Consistently simulating a full scissor parallel system driven by a single joint
Posted: 07 Dec 2018, 17:17
Hi everyone,
I am trying to simulate a single-jack-actuated scissor elevator system, which is a parallel system. The real system, just as the one I try to simulate, only has one actuated (prismatic) joint (the jack) and all others are passive.
To build the structure, I joined dynamic pure shapes (I used spheres) with standard joints, and dressed up the pure shapes with a non dynamic visual layer (non-pure shapes taken from my CAD).
To perform the loop closures of my parallel system, I used 5 pairs of linked dummies with a « dynamic, overlap constraint » link type, which are either attached to pure shapes or to joints.
The scene can be downloaded at this link :
https://drive.google.com/open?id=1F51_U ... CD2WSsE_PE
My first question is related to my choice of using this type of linked dummies. My goal is to control the motion of the upper table of the elevator by controlling a single actuator's velocity (the jack).
Do you think my approach is appropriate?
Regardless, seeing that my simulations were very unstable (except when I used vortex dynamic engine), I tried to follow V-REP dynamic simulation design considerations : http://www.coppeliarobotics.com/helpFil ... ations.htm, which were really helpful.
These led me to use spheres instead of long thin cuboids for my scissors parts, and to set rather large masses and moments of inertia for them. This solved the problems of stability to a certain extent (it is now stable under Bullet 2.78).
My problem is now that the structure wobbles slightly before stabilising to a rest configuration, for which the upper table is a few centimeters bellow where it should be. I would like to reduce this wobble and inaccuracy as much as possible.
Would you have any hint to improve this matter ?
(I tried to play with masses and moments of inertia, but my approach to changing them is quite chaotic and doesn't improve matters.. If you had any empirical guidelines, they would really be appreciated :) ! )
Kind regards,
David
Note that I am using V-REP v3.3.2
I am trying to simulate a single-jack-actuated scissor elevator system, which is a parallel system. The real system, just as the one I try to simulate, only has one actuated (prismatic) joint (the jack) and all others are passive.
To build the structure, I joined dynamic pure shapes (I used spheres) with standard joints, and dressed up the pure shapes with a non dynamic visual layer (non-pure shapes taken from my CAD).
To perform the loop closures of my parallel system, I used 5 pairs of linked dummies with a « dynamic, overlap constraint » link type, which are either attached to pure shapes or to joints.
The scene can be downloaded at this link :
https://drive.google.com/open?id=1F51_U ... CD2WSsE_PE
My first question is related to my choice of using this type of linked dummies. My goal is to control the motion of the upper table of the elevator by controlling a single actuator's velocity (the jack).
Do you think my approach is appropriate?
Regardless, seeing that my simulations were very unstable (except when I used vortex dynamic engine), I tried to follow V-REP dynamic simulation design considerations : http://www.coppeliarobotics.com/helpFil ... ations.htm, which were really helpful.
These led me to use spheres instead of long thin cuboids for my scissors parts, and to set rather large masses and moments of inertia for them. This solved the problems of stability to a certain extent (it is now stable under Bullet 2.78).
My problem is now that the structure wobbles slightly before stabilising to a rest configuration, for which the upper table is a few centimeters bellow where it should be. I would like to reduce this wobble and inaccuracy as much as possible.
Would you have any hint to improve this matter ?
(I tried to play with masses and moments of inertia, but my approach to changing them is quite chaotic and doesn't improve matters.. If you had any empirical guidelines, they would really be appreciated :) ! )
Kind regards,
David
Note that I am using V-REP v3.3.2