modelling a ramp in simscape multibody such that one end of ramp is connected to a sliding body connected using revolute joint and other end is free falling due to gravity

Hello All,

I am new to simscape multibody.

I am currently facing issue when I am adding force to body 1 for sliding - the body 2 is lifting up due to the velocity of body 1 and the dropping to floor.

What I am looking for as behavior is that the body 2 stays straight for travel/ sliding and drops (hinge type) due to gravity only till it reaches the floor.

Answer 1

[Shishir Reddy]

Hi @Karansinh

The issue that you are encountering, where the ramp lifts before dropping is likely caused by inertial effects during the sliding motion of the base. Kindly refer the following workarounds to fix this.

1. Constrain the Sliding Motion Properly

Make sure the sliding body (to which the ramp is attached) is connected to the ground using a 'Prismatic Joint'. This will limit its movement to a straight line (e.g., along the X-axis) and prevent unexpected motions in other directions.

2. Model the Ramp Hinge correctly

Connect the ramp to the sliding body using a 'Revolute Joint' at one end. This joint should allow the ramp to rotate freely due to gravity. Do not apply any torque or motion input to this joint, gravity should be the only driver.

3. Tune Mass and Inertia

Ensure both the ramp and the sliding body have realistic 'mass' and 'inertia' values. If these are too small, the ramp can behave erratically and lift off due to the sliding body's acceleration.

For more information regarding 'prismatic' and 'revolute' joints, kindly refer the following documentations -

https://www.mathworks.com/help/sm/ref/prismaticjoint.html

https://www.mathworks.com/help/sm/ref/revolutejoint.html

I hope this helps.

[Karansinh]

Hello Shishir,

Thank you for your reply.

I tried your suggestion.

In my original model, the BD01 is correctly sliding on the base plate using prismatic joint between the top of base plate and bottom of BD01. I had to add force for initiating the sliding motion of BD01. I might be providing more force (calculated using rotation of the motor/ pulley) that is still leading to ramp which is attached using revolute joint to BD01 lift up due to inertia. correct?

I have added custom mass as 10kg and 60kg to the respective body.