Learning Forum

[santhoshkumarvasanthakrishnan]

Hello I am trying to simulate a Ball Bearing rolling around outer race when the inner race rotates in Rigid Dynamics. Following are the Boundary conditions :

1. Inner Race is a Rotary Joint which runs at 100 RPM.
2. Outer Race is a Fixed Joint.
3. Ball surface has frictional contact with outer race with 0.15 coeff of friction.
4. Ball surface has frictional contact with inner race with 0.15 coeff of friction.

When I simulate, the inner race rotates but the ball does not roll. Where am I going wrong ? Do I need to model the ball with some kind of joint ? Or is there any constraint that the ball needs to have ?

 

[Ashish Khemka]

Hello,

Can you check for the following?

1. Is the load step applied or ramped? Try a ramped load.
2. Reduce the initial time step size.
3. Is there a normal force acting on the balls? 
4. If the above does not help then try replacing the Rigid Dynamics simulation with a Transient Structural one and then solve the model:

 

Regards,

Ashish Khemka

[andres.perez2001]

Hi, I'm running a similar simulation for a roller bearing, but I'm having the same issues. I'm simulating in Rigid Dynamics, just like you. I have the same problem. Although my inner race rotates at 60 RPM, it also rotates and doesn't transmit the rotation to the rolling elements. Have you had any progress? I'm looking for tutorials or guides, but there's very little information.
I'll attach photos of my case. I removed rolling elements to run simulations faster, but I still haven't found a solution. I'm using frictionless contacts between the elements and the cage. I use a planar joint between the cage and the rolling elements. For contact between the rolling elements and the inner race, I use forced frictional sliding. In the images I'll add now, I'm testing with a universal joint and a 180° rotation just to get the system moving, but it's just one more test among the many I'm doing.

[santhoshkumarvasanthakrishnan]

As Ashish Khemka has mentioned above, I ran the simulation in Transient Structural with the following boundary conditions :

• Inner Race is a Rotary Joint which rotates for 10 degrees
• Outer Race is a Fixed Joint.
• Ball surface has frictional contact with outer race with 0.15 coeff of friction. (Try with frictionless contact with assumption that there is a lubricant)
• Ball surface has frictional contact with inner race with 0.15 coeff of friction. (Try with frictionless contact with assumption that there is a lubricant)
• There is only one ball.
• Define all the bodies Rigid instead of Flexible @ Geometry.
• Give very small time steps (may be 0.0001 s)

But what i found was that the ball certainly rolls due to the inner race rotation but, it rolls in a very weird way. I think this is due to not having a cage. I think cage constraints the ball and this has to be modelled properly. You can give friction or frictionless contact b/w the ball and cage. Try running the simulation with this setup.

And also if your bearing has clearances with ball & races, ball & cage.Try preloading in the first load step and then in the next load step try to rotate.