Question about ball joints

[Bob De Quatre]

Hi guys,

First I apologize if it's not the right location to ask that kind of questions...

I've used bricks with ball joints (57909 and 57910) on this big guy's elbow but I'm a bit disappointed by the lack of friction. Do you think Bionicles parts could have more frictions? How would you do if you had to improve it?

AG: Monkey Business by BobDeQuatre, on Flickr

[ddeklerk]

I am not sure whether Bionicle ball and socket joints have more friction, but there is a friction adder part that also acts as an extension for the socket. Here is a link to the part on Bricklink.

Alternatively, you could use the Exo-Force style ratchet joint. Those are comprised of these three parts. 1, 2, 3.

[YellowCorvette]

The MOC looks pretty cool!

Anyway, the easiest way to adding friction to the balljoints I can think off is by adding this part (http://brickset.com/parts/6106472) to the balljoints. You can use ratcheted joints from the Exo-Force sets or adding a additional balljoint support like in several Bionicle and Hero Factory Titan sets.

[Bob De Quatre]

Thanks for the quick answers! I've made a test using ratcheted joints but they don't really work. I'll make a test with that extender part, but I only have two of them and there's already one in use in this MOC (and that makes me wonder why I didn't thought of using it before!!)

[Onepu the Protector]

The friction of a ball joint/ball socket piece usually varies from piece to piece and often depends on how much it was used.

[PicnicBasketSam]

Yep, new joints have more friction and those friction extenders help a lot. Although the Uniters having them on their ankles is really strange...

[Pate-keetongu]

Those "Technic, Brick Modified 2 x 2 with Ball Receptacle and Axle Hole"-style parts have some differences, too. You seem to have used the original mold (2007-2008, I think), but there are two newer ones, 62712 and 92013. They have more friction, and whereas 62712, a child of unlucky ball socket overhaul, might be prone to breaking, 92013 is perfect in very way.

Of course the friction extension piece mentioned above is the tighest, but unfortunately only available in dark bley.

[Aanchir]

For elbows something else to keep in mind is that a joint like the ones you used will have less friction than a joint like the knees of the Future Flyer or the knees and left arm of The King's Mech. This is not due to any differences in the dimensions of the ball or ball cup, but rather due to the direction the ball cup has to rotate. When the ball cup wraps around the ball horizontally, it is easier for the ball to slip vertically (and thus, for the elbow to flex or straighten based on forces like gravity or inertia). But when the ball cup wraps around the ball vertically (i.e. in the same direction the piece is expected to rotate for typical elbow movement), every point of contact is working to its fullest potential to prevent slippage. This is why B-type CCBS beams exist even though A-type CCBS beams allow a lot more free movement.

Of course, I understand that the way you've constructed the elbows offers a lot more free movement than a joint like on the knees of the Future Flyer. But sometimes friction has to come at the expense of free movement. Also, there are other ways you can compensate for this, such as changing the construction of the shoulders so that they can rotate in front of the body a bit like real human shoulders would if, say, you try to hug yourself. But of course, since this is a robot creation, full human-like movement might not even be the best objective to work towards.

Taking this a bit further: since a joint construction like the legs of the Future Flyer or King's Mech basically does limit the joint to the one axis of rotation where the friction is strongest, then at that point you could even potentially create more friction by doubling up the ball joint, like in the knees of Black Phantom or Takanuva. Of course, this is generally easier to do in a Technic-based MOC than a more System-based MOC.

Hope these tips help and that the way I phrased them isn't too confusing! I don't really have an engineering background so I don't always know the words to describe why something works how it does.

Edited July 25, 2016 by Aanchir

[Bob De Quatre]

Thanks everyone for your answers! I'm not really familiar with all those joints and it helped a lot!

I tried using the friction extension part and it worked well without changing much of the design. I just had to move the "Technic, Brick Modified 2 x 2 with Ball Receptacle and Axle Hole" by one stud inside the forearm (btw I only own 57910 and no 92013) and add a plate layer to raise the wedge under the cup ball part. Now I need to find a better solution for the shoulder

New arm by BobDeQuatre, on Flickr