Sports Biomechanics Lab > Blog > Summer Intern work: Yeadon's inertia model and GUI development for OBD
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Summer Intern work: Yeadon's inertia model and GUI development for OBD

by Christopher Lee Dembia — last modified Jul 18, 2011 08:35 PM

This is Chris, a half-summer intern here at the UC Davis Sports Biomechanics Lab. I just finished an undergraduate program in mechanical engineering, and thought it would be a good idea to check out the West Coast. I wanted to help with some of the bicycle research here. I like bikes because there's no debate about their role in a greener society. As a form of transportation, they allow people to feel like they're still in control of their means and their behavior. A bicycle rider accounts for about 80% of the weight of a bicycle-rider system. It's right-sized technology. Davis and its bike culture quickly made an impression on me.

I want to share a little bit of the work I've been doing. I've had two projects. Both are programming projects.


In 1990, Yeadon published a model of a human that consists of 39 so-called "stadium solids" [1]. The model can be used to estimate the rigid body inertia properties (mass, center of mass, and inertia tensor) of a human or of parts of a human. The lab has used this model in the past, but is now using it in a bicycle model that includes a rider. Thus, this project is part of this lab's larger NSF-funded system identification project (info here). The human, or bicycle rider in this case, is defined by 95 measurements and by 21 joint angles.

Yeadon Human Inertia Measurements

I have written a python module takes in the 95 measurements of a human and the human's joint angles, and produces the inertia properties of the human. With these inertia properties, it is possible to incorporate a human in a multi-body dynamics model of a bicycle.


The lab is working on a program called Open Bicycle Dynamics that features nonlinear dynamics equations for the Whipple bicycle model. It allows a user to input bicycle parameters, and obtain stability data and to perform a simulation of the motion of a bicycle. These features are mostly incorporated, but can only be accessed through a command window/terminal. My project has been to develop a graphical user interface (GUI) for the program. An early view of the GUI is in the image below. It is hoped that a GUI will eliminate the learning curve for the software in order to hasten its use by a larger group of people, perhaps including bicycle designers.

OBD GUI early development

[1] Yeadon, M. R. (1990b). The simulation of aerial movement–iii. the determination of the angular momentum of the human body. Journal of Biomechanics, 23(1):75 – 83.

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Avatar Posted by Efried at Aug 28, 2011 10:10 PM

I'm searching for exemplary data as input when abusing the "half vehicle" bicycle model for a real bicycle.
I have measured the yaw inertia of the bicyle and need to add the driver to calculate the yaw dynamic index. (simple_bicycle.m))
Adding a few data about cornering stiffness, I will get the lateral and longitudinal accelerations and this forces for checking friction at both wheels also replacing static load on the axles by danamic. Also the Matlab file I found calculates the critical speed for Stability (Rocard basic model)
I know that the approach is simple but I see no other way having only little time to complete the analysis.
Any help is appreciated


Avatar Posted by Jason Moore at Aug 28, 2011 11:17 PM
I would suggest simulating the linear Whipple bicycle model. The best reference is[…]/1955.abstract which has the basic equations. You will have to do some work to get the tire forces. Or check out the work by both Robin Sharp and Vittore Cossalter for more complicated models with tire forces.

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