Trying to calculate the net force/torque of a rock climber on a wall

[seedygrains]

Hey Everyone,

I am working on making a simulation of a rock climber on a wall in 3D space. The end result is to help visualize the free body diagram of the climber and show how moving your limbs moves your center of mass and changes the forces on your hands and feet.

I've been struggling to write the net force/ torque equations for this simulation and was hoping someone here would be able to help me out.

The question I'm trying to solve is this:

For a body with a known center of mass and 1-4 anchor points, what is the minimum magnitude and direction of the force required at each anchor point to keep the body static?

In the event that the equation is unsolvable (for example if there are only two anchor points and the center of mass isn't on the same vertical plane as the points) I would like to calculate the net torque on the center of mass.

Any help or suggestions on how to write these equations is greatly appreciated!

 

[Baluncore]

The end result is to help visualize the free body diagram of the climber and show how moving your limbs moves your center of mass and changes the forces on your hands and feet.

Welcome to PF.
I believe you will need a (numerical) model of the skeletal linkage, with each limb and the body having a centre of mass. The solution would be that of a dynamic 3D linkage, a structural space frame. The degree of freedom of the joints between the limb-links would be limited to match the human skeleton.

 

[berkeman]

I am working on making a simulation of a rock climber on a wall in 3D space. The end result is to help visualize the free body diagram of the climber and show how moving your limbs moves your center of mass and changes the forces on your hands and feet.

Welcome to PF. Fun project!

What computer language and tools are you using for these simulations? What is your end goal -- Animations for realistic film making scenes, or helping elite climbers to improve their skills, or etc.?

The static FBDs are pretty straightforward, but there are definitely complications for transient simulations:

• Coefficients of friction between different surfaces (skin, rock, climbing shoes, etc.)
• Forces in jams (how strong are your hands and fingers?)
• Strength of arms and wrists and legs and feet in different moves
• Fatigue of the same...

Have you done similar simulations and computer animations for any other athletic moves in the past?

 

[seedygrains]

Welcome to PF.
I believe you will need a (numerical) model of the skeletal linkage, with each limb and the body having a centre of mass. The solution would be that of a dynamic 3D linkage, a structural space frame. The degree of freedom of the joints between the limb-links would be limited to match the human skeleton.

Thanks for the welcome!

I do have something like this so far, (see screenshots attached), I have a mass and position for each limb and use those to determine the center of mass of the climber.

I use the relationships between the positions of each joint and the lengths of each limb to control the motion of the body when you click and drag each part around (moving the hand moves the elbow which moves the shoulder, etc..)

Do you mean that I will need to know how forces move between the limbs in order to calculate the force on the hands? If we assume the climber can stay perfectly rigid, will that remove that need?

I was hoping we would be able to do this calculation using only the position of the center of mass and the positions of the hands/feet on holds

 

[seedygrains]

Welcome to PF. Fun project!

What computer language and tools are you using for these simulations? What is your end goal -- Animations for realistic film making scenes, or helping elite climbers to improve their skills, or etc.?

The static FBDs are pretty straightforward, but there are definitely complications for transient simulations:

• Coefficients of friction between different surfaces (skin, rock, climbing shoes, etc.)
• Forces in jams (how strong are your hands and fingers?)
• Strength of arms and wrists and legs and feet in different moves
• Fatigue of the same...

Have you done similar simulations and computer animations for any other athletic moves in the past?

Thanks for the welcome!

I'm doing the project in VPython. I haven't done anything like this in the past but I just started rock climbing and found out about VPython so I thought, why not :)

I do agree with the complications, at first I'm trying to just have the body grab holds assuming that the person is strong enough to hold themselves statically in any position. Once I get this far I'd like to add some more features in terms of being able to make a wall of different angles and allowing the user to choose from holds which have different angles, coefficients of friction, and sizes (which I'm thinking would affect % of body weight that could be supported)

The end goal for now is to show how changing your body position affects how hard you need to pull on the holds.