Lipko]

It it allowed for the liftarm to be 2 studs think towards the inside of the boom?
You could utilize studded parts that fit technic. 2L beams with 2 holes+normal studded beams, or something with this part:

 

 

Edited January 7, 2020 by Lipko

[Jundis]

As you already use 3L plates, another possibility would be to use 3L jumper plates connected to liftarms?

[Frequenzberater]

Maybe using just a rope could be an option? 

[Alasdair Ryan]

To be honest,like the others have said the point where I would of found out I would be working with 1/2 stud lengths I would of redesigned the boom section.

One suggestion would be  to use could try using plates and tiles to connect the two ends diagonally, this would not be very strong though.

Edited January 7, 2020 by Alasdair Ryan

[Doug72]

A lattice structure for a crane can be be made using standard Lego Technic Beams, without need for 1/2 stud parts.

See image.

Edited January 7, 2020 by Doug72

[bj51]

Thanks for all the input !

@Lipko : I'd like to keep the witdh to 1 stud, so as to keep with the aspect of the other liftarms. But your idea would definitely work !

@Filipe : Yes, the holes at both ends need to be free, because this assembly is then sandwiched between plates in the first hole (as you can see on the pictures above) and it is skewed, so there can be nothing in the second hole.

@Jundis : I've tried with plates and jumpers, it kinda works. For example, i can join a 3L liftarm and a 5L liftarm with plates and jumpers, but that leaves a hideous gap, and it's not very sturdy.

@Doug : Yes, but i'm constrained by real dimensions, so the angles can't really be changed, otherwise it'd be too easy. ;)

Apart from the solution i presented, my last resort is to use the same lattice width as the other side of that boom, thus having a square section instead of a rectangular one, but i'll have to see if the overall design and aspect won't suffer too much.

Edited January 7, 2020 by bj51

[Frequenzberater]

Another Idea could be using flat system bricks + jumper plates. 

[Gray Gear]

44 minutes ago, bj51 said:

@Doug : Yes, but i'm constrained by real dimensions, so the angles can't really be changed, otherwise it'd be too easy.

Just change the damn angles a little and make it sturdy instead. If thats that easy then you wouldn't have to make a new topic. Please people, figure stuff out yourself instead of creating a new topic for every little bump in your road. Also, if you really have to ask, please do it in a topic it fits in, instead of creating a new one right away. 

Rant over, please dont get offended, but stuff like this is annoying, and I know I am not the only one thinking that way. 

[KrasiniArithmetic]

8 minutes ago, Gray Gear said:

Just change the damn angles a little and make it sturdy instead. If thats that easy then you wouldn't have to make a new topic. Please people, figure stuff out yourself instead of creating a new topic for every little bump in your road. Also, if you really have to ask, please do it in a topic it fits in, instead of creating a new one right away. 

Rant over, please dont get offended, but stuff like this is annoying, and I know I am not the only one thinking that way. 

So he starts a topic with a specific question (how to build a strut 9.5L) and your response is to tell him that his question is not valid and that you're annoyed at him for asking? That's really not very helpful of you. I can't speak for everyone, but I do find myself wondering if you might indeed be the only one thinking that way.

[bj51]

Sorry if I annoyed you, but that's not just a "little bump in my road". I've been working on these lattices for about a year now, and I tested TENS of possible combinations and scales, rebuilding every section each time. From 1/25 to 1/48, i've done them all. This is 1/37, by the way.

My goal is of course to get something sturdy, but not at the cost of looks and design. Otherwise why bother ? I want to recreate an existing crane, and that comes with constraints and obligations. This particular section of boom has 5 arms in the lattice, so I can't just change the angles, even a little bit, otherwise they wouldn't fit anymore.

I can't go to a bigger scale because the crawler part alone is already in the 5000 parts, and I can't go smaller because the lattices would be even harder to fit.

It's so hard to explain on a forum in a second langage, rather than in person with the bricks in your hands, and that's so frustrating !

[Gray Gear]

11 minutes ago, KrasiniArithmetic said:

So he starts a topic with a specific question (how to build a strut 9.5L) and your response is to tell him that his question is not valid and that you're annoyed at him for asking? That's really not very helpful of you. I can't speak for everyone, but I do find myself wondering if you might indeed be the only one thinking that way.

I am not saying its not a valid question - but I bet there already is a thread this question could have been asked in. If you put a year of work into this, the I tip my hat to you, thats dedication.

Edit: In a huge Model like this you'll want all the stability you can get, and thats by using full length liftarms. But thats just my opinion, so...

Edited January 7, 2020 by Gray Gear

[Filipe128]

What's the big deal about creating a new topic anyway?

@bj51 when you can't figure out a solution for a problem, the best thing is to do is to change what's causing the problem in the first place. If you can't do that either, I think the solution you already found is quite good and not as bulky as it might look, especially compared to the scale of the model you're building.

I was also thinking about using an 11L liftarm but changing the way it attaches to the body. Maybe interrupt the 13L DBG liftarms and use jumper plates to attach the liftarm, would that be possible?

[skppo]

Would it be possible to build it with stacked plates at an odd angle ending with these pieces?

Not sure how durable it would be...

Do you need the 1U liftarms between the attachment points?

[higgins91]

9.5L:

proposition by alex peraux, sur Flickr

 

[bj51]

I've tested a solution brought to me by Cypr-21 on the french AFOL forum TechLUG (new version on the right) :

In my old version, I already separated each 9.5L liftarm by 1 1L liftarm, because if I had put them together, as on every other of my lattices, it would have required a 10.2L liftarm, which is even less easy to make than a 9.5L one. But I didn't think once to separate thme by more than 1 stud. Here it needs a 9.06L liftarm, which a 9L fits nearly perfectly. You can see they're now the same size and angle on both the 12m and 6m section, which I tried to avoid for some reason (I think it's visually important to make the difference between the 2 sections, and the angle of the lattice helps with that).

What do you think ?

[howitzer]

56 minutes ago, higgins91 said:

9.5L:

proposition by alex peraux, sur Flickr

 

This one pivots at both axle connections so it's probably not suitable solution. But you could use the same principle and use similarly stacked 4- and 5-length liftarms with axleholes at ends.

[Alasdair Ryan]

1 hour ago, howitzer said:

This one pivots at both axle connections so it's probably not suitable solution. But you could use the same principle and use similarly stacked 4- and 5-length liftarms with axleholes at ends.

I was just thinking the same thing.

[nerdsforprez]

5 hours ago, KrasiniArithmetic said:

So he starts a topic with a specific question (how to build a strut 9.5L) and your response is to tell him that his question is not valid and that you're annoyed at him for asking? That's really not very helpful of you. I can't speak for everyone, but I do find myself wondering if you might indeed be the only one thinking that way.