Circular conveyor belt simulation

[hazidh]

Hello, I created a Box and placed it on the circle board, modified the contacts in onContactModify, and added a linear speed to each contact by contacts.setTargetVelocity(j, pxVelocity), but it ran in a larger and larger circle, is there a good solution

[vreutskyy]

Hello @hazidh
That's expected as rigid bodies move linearly during the simulation step and only change direction between steps. So if you apply velocity tangential to the circle, on the next step your rigid body will be farther from the circle center. Did you try to compensate by adding some velocity toward the circle center?

[hazidh]

No. How do I add some velocity toward the circle center, I'm just onContactModify inside for each contact add tangential velocity by contacts. SetTargetVelocity (j, pxVelocity)

[vreutskyy]

The same way you apply tangential velocity. Just add some centripetal velocity to it.

[hazidh]

Thank you for your reply. I would like to ask how deltaTime is defined

[hazidh]

It still seems to shift when I test the code

[hazidh]

I calculate the Angle between the conveyer-box and the Box-Contact, and find the third side (the green line in the figure). This side is the theoretical radius of the Contact. Then I subtract it from the actual length of the conveyer-contact to get the error value, and multiply it with the radial velocity. It seems to work fine, but I don't know if this solution is feasible or if there are potential problems.

float dot = geomToCenter.normalize().dot(geomToContact.normalize()); 
float angleRad = (float) Math.acos(dot);
float radius = (float) Math.sqrt(conveyorRadius * conveyorRadius +
        geomToContact.length() * geomToContact.length() -
        2 * geomToContact.length() * conveyorRadius * Math.cos(angleRad));

float speed = angularSpeed * contactToCenter.magnitude();
float centerDisError = contactToCentermagnitude() - radius;
PxVec3 velocity = tangentialVelocity * speed;
PxVec3 toCenterVelocity = toCenterDirection*(centerDisError * speed);
PxVec3 correctedVelocity = tangentialVelocity + toCenterVelocity ;
contacts.setTargetVelocity(contactIndex, correctedVelocity);

[vreutskyy]

deltaTime is your time step - the value you pass to PxScene::simulate()

whatever works for you

[hazidh]

After I set the same as simulate, it still appears that the radial rotation is further and further
#380 (reply in thread)

[hazidh]

Hello Sir, I found that when I use these two lines of code to make the Box move in a circle, its rotation attitude around the center will change. For example, the Angle from the center is 0 at the beginning, but it will have a certain Angle around the center, such as the picture.May I ask why？

 float speed = angularSpeed * contactToCenter.length();
 PxVec3 velocity = tangentDirection*speed;
 contacts.setTargetVelocity(j, velocity);

[AccessViolationEnjoyer]

You need to scale the velocity according to how far out you are from the center of the circle. The contact points that are further away from the center need a higher velocity.

Typically, for a curved conveyor, the conveyor’s speed represents the speed along the centerline. So you need to multiply the speed by contact_radius / centerline_radius.

If you do it correctly, the box won’t rotate, but it will spiral outwards slowly due to the fact that the body is moved in a straight line over the timestep.

[hazidh]

Thank you for your reply. I think there is something wrong with my calculation.