Robot is moving continously without any velocity

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vrvasudev
Posts: 5
Joined: 15 Mar 2018, 08:33

Robot is moving continously without any velocity

Post by vrvasudev » 06 Sep 2018, 16:19

Hi there,

I am designing a differential drive robot having two wheels at the back and two caster wheels at the front.
For the caster wheels, I have designed a small structure that will replicate the caster wheel motion.
when I start the simulation, the robot is moving continuously to the front side. I have given sufficient inertia according the dimensions and shape of the object.

Please help :)

fferri
Posts: 238
Joined: 09 Sep 2013, 19:28

Re: Robot is moving continously without any velocity

Post by fferri » 06 Sep 2018, 18:05

Make sure to fully read and understand Designing dynamic simulations.

If you only need the casters to balance the robot, you can consider replacing them with a simple static respondable frictionless sphere, which would be more stable and less CPU expensive. You can keep the caster for visual purposes (i.e. turn off dynamic and respondable bits) and adjust its orientation according to the kinematic model and velocities of the robot.

vrvasudev
Posts: 5
Joined: 15 Mar 2018, 08:33

Re: Robot is moving continously without any velocity

Post by vrvasudev » 07 Sep 2018, 04:24

Hi fferri,

Thank you for the reply. I have tried with sphere, it is working fine with it i.e., no motion in robot when there is no external velocity given. But I want to try with the caster wheels which looks and operate like real caster wheels.

For the design of single caster wheel, I attached a vertical revolute joint from robot to a plate, to this plate there is one more horizontal revolute joint to which a small cylinder is added(this will act as caster wheel). For these two motors i have used Force/Torque mode and motor is disabled in order to provide only joint motion. Similarly one more caster wheel is designed.

I have considered all the necessary parameters and design considerations mentioned in the page Designing dynamic simulations, especially, Design considerations 6- 8.

Even though the robot is moving slightly towards the front direction. I want the robot to be stable when there is no joint target velocity given as input to the rear wheel motors.

Thank you in advance :)

fferri
Posts: 238
Joined: 09 Sep 2013, 19:28

Re: Robot is moving continously without any velocity

Post by fferri » 10 Sep 2018, 16:41

Did you try using the Vortex engine? It should be more stable than ODE and Bullet.

Also ODE should be more stable than Bullet in some cases.

vrvasudev
Posts: 5
Joined: 15 Mar 2018, 08:33

Re: Robot is moving continously without any velocity

Post by vrvasudev » 21 Sep 2018, 11:45

Thank you fferri.

The model is working now, I re-read the design considerations and modelled the robot accordingly. The problem is with mass and inertia distribution. Now, it is working with the new design.

Thanks once again :)

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