Wednesday, September 29, 2010

How Mini LA's might work

Ever since pictures for the first 1H2011 sets started appearing, the FOLT (Fans Of LEGO Technic ) community latched onto a new part present on the 8069 Backhoe, looking like a miniature of a Linear Actuator.

Since it is significantly smaller than the LA we all know and love (and some hate...), it has been discussed if a part with this size and functionality is possible for a feasible cost. Two theories emerged: the first says that the Mini LA (called "mLA" in the rest of this post) is too small to work and is just a decorative element, like the Technic Axle Joiner Perpendicular with Extension, and the second says that it is a truly functional element.

Personally, I'm for the second theory, because, if the mLA's aren't functional, the Backhoe, a set supposedly costing 49.99€, would be severely overpriced for the functions it had: only steering and possibly the outriggers. At least the 8264 Hauler had the excuse of being motorised...

So, supposing the mLA is indeed functional, how does it work? Judging by the single available picture, I think the inner rod is too thick for the external diameter for the part to have the same three-layer structure the large LA has (fixed outer shell, rotating intermediate sleeve, sliding inner piston). Therefore, the next question is how to transform rotational movement into linear movement in a cylindrical shape, as simply as possible and with the lowest cost. A few fan theories have emerged; among those, there's one I think is the most likely to have been implemented, and, based on the picture we have, I've made some crude renderings to help understand how it might work

The mLA might work similarly to the regular LA, but without the external, fixed sleeve. It may be composed of three sub-parts, marked in these pictures in different colours: the red bracket, the green sleeve and the blue piston. The bracket, unlike the regular LA, is permanently attached to the rest of the part to allow for an overall smaller size. The screw has an input axle instead of an axle hole, unlike other Power Functions parts like LA's and motors, also to save on size. The piston doesn't differ much from the regular LA.

When the input axle is rotated, the whole outside rotates, unlike the regular LA, which has a fixed shell over the rotating sleeve. The inside of the sleeve is threaded, which, when it rotates, pushes or pulls the piston. To save costs (four mLA's on a 49.99€ set, when a set with four regular LA's costs a LOT more), all the sub-parts are probably made in plastic. This reduces the strength of the part, but, since the expected loads are also smaller, this shouldn't be a problem. For a comparison, the large Pneumatic cylinder's piston is metallic, whereas the smaller version's piston is plastic. Unlike the regular LA, there should be no room for any integrated protection mechanism to prevent straining the mLA when it reaches the end of its travel... but judging by the general opinion about the regular LA's protection, nobody will miss this feature.

This theory has the obvious disadvantage of the whole outer casing (save for the bracket) spinning when working, and that's blatantly unrealistic. Also, the sleeve must be securely attached to the bracket, so that it doesn't come off under load. The cutaway image I made shows a possible solution, but I'm not sure how that detail can be manufactured cheaply and effectively. On the bright side, I think this is the simplest design that can work.

Not many months left to know for sure... In the meanwhile, do you think mLA's are just decorative, or do they work differently?


Daniel said...

This is certainly the most likely all plastic solution.

I believe there will be metal parts, so I think the alternative solution (where the rod acts as a sleeve) will be used. This would be stronger, but would probably generate more friction.

Conchas said...

Thanks for your wonderful sketches Alexandre!

"mLA" is also a cute and so short acronym. Brilliant! :)

I can see another way to make it work (sorry, I have not prepared a sketch).

The sleeve and bracket would be one single part (no sleeve rotation and no screw).
Then two inner parts allowing inter-rotation along the axis: One base with axle or axle-hole and a protruding screw axle in the opposite direction (this whole part could be metallic), and one hollow plastic rod with screw, sliding into the sleeve as the base rotates.

Let's see who comes closer to the actual solution. :)

Andre said...

Great post AVCampos, very well done.

In spite of being functional,I don´t think that solution is very strong and durable for the kids and for us to play.

3 separate plastic parts (with 2 of them moving) are definitely more clumsy than the lLA (large linear actuator)solution with only one moving part.

I agree with Conchas that the mlA will be similar to the lLA, and it doesn´t need to have an input axle instead of an axle hole, but who knows...

Anonymous said...

Since the mLA will be "cranked" up and down via knobs (and not Power Functions motors), the movement should be quite slow. I think the first sketch reflects the (simple, low-cost) version that TLG will end up manufacturing.

Philo said...

This seems a working possibility, but as designed there is no way to put the screw in the body (no thread on tip). So it would probably need another (glued) part to close the body after the piston is inserted.

Anonymous said...

Here is how I think it will work:

The green part and the rod are both made of metal.

Conchas said...


Yes, that basically fits my view as described above.

It might have the same problem as described by Philo, if we don't want the rod to pull-off easily.
However it could be overcome, if the rod has a small edge on the bottom and gets into the sleeve with a small pressure.

Al said...

"that's blatantly unrealistic"

Oh, so no different to the larger ones then ;^)

Personally I think the outer sleeve is fix to the base, not rotating. The blue part is a hollow tube threaded up the middle with a threaded rod running up the middle of that to the axle at the back.

Nice illustrations BTW!

Anonymous said...

i think the green part is not fixed to the bracket, instead it is just a modified axle

santi said...

If the green part were not to be fixed to the bracket, then, when contracting the actuator, it would come off. Thus, it has to be fixed, right?

AVCampos said...

@Conchas and Anonymous: I thought about that possibility too, but it appeared to me too expensive/cumbersome to be applicable on such a small size and in such large number on a set in this price range. In fact, that's the exact mechanism I thought about many years ago and suggested to LEGO (and in which I stupidly forgot to include the picture I made at the time), and which I thought the standard LA's used.
However, I'm not sure if the probable piece cost (again, four of these on a 49.99€ set) allows for this complexity and the use of metal... but soon we shall see. ;)

@Philo: Yes, that's something I too saw on the proposed design, and the only possibility I saw was that the bracket is composed of two assembled halves, possibly glued. One of them could be something like in the cutaway drawing, except that the mounting axleholes would be completely part of one of the halves.

When I have time, I'll try to do some sketches of both the three-layer suggestion and how the two-layer suggestion could be assembled.

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