Thursday, September 16, 2010

Is it my 8043 wearing into dust?

...virtually any LEGO set with moving parts, is wearing into dust over time (a very long time hopefully). But this one maybe into an accelerated path.

When the first LEGO Linear Actuators (LAs) were released back in 2008, I opened one for a couple of review here at TBs [1] [2]. Fortunately I still have it with me and decided to make a test.

Like a blade, it looks the rod screw is sharp enough to cut the sleeve into pairings, if submitted above a certain pressure. Some manual tests confirmed it right away.
Whether this can be the root cause of the problems that many experienced with the 8043 Motorized Excavator, is still requiring confirmation, but nevertheless I thought worthwhile to show it in the video below.

Sorry for the video darkness, but it was filmed at late night with a compact camera and poor lightning conditions.
Yes, the video is almost one month old and it has been kept unlisted at YouTube, but I just didn't want to release it before.

However after the first idea and tests, something was still not making sense for me...
Because the steel rod has a right-handed screw, damage could happen while retracting the LA under compression (pushing strong the rod), or extending the LA under negative compression (pulling strong the rod).
The Excavator shows major problems in a different situation - While extending the LAs under compression (pushing the rods heavily, under the boom weight).
But why should this become an issue? Why the damage could not be happening whenever the Boom descends under the stress of its weight, instead of when it raises?
I think this could be exactly what it is happening.

It was to demonstrate this effect that I've prepared the video above, where you can see the sleeve (guess it might be Teflon) to discard into parings.
The remains are so thin that you can't see them directly on the video, but just on the final snapshots taken with macro mode.

Again, I don't know if this is the cause of the problems, but it could perfectly be at least part of it.
It may not explain all the observations, but when it comes to failures, many events could be happening and triggering other side effects or secondary failures. Furthermore, multiple failures are the hardest ones to understand.

Notice this video was produced with an LA from 2008, so it can't have any relation with an eventual problem with a recent production batch. Thus if it has any relation with the boom problems of 8043, it may affect every LA produced since ever. Furthermore at the Designers blog it is written "The solution was to modify them and place the new linear actuators in all new sets that we will produce").
I don't know which process does the TLG subcontractor uses to produce the steel rods with terminal screw (machining doesn't look to be, injection or press molding maybe), but even if this doesn't explains it all, it looks the screw finishing may need some improvements in order to avoid wearing the sleeve under heavy loads.

Of course, with the limited technical resources that I have access, there is no way to compare the force I'm doing in the video, with that caused by the excavator digging arm over the LAs. So the video can't be taken as an evidence of what's going on inside 8043 LAs.

Despite my curiosity, I have not yet decided to break and open another LA from those running in my excavator arm, to see what's going on inside. Also because the casing parts are glued together and it wouldn't be easy to open one with a saw, without contaminating the interior with some sawdust, regardless if there is already some dust inside or not. Thus making it difficult to become conclusive.

But one thing is for sure, once I get some of the LAs in my hand, I must open one trying see how they differ from the initial ones.

Meanwhile more information coming from TLG, provides answers to some questions previously raised at several forums:
  • There will be no immediate difference between the old and the new Linear Actuator, thus a different color coding is not going to be used.
    However it will be possible to see the difference by checking the production code on the actuator. It's located just below the orange cross hole (code yet to be known).
    This way it will be possible to avoid mixing old and new LAs, preventing you to use the wrong ones at your 8043 again.

  • The Service Bag will contain 4 new Linear Actuators and a few extra parts to fix the track problem..


Unknown said...

You cannot produce a project with different materials. You can not create an LA with a steel screw against a plastic collar. I am an engineer and this video example is terrible. Lego as times moves forward needs to get some materials engineers into there design team. It is uncomprehensible that Lego would create a product that I would expect to last 30 years with a metal on plastic design. Pathetic. Designs that are visually cool and very functional without that engineering grounding will not stand the test of time.

TechnicBRICKs said...

Quite pertinent the comment about the usage of different materials, working together on the same contact surface!

blakbird said...

@spacitw - I disagree in principle. It is actually quite common to use metallic and plastic threaded parts together, just as it is common to use metallic and plastic gears together. The difference in material elasticity and thermal expansion coefficient must be taken into account, but it is not a "rule" that you can't mix materials. In fact, it is more or less a "rule" in aerospace never to make a threaded combination out of the same (metallic material). The material tends to gall.

@ Conchas - I'm not sure the direction of the screw thread makes all the difference. I bet it would produce plastic dust even when loaded in the direction opposite the screw, just not as much.

Even after the parts pack is released, we may never get a firm answer from LEGO about exactly what the problem was in detail.

TechnicBRICKs said...


this assuming the problem gets 100% solved. Hopefully!! :)

You must be right about your observation on the screw direction.
After all the screw protrusions may go on both sides of the screw.

Al said...

I don't believe this to be what is causing the problems with the excavator, but it does show that there could be a whole new problem with the LAs over time. I wonder if TLG have noticed this as part of their investigation.

I am still wondering what modifications they have made to the LA. I guess they won't release that information as they have no real need to give away interlectual property for free, but if i'm honest, my hopes are not high for a properly satisfying solution for those that like LAs, more of an "it'll have to do" solution.

minks502 said...

I think the if you don't get the two actuators perfectly in sync, you will always have one pulling or pushing on the other, even if it just a little bit. The problem could be builder error because I've had no problems with mine.

Anonymous said...

I have 14 LAs. I would assume that all of them are susceptible to this problem. I wonder if they are going to replace all or just the ones in 8043.

And are they going to ask for the old LAs back in order to get the service pack?

TechnicBRICKs said...


I'm sure not, as all the LAs in previous models, perfectly fit their purpose on respective model.

Al said...

All four LAs in the excavator will be replaced with the new LA and (I think) all future sets with LAs will have the new LA. Past sets don't really need replacement LAs.

Krika99 said...

Track problem? I thought I was the only one with the track problem. It keeps turning to one way. :(

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