This tutorial outlines the process to build a model for a bike pedal and crank and how to assign force data from analog signals. This tutorial assumes your human model is already built. Follow this tutorial to create a model before continuing Building 6DOF Model. This tutorial will have two parts, the first part will show how to create the model for the bike pedal and crank, and the second will show the force data processing.

The following c3d files can be downloaded as a starting point: Bike Model c3d Starter

Full completed CMZ can be downloaded here: Bike Model CMZ Complete

Full built model with properly assigned forces.

Building this model is very tedious as there are a lot landmarks and segments required. It is important to follow the order outlined below as certain landmarks and segments are build off previously defined items. To create a new landmark click on the Landmarks tab, select Add New Landmark, input the definitions below and press Apply. Not that when inpotting the definitions below the pedal landmarks and their iffsets are specific to this dataset and would need to adjusted for different data.

To build a new segment select the Segment tab input your desired segment name, ensure the segment type is Visual 3D, select Create, input the definitions for the segments shown below, and select Apply.

The first set of landmarks define a virtual position for the cranks

The following set of landmarks define virtual positions from the pedal markers in the LAB

The following set of landmarks are for the Bike Lab Coordinate systems.

We can now define our first segments.

We can now define the next group of Landmarks built using the segments created above.

We now have all the required Landmarks to define the final 4 segments.

You should now have all the landmarks and segments built for your model and you human and bike model should resemble the following.

Force data from bikes is often imported using analog signals not force plates. Data requires processing to interpret. The following steps will show the command pipeline used for this process. The completed pipeline can also be downloaded here. Not there are values specific to this data such as variable names and lever arms based on pedal size that will need to be changed based on the specific data.

The original force data is very noisy so a low-pass filter is used to smooth the data. The command Lowpass_Filter can be under Signal Filter press » to add to your pipeline.

Lowpass_Filter
/SIGNAL_TYPES= ANALOG
! /SIGNAL_FOLDER=ORIGINAL
! /SIGNAL_NAMES=
! /RESULT_FOLDER=PROCESSED
! /RESULT_SUFFIX=
! /FILTER_CLASS=BUTTERWORTH
 /FREQUENCY_CUTOFF=6.0
 /NUM_REFLECTED=6
! /NUM_EXTRAPOLATED=0
/TOTAL_BUFFER_SIZE=20
! /NUM_BIDIRECTIONAL_PASSES=1
;

Once smoothed the Evaluate_Expression command can be used to determine the Force in each pedal before using the Transform_Data_Coordinate_System to convert force values to the Lab.

/Right

Evaluate_Expression
/EXPRESSION= VECTOR((-1.0*ANALOG::PROCESSED::Force.Fx_2),((1.0*ANALOG::PROCESSED::Force.Fy_3)+(1.0*ANALOG::PROCESSED::Force.Fy_4)),((1.0*ANALOG::PROCESSED::Force.Fz_3)+(1.0*ANALOG::PROCESSED::Force.Fz_4)))
/SIGNAL_TYPES=ANALOG
! /SIGNAL_FOLDER=PROCESSED
/SIGNAL_NAMES=Force.Fx_2+Force.Fy_3+Force.Fy_4+Force.Fz_3+Force.Fz_4
! /SIGNAL_COMPONENTS=
! /RESULT_TYPES=DERIVED
/RESULT_FOLDERS=FORCE_RIGHT
/RESULT_NAME= FORCE
! /APPLY_AS_SUFFIX_TO_SIGNAL_NAME=FALSE
;

Transform_Data_Coordinate_System
/SIGNAL_TYPES= DERIVED
/SIGNAL_FOLDER=FORCE_RIGHT
/SIGNAL_NAMES= FORCE
! /FROM_SEGMENT_CS= Right Pedal
/TO_SEGMENT_CS= LAB
/RESULT_TYPES= DERIVED
/RESULT_FOLDERS= FORCE_LAB_RIGHT
!/RESULT_NAME=
! /APPLY_AS_SUFFIX_TO_SIGNAL_NAME=TRUE
/ORIENTATION_ONLY=TRUE
! /USE_DATA_RATE=FALSE
;

============
/Left
============

Evaluate_Expression
/EXPRESSION= VECTOR((-1.0*ANALOG::PROCESSED::Force.Fx),((1.0*ANALOG::PROCESSED::Force.Fy)+(1.0*ANALOG::PROCESSED::Force.Fy_2),((1.0*ANALOG::PROCESSED::Force.Fz)+(1.0*ANALOG::PROCESSED::Force.Fz_2)))
/SIGNAL_TYPES=ANALOG
! /SIGNAL_FOLDER=PROCESSED
/SIGNAL_NAMES=Force.Fx+Force.Fy+Force.Fy_2+Force.Fz+Force.Fz_2
! /SIGNAL_COMPONENTS=
! /RESULT_TYPES=DERIVED
/RESULT_FOLDERS=FORCE_LEFT
/RESULT_NAME= FORCE
! /APPLY_AS_SUFFIX_TO_SIGNAL_NAME=FALSE
;

Transform_Data_Coordinate_System
/SIGNAL_TYPES= DERIVED
/SIGNAL_FOLDER=FORCE_LEFT
/SIGNAL_NAMES= FORCE
! /FROM_SEGMENT_CS= Left Pedal
/TO_SEGMENT_CS= LAB
/RESULT_TYPES= DERIVED
/RESULT_FOLDERS= FORCE_LAB_LEFT
!/RESULT_NAME=
! /APPLY_AS_SUFFIX_TO_SIGNAL_NAME=TRUE
/ORIENTATION_ONLY=TRUE
! /USE_DATA_RATE=FALSE
;

In order to change the force assignments the Center Of Pressure and Freemoment for each pedal are also required. First we must compute the moment, followed by the COP and finally the Freemoment.

Note that the decimal coefficients are lever arm measurements that will change based on pedal size.

============
/Right
============

Evaluate_Expression
/EXPRESSION=VECTOR((0.02845*DERIVED::FORCE_RIGHT::FORCE::Y),((0.01945*ANALOG::PROCESSED::Force.Fz_4-0.01945*ANALOG::PROCESSED::Force.Fz_3)-0.02845*ANALOG::PROCESSED::Force.FX_2),((0.01945*ANALOG::PROCESSED::Force.Fy_4-0.01945*ANALOG::PROCESSED::Force.Fy_3)))
/RESULT_NAME=MOMENT
/RESULT_TYPE=DERIVED
/RESULT_FOLDER=FORCE_RIGHT
;

============
/Left
============

Evaluate_Expression
/EXPRESSION=VECTOR((0.02845*DERIVED::FORCE_LEFT::FORCE::Y), ((-0.01945*ANALOG::PROCESSED::Force.Fz + 0.01945*ANALOG::PROCESSED::Force.Fz_2) - 0.02845*ANALOG::PROCESSED::Force.FX), ((0.01945*ANALOG::PROCESSED::Force.Fy - 0.01945*ANALOG::PROCESSED::Force.Fy_2)))
/RESULT_NAME=MOMENT
/RESULT_TYPE=DERIVED
/RESULT_FOLDER=FORCE_LEFT
;

============
/Right
============

Evaluate_Expression
/EXPRESSION=VECTOR((-1 * DERIVED::FORCE_RIGHT::MOMENT::Y / DERIVED::FORCE_RIGHT::FORCE::Z), (DERIVED::FORCE_RIGHT::MOMENT::X / DERIVED::FORCE_RIGHT::FORCE::Z), (0.0*analog::processed::Force.Fx_2))
/RESULT_NAME=COP
 /RESULT_TYPE=DERIVED
 /RESULT_FOLDER=FORCE_RIGHT
;

Transform_Data_Coordinate_System
/SIGNAL_TYPES=DERIVED
/SIGNAL_NAMES=COP
/SIGNAL_FOLDER=FORCE_RIGHT
/FROM_SEGMENT_CS=Right Pedal
/TO_SEGMENT_CS=Lab
/RESULT_TYPE=Derived
/RESULT_FOLDER=FORCE_LAB_RIGHT
/RESULT_SUFFIX=
/ORIENTATION_ONLY=FALSE
! /USE_DATA_RATE=FALSE
;

============
/Left
============

Evaluate_Expression
/EXPRESSION=VECTOR((-1*DERIVED::FORCE_LEFT::MOMENT::Y / DERIVED::FORCE_LEFT::FORCE::Z), (DERIVED::FORCE_LEFT::MOMENT::X / DERIVED::FORCE_LEFT::FORCE::Z), (0.0*analog::processed::Force.Fx))
/RESULT_NAME=COP
 /RESULT_TYPE=DERIVED
 /RESULT_FOLDER=FORCE_LEFT
;

Transform_Data_Coordinate_System
/SIGNAL_TYPES=DERIVED
/SIGNAL_NAMES=COP
/SIGNAL_FOLDER=FORCE_LEFT
/FROM_SEGMENT_CS=Left Pedal
/TO_SEGMENT_CS=Lab
/RESULT_TYPE=Derived
/RESULT_FOLDER=FORCE_LAB_LEFT
/RESULT_SUFFIX=
/ORIENTATION_ONLY=FALSE
! /USE_DATA_RATE=FALSE
;

============
/Right
============

Evaluate_Expression
/EXPRESSION=VECTOR((0.0*analog::processed::Force.Fx_2),(0.0*analog::processed::Force.Fy_3),(Derived::FORCE_RIGHT::MOMENT::Z - Derived::FORCE_RIGHT::FORCE::Y * Derived::FORCE_RIGHT::COP::X + Derived::FORCE_RIGHT::FORCE::X * Derived::FORCE_RIGHT::COP::Y))
/RESULT_NAME=FREEMOMENT
 /RESULT_TYPE=DERIVED
 /RESULT_FOLDER=FORCE_RIGHT
;

Transform_Data_Coordinate_System
/SIGNAL_TYPES=DERIVED
/SIGNAL_NAMES=FREEMOMENT
/SIGNAL_FOLDER=FORCE_RIGHT
/FROM_SEGMENT_CS=Right Pedal
/TO_SEGMENT_CS=Lab
/RESULT_TYPE=Derived
/RESULT_FOLDER=FORCE_LAB_RIGHT
/RESULT_SUFFIX=
/ORIENTATION_ONLY=TRUE
! /USE_DATA_RATE=FALSE
;

============
/Left
============
Evaluate_Expression
/EXPRESSION=VECTOR((0.0*analog::processed::Force.Fx),(0.0*analog::processed::Force.Fy),(Derived::FORCE_LEFT::MOMENT::Z - Derived::FORCE_LEFT::FORCE::Y * Derived::FORCE_LEFT::COP::X + Derived::FORCE_LEFT::FORCE::X * Derived::FORCE_LEFT::COP::Y))
/RESULT_NAME=FREEMOMENT
 /RESULT_TYPE=DERIVED
 /RESULT_FOLDER=FORCE_LEFT
;

Transform_Data_Coordinate_System
/SIGNAL_TYPES=DERIVED
/SIGNAL_NAMES=FREEMOMENT
/SIGNAL_FOLDER=FORCE_LEFT
/FROM_SEGMENT_CS=Left Pedal
/TO_SEGMENT_CS=Lab
/RESULT_TYPE=Derived
/RESULT_FOLDER=FORCE_LAB_LEFT
/RESULT_SUFFIX=
/ORIENTATION_ONLY=TRUE
! /USE_DATA_RATE=FALSE
;

With all values calculated the force assignments for the Right and Left feet can be set. Select Add/Modify Segment Assignment To Force under the Force tab in the upper toolbar.

Select Add Segment Assignment and enter the following values. Change the end frame to the last frame in your specific trial.