Problems with selfbuild 8421 mobile crane

[Jan]

A week ago I got my old TECNIC Lego down from my attic as I thought my son is now old enough to have fun with it. While he was making the models I once made (851/ 854 / 855 / 8859) I suddenly found the all new box number 8287 again. I bought it one and a half years ago for little more than 10 euro's at a removal sale. Mainly for the nice amount of bushes gears etc I would need to replace the broken and missing ones in my old sets.

So the first thing I did was looking at peeron to see what TECHNIC models have been making use of this motor. Besides some RC models I only found one other model, the 8421 mobile crane. After downloading the manuals I found out that it is also using the driving ring, the idler gears and all the other goodies that came with the 8287. As well as pneumatics, that I got as soon as they hit the stores back then in 198?.

So with all the TECHNIC stuff my son collected in the last years, which is quite a lot as you get TECHNIC material in almost each City, Powerminers, Atlantis set, we started building.

First the upper part, as the motor is there as well as the driving ring and the pneumatics. Well and that's where the problem comes in. As you can see on the photo I have only one pneumatic cylinder instead of two, but the fact that the boom doesn't fully erect doesn't bother me to much, as this is just playing around with the new TECHNIC parts. The problem is that cylinder doesn't get up by pressing the pump, and that it can't bear the load of the boom. (I hold it up with my hand on the photo) So what is wrong? Is it the cylinder from 198?, or the fact that I use an old type of pneumatic block, valve and pump. Did the pneumatics evolve over time? Or is it just that because I only have one cylinder the attachment point is not good.

And having said that, what would you advise me to do. Just buy new pneumatics, or leave the pneumatics for what they are and choose for the new linear actuators?

Aside of the above, is it correct that when using the motor in the crane, in both positions of the lever the wire is moving, with or without retracting or extending the boom?

Thanks in advance for any input,

Jan

Edited November 4, 2010 by Jan

[Alasdair Ryan]

hi jan try getting rid of the valve bock you want need it as there is enough weight in the boom to force it down,once you have extended your ram to what ever height move the switch to the middle if you are finding that it want stay up then maybe in buy yourself a new type of ram,the new liner actuators are stronger than pneumatics but people tend to use them with a motor.

your wire should rise and lower hock but also rise and lower along with extending and retracting the boom

Edited November 4, 2010 by Alasdair Ryan

[Blakbird]

And having said that, what would you advise me to do. Just buy new pneumatics, or leave the pneumatics for what they are and choose for the new linear actuators?

The old pneumatic actuators have the same area so theoretically have the same force output as the newer ones. It may just be that your actuator has leaky seals due to its age.

A new linear actuator would not be able to handle the weight since the LA's fail on the 8043 boom and the 8421 boom is even heavier. They would work for a while, but I'd use pneumatics.

hi jan try getting rid of the valve bock

It is impossible to use the old pneumatics without a valve block because there is only one port.

[DLuders]

You could try to lube the internals of the pneumatic pump by following the steps in this YouTube video:

http://www.youtube.com/watch?v=ooB8q4DZXz4

I would not use WD-40, however, since it softens some plastics. Use Olive Oil.

Edited November 5, 2010 by DLuders

[Tobbe Arnesson]

A new linear actuator would not be able to handle the weight since the LA's fail on the 8043 boom

Well those were faulty parts now fixed.

[Blakbird]

Well those were faulty parts now fixed.

Even the new actuators would be working very hard to lift the 8421 boom and I predict they would be heavily damaged over time. Conchas showed how significant loading produces plastic chips inside the actuator.

[GuiliuG]

Even the new actuators would be working very hard to lift the 8421 boom and I predict they would be heavily damaged over time. Conchas showed how significant loading produces plastic chips inside the actuator.

This effect is decrease with the greace i think.So yes, loading will produce plastic chips but this effect also occures in pneumatic cylinders with time ( even if it's less remarkable than in the La )

And personnaly i think that one La powered by a Xl with just three or five gears is not a problem

Edited November 5, 2010 by GuiliuG

[allanp]

I would stick with the pneumatics, I really have no time for LAs, even the new ones. I really need to do a test to see how powerful pneumatics are compared to LAs, pneumatics just seem much more powerful to me but I seem to be in the minority in that respect. Besides even if the pneumatics were weaker i'de still prefer them to LAs in most cases.

Correct me if i'm wrong blakbird, but I thought you only really needed the valve block if there is no external force (like the weight of the boom) to retract the cylinder. Besides the original crane only used one port on each cylinder.

[allanp]

This effect is decrease with the greace i think.So yes, loading will produce plastic chips but this effect also occures in pneumatic cylinders with time ( even if it's less remarkable than in the La )

Really, I have never noticed any effect like this with pneumatics, and I lift some huge loads with them at times, often more than what LAs can handle.

Loading an LA will also increase friction, decreasing efficientcy to the point of stalling a motor or activating the clutch without having transfering much of the motors power into linear power.

Edited November 5, 2010 by allanp

[Blakbird]

This effect is decrease with the greace i think.So yes, loading will produce plastic chips but this effect also occures in pneumatic cylinders with time ( even if it's less remarkable than in the La )

The LA produces chips because the harder metallic male threads cut the softer polyamide female threads. This effect cannot happen with pneumatics because there are no sharp parts. The only thing to wear out on pneumatics is the seals, but this is a function of time, not load.

Correct me if i'm wrong blakbird, but I thought you only really needed the valve block if there is no external force (like the weight of the boom) to retract the cylinder. Besides the original crane only used one port on each cylinder.

No, you have to have the valve block. The pump has no check valve because it needs to produce both pressure and suction. If you don't use the valve block, there is no way to push the pump more than more time because there is nowhere to draw air into the system or let it escape. This all happens in the valve block. In order to do multiple strokes and build pressure, you have to have the valve block.

[CP5670]

You're probably best off getting some modern pneumatics like the original set uses. The pre-1989 pneumatic system is pretty weak in general (the pistons seem to leak air more easily than the newer type), and would have a lot of trouble lifting something as heavy as the 8421 boom. As others have said, the load would probably be too much for LAs as well.

[allanp]

No, you have to have the valve block. The pump has no check valve because it needs to produce both pressure and suction. If you don't use the valve block, there is no way to push the pump more than more time because there is nowhere to draw air into the system or let it escape. This all happens in the valve block. In order to do multiple strokes and build pressure, you have to have the valve block.

Ah, of course. Silly me. I forgot that the old pumps did not have a check valve like the current ones do.

[DLuders]

This Wikipedia article talks about the "Generation 1" and "Generation 2" Lego Pneumatics:

"Generation 1

The first generation of LEGO Pneumatics ran from 1984 through 1988. This generation was simple compared to the later generations. The pneumatic cylinders, for example, only had one input valve. This meant that in a simple pump->switch->cylinder setup, the cylinder rod could only push outwards, requiring gravity to pull it back in.

A pneumatic distribution block piece was utilised (along with a switch) in order to enable pulling as well by creating vacuum instead of pressure in the cylinder, however, this had limitations and often made pneumatic circuits quite complex."

"Generation 2

In 1989, the LEGO pneumatic line was revamped, and a new cylinder and pump piece were introduced. The old cylinders and pumps were discontinued. The chief difference is that the new cylinder had two input valves now, which allowed both pushing and pulling without needing complex circuits involving the distribution block piece.

Over the years, several new pieces were introduced in this line as well. The new pump was spring based, and could only be operated by hand, which limited pneumatic power to how fast it could be manually pumped. This obviously limited the power of pneumatic circuits. So in 1992, LEGO introduced two new pieces; a small pump and a small cylinder. The small pump did not have a spring on it, and it was designed to be operated by a motor, which would allow for much more powerful pneumatic creations. As of 2006, the small pump has only appeared in one model set (8868 Air Tech Claw Rig) and a few parts sets (no longer available), so it is mostly a piece found on LEGO sets built by extreme enthusiasts. These pieces can no longer be obtained through the LEGOEducation Store.

In 1997, LEGO introduced the Air Tank, which acts like a battery, storing compressed air so that even more powerful pneumatic circuits can be created. This piece is also very popular with the enthusiast community, but many feel that it was underutilised by LEGO, as it only appeared in 3 model sets and a parts pack. This set was available at the LEGO Education Store as well, until the beginning of 2006, when LEGO officially discontinued the piece due to budgetary reasons.

In 2003, LEGO discontinued the old cylinder and switch parts, and made new "studless" versions to fit in with their transition towards removing studs from Technic sets.

In 2008, LEGO re-introduced the Air Tank in an add-on set intended for the educational market. This set also introduced a new part, a manometer.

In 2010, Lego released a set with the pneumatics, the Tractor with Log Loader. This is the first set to include the pneumatics since 2006."

"Pneumatic distribution block

These pieces used a special kind of one-way valve inside of them, and three ports on the outside. The leftmost port could only have air going into it, no air would ever come out. The middle port could have air going in or out. The right port could only have air coming out of it, no air could go into it.

Using these, it was possible to make the Generation 1 cylinders pull down as well as push up, however the pulling wasn't as strong as the pushing, and this prompted Lego to redesign the pneumatics into an easier-to-use and stronger system.

These were discontinued when Lego switched to Generation 2, in 1988."

The various Lego Pneumatic parts are shown on this Bricklink Catalog page.

Edited November 6, 2010 by DLuders

[Alasdair Ryan]

i used the old peumatics with a new pump in my first post

[Jan]

Wow, what a lot of replies, I went through them all and want to thank you for your help.

Things I conclude, and please tell me if I am wrong, are:

- my pneumatics are aged, and leak air at a certain pressure. replacing parts of it leaves me with an outdated and more difficult system.

- new pneumatics are stronger, or at least as strong as a lineair actuator.

@Dluders, my pneumatic cylinder looks different than the one shown in the movie, and seems unopenable.

@Blackbird, I liked the informative text on your website a lot, and havent't come across it earlier. I need to check out your site more thoroughly.

thanks so far,

Meanwhile I stopped with the crane and put all my energy in a mixed up supercar from the studded era before the 8880. See if that gives me some extra insight in the Technic innovations over the years. After that I really need to invest in some new parts.

Jan

[Alasdair Ryan]

Wow, what a lot of replies, I went through them all and want to thank you for your help.

Things I conclude, and please tell me if I am wrong, are:

- my pneumatics are aged, and leak air at a certain pressure. replacing parts of it leaves me with an outdated and more difficult system.

- new pneumatics are stronger, or at least as strong as a lineair actuator.

@Dluders, my pneumatic cylinder looks different than the one shown in the movie, and seems unopenable.

@Blackbird, I liked the informative text on your website a lot, and havent't come across it earlier. I need to check out your site more thoroughly.

thanks so far,

Meanwhile I stopped with the crane and put all my energy in a mixed up supercar from the studded era before the 8880. See if that gives me some extra insight in the Technic innovations over the years. After that I really need to invest in some new parts.

Jan

that one is longer than the one you are useing in the first photo?

[Jan]

that one is longer than the one you are useing in the first photo?

Thats correct, I use the shorter one, but it looks the same. What I meant was, that there is no easy removable black endcap on it as shown in the movie.