Step 16.2: Motion-Path FB, Ram-R: Engine Valve Cam

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Step 16.2: Motion-Path FB, Ram-R: Engine Valve Cam

Motion-Path: Ram-R and Ram-P

We can use the Motion-Path FB to build two new Dyads:



An application of the Ram-R dyad is to model an engine valve cam where we want to specify the distance between the center of the rotating cam and the center of the roller on the rocker.

Another application is to specify the motion of a Linear Actuator that drives a scissor lift.

Ram-R Dyad



STEP 1: Edit the Base-Part to add a horizontal LineRed-14-1b that is ~200mm long.  

STEP 2: Close the Part-Editor

STEP 3: Red-14-2 Add two Parts

STEP 4: Edit the length of the left Part to ~160mm long and the right-hand to ~180mm long.

STEP 5: Red-14-3 Add Pin-Joints between the start-Points of each Part and each end of the Line in the Base-Part.

Step 5 is complete.


Add a Motion-Path FB

STEP 6: Click Kinematics-FB Toolbar > Add Motion-Path FB

You add a Motion-Path FB to a sketch-path - we will select the CAD-Line.

STEP 7: Click the CAD-Line along the center of the Part on the left.

STEP 8: Click OK-tiny-11-15 in the Command-Manager.

The Motion-Path FBRed-14-1b is in the graphic-area. The Motion-PointRed-14-2 is at the start-Point of the CAD-Line along the left Part.


Add a Motion to the Motion-Point

STEP 9: Add a Motion FB and a Linear-Motion FB to the graphic-area.

STEP 10: Connect wires between the FBs in the usual way.



Edit the Motion FB and its Output Data-Type

STEP 11: Edit the Motion FB to open the Motion FB dialog-box

In the Motion FB dialog-box

STEP 12: Click LinearRed-14-4 as the Output Data-Type

Close the dialog box.

When you connect a Motion FB to a Motion-Path FB, you MUST edit the Output Data Type to Linear or Rotary.

Step 12 is Complete.


Edit the start Position of the Motion-Point.

We want the Motion-Point to start its motion along the CAD-Line at the minimum radial distance from the center of the Cam to the center of the Roller.

In this case, the minimum radial distance is 40mm

STEP 12: Edit the Motion-Path FB

In the Point Parameters separator

STEP 13: Edit Linear Offset = 40mm

STEP 14: Close the dialog

Step 14 is Complete

Now we can add a Pin-Joint.


Add Pin-Joint

STEP 15: Click Kinematic-elements toolbar > Add Pin-Joint

STEP 16: Click the end-Point of the Cad-Line in the right-hand Part and then the Motion-Point that is at 40mm along the CAD-Line

The Pin-JointRed-14-6 joins the two Parts.


The Parts are now kinematically-defined Parts. with Green Part-Outlines.

The Ram-R dyad has  two closures. To change the closure of the Ram-R dyad:

STEP 17: Click Kinematic element toolbar > Change Dyad ClosureRed-14-7

STEP 18: Click a Part-OutlineRed-14-8 in the Ram-R dyad


STEP 19: Click OK-tiny-11-15 in the Command-Manager.

STEP 20: Cycle Run menu > Cycle
- or -
ALT+C keys

You will see the Motion-Point move along the CAD-Line


Add the Cam Roller

Note: This cam is not going to be useful for an engine - it shows only one principle!

STEP 21: Edit the Part on the right to add a Circle at the end-Point of the CAD-Line

STEP 22: Do Solid menu > Add Profile and click the circleRed-14-9



Add the Cam-Part

STEP 23: Add a PartRed-14-10a and join it with a Pin-Joint at the left of the Line in the Base-Part.

STEP 24: Add Motion-Dimension to the Part and connect to it a Linear-Motion FB

The new Part is horizontal - the Base-Value is 0º


Add the 2D-Cam

STEP 25: Do Machine elements > Add 2D-Cam  

Select the new PartRed-14-10a and the ProfileRed-14-9

The 2D-Cam is now in the graphic-area.

Note: I would not normally recommend you model a cam in this way. It is only to illustrate the possibility.



We call this kinematic-chain the Ram-R Dyad

The Ram-R Dyad is represented by the R-R-R Dyad.

The rotating Cam-shaft is represented by a Rocker