Re: Quick question: Object moves different amount each frame despite constant velocity.

2023-05-16T03:39:17+00:00

Also curious is: the distance traveled along the x-axis does not agree with your speed and timestep:

Code:

time = 0.05 secrate = 250 m/secdistance = rate * time =  250 m/sec * 0.05 sec = 12.5m

I wonder if you're bumping up against a maximum speed limit, especially since your total speed is so steady. Maybe try measuring things at slower speeds?

Statistics: Posted by drleviathan — Tue May 16, 2023 3:39 am

Quick question: Object moves different amount each frame despite constant velocity.

2023-05-12T17:39:02+00:00

I have a vehicle (but I think the issue exists with normal rigid bodies) in a scene with a constant timestep that I get the position of each frame, to simplfy:

Code:

//world->stepSimulation(deltaMS / 1000.0);world->stepSimulation(0.05,1,0.05);if(car->getCurrentSpeedKmHour() > someValue)//if(car->getRigidBody()->getLinearVelocity().length() > someValue){     car->getWheel(0).applyEngineForce(someOtherValue);     car->getWheel(1).applyEngineForce(someOtherValue);}btVector3 pos = car->getRigidBody()->getWorldTransform().getOrigin();float changeInPos = pos.x() - lastPos;lastPos = pos.x();std::cout<<"Change in pos: "<getRigidBody()->getLinearVelocity().x()<<"\n";

I could end up with output like this:

Code:

Change in pos: 4.2 Velocity 250.0Change in pos: 4.1 Velocity 250.0Change in pos: 3.9 Velocity 250.0Change in pos: 4.2 Velocity 250.0Change in pos: 3.7 Velocity 250.0Change in pos: 4.5 Velocity 250.0Change in pos: 4.3 Velocity 250.0

If the timestep is constant, and the velocity is constant, what is the issue? Why is change in pos not the same every time?

Statistics: Posted by GeanGean — Fri May 12, 2023 5:39 pm

Real-Time Physics Simulation Forum

Re: Quick question: Object moves different amount each frame despite constant velocity.

Quick question: Object moves different amount each frame despite constant velocity.