Grasp 2 finger Sphere Simulator


Hello Cristian and Hello to everyone

I have been blabbering about simulators and decided to write a little one that is functional enough for the community to evaluate and see if useful.

You need to install free cdf player: (only on Windows and Mac)

You might want to see a paper to get some ideas how the code was organized, p. 2 suffices:

This is a simulator which allows you to enter rotation values for the joints and test to make sure the tips can hold a ball.

The dynamics of the movements are correctly modeled as these papers indicate. Assume the ball is squishy or like a air balloon and the tips are sticky like your finger how they stick to the rubber of a balloon. All kinds of other GRASP could be modeled.

However 20 times a second the position of the ball is computed numerically to assure that it matches the output of the rotary joints.

This is not the way eventually we do the simulators, in this case I cheated and actually solved for the position of the ball using advanced numerical algorithms.

In the final product we will not solve, rather have ways to estimate the solutions with simple matrix multiplications or few such operations without using solvers. Or we train the hand to learn how to grasp… which requires this simulator to generate the training data…

When there are no solutions the ball disappears, you need to back track. This is equivalent of ball falling off your hand or balloon popping since you pinched it hard.

For now this is to show you what I meant by simulators.

Cristian for example could use these sorts of simulators to test his motors and actuators to drive the hand from a CDF file like this. I suggest we build huge numbers of these simulations and provide training and proper documentation for everyone to use.

Use this to learn how to manipulate 3D structures on CDF screen:



Forgot: ball is transparent


These CDF files are very powerful pieces of software.

In them we can solve and mode terrific mathematical structures and dynamical models and solve them almost in real-time.

Cristian can then use these with serial and parallel interface to his hand’s micro-controller board. In other words, the CDF file allows the user to simulate a particular hand grasp dynamics and then send the signals to the micro controller board to mimic the same with the actual 3D printed hand.

Of course in many occasions what is on the screen does not match the hand configuration or micro controller issues errors.

Then debug… debug …


thanks @dara, i will see the links and documents during the weekend.


take your time and thank you for your time. These might not be the right applications for this forum.


I also coded Interference Analysis for the ball vs the fingers, see:

I did not turn it on for the CDF I posted here. Because each test takes about 4 seconds on a fast machine!

But many solutions of the Grasp and hand motion are not valid since the fingers and joint motors and wrist and the object held collide with each other.

In the next version of the code I will setup a checkbox button to turn the interference analysis on or off.



I am viewing your work in details, Cristian you are extraordinary designer!! My congratulations on your talent and creativity.


isn’t my work, the extraordinary designer is @Renato, I just help him with biomechanical, engineering and 3d printing part


Ok both you and Renato. Hope someone introduce me to him and I extend the compliments