2021.1.1124.2 Bar Linkage Solver

1 Overview
2 Where to find
3 Feature layout
4 How to use - Part A
5 How to use - Part B

Overview

A Bar Linkage Solver is a combinatory joint which allows you to quickly create an bar linkage using Wheel Joints and a Prismatic Joint. Bar linkages are commonly used in hydraulic systems (such as crane arms).

The Bar Linkage Solver can easily be used for Kinematic Synthesis (n-bar linkages by combining <4 bar link systems).

A Bar Linkage Solver controlling a piston pushing an arm

Where to find

The Bar Linkage Solver component can be found under Mechanics > Add Kinematics > Bar Linkage Solver.

It can also be accessed from the GameObject menu or from the Hierarchy Context menu.

A new GameObject will be created if you do not have a GameObject selected. Otherwise, the Bar Linkage Solver will be added to the selected GameObject.

Feature layout

The image below shows the complete feature layout of the Bar Linkage Solver component.

Generic Joint Settings
Pass Priority	Priority of the kinematic chain calculations. Higher numbers are calculated earlier
Enforce Outside Playmode	Enforces the prismatic joint in edit mode
Prevent Kinematic Update	Removes the prismatic joint from the kinematic chain calculations
Prevent Further Kinematic Update on this GameObject	Allows lower priority kinematic transforms on the same GameObject to be skipped in calculations
Allow Direct User Input	Allows the user to manipulate the prismatic joint with the scene gizmo
Min. User Input Translation Offset	The minimum value the user must input before translations are applied
Min. User Input Rotation Offset	The minimum value the user must input before rotations are applied
Kinematic Chaining
Opposing Relation Instance	The kinematic transform to which you want to link the prismatic joint to
Relation Direction	Describes the direction of the manipulation of the Transforms. The following options are available: BIDIRECTIONAL: Allows for both kinematic transforms, when they are being manipulated, to manipulate each other equally RECIEVE_ONLY: Allows for the prismatic joint, when it is being manipulated, to manipulate the opposing kinematic transform, but not the other way around SEND_ONLY: Allows for the opposing kinematic transform, when it is being manipulated, to manipulate the prismatic joint, but not the other way around
Relation Type	Not yet implemented
Motion Direction is Reversed	When enabled, the manipulation to/from the opposing kinematic transform is inverted
Bar Linkage Triangles
Add Triangle	Allows the user to add a new triangle with a random color to the Bar Linkage Solver
Triangle ##	Shows the ID of the triangle, the names of the two Wheel Joints in the triangle and whether the triangle is the leading triangle
Color Picker	Allows the user to change the color of the triangle
Delete Button	Allows the user to delete the triangle from the Bar Linkage Solver
Leading Triangle / Set as Leading	If the triangle is the leading triangle, that will be displayed. Else a button will appear to set the triangle as the leading triangle
Moving Pivot	The Bar Linkage Solver is the Moving Pivot by default. This is a constant field and is shown for clarity
Fix Pivot	Allows the user to assign a Wheel Joint as Fix Pivot
Hinge Point	Allows the user to assign a Wheel Joint as Hinge Point
Draw Triangle Gizmo	Allows the user to toggle the triangle gizmo
Limit Relation & Update Settings
Spline Input field	Defines the spline to which the Prismatic Joint is bound to
Prismatic Joint Settings
Spline Constraint Lenght	The length of the spline
Current Spline Position	Normalized position of the Prismatic joint over the spline between 0 and 1
Target Control Point	The Spline point to be used for Update Limit ControlPoint
Update Limit ControlPoint	Updates the Target Control Point to the current spline position

How to use - Part A

To create a Bar Linkage Solver, you first need the right setup. This setup will include several fixed arms, Wheel Joints and a Piston (this requires a SplineUNDEFINED ). Part A of the How to use will guide you through the process of creating this system
Example of a system suitable for a Bar Linkage Solver.
Add a 2021.1.1124.2 Wheel Joint to each of the rotational points
Make sure the Wheel Axis Direction of the Wheel Joints are aligned with the desired rotation
After all Wheel Joints are added, create a Spline to control the range and postion of the Piston. Align the Spline Control Points to the Piston Rod. Holding V enables snapping to vertices in Unity
Make sure the Spline is parented under the Piston. Your system is now set up to add a Bar Linkage Solver

How to use - Part B

This part will show you how to add a Bar Linkage Solver, to your previously created system. A Bar Linkage Solver requires the creation of several triangles.

Add a Kinematics Controller, this can be found under Mechanics > Add Kinematics > Kinematics Controller
Make sure the Kinematic Controller is placed above the system in the Hierarchy
Add a Bar Linkage Solver to the prismatic component in the system. This can be found under Mechanics > Add Kinematics > Bar Linkage Solver. The prismatic component is the piston part that controls the system
Assign the Spline as the constraining spline for the Bar Linkage Solver
Create a Triangle
Assign the Fix Pivot and the Hinge Point for the Triangle
Turn on Enforce outside playmode, the first Triangle should work now
Create a second Triangle and follow the same steps
The Bar Linkage Solver is now complete