Tutorial - How to animate a parallelogram

Parallelogram

For the following animation tutorial, we will link parts of the parallelogram together and control the moments using these links and the Inverse Kinematics feature.

Before you start, if you don't have any previous experience with Bongo. You might want to have a look at how animation hierarchies works in Bongo 2.

 

Click to play animation example:

 

How to start? 

We will start by naming all the parts to be able to clearify things.

 

Secondly we will have to get some movement into the animation. We need a driving motor for the link chain.

  1. Open up the model parallelogram.3dm
  2. Select Object A
  3. Move the timeline slider to tick 50.
  4. Press the Animate -button
  5. Switch to Rotation Mode on the timeline, and edit the z-axis angle value to be 20.
  6. Move the timeline slider to tick 99.
  7. Edit the z-axis angle value to be 0.

 

Click to play animation example, it should look like this:

 

 

How to create the chain?

 

  1. From the Bongo Menu Select Utilities, and then Link Chain.
    -Or-
    Click on the Link Chain icon in the toolbar.
    -Or-
    Use the BongoLinkChain command.
  2. At the Select Parent prompt, select the Object A.
  3. At the Select Point To Move Pivot To prompt. Press Enter.
    No need to move object's pivot, since it is already in place.
  4. At the Select new link  prompt, select the Object B.
  5. At the Select Point To Move Pivot To prompt. Select the center of the corner by having OSnap to Mid and Smart Track on, see image below.


     6. Press Enter to end the command.

Now Object B follows the movement of Object A.

 

If you have a look at the first video, you can see that what we want is for Object C, to stay in place and mimic the movement of Object A, while Objects B and  C moves to connect  A and C. In order to make this possible the pivot of Object C, must stay in the middle of the object. However, in the corner where Objects B and C meet, we would need to have a pivot point that would make it possible for that corner to rotate. Otherwise we will end up with a moment like this:

 

 

To prevent this from happening and to get that extra pivot point, we will add a point.

  1. From the Bongo Menu Select Utilities, and then Link Chain.
    -Or-
    Click on the Link Chain icon in the toolbar.
    -Or-
    Use the BongoLinkChain command.
  2. At the Select Parent prompt, select the Object B.
  3. At the Select Point To Move Pivot To prompt. Press Enter.
    No need to move object's pivot, since it is already in place.
  4. At the Select new link  prompt, select the Point 1 in the "corner". Select the point by having Osnap to Point on, see image below.
  5. At the Select Point To Move Pivot To prompt. Press Enter.
    No need to move object's pivot, since it is already in place.
  6. At the Select new link  prompt, select the Object C.
  7. At the Select Point To Move Pivot To prompt. Press Enter.
    No need to move object's pivot, since it is already in place.
  8. At the Select new link  prompt, select the Object D.
  9. At the Select Point To Move Pivot To prompt. Select the center of the corner by having OSnap to Mid and Smart Track on, see image below.
  10. At the Select new link  prompt, select the Point 2 in the down left corner. Select the point by having Osnap to Point on, see image below.
  11. At the Select new link  prompt, press enter to end the command.


Why did we add the point to the end?


The point we added to the end will be the point to where our IK chain ends, our goal. The goal however needs a partner, something to hold on to, be constrained to. The point - the partner, the pivot, that we will constrain our chain to will have to move along with Object A. It can't be Object A itself since it has it's pivot in the middle of the object and we want our chain to be constrained to the down left corner. To solve this we will add a point as a child of Object A.
  1. From the Bongo Menu Select Utilities, and then Link Chain.
    -Or-
    Click on the Link Chain icon in the toolbar.
    -Or-
    Use the BongoLinkChain command.
  2. At the Select Parent prompt, select the Object A.
  3. At the Select Point To Move Pivot To prompt. Press Enter.
    No need to move object's pivot, since it is already in place.
  4. At the Select new link  prompt, select the Point 3 in the down left corner. Select the point by having Osnap to Point on, see image below.
    Note: Please make sure you do not select the point you just added to the other chain. The point you should selelect should only be called Point nothing else.
  5. At the Select new link  prompt, press enter to end the command.

Click to play animation example, it should look like this:

 

As you notice, without the help of the IK -settings, the whole chain will rotate with the parent. To prevent this from happening, we will set up the IK -settings for the children.

 

Setting up the IK

We will start by setting up the first child after the parent. In this case, it is Object B

 

  1. Select Object B and go to the Properties Tab > Bongo.

  2. Under Constraints and Joints, select Part of an IK chain > Joint.

    We will make this into a Hinge Joint that will be allowed to rotate around the z-axis.
    The Hinge and Z-axis should be selected as the default value.

  3. Select the Point 1 that's a child of Object B. 

  4. Under Constraints and Joints, select Part of an IK chain > Joint. The Hinge and Z-axis should be selected as the default value.

  5. Select Object C, and in the the Properties Tab > Bongo.

  6. Under Constraints and Joints, select Part of an IK chain > Joint and Constraint.
    The reason why Object C needs to be a joint and a constraint is because we want the object to rotate with Object A and at the same time stay in place.
  7. The Joint Type should be Hinge and around the z-axis. Pivot constraint should be set to Keep pivot location the same.

  8. Select Object D, and in the the Properties Tab > Bongo.

  9. Under Constraints and Joints, select Part of an IK chain > Joint. Joint Type should be Hinge and Z-axis rotation.

  10. Last select the Point 2 at the end of Object D, that's a child of Object D.
  11. Under Constraints and Joints, select Part of an IK chain > Constraint.
  12. In the Pivot Constraints Options, press the Select target object -button. Select the Point 3 that's a child of Object A, as the target.
    We want the two points to stay together, so that the square of the parallelogram stays in place.

Now the whole IK -chain should have a driving motor, a start and an end (goal) and therefore be complete. If you now play the animation is should look like this:

 

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