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• Theoretically, what could be done to a rod and ball joint to increase the swivel angle?

• Is it worth talking about the swivel angle?

• Did that make sense, or should we go over what the swivel angle means?

• Could you show us what the swivel angle means?

• Yeah, okay.

• So here's a rod-end ball joint, or sometimes it's called a heim joint.

• It just spins around like that.

• And typically, you'll have a rod that goes through it like that.

• And this rod will be usually fixed in place so that the ball joint can't slide back and forth like that.

• It'll just be fixed relative to the axial length of your rod.

• But this rod can swivel like this.

• And if we look at it, this is the lowest position that your rod can be.

• And then this is the highest position it can be.

• And so the difference there, so if we use some tools here to approximate that angle, you're going to have a line there.

• And then if we come down like this, we're going to have another line right here.

• So this angle right here, that angle, that is the maximum swivel angle that this ball joint will accommodate.

• So if this is 90 degrees, how much would we approximate that this swivel angle is?

• Yeah, so that's maybe 65 degrees or something like that.

• And actually, 65 degrees is usually kind of an upper limit for these rod-end ball joints.

• Most of them are actually down more like 25 or 30 degrees, but then they have these super swivel ball joints that go even further.

• I believe this is one of those super swivel varieties.

• Okay, so now that we've talked about what that swivel angle is, let's say theoretically we could get 65 degrees right here, but our application needs 70 degrees, just a little bit more than what we can actually accommodate.

• How might we modify something, either the rod or the ball joint?

• How might we modify it so that we can get another 5 degrees?

• I do have a question.

• Could you access the lesson?

• Oh yeah.

• So the question was, if we scroll all the way up, what's important to remember, point number one, and go to 1A.

• Okay.

• It says, allows for 3 degrees of rotational freedom.

• So you said 3 degrees here, but it shows that we have approximately 65 there.

• Oh, I see.

• I see the confusion. 3 degrees, a degree of freedom, in this context, doesn't mean a degree of angle.

• A degree of freedom would mean motion.

• For example, let's draw something.

• Actually, let's take a look at this rail and carriage.

• This rail and carriage allows for one degree of freedom, just back and forth.

• It doesn't have anything to do with an angle measurement, but when we say one degree of freedom, it means it can move back and forth.

• It could be rotational also.

• There are really just two types of degrees of freedom.

• There's linear motion, so this, and then there's rotational motion, so like a shaft that was spinning like that.

• Those are the types of degrees of freedom.

• You can have up to 6 degrees of freedom.

• For example, in a CNC machine, some people talk about 5-axis CNC machines, and that the 5-axis, the 5 degrees of freedom, would be 3 in the linear direction, so you'd have 1 here, and you'd have 2 there, like that way, and then you'd have 3 up and down like this, so those are 3, but we're talking about a 5-axis CNC machine.

• The other 2 degrees of freedom would be rotational, so you might have rotation like that, and then you might also have rotation in that direction.

• When we say 3 degrees of freedom, what we're saying is it can move in 3 different methods of motion.

• Let's find the 3 degrees of freedom.

• Back and forth, 1, rotation, 2, where's the 3rd?

• Typically, you're not moving back and forth like this.

• If you're using a ball-end rod joint or a rod-end ball joint, you're usually going to lock the rod into the ball joint, so this degree of freedom usually is not happening.

• Again, talking about degrees of freedom, x, y, and z are typically used to describe the 3 different directions of motion, so if we were to draw that out in 3D, it might look something like this, where this is up and down, this is out in that direction, and then this is this direction, so this might be the x-direction of freedom, the y-direction of freedom, and the z-direction of freedom.

• About each of those directions, you can also have rotational.

• So this would have 6 degrees of freedom, right?

• That's right. 6 degrees of freedom is really the most degrees of freedom that anything can have.

• For this one right here, we're not going to count this one.

• Technically, that's possible, but usually you're not going to have that in a rod-end ball joint, but you'd have this right here.

• Which is what?

• This is a rotational degree, so if we were looking...

• Let's see, what's the best way to look at that?

• If we align it like this, so this axis, this rod right here, let's say that that's our x-axis, and we're able to rotate in this direction, so which axis of rotation would that correspond to in our little sketch here?

• Y?

• No.

• What, z?

• Z.

• Yep, it would be z, exactly.

• Then that has to be y, I suppose.

• Yep, that's y.

• And then the third one, which realistically, maybe I shouldn't even say a third degree, because it's probably not common either, but it could be, you could use it.

• It would be...

• It's kind of hard to see it rotating.

• Let's see, I think there's a feature.

• There we go, you can see that feature moving now.

• That would be the third degree of rotation, which is which one?

• X.

• Yep, x.

• So those would be the three degrees of rotation, and really it's z here, and y there.

• Those are the main two degrees of freedom.

• Okay, so back to the original question, which was, theoretically, what could be done to a rod and ball joint to increase the swivel angle?

• Yes.

• And what I thought, we could wear it out, I suppose.

• So I just chip away, right here, just start chipping away, and chipping away at the top, so I can reach higher or lower.

• Right, yeah.

• So show...

• Let's look at exactly where the limit to that rotational travel occurs.

• Yeah, right there, right?

• Right here, the rod strikes the casing for the ball joint, and that's what limits its travel.

• So just like you said, yeah, use the term wear away.

• I would probably use something more intentional, like cut the rod, cut a feature around the diameter of the rod to make that part of the rod smaller in diameter and increase that travel.

• That's probably the easiest thing to do.

• Technically, you could also machine away some of the material on the casing so it doesn't strike the casing there, but that's going to be a more difficult operation to perform.

• Is that recommended?

• No.

• Not recommended to machine away some of the casing.

• I think it would be permissible in certain applications to turn down the diameter of your rod.

• You could get away with that, but I would not cut the casing of the ball joint.

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Theoretically, what could be done to a rod and ball joint to increase the swivel angle?

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# Mechanical Design: Rod End Ball Joints Discussion

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Amy Lin posted on 2024/07/31
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