suffocation

stringless three-section boom

Recommended Posts

Is anyone aware of a three-section boom that doesn't use a string to extend and withdraw the third section? I've hunted high and low but haven't come up with anything; my own attemps have failed miserably.

I've noticed that string solutions tend to deteriorate over time and I'm growing weary of dismantling booms and putting in new strings every time my nephews visit.

Thanks in advance :classic:

Share this post


Link to post
Share on other sites

Perhaps you can use gear+rack or something, question that actually comes to my mind at the first place is what dimensions should it be?

Share this post


Link to post
Share on other sites

I´ve found some Italy guy, that made five section boom mobile crane which is using some kind of locking mechanism to extending boom. 

Quote

 

 

Edited by Kladovec

Share this post


Link to post
Share on other sites

Thanks for the tips, lads :wub:

The boom should be in the 7x7 range and some 60 studs long (folded) - it's not to scale or anything, I just need something that works consistently and keeps the kids happy, so any deviation from those measurements isn't a problem.

I'm not sure a gear rack solution is feasible - I can't for the life of me figure out a way to extend the third section once the second one has been extended. Of course, one could extend the third section before the second section, I suppose.

The Italian guy who build that huge crane must be some sort of genius as well as a PhD in Mechanical Engineering (his writing is impeccable, too, which is a rare trait nowadays) but, alas, his solution also involves strings.

The nylon wire idea is worth a try.

Worst-case scenario, I'll either go with a lame two-section boom à la 42082 or revert to a string solution like in 42009, which at least has the upside of being slightly less atrocious to re-string.

Share this post


Link to post
Share on other sites

Hm...7 x 7 section and inside 5 x 5 and then 3 x 3?, You should consider building two sections inside with technic bricks and use gear racks on them...that is what comes to my mi mind...it is something that awaits me in future when I decide to make my crane version to fit current MOCs (that are still in development phase)

Regards Andrew

Share this post


Link to post
Share on other sites

You could replace the string in the traditional solution with two gear racks and a gear. Fix one rack to the first section and the other to the third section. Then attach a gear (or gears) to the second section so that it couples the two gear racks. Then you just need to figure out how to drive the second section with a third gear rack.

Share this post


Link to post
Share on other sites

I made somethig similar a long time ago. It works and is quite compact, but the chain really isn't a good solution... It was made before the introduction of technic rectangular panels and the longer pneumatics, and was never put to use in a model as I didn't like the look of the over sized pneumatic cylinders...

14072011253.jpg14072011264.jpg14072011260.jpg14072011267.jpg14072011268.jpg

I have also been working on a solution using the long axles from the crane sets and a sliding 12 tooth gear to engage the third section after the second is fully extended.

In this setup I am also planning on using a second gen mindstorms brick to mix motors so that the string maintains height when the boom is extended. I will probably not get this done in a long time as I lack building time, but the ideas are free for all.

 

-ED-

Share this post


Link to post
Share on other sites

You could use 2 gear racks with a gear wedged in the midle. Actuate the gear and the inner rack will move at 2x speed of the gear. So outer rack is biggest profile. The gear is the middle profile which is actuated. And the inner gear rack is smallest profile.

Share this post


Link to post
Share on other sites

Large cranes have a type of boom called pin-and-latch, where 1 hydraulic ram pushes out the thinnest section first, pins extend and hold it in place, the cylinder retracts, grabs onto the next larger section and pushes it out and the process repeats.

Maybe with the new longer linear actuators something like this could be feasible.

 

 

Share this post


Link to post
Share on other sites

I take the main issue with the string is lack of tension retention rather than disconnecting entirely, Going the other way is a good choice; 1 string that extends both boom sections would not have the problem of tension and would lightly be simpler as you would not need to drive the sections down (thx gravity). With this method was able to get 3 moving boom sections before the friction became excessive and prevented the boom from extending/retracting unassisted. 

Share this post


Link to post
Share on other sites
3 hours ago, Metagross555 said:

Large cranes have a type of boom called pin-and-latch, where 1 hydraulic ram pushes out the thinnest section first, pins extend and hold it in place, the cylinder retracts, grabs onto the next larger section and pushes it out and the process repeats.

Maybe with the new longer linear actuators something like this could be feasible.

The real cranes extend every section in 2 steps.

The new LAs have only 8 studs more .... thats not enough !

He want a 60 stud beam, thats 5 pannels.

The Problem : How will you pin it at every step? With an extra LA ??

Share this post


Link to post
Share on other sites
Spoiler

p_20190712_214625_vhdr_auto.jpg

I though nylon wire (fish line) work stably, 0.5 mm fish line can offer 16 kg

i built my crane with fish line and it works well

 

Edited by mitx2529

Share this post


Link to post
Share on other sites
On 10/18/2019 at 6:14 PM, suffocation said:

Thanks for the tips, lads :wub:

The boom should be in the 7x7 range and some 60 studs long (folded) - it's not to scale or anything, I just need something that works consistently and keeps the kids happy, so any deviation from those measurements isn't a problem.

I experimented with using the red frictionless gear and a rack on both sections so I could operate the sections separately, but added an extra to the boom pivot. I was able to make the 3 sections extend at the same time with the red gear and two gear racks. I will try to make a mock-up tomorrow.

Share this post


Link to post
Share on other sites

Thanks to everyone for all the ideas :wub:

Haven't come up with anything efficient yet (my single-digit IQ doesn't help) but I'll keep trying.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.