## General Mechanical

#### Rigid dynamics pulley system

• Mordrag
Subscriber

I'd like to simulate a complex mechanism with pulleys. I need to size a motor to lift an object at a constant velocity. I'm in the debugging phase right now with just a simple pulley system. The force reaction of TJ_01 should read m*g=98 N. However, Ansys shows it's zero. If I put force instead of displacement joint load as TJ_01 boundary condition, I can see that the system works as intended (F_01<98 N causes descent of the 10 kg and F_01>98 N causes ascent). However, I can't use this approach in the complex system that I want to model. Also, I would like to incorporate the friction from the pulley rotation and which is currently zero as the RJ_01 reaction force is also zero.

Does anybody work with the rigid dynamics module and can help me?

• 1shan
Ansys Employee
Instead of a displacement joint load could you use a remote displacement at the upper blocks face and see if you get the expected reaction at TJ_01?
Regards Ishan.
• Mordrag
Subscriber

thanks for the tip, I thought about it as well, but then I forgot to try it. To my surprise it works and I get the correct reactions in both TJ_01 & TJ_02. However, I get zero reaction (moment/force) resulting from the 10 kg on the RJ_01 (pulley). I can model the friction by commands/variable load ACT.
• Mordrag
Subscriber
Btw, I see that you are an Ansys employee - can you tell me the reason why the joint reaction doesn't appear if loaded by joint condition but once loaded by RD, the reaction is there? In both cases, the forces are present in the system (as demonstrated by the test by force loading in my 1st post). Not to mention that mixing remote displacements with joints seems prone to error (over constraint).
I do several projects in Rigid Dynamics per year and almost every time I experience some strange behaviour like this which is really frustrating to debug for complex models. So any inside view could really help me to understand better what things are to be avoided when using the Rigid Dynamics module.