Cable Modelling in Vrep

[vigneshkc]

Hi,

I am trying to model a cable driven parallel robot. So , Initially I am trying to model a single cable and when I am successful at that I plan to proceed to the actual robot.

I have seen some models in the forum to represent ropes which I am able to understand.

I know the standard way to model a cable in the robot : Base>>Spherical_joint>>rigid_body1>>prismatic_joint>>rigid_body2>>spherical_joint>>rigid_body3

I want to model the cable in such a way that if the prismatic joint is in tention it will apply the actual tension force on the rigid_body3, but if the prismatic joint is experiencing compression forces it will transmit zero force to the body ie just like a cable which can hold only tension forces.

Any help will be greatly appriciated :)

Thanks and Regards,
Vignesh K.C.

[coppelia]

Hello,

what about something like:

Code: Select all

baseObject --> sphericalJoint --> cablePart1 --> prismaticJoint1 --> cablePart2 --> primaticJoint2 --> cablePart3 --> sphericalJoint --> object

Instead of using one prismatic joint, use two of them. The first is controlled in position or force, then second is free but will lock at either limits.

Cheers

[vigneshkc]

Hi,

Thanks a lot for your reply.

I am trying out a planar cable robot. This is what i came up with
Base>>revolute_joint1>>rigidbody1>>prismatic_joint2>>rigidbody2>>revolute_joint2>>rigidbody3>>revolute_joint3>>rigid_body4

Basically when I am adding an extra rigid_body I am able to get better results. It behaves as expected; prismatic joint transfers zero force in compression and works well in tension. But after the prismatic joint moves for a certain distance there is a problem in the simulation. I was trying to make it better.

I tried the scheme you suggested. But since the Prismatic_joint2 is free the gravitational force just pulls the cablepart3. Please have a look at the link for reference.

https://drive.google.com/drive/folders/ ... sp=sharing


Thanks and Regards,
Vignesh K.C.

[coppelia]

Not sure I understand. I can't find any reference to the mentioned Prismatic_joint2 or cablepart3 objects.

Disabling gravity gives some very strange result with Vortex, but the other engines look fine.

Cheers

[vigneshkc]

Hi,

For example in loop_1, P_7 is the prismatic_joint2 and Cuboid_13 is the cablepart3 in the shared model.

My question was if gravity is enabled wont the second prismatic joint get activated with the external force since it is free?

Thanks and Regards,
Vignesh

[coppelia]

The joint is free, but parallel to the floor. So in theory, the gravity has no influence on that (on your whole mechanism for that matter, since it is entirely planar). In theory, because each engine operates in a different manner.

You could also try to put your mechanism on the floor, and set the friction of the floor to 0, to see if that makes a difference.

Cheers