Oleg and Yan – thanks for the input, we’ll do our best to take a look and get to the bottom of this, that is, fix if it’s a problem, or let you know if the code should have been used differently.
Dan --------------------------------------------- Bernard A. and Frances M. Weideman Professor NVIDIA CUDA Fellow Department of Mechanical Engineering Department of Computer Science University of Wisconsin - Madison 4150ME, 1513 University Avenue Madison, WI 53706-1572 608 772 0914 http://sbel.wisc.edu/ http://projectchrono.org/ --------------------------------------------- From: [email protected] <[email protected]> On Behalf Of ???? ?????? Sent: Saturday, April 5, 2025 7:13 AM To: ProjectChrono <[email protected]> Subject: [chrono] Re: Issue or Bugs report: Accelerometer output not correct. Wrong gravity and wrong direction Hello, I faced the same problem. The reason is that the acceleration calculation only takes into account the offset position (m_offsetPose.GetPos()) without the orientation (m_offsetPose.GetRot()) (chrono_sensor/sensors/ChIMUSensor.cpp<https://urldefense.com/v3/__https:/github.com/projectchrono/chrono/blob/30cd3f2702cb58182e46d5b2724d2d2850a50e21/src/chrono_sensor/sensors/ChIMUSensor.cpp*L34-L39__;Iw!!Mak6IKo!PDl5lzOZXzDEnu0UxZEKs5uX2DpD2v9f3OYhoT18t_0vbscXiaHD58E-I3f2VN-jF5bCY5B_oN9FO8cL6w_U$>): CH_SENSOR_API void ChAccelerometerSensor::PushKeyFrame() { ChVector<double> tran_acc_no_offset = m_parent->PointAccelerationLocalToParent(m_offsetPose.GetPos()); ChVector<double> tran_acc_offset = -m_parent->GetSystem()->Get_G_acc(); tran_acc_offset = m_parent->GetRot().Rotate(tran_acc_offset); m_keyframes.push_back(tran_acc_no_offset + tran_acc_offset); } I made my own implementation of the accelerometer. I'm attaching it. Maybe when I have time I'll make a pull request with these edits to the main repository. четверг, 19 декабря 2024 г. в 23:08:29 UTC+7, Yan Dong: Hi, I'm using Chrono 8.0.0, C++. I want to output accelerometer attached on a ChBody, but the acc output seems to be the acceleration on world frame not on the box frame. Also, I have find the acc output of gravity is strange. Here're my findings: 1. About the gravity: I set the gravity to be (0,0,-10), and I release the acc attached on a box to fall freely. The acc output is zero which is desired because no external force on box. Now I rotate the box, making the z-axis pointing downward, by: box->SetRot(Q_from_AngAxis(chrono::CH_C_PI, { 1, 0, 0 })); then the IMU output is now (0,0,-20). Which I think should be 0 becase the free falling has no external force. The real imu is 0 indeed. 2. About the extrinsics: I change the IMU attached extrinsics to the body, and I find the IMU output do not change at all no matter the what the extrinsics is:" auto ext_zero = chrono::ChFrame<double>({ 0, 0, 0 }, Q_from_AngAxis(chrono::CH_C_PI, { 1, 0, 0 })); auto acc_ = chrono_types::make_shared<ChAccelerometerSensor>(box, 100, ext_zero, nullptr); 3. then I further find that the acc output seems to be the acceleration of the body in terms of the world frame but not its own frame. I add the an external world's X direction force and I find no matter the box is rotated (to negtive x direction) or the extrinsics is rotated, the Accelerometer output is always on x+ direction. So my questions are: a). How you implement Accelerometer calculation? What's the Accelerometer output's reference frame? b). How is the gravity effect on Accelerometer calculated? I guess is by relative moving frame together with the global gravity settings? But it's not true for a real Accelerometer. Here's my code. The 3 above findings are tested by codes with comments: --------------------------------------------------- ChSystemNSC sys; chrono::sensor::ChSensorManager manager_(&sys); sys.SetCollisionSystemType(ChCollisionSystem::Type::BULLET); sys.Set_G_acc({ 0, 0, -10 }); sys.SetSolverMaxIterations(20); auto ground_mat = chrono_types::make_shared<ChMaterialSurfaceNSC>(); double friction_mu = 1.0; ground_mat->SetSfriction(friction_mu); ground_mat->SetKfriction(friction_mu); auto box = chrono_types::make_shared<ChBodyEasyBox>(1, 1, 1, 1.0, true, true, ground_mat); box->SetPos(ChVector<>(0, 0, 0.5)); // 1. Gravity Issue Rotate or Not. // box->SetRot(Q_from_AngAxis(chrono::CH_C_PI / 1, { 1, 0, 0 })); box->SetMass(1); box->SetInertiaXX(ChVector<>(1, 1, 1)); box->SetBodyFixed(false); box->SetCollide(true); // sys.AddBody(box); // 2. Extrinsics Issue auto ext_zero = chrono::ChFrame<double>({ 0, 0, 0 }, Q_from_AngAxis(0, { 1, 0, 0 })); auto acc_ = chrono_types::make_shared<ChAccelerometerSensor>(box, 100, ext_zero, nullptr); acc_->SetName("IMU - Accelerometer"); acc_->SetLag(0.0f); acc_->SetCollectionWindow(0.01); acc_->PushFilter(chrono_types::make_shared<ChFilterAccelAccess>()); manager_.AddSensor(acc_); int imu_last_count_ = 0; // 3. Accelerometer direction issue by external force // std::shared_ptr<ChBody> ground; // create_ground(sys, ground); // I created a ground. // auto force1 = chrono_types::make_shared<ChForce>(); // box->AddForce(force1); // force1->SetMode(ChForce::FORCE); // force1->SetAlign(ChForce::WORLD_DIR); // force1->SetF_x(chrono_types::make_shared<ChFunction_Const>(20)); // force1->SetF_y(chrono_types::make_shared<ChFunction_Const>(0)); // force1->SetF_z(chrono_types::make_shared<ChFunction_Const>(0)); while(1){ auto bufferAcc = acc_->GetMostRecentBuffer<UserAccelBufferPtr>(); if (bufferAcc->Buffer && bufferAcc->LaunchedCount > imu_last_count_) { AccelData acc_data = bufferAcc->Buffer[0]; std::vector<double> acc(3); acc[0] = acc_data.X; acc[1] = acc_data.Y; acc[2] = acc_data.Z; cout << acc[0] << ", " << acc[1] << ", " << acc[2] << endl; imu_last_count_ = bufferAcc->LaunchedCount; } manager_.Update(); sys.DoStepDynamics(0.001); } --------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. 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