It looks like you are on the right track. As you probably noticed, the SimMechanics bouncing ball demo (mech_bouncing_ball.mdl) implements only the contact force perpendicular to the ground. So you will need more.

If you want your robot to move forward (parellel to the ground), you will need to implement contact in this axis too. My model does that, but does not implement stick and slip.

For the stick and slide part, I recommend looking at the documentation for the “Joint Stiction Actuator”. I am not sure if you will be able to use this block directly, but its documentation should give you some ideas.

Thank you

am tring to draw a swinging leg with 2 links and a mass on the tob..
but the system is falling down when appling a force at a certain time???

how i could solve it

While motion generation the body should roll side-to-side, and then the legs will be lifted by the pitching function.
At the beginning the left leg is lifted as the body rest on the right leg which supports the body without slipping because of friction.
Then, when the left leg should support the body it slips because the right hip and knee are bended but the foot doesn’t move forward (s locked with the ground).
I hope that my problem is clear now.

By the way, I suggest to introduce a new block to SimMechanics represents the ground contact (reaction forces) in a simple way so that beginners can use it.
Also, I would like to share some of my SimMechanics models in the future :).
Regards,
Asiya

Unfortunately I think I am missing a few things to be able to help you.

The Bushing joint alone should not cause any restriction, because it allows 6dof motion. Do you connect actuators to it? do you have other explanations on why it causes restriction?

In general, I recommend using the Six-DoF joint instead of the Bushing, because it does not suffer from Gimbal lock.

I hope this helps.

Guy

Thank you for the useful model.
I have done the walking robot using the bouncing ball example provided by Matlab/Simulink Help and it is working fine. This by appling 4 contact point in each leg (plate-like).
However, I did apply the friction but the bushing joint is causing a restriction for my model.
For example, if I did attach the Bushing joint to the body center of mass only, the rolling motion will be restricted and the robot will looks like swinging on air and it’ll not move forward!!
But If I did attach it on one foot and connect it to ground block, it will stick with ground in the double suuport phase and the other leg will swing and vise versa if I did attach the bushing joint to boot foots.

So can you help me??

Regards

@fady – In MATLAB, cd to the directory with the model, then type the model name. Then, from the Simulink interface, press the triangular play button, or from the Simulation menu, click Start. Good luck!

1. The implementation of the robot-floor interaction depends on the goal of your simulation. In general I recommend choosing the simplest implementation that gives you the accuracy you need. If you only care about the kinematics of the robot, a planar joint is a good solution. It is simple and should simulate fast. At the other end of the spectrum, if the dynamic of the wheel-floor interaction is important, you can go in details. Sense velocity and position of each wheel and compute the resulting force/torque to apply back to each wheel. The configuration of your wheels also can influence your choice. An holonomic configuration is easy to model with just a planar joint, while a car-like configuration requires more constraints.

2. I never used the Proximity Sensor of the V-Realm Builder, so I cannot comment on that. In SimMechanics there are multiple ways to use joints to model non-contact sensors, like a laser for example. I just published an example of this type of implementation (The link should be available tomorrow, April 21st):

http://www.mathworks.com/support/solutions/en/data/1-EPZNH8/index.html

However, usually ultrasonic sensors detect obstacles in a sort of cone shaped zone. For that I don’t see any ready-to-use solution. I would start by measuring the coordinates of the relevant CS. Then I would compute the limits of the zone covered by the ultrasonic sensors and see if any of the target CS are inside. This type of computation might be easier to implement in a script than using blocks, so I think I would use the MATLAB Function block (previously Embedded MATLAB Function block).

Guy