Ball Cup, High Friction with Rubber.
At least, that’s what Brickset and the LEGO Group call it. The name is a little awkward. And a little suggestive. Bricklink refers to it as a Hero Factory Arm/Leg Extender with Ball Joint and Ball Socket. Neither of these names is particularly catchy.
I first encountered this piece when putting together the new Creator set 31085: Mighty Dinosaurs. While this is the first Creator set to feature it, it is by no means a new piece.
Appearing initially in 2012, this piece has featured heavily on the constraction figures, with themes such as Hero Factory, Bionicle 2: the Rebirth; Star Wars; Chima and DC Superheroes. More recently is has appeared in several Ninjago sets and a couple of NEXO Knights sets, particularly those involving dragons or mechs, as well as the ClayFace Splat Attack (70326,70327,70593,70595,70627 and70904). It was also present in 75156 Admiral Krennic’s Shuttle Craft, from Rogue One. Having little experience with buildable figures such as Bionicle and the like, and having not put together the mech sets and large dragons from Ninjago, I was unlikely to have encountered it until now.
When this piece first appeared, the rubber was trans clear, and more recently has been made black. It sits between a ball joint and the cup for ball. It has two functions: it makes the limb a little longer (Approximately 8 mm longer in fact) and it increases the force required to overcome the friction that is holding a ball joint in place. But more on that later.
This component does not appear to have any other connection points within LEGO System. It has holes in the sides which ALMOST accept a stud, but not quite. It just acts as an intermediary piece in a ball joint. It is currently only available in dark stone grey (dark blueish grey).
How does it increase the friction within the ball joint?
The rubber protrudes from a small hole at the base of the cup, making contact with the ball, and reducing unwanted movement at the joints. A small amount of rotation is possible at the ball end of the piece when it articulates with a cup for the ball.
Investigating the strength of the grip/slip reduction:
So how much difference does this piece make, opposing movement? I set up the following apparatus to test the effect of this element. This is essentially a first order lever: 2 1×16 bricks are attached to the brick with the ball, and a load is progressively added to the end of the lever. I used standardised 2×4 bricks as my load. The lever was supported while the bricks were added, and the support then removed.
The ‘naked’ ball joint was fairly steady up until the fifth brick was loaded on the lever. When six bricks were loaded onto the lever, the joint rapidly buckled under the load, with virtually no drag.
After inserting the ‘joint extender’, I was able to add up to 16 bricks to the lever, before it started to buckle, and 20 before it collapsed completely under its own weight. The collapse with this element in was also much slower and controlled, compared to the ball joint without the ‘stiffener’. I do not wish to guess the exact ramifications of this in terms of increased mass of model able to be built if this element is inserted between the ball and cup of these joints. Certainly it should prevent smaller models collapsing under their own weight. It would appear that the relative force required to overcome the frictional resistance of the ball joint in increased by a factor of 3-4, with static loading.
I wish I knew about this element a year or so ago: I was building a dragon, and repeated challenges to get it standing up resulted in me changing over to use click joints. However this change significantly reduced my ability to pose the model, which I ultimately supported using part of the scenery.
I first encountered this element as part of the 31058 Mighty Dinosaurs Creator Set. Its primary role was to support the Tyrannosaurus Rex’s legs, should they begin to splay apart. This would easily happen if this element was left out. As a Creator 3-in-1 set, it has 3 models in the set: the Tyrannosaurus Rex, a Pteranadon and a Triceratops. Each of these builds stands up well against the others, although the T-Rex is my favourite out of all of them. The box also advertises a 4th model – a Brachiosaurus: at least I think it is a brachiosaurus – which is cute, but not as grand as the other builds. I shall review that set in coming weeks.
In summary, the Ball Cup, High Friction with Rubber is a suggestively named, and highly specific piece. It has two functions, and performs both of them well, increasing the static load resistance of these ball joints by in excess of 300%! Crossing it over to the Creactor sets will encourage AFOLs without a working knowledge of the constraction system to use these ball joints as load bearing joints more frequently.
I hope you have found this discussion of interest. Is this a technique you know about? Will you be able to employ it in future builds? Have I brutally misused a number of engineering terms?
Why not comment below.