What are the axes on a ball joint?

[elf]

I've read (somewhere on the Internet, so I know it's true) that a ball joint has three degrees of freedom or axes. I put a ball bearing on a magnet attached to a washer, then put a machine screw on the ball bearing. The machine screw can move to any position on the upper hemisphere of the ball bearing. The washer is constrained to only allow rotation. How many axes do I really have here and what are they called?

Here's a snapshot of it:

[The Artful Bodger]

The screw can be moved left-right, thats the 'x' axis, up and down (i.e. towards and away) that the 'y' axis and the screw can be rotated which is the 'z' (?) axis.

YMMV

[vpt]

That sounds right to me.

[Lew Hartswick]

The screw can be moved left-right, thats the 'x' axis, up and down (i.e. towards and away) that the 'y' axis and the screw can be rotated which is the 'z' (?) axis.

YMMV

Not in my (math) terms. Up Down is Z The rotation is not one of the
X Y Z "Cartizian" (Sp?) coordinates. In an aircraft that "rotation"
one is Yaw along with Pitch and Roll but don't know that in Math
class I remember the three rotation ones being discussed. :-(
So I guess there are 3 but the one is NOT Z.

On thinking more about it I don't think there is really an X or Y either. They are Translation motions
so the 3 are just as in an airplane . Pitch, Roll, Yaw.
...Lew...

[blowlamp]

It's got an infinite number of rotational axes hasn't it?


Martin.

[Barrington]

Although they don't correspond to the 'natural' motions of the part in any obvious way, there are simply three rotational degrees of freedom around the normal cartesian X,Y and Z axes. (With the origin in the centre of the ball.)

That is to say, any possible orientation of the bolt can be achieved by rotating it the appropriate amounts around the origin (e.g.) first in X, then in Y, then in Z.

We don't tend to see it that way because it can be very tricky to imagine how to perform the required moves.

Cheers

.

[mklotz]

The orientation of the screw in space can be described with two angles; an azimuth angle that represents rotation about the vertical and an elevation angle that represents its angular elevation above the horizontal. The third degree of freedom is rotation about the screw axis.

[Highpower]

X, Y, and ط?

[Jaakko Fagerlund]

X, Y and C, if presuming that the screw is along Z axis. So three.

[philbur]

Do you really want to know or is it just to find out how many people here currently have nothing better to do than try to answer a question they should have Googled.

Simple answer, Google: Degrees of freedom (mechanics)

Phil

[Dragons_fire]

The Screw would be moving in the a, b, and c axis. The bolt is rotating, so it would be moving in the rotational axis.

If you slid the washer ( and whole assembly) forward/back, left/right or up/down, you would be moving in the x,y, and z axis

[The Artful Bodger]

Not in my (math) terms. Up Down is Z The rotation is not one of the
X Y Z "Cartizian" (Sp?) coordinates. In an aircraft that "rotation"
one is Yaw along with Pitch and Roll but don't know that in Math
class I remember the three rotation ones being discussed. :-(
So I guess there are 3 but the one is NOT Z.

On thinking more about it I don't think there is really an X or Y either. They are Translation motions
so the 3 are just as in an airplane . Pitch, Roll, Yaw.
...Lew...

Pitch, roll, yaw would work. Also lattitude, longitude and time (with reference to the terrestrial sphere!)?

[justanengineer]

X, Y and C, if presuming that the screw is along Z axis. So three.

I agree. This is a standard question in engineering 101.

[cameron]

Do you really want to know or is it just to find out how many people here currently have nothing better to do than try to answer a question they should have Googled.

Simple answer, Google: Degrees of freedom (mechanics)

Phil

Perhaps elf just wanted to see how many people would suggest it's better to look it up on Google rather than use one's head ?

[elf]

Perhaps elf just wanted to see how many people would suggest it's better to look it up on Google rather than use one's head ?

Or perhaps elf needed an interpreter for the Google results

Here's a sample:
"Now, let be the sample mean. The random vector can be decomposed as the sum of the sample mean plus a vector of residuals:

The first vector on the right-hand side is constrained to be a multiple of the vector of 1's, and the only free quantity is . It therefore has 1 degree of freedom"


p.s. Thanks everyone for explaining it well.