Wiki Documentation Site

User Tools

Site Tools

You are here: Main Page » visual3d » documentation » kinematics_and_kinetics » external_forces » Forces FAQ
visual3d:documentation:kinematics_and_kinetics:external_forces:forces_faq

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
visual3d:documentation:kinematics_and_kinetics:external_forces:forces_faq [2026/02/06 18:12] – wikisysopvisual3d:documentation:kinematics_and_kinetics:external_forces:forces_faq [2026/02/06 18:12] (current) – wikisysop
Line 3: Line 3:
 ==== FAQs ==== ==== FAQs ====
  
-**Question**: I’m doing **inverse dynamic analyses** but in some trials my participant has **two feet on one force platform** at the same time, and in others **one of their feet is simultaneously in contact with two different force platforms**. What should I do?\\+**Question**: I’m doing **inverse dynamic analyses** but in some trials my participant has **two feet on one force platform** at the same time, and in others **one of their feet is simultaneously in contact with two different force platforms**. What should I do?
  
  
Line 14: Line 14:
  
  
-**Question**: When I look at **“Data Values”** in a FORCE signal, within the Signals and Events tree, what are the **X SUB, Y SUB and Z SUB** values?\\+**Question**: When I look at **“Data Values”** in a FORCE signal, within the Signals and Events tree, what are the **X SUB, Y SUB and Z SUB** values?
  
  
Line 26: Line 26:
  
  
-**Question**: How do **force assignments** work?\\+**Question**: How do **force assignments** work?
  
  
Line 37: Line 37:
  
  
-**Question**: What does **CalTester** do?\\+**Question**: What does **CalTester** do?
  
  
-**Answer** (click to expand)+**Answer**
  
 The COFP signal is created by transferring the centre of pressure calculated inside the force platform’s coordinate system into the global, laboratory coordinate system. This transfer is based on the location of the force platform’s corners and the offset between the top of the force sensors and the top of the platform’s surface. The correct position of the COFP is key to accurate inverse dynamic calculations. Put simply, CalTester allows you to compare the position of the COFP, which has been transformed from the force platform’s coordinate system into the global, laboratory coordinate system with how that position is represented using motion capture data. We can do this because we know where the end of the calibrated CalTester rod is in space, and can compare this to the calculated position of the COFP. The two can then be ‘calibrated’ to bring them closer together by altering the force platform location parameters. In order to ensure best results it is important to follow a few simple steps. Always Begin the data capture with the CalTester rod not in contact with the force platform, but make sure the base plate is in situ. This allows Visual3D to calculate a baseline zero for all the force platform channels. Once the rod is in contact with the base plate, the CalTester should be the only thing that comes in contact with the force platform. Ensure the rod is loaded longitudinally with a load of at least 200 N and that, during the data collection, the angle of the rod is no more than about 20 degrees. This will maximise accuracy of COFP calculation from the kinetic data and prevent the CalTester rod’s tip sliding away from the bottom of the dimple in the base plate and being elevated. See [[https://www.c-motion.com/v3dwiki/index.php/CalTester|CalTester]] The COFP signal is created by transferring the centre of pressure calculated inside the force platform’s coordinate system into the global, laboratory coordinate system. This transfer is based on the location of the force platform’s corners and the offset between the top of the force sensors and the top of the platform’s surface. The correct position of the COFP is key to accurate inverse dynamic calculations. Put simply, CalTester allows you to compare the position of the COFP, which has been transformed from the force platform’s coordinate system into the global, laboratory coordinate system with how that position is represented using motion capture data. We can do this because we know where the end of the calibrated CalTester rod is in space, and can compare this to the calculated position of the COFP. The two can then be ‘calibrated’ to bring them closer together by altering the force platform location parameters. In order to ensure best results it is important to follow a few simple steps. Always Begin the data capture with the CalTester rod not in contact with the force platform, but make sure the base plate is in situ. This allows Visual3D to calculate a baseline zero for all the force platform channels. Once the rod is in contact with the base plate, the CalTester should be the only thing that comes in contact with the force platform. Ensure the rod is loaded longitudinally with a load of at least 200 N and that, during the data collection, the angle of the rod is no more than about 20 degrees. This will maximise accuracy of COFP calculation from the kinetic data and prevent the CalTester rod’s tip sliding away from the bottom of the dimple in the base plate and being elevated. See [[https://www.c-motion.com/v3dwiki/index.php/CalTester|CalTester]]
visual3d/documentation/kinematics_and_kinetics/external_forces/forces_faq.1770401549.txt.gz · Last modified: by wikisysop