Defining Single-Axis Motion with Revolute and Slider Joints

1. The Revolute Joint: Creating Rotation

A Revolute joint constrains the motion between two components to a single rotational axis, just like a pin in a hinge. It removes all three translational degrees of freedom and two rotational degrees of freedom, leaving only one axis of rotation free.

The process is very similar to creating a Rigid joint. You use the Joint or As-Built Joint command, select the two components you want to relate, but instead of choosing "Rigid" for the motion type, you'll select Revolute.

The video below gives an excellent demonstration of how to apply a Revolute joint to create a hinge.

Setting Realistic Motion with Joint Limits

By default, a Revolute joint allows for 360 degrees of rotation. This is fine for a wheel, but not for a door or a lid that should stop at a certain point. To control this, you can edit the joint and define Joint Limits.

This feature is what makes your digital prototypes behave like their real-world counterparts. You can set minimum and maximum angles of rotation to prevent components from passing through each other.

The next part of the same video clearly explains how to set these limits.

2. The Slider Joint: Creating Linear Motion

The Slider joint works on the same principle as the Revolute joint but for linear motion. It constrains components to move back and forth along a single axis. This is the joint you would use for a drawer, a piston in a cylinder, or any part that needs to slide in a track.

You apply it in the same way as other joints:

1. Activate the Joint or As-Built Joint command.
2. Select the two components.
3. In the Motion tab, select Slider.
4. Select a reference edge or axis that defines the direction of sliding.
5. Just like with Revolute joints, you can then define Joint Limits to set the minimum and maximum travel distance.

The following resource provides a clear, step-by-step guide for applying a Slider joint with motion limits in the context of a tripod leg assembly.

3. Hands-On Practice

It's time to apply these concepts. We'll create two small, separate designs to isolate each skill. Since your preference is to design from scratch, this will be great practice.

Practice A: Box with a Hinged Lid (Revolute Joint)

1. Start a new design.
2. Create the Box:
   • Create a sketch on the ground plane (XY). Draw a 100 mm x 60 mm rectangle.
   • Extrude it upwards by 40 mm to create a new body.
   • Use the Shell tool (Modify > Shell) to hollow out the box. Click the top face and specify a thickness of 3 mm.
   • In the Browser, right-click the body and select Create Components from Bodies. Name this component Box.
   • Ground the Box component (right-click > Ground).
3. Create the Lid:
   • Create a new sketch on the top rim of the Box.
   • Draw another 100 mm x 60 mm rectangle.
   • Extrude it upwards by 3 mm, ensuring the operation is set to New Component. Name it Lid.
4. Apply the Hinge:
   • Because the Lid is already in its final closed position, we can use an As-Built Joint (Assemble > As-Built Joint).
   • In the dialog, select the Lid and Box components.
   • Set the Motion Type to Revolute.
   • For the Position, hover your mouse over one of the long, top outer edges of the Box until a joint origin icon appears at its center. Click to select it. This defines your hinge axis.
   • Click OK.
5. Test and Refine:
   • Click and drag the Lid. It should pivot around the edge you selected.
   • Find the joint in the Browser (under the Joints folder), right-click it, and select Edit Joint Limits.
   • Check the boxes for Minimum and Maximum. Set the minimum to 0 deg and the maximum to 95 deg.
   • Click OK. Now, the lid should open just past vertical and stop, mimicking a real box.

Practice B: Block in a Track (Slider Joint)

1. Start a new design.
2. Create the Track:
   • Create a sketch on the front plane (XZ). Draw a C-shaped profile for a track. For example, a 40 mm tall by 20 mm wide channel with 3 mm thick walls.
   • Extrude this profile 150 mm to create a new component. Name it Track.
   • Ground the Track component.
3. Create the Sliding Block:
   • Create a new sketch on the end face of the Track.
   • Draw a rectangle that fits inside the channel with a small clearance (e.g., if the inside of the channel is 14mm wide, make your block 13.8mm).
   • Extrude this rectangle 25 mm, ensuring the operation is New Component. Name it Slider.
4. Apply the Slider Joint:
   • Use an As-Built Joint. Select the Slider and Track components.
   • Set the Motion Type to Slider.
   • For Position, select one of the long edges of the Track to define the direction of motion.
   • Click OK.
5. Test and Refine:
   • Drag the Slider block. It should move freely along the track.
   • Edit the joint's limits. Set the Minimum to 0 mm and the Maximum to 125 mm (150 mm track length - 25 mm block length).
   • The block should now slide from one end to the other and stop correctly.

Conclusion

Excellent work. You've now moved beyond static assemblies and can create designs with intended, predictable motion. This is a massive step toward designing functional parts for your projects.

Key Takeaways:

• Revolute Joints are for single-axis rotation (hinges, pivots).
• Slider Joints are for single-axis linear motion (tracks, drawers).
• The application process involves selecting the components, the motion type, and a position/axis for the motion to occur around.
• Joint Limits are essential for simulating realistic mechanical constraints and preventing parts from moving through each other.

In our next lesson, we will focus more on the As-Built Joint. While we used it today for convenience, the next session will formalize the strategy of when and why to use it, particularly in the context of "top-down" design where components are designed in their final assembled positions.