Learning Forum

[Emperor]

Hello everyone, I'm working on a multibody arm arm and I would like to do a static analysis. I'm wondering for the links (1 2 3), do we need to create rigid bodies on the two bodies associated with the same master node? For the force I put a distant force at the center of gravity of the cube, is it good? 

Thanks,

[1shan]

nPlease check a similar tutorial at https://courses.ansys.com/index.php/courses/time-domain-dynamic-problems/lessons/homework-quizzes-simulation-examples-time-domain-dynamic-problems-lesson-6/nRegards,nIshann

[peteroznewman]

nYou label three joint axes, 1,2,3. What is at each of these joint axes to drive the angle between the attached links? There are many drive systems to move an articulating arm. Common methods include cables that attach to pulleys at some radius from each joint axis, there are direct drive motors, and hydraulic cylinders. I think you need to model the drive mechanism before you can do a Static Structural analysis of the articulating arm.n

[Emperor]

Hello nthe realization of the calculation with the engine will finally be done on another software (Adams), what finally interests me here is to create rigid bodies to represent the link, I know it's possible on APDL, but on Workbench I'm looking for it but I can't find it. I need to see if the deflection of the arm is within a reasonable standard when subjected to its own weight and load F.nThanks for your recommendation n

[peteroznewman]

ArraynPlease define what you mean by link.nWhen I use the term link, I mean the large body that goes between the joints, such as the green body between numbers 2 and 3 in your image above.nThat body can be found under the Geometry branch in the Outline in Mechanical. Click on that body in the Outline and in the Details window, you can set the Behavior from Flexible to Rigid. That is how you make a link rigid.nI am confused because you ask how to make a link rigid and at the same time you say you want to see the deflection of the arm. What you call an arm I call a link, but more importantly, if the arm is rigid, there is no deflection!nI understand what Adam can do. ANSYS has a similar (but less capable) software called Rigid Dynamics. In that module, all the links are rigid and only joints are defined. In that module, you can calculate the forces and torques going through each joint, which is useful to know to size the motors needed at each joint. You can also calculate the velocity and acceleration of each link as the mechanism goes through its motion. Those accelerations at a particular time stamp can be sent to a Static Structural for analysis of the deformation of the links, which become Flexible bodies in Static Structural.n

[Emperor]

,I need to size an arm with 2 joints. First, I ask myself if the constructed arm supports its own weight and the load applied at the end (which at first is a mass, which I convert into effort). So I do a static analysis to find out if this is the case. Given that I have links (1 2 3), normally at link 2 one has a pivot, but I put myself in the worst case, i.e. where the angle with the horizontal is 0° and I want to make a rigid body (master and slave nodes to stiffen), in link 1, I finally put my embedding and at link 3 I apply a force. We must have the value of the arrow to anticipate the collision with the truck.nI made an example on hypermesh (optistruct solver) hoping to be clearer.nThank you for your answersnnn

[peteroznewman]

nYou show a link with holes in the end where a pin could go through to make a Revolute Joint.nIf you have two links and two Revolute Joints and you arrange them horizontally, when the simulation runs, those links will act as a double pendulum and swing back and forth.nIf you lock the rotation of the revolute joint, then the arm would remain horizontal.nI asked you to show or design the detail that allows the torque required to hold the revolute joint fixed. You haven't shown that level of detail. Those details are where the high stress will be. The mesh you show has no detail to show how the torque is applied to the arm. What does that? In real mechanisms, there is a hydraulic cylinder that creates a large force on a protrusion from the arm.n

[peteroznewman]

[Emperor]

nthank you for your feedback, nfinally I was able to simulate what I wanted n