How to fix btmultibody in the dynamic world?

[mirsking]

Hi, there.
I'm now working on physic simulation of a robot gripper. The gripper has a base link and three fingers.
To simplify the task, I only make a URDF file for the gripper, not all the robot.
After I load the robot gripper in the dynamic world and run stepSimulation, the robot gripper just move strangely.
It move to the anywhere in the whole space.
Since I already set the gravity, it doesn't make scene.

Therefore, I'd like to find a way to fix the gripper into the land, while I can stll move the gripper's fingers.
Need your help.
Thank you!

[mirsking]

Hi, there.
I'm now working on physic simulation of a robot gripper. The gripper has a base link and three fingers.
To simplify the task, I only make a URDF file for the gripper, not all the robot.
After I load the robot gripper in the dynamic world and run stepSimulation, the robot gripper just move strangely.
It move to the anywhere in the whole space.
Since I already set the gravity, it doesn't make scene.

Therefore, I'd like to find a way to fix the gripper into the land, while I can stll move the gripper's fingers.
Need your help.
Thank you!

P.S. I have notice a function called setupFIxed of btMultiBody and don't understand its usage.
I'm a newer for bullet. Thank you!

[benelot]

You might want to try the fixed base option for your gripper if you want it to be fixed in space. The setupFixed() method is to create a fixed joint between the links of your gripper, meaning the links can only be moved together whilst the fixed joint fuses them together. Check out the btMultiBody demos for more information.

[mirsking]

You might want to try the fixed base option for your gripper if you want it to be fixed in space. The setupFixed() method is to create a fixed joint between the links of your gripper, meaning the links can only be moved together whilst the fixed joint fuses them together. Check out the btMultiBody demos for more information.

I read the demo and notice that what I need to do is set the first link's mass to be zero. And it works, thanks.