Robotino problem

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philotuxo
Posts: 6
Joined: 25 Feb 2013, 01:40

Robotino problem

Post by philotuxo » 03 May 2013, 00:48

Hello,

I'm trying to simulate the Robotino robot on V-Rep. I have so far:
1- imported from an urdf file (originally used for gazebo).
2- corrected the measurements according to the real robot.
3- written a ROS script to control via joystick.

To simulate the wheels of robotino I put free joints perpendicular to the revolute base joints of the wheels. The respondable is linked to theses free joints. A sample video can be viewed here: http://www.youtube.com/watch?v=-S-czPGUPlw

The problem is that the robot movement is not stable, and we can see that the robot draws an arc while strafing right or left.

I also tried a version without any free joints. The result was even worse. In the second video, only commands of straight movement were sent to the robot, but the robot makes weired angles when expected to turn 90 degrees or to go straight: http://www.youtube.com/watch?v=F7vsCyQv7WY

Does anyone know how to simulate the Mecanum wheels of the Robotino robot? Or what are the tricks?

coppelia
Site Admin
Posts: 7266
Joined: 14 Dec 2012, 00:25

Re: Robotino problem

Post by coppelia » 03 May 2013, 01:18

Hello,

It is difficult to know what is wrong from the videos.
Have you seen and understood how the omniwheels on the KUKA YouBot are simulated in V-REP?

Actually, this is how it is done:
  • The wheel is composed by 2 spheres and 2 revolute joints in following configuration: robotBody - activeJoint - nonRespondableSphere - passiveJoint - respondableSphere
  • The 2 joints have to be at their specific angle (perpendicular in your case)
  • There must be a non-threaded child script attached to one of those objects, preferably the first joint. It is in charge of resetting the respondableSphere and reorienting the passiveJoints, and this in each simulation loop
Drag the YouBot model into the scene, start the simulation, then click the visualize and verify dynamic content toolbar button. Then make it move forward/sideways. Notice how the free joints (colored in blue) always stay more or less horizontal? This only happens because of the child scripts. You can try disabling the child scripts (e.g. by removing them), then do the same again.

Keeping the passive joints (i.e. free joints) horizontal is the secret. This way of doing allows an almost perfect simulation of any omnidirectional wheel: smooth operation on any ground, also non-flat. And no jumping up/down (as would happen if you try modelling the small rollers, at least in the YouBot case).

http://www.youtube.com/watch?v=PFabXCQj ... 3jBcMigp5g

Cheers

philotuxo
Posts: 6
Joined: 25 Feb 2013, 01:40

Re: Robotino problem

Post by philotuxo » 04 May 2013, 17:12

Wow!
coppelia wrote:
  • The wheel is composed by 2 spheres and 2 revolute joints in following configuration: robotBody - activeJoint - nonRespondableSphere - passiveJoint - respondableSphere
  • The 2 joints have to be at their specific angle (perpendicular in your case)
  • There must be a non-threaded child script attached to one of those objects, preferably the first joint. It is in charge of resetting the respondableSphere and reorienting the passiveJoints, and this in each simulation loop
Even though I couldn't explain the problem properly, you answered accurately. As you have told, the problem was the movement of the free wheels, and the solution was the scripts for each wheel.

I did use the wheel design of the Youbot, but I had not noticed those scripts before while I was examining it. I had done the two options you mentioned, but the third was missing.

Thank you very much!

With those scripts appropriately added we have a stable Robotino robot. How can I share the robot with the community? Through the forums?

coppelia
Site Admin
Posts: 7266
Joined: 14 Dec 2012, 00:25

Re: Robotino problem

Post by coppelia » 04 May 2013, 18:56

Glad it worked ;)

You can send us the model/scene, and we will add a section on the website about user contributions. We try to avoid having too heavy items on the forum.

Cheers

Ahmed_Yacine
Posts: 13
Joined: 01 Oct 2014, 13:19

Re: Robotino problem

Post by Ahmed_Yacine » 02 May 2015, 17:13

Hi,
I am starting a project on the navigation of robotino in dynamic environment and I need the robotino model in v-rep,
it will be a great help from you if you can share the robot model with me.
my email is ab_benmakhlouf at yahoo dot fr
thanks.

racuna
Posts: 1
Joined: 25 Jun 2015, 15:44

Re: Robotino problem

Post by racuna » 26 Jun 2015, 11:18

Hi I am also interested on the model of the robotino if you still have it :).

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