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?