Need guidance to create a simple simulation in Gazebo

gazebo

asked 2012-06-02 18:40:19 -0500

TurtleBot_Fan
287 ●19 ●28 ●33

updated 2012-07-24 15:46:51 -0500

I would like to create a simple simulation of a ball screw mechanism. I understand how I must create a mesh of a threaded ball screw hex nut and a mesh of a threaded ball screw shaft, but how would I connect them joint-wise?

How do I make the threaded bolt shaft turn to move the nut?

Is it necessary to do this as a plugin, and if not, would it be better to do it as a plugin as an easily distributable example for others?

Thanks.......................

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are you trying to model the ball screw itself, or just the effect of the ball screw? Could you create the effect using a prismatic joint? http://gazebosim.org/wiki/sdf_joint

JonW ( 2012-07-12 21:27:16 -0500 )edit

What general approaches have you considered? This is outside of the realm of what Gazebo is usually used for, so providing additional context might help the community answer if certain approaches are good or bad.

Ryan ( 2012-07-18 12:41:18 -0500 )edit

Hi @TurtleBot_Fan, I notice you're still having problems here. What have you tried so far in terms of joint types to connect the two links?

Ryan ( 2012-07-22 06:20:41 -0500 )edit

JonW, I want to model the ball screw mechanism so I can accurately simulate a Linear Actuator that will be coupled with a titanium spring much like the SAFFIR Humanoid uses.

TurtleBot_Fan ( 2012-07-24 15:39:44 -0500 )edit

Ryan, I don't see an appropriate joint type to try, so I am stumped, hence needing guidance. I was hoping someone already did this or somthing similar already so I could push forward to more important problems instead of reinventing the wheel at this elementary level.

TurtleBot_Fan ( 2012-07-24 15:46:01 -0500 )edit

Ryan, You mentioned my simulation to be "outside the realm of what Gazebo is usually used for". I'm under the impression that DARPA deemed Gazebo to be the simulator of choice for the Humanoid-centric latest Grand Challenge, so it seemed doing the simulation I proposed would be simple compared to a complete Humanoid simulation. I expected more existing support already done along the lines of my ball screw simulation due to DARPA's selection of this simulator.

TurtleBot_Fan ( 2012-07-24 16:03:41 -0500 )edit

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answered 2012-07-24 16:24:29 -0500

hsu
5735 ●31 ●62 ●89

gazebo supports a screw joint natively, if you take a look at pr2_description, there's a small example in torso.gazebo.xacro:

  <joint:screw name="${name}_screw_torso_lift_joint">
      <body1>${name}_motor_screw_link</body1>
      <body2>${name}_link</body2>
      <anchor>${name}_motor_screw_link</anchor>
      <anchorOffset>0 0 0</anchorOffset>
      <axis>0 0 1</axis>
      <threadPitch>3141.6</threadPitch>
  </joint:screw>

here is a video of a simple screw joint

if this is what you were looking for, I can provide a more succinct example?

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That should do the trick! Did you implement more such complex joints? And how is this implemented?

bit-pirate ( 2012-07-24 16:32:53 -0500 )edit

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answered 2012-07-24 16:03:10 -0500

bit-pirate

2062 ●24 ●47 ●55

I'm not a Gazebo expert, but it might work, if you combine a prismatic and a revolute joint. You would then need to couple them for the proper simultaneous motion.

We have coupled joint in our robot, but the coupling and publishing of the according joint positions is done outside Gazebo (we are actually not using Gazebo, but the idea is the same).

So, I don't know if this could be done inside a Gazebo plugin or you would need to write an extra (ROS) node for publishing the positions for the prismatic and revolute joint.

Hope this helps a bit. Good luck!

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Thank you so much! This is great feedback.

TurtleBot_Fan ( 2012-07-24 16:07:13 -0500 )edit

Can anyone that's a Gazebo/ROS expert add more insight to the above post?

TurtleBot_Fan ( 2012-07-24 16:08:01 -0500 )edit

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Need guidance to create a simple simulation in Gazebo

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