2-axis joystick simulation: 2 joints and a dummy link

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baxter
Posts: 4
Joined: 03 Apr 2017, 17:18

2-axis joystick simulation: 2 joints and a dummy link

Post by baxter » 12 Apr 2017, 15:36

Hi all,

I am simulating two-axis joysticks as 2 revolute joints connected via a tiny plane as the picture below shows.
The plane is only a workaround to make the simulation possible: a Dummy would be better here, but it breaks the dynamics chain.

Is there any way to replace this plane by a dummy somehow, or eventually to limit the impact of the plane in the simulation?

The plane could be moved far away from the scene to make sure it does not collide any other object. But since the mass can't be zero, moving the plane also moves the center of mass and unbalances the joystick.

Image

coppelia
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Posts: 7272
Joined: 14 Dec 2012, 00:25

Re: 2-axis joystick simulation: 2 joints and a dummy link

Post by coppelia » 13 Apr 2017, 13:26

Hello,

the best would be to use a small sphere or cuboid, that is not respondable. This way it won't interfere with the other respondable objects. Additionally you can also hide it in a different layer.
Finally, the mass and inertia of that intermediate body is important and will directly influence the stability of your dynamic simulation (mainly Bullet and ODE, since they are very sensitive to large mass/inertia ratios). Make sure you have read the design considerations 6-8 on this page.

Cheers

Jendker
Posts: 10
Joined: 23 Jan 2019, 15:32

Re: 2-axis joystick simulation: 2 joints and a dummy link

Post by Jendker » 11 Feb 2019, 18:22

If I may ask in the old thread, I have the same question.

Would sphere as small as 0.001 mm and of weight of couple of grams be also fine as the coupling between two joints? I would like to avoid it influencing the calculation, so would like to make it as small as possible, but maybe it would be actually in conflict with 7th Design consideration? I am working on dynamic model.

coppelia
Site Admin
Posts: 7272
Joined: 14 Dec 2012, 00:25

Re: 2-axis joystick simulation: 2 joints and a dummy link

Post by coppelia » 12 Feb 2019, 10:32

Yes, this is in conflict with design consideration 7, indeed. Unless you use the Vortex engine, which is much more tolerant in that aspect.
You can always try, but if you notice a wobbly or soft behaviour in the joint construction, this means that you have gone too far..

Cheers

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