Fix: Joint Angles Bug

[caiobarrosv]

ZeroSim hinge joints limits the joint angle in the range [-180, 180] degrees.

This limitation can be avoided by using Configurable Joints instead of Hinge Joints.
However, instead of implementing the Configurable Joints, check the possibility to use Articulation Body instead.

​
https://docs.unity.cn/Manual/physics-articulations.html

There are unanswered questions about this on the Unity forum:

• Question 1
• Question 2

[caiobarrosv]

Just found out that unity updated this in 2022.2.0 version:

• Physics: Enabled the option to extend angular limits for Hinge Joint.

Gooren says in this post that:

"Currently, HingeJoint in Unity allows a maximum limit from -PI to +PI.

PhysX, however, doubles this limit from a total of 2PI to a total of 4PI since version 4.0 with the use of the eENABLE_EXTENDED_LIMITS flag."

[micahpearlman]

@caiobarrosv can you see if ZeroSim works for 2022.2.0 or greater. One thing is that we want to avoid is supporting non-LTS versions of Unity. As I can see the latest LTS version is 2021.3.8f1. If ZeroSim works with 2022.2.0 we can add in the README.md that if this issue comes up then update to 2022.2.0 -- but we do not generally support non LTS Unity versions.

[caiobarrosv]

ZeroSim is working with Unity 2022.2.5f1 (I just tested the controller manager service).

In this version we have Extended Limits option but it is not working properly.
Even if we set the limits to [-360, 360], the spring target position can only be set in the range [-180, 180].

I posted this issue on the Unity forum - Link

I tried using Motor instead of Spring, but if we set the limits above 180 degrees, the joint will not respect the limitation and will not stop.

[caiobarrosv]

The articulation body allows joint angles more than 180 and less than -180.
My recomendation is to remove all the hinge joints from robot manipulators in example scenes like the UR10_test.scene and alert users about this joint limitation issue.

Although the last LST version is the 2021.3.8f1, after this version we had a lot of important updates for Articulated bodies like:

• 2021.1.9:

  • Physics: Fixed a crash when attempting to access the Rigidbody from the result of a OnCollision callback, when the object we've collided with is a ArticulationBody. The Collision.rigidbody member is now null in this case. (1320314)

• 2021.1.15:

  • Physics: Added: Added a property for retrieving ArticulationBody components during a collision event. Articulation bodies can be retrieved by Collision.articulationBody​
  • Physics: Added: Added a property for retrieving either ArticulationBody or Rigidbody components to collision events under Collision.body.​
  • Physics: Corrected contact event behavior for the ArticulationBody component so that it matches Rigidbody component behavior. (1339908)

• 2021.1.17

  • Physics: Overhauled the articulation gizmos to have better functionality and to better match other Unity gizmos' style
  • Physics: Fixed an Clamp ArticulationBody mass issue when loading data from disk was not within the valid range for the physics engine. (1316719)

• 2021.1.19

  • Physics: Fixed an issue where the Articulation Bodies were not being visualised in the Physics Debugger. (1343929)​

• 2021.1.28

  • Physics: Fixed an issue where the Articulation Drive did not affecting the joint in Articulation Body when the collider volume was very small. (1330968)

• 2021.2.0

  • Physics: Added icon for Articulation Body Anchor Transform tool.
  • Physics: Added units of measurement to the Articulation Body properties in the scripting documentation.
  • Physics: Improved Articulation Body anchor limit gizmos.
  • Physics: Rearranged the ArticulationBody properties. Moved Damping and Friction after Mass.​
  • Physics: Added: Expose ArticulationBody.collisionDetectionMode property to set various collision detection modes, like Discrete, Continuous and etc.​
  • Physics: Added: ForceMode argument to ArticulationBody.Add force and related functions.​
  • Physics: Added: Property for retrieving ArticulationBody components during a collision event. Articulation bodies can be retrieved by Collision.articulationBody.​
  • Physics: Added: Property for retrieving either ArticulationBody or Rigidbody components to collision events under Collision.body.​

• 2021.2.1

  • Physics: Fixed the ArticulationDrive.forceLimit to actually use forces instead of impulses. Projects with custom set force limit should review values, and consider dividing them by the simulation delta. (1370338)

• 2021.2.8

  • Physics: Fixed an issue where multi-selecting Articulation Bodies would set some properties to the same value. (1379145)

• 2021.2.9

  • Physics: Fixed a crash when switching an ArticulationBody to immovable during a collision event. (1338600)

• 2021.2.12

  • Physics: Fixed ArticulationBody.SetJointPositions and similar setter using List.Capacity instead of List.Count to determine the element count and throwing errors because of that. (1347970)

• 2021.3.9

  • Physics: Fixed Articulation Bodies teleporting to NaN coordinates when changing joint type at runtime. (UUM-7418)​

• 2021.3.12

  • Physics: Fixed ArticulationBody indices not matching when using methods like GetJointPositions and GetDriveTargets. (UUM-1805)​

• 2021.3.14

  • Physics: Fixed ArticulationBody SetDriveTargets and SetDriveTargetVelocities methods checking List capacity instead of count and improved the error message. (UUM-12713)

• 2022.1.0

  • Physics: Improved the Physics Visualiser layout and moved the Rigidbody and Articulation Body Info panels to the Physics Visualiser.​
  • Physics: Updated ArticulationBody.AddForce and other related method Scripting API documentation with information about current PhysX limitations.​
  • Physics: Clamped the Articulation body drive lower and upper limits to each other. (1310004)

• 2022.1.23

  • Physics: Fixed ArticulationBody SetDriveTargets and SetDriveTargetVelocities methods checking List capacity instead of count and improved the error message. (UUM-12713)

• 2022.2.0

  • Physics: Added an option to override Layer collisions for Colliders, Rigidbodies, ArticulationBodies and Character Controllers, which allows to fine tune which bodies should collide with what layers.
  • Physics: Added: ArticulationBody.GetJointExternalForces method which allows to get the forces in reduced space needed to counteract forces applied in the general space for your Articulation chain.​
  • Physics: Added: Drive type enumerator for Articulation Body drives.
  • Physics: Added: Expose additional ArticulationDrive setters that allow direct access to the properties.
  • Physics: Added: Expose setting inertia tensor and center of mass for Rigidbody and ArticulationBody components from the Inspector.​
  • Physics: Added: Methods for getting accumulated force and torque for Rigidbodies and Articulation Bodies.
  • Fixed Articulation Bodies with spherical joints spinning uncontrollably in some scenarios. (1418715).
  • Physics: Fixed ArticulationBody Anchor rotation values disappearing when Inspector window width is reduced. (1393075)​
  • Physics: Fixed different Force Modes overwriting previously applied forces for Articulation Bodies. (1349587)

I would try to keep it as updated as possible if the goal is to use robotic arms with articulated body.
Maybe for mobile robots we can still use regular joints.