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DarkShadow73

8421 Crane Boom issue

75 posts in this topic

Hi again-

I am wondering what the owners, and I'm sure there are a lot of them on this forum, that have the 8421 Crane use to keep the boom up when extended. The 2 cylinders just don't seem to have the power to keep the boom up and in the morning the boom has crashed down. It drives me nuts and nothing seems to work to keep the boom up for a length of time, like say many hours. I have tried about everything I can think of, I've checked to make sure all the hoses, valves and cylinder openings(for the air) are very tight, but apparently they still leak some air overnight, same thing goes for the 8455 Loader, you can't keep the backhoe digger on the rear straight up, it just sinks slowly. Any ideas?

Thanks, Eric

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Air always leaks out a bit. Try LA instead of pneumatics?

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Hi Eric,

as Zblj said, air will alway leak somewhere, most probably from the cylinders directly (from the high pressure to the low pressure compartment) - the hoses are pretty much tightly sealed to the plastic enclosures of the pneumatic elements. Had the same issue - and in reality you have that as well. Re-pressurizing the system is the way out. Not straight forward to implement, but entirely possible: First you have to detect the pressure loss. Since there are no off the shelf LEGO pressure gauges you need to have a sensor somewhere. In case of your boom it could be a touch sensor mounted in a way that is pressed or released immediately after some downward movement. Hook that up to any of the LEGO intelligent bricks, attach a motor to drive a pneumatic pump, favorably feed the air into a tank as buffer reservoir and hook that up to the main pressure line.

You could also build a pressure gauge from a cylinder, a shock absorber providing the counter force, and a switch. In that case you could adjust the trigger point in a way that the boom doesn't even move at all.

Lot of work for just that (and somewhat costly) - but it is close to reality and fun to watch.

Or use, as Zblj suggested, LA's

Regards,

Thorsten

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Hi Thorsten -

Yeah sounds like a lot of work and expense. I'm not really great at modifications unless they are spelled out clearly in instruction form, have lots of pneumatic parts, but nothing like what you are talking about, sounds more like specialized parts...guess I'll just deal with the stock build and re-raise the booms on those 2 models. I actually considered trying some kind of prop, like those flexible hoses used in some sets to block up the cylinders, may help, just have to get the right lengths cut.

Thanks, Eric

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I am in investigating the possibility of a compressor to replace the battery box at the back......

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Build it like Han's XL use 4 cylinders, and plumb the other outlets for the down force. I did that and it helped withthe going down in a controled manner problem, seemed to help hold it longer in the air too.

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You should be able to add a compressor in it connected to the buggy motor,but like Dan-in-the-ice-cream-van says try Hans mod first.

You can find it Here. :classic:

Edited by Alasdair Ryan

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I just finished collected for HANS 8421XL and will be using one of the 100mm ones

http://store.firgell...ts.asp?Cat=1822

Its possible it wont be strong enough to hold the HAN boom in which case I will double them up. The best part about these accuators is that they feature the motor as well as the accuator so its not as expensive as it seems.

Ill let you know how it goes. I hated that I couldn't leave the 8421 "on display", and I lack the ability to create a decent working version of opposed LA's.

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Any pneumatic system under load will bleed pressure over time. There is nothing wrong with your parts. Hydraulics will eventually do the same thing, it just takes longer. There is nothing you can do to the pneumatics themselves to make them hold over time.

If you want to lock your model with the boom raised, just make the axles at the end of the actuators longer and attach some Technic beams to them to hold the length (see image below). If you don't want to make the lock link so long, just attach it further back on the boom instead (2nd image).

lock.jpg

lock2.jpg

I just thought of one final solution which uses the pin holes on the sides of the pneumatic actuator brackets. I like this one the best. Unobtrusive appearance if you use yellow.

lock3.jpg

Edited by Blakbird

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Is anyone else jealous of how quickly eric can do that?

Yep! Looks nice too, and an elegant solution for displaying the model with the boom fixed as well.

Edited by Technic Gearhead

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Is anyone else jealous of how quickly eric can do that?

Yep! Looks nice too, and an elegant solution for displaying the model with the boom fixed as well.

Not really,if you are good at cad its not hard. :grin:

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You should be able to add a compressor in it connected to the buggy motor,but like Dan-in-the-ice-cream-van says try Hans mod first.

You can find it Here. :classic:

You should be able to add a compressor in it connected to the buggy motor,but like Dan-in-the-ice-cream-van says try Hans mod first.

You can find it Here. :classic:

I see, well I got your ice cream van right here. its orange and it weighs about 8000 lbs, sqwish you like a bug :tongue:

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I see, well I got your ice cream van right here. its orange and it weighs about 8000 lbs, sqwish you like a bug :tongue:

I am too valuable too squish. :tongue:

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The locking plates is the way to go, if you look around real sales yards for this type of heavy plant or displays at trade shows and the like, cylinder locks are often visible to make sure the viewing public are safe. The ones I have seen are almost always red, I think this is so the operator of the machine knows not to try and lower the boom.

One odd thing is I have the 8421 and 8455 as you do and both the boom and back how will drop over time, however, my 8862 will hold any position for as long as you like. It must be to do with the forces acting on the rams, anyway good luck

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I rather like Blakbird's idea, I might implement that idea, I have tons of yellow beams. One would assume you have to remove the beams to let the boom back down to its resting position?

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I rather like Blakbird's idea, I might implement that idea, I have tons of yellow beams. One would assume you have to remove the beams to let the boom back down to its resting position?

Yes. If you really want it to be realistic, you'll put little "remove before operation" tags on the lock links. These really exist.

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why not something like this?

8190857227_f7d13b85a6.jpg

8190857119_9a55433904.jpg

they will simply put on the cylinder rod without any technical change on the crane. in real life there will be used open steel tubes to prevent the boom for moving down during service

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Hi Eric,

as Zblj said, air will alway leak somewhere, most probably from the cylinders directly (from the high pressure to the low pressure compartment) - the hoses are pretty much tightly sealed to the plastic enclosures of the pneumatic elements. Had the same issue - and in reality you have that as well. Re-pressurizing the system is the way out. Not straight forward to implement, but entirely possible: First you have to detect the pressure loss. Since there are no off the shelf LEGO pressure gauges you need to have a sensor somewhere. In case of your boom it could be a touch sensor mounted in a way that is pressed or released immediately after some downward movement. Hook that up to any of the LEGO intelligent bricks, attach a motor to drive a pneumatic pump, favorably feed the air into a tank as buffer reservoir and hook that up to the main pressure line.

You could also build a pressure gauge from a cylinder, a shock absorber providing the counter force, and a switch. In that case you could adjust the trigger point in a way that the boom doesn't even move at all.

Lot of work for just that (and somewhat costly) - but it is close to reality and fun to watch.

Or use, as Zblj suggested, LA's

Regards,

Thorsten

http://www.bricklink.com/catalogItem.asp?P=64065

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Hi Bricktrain,

yeah saw manometer in Seepos's breath taking Peterbilt thread - for the first time. Thanks for the link!

What I meant though was a switching functionality - as far as I know the manometer does not have that, right? But Alasdair Ryan has shown in the very same thread how to get that, entry 7. This is a very elegant solution - no PBricks required at all, I love it.

Regards,

Thorsten

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Hi Bricktrain,

Alasdair Ryan has shown in the very same thread how to get that, entry 7. This is a very elegant solution - no PBricks required at all, I love it.

Regards,

Thorsten

Who's he?

Sheepo used springs instead of rubber bands in his truck,that design that I posted was taken from Jennifer Clark's page.

Edited by Alasdair Ryan

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why not something like this?

8190857227_f7d13b85a6.jpg

8190857119_9a55433904.jpg

they will simply put on the cylinder rod without any technical change on the crane. in real life there will be used open steel tubes to prevent the boom for moving down during service

That's not a bad idea, would work on the 8421 at the very least, possibly the 8455's backhoe arm too...thanks to all for the ideas...gives me some thoughts, I've had both sets since 2005 and it just bothers me that the cylinders on the backhoe arm drop and the boom on the 8421, you want realism as most real cranes leave their booms in the upright position and backhoe/loaders always leave their booms up when not in use...

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