Multiple motor actuation

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TomDelaney
Posts: 22
Joined: 31 Jul 2022, 19:48

Multiple motor actuation

Post by TomDelaney »

Hello,

I have a cuboid which I want to control with a prismatic joint and a revolute joint. These joints are not related to eachother as they are not fixed in the same position. I would like for both joints to be in dynamically enabled mode in order to set the amount of force they exert onto the cuboid just by themselves.

For the prismatic joint I want to be able to set it's force and also for it to be able to move while being fixed at one end of it. Also for it to be able to move without exerting force to the cuboid if needed.

For the revolute joint I want to be able to set the force it exerts and it to be influenced by the prismatic joints pulling of the cuboid. So whenever I pull with the prismatic joint the angle of the revolute joint changes.

I have uploaded the simulation in the following drive: https://drive.google.com/drive/folders/ ... L-ZLlRrxsj. It is called multiple_motor_actuation.ttt .

I would really appreciate if you could take a look at it and help me out.

coppelia
Site Admin
Posts: 10339
Joined: 14 Dec 2012, 00:25

Re: Multiple motor actuation

Post by coppelia »

Hello,

you have a looped mechanism. So you need to make sure that you have enough degrees of freedom for the mechanism to be able to move: your prismatic joint is attached to 2 blue shapes. Make sure that those two shapes are attached to base and humerus via spherical joints, e.g.:

Code: Select all

base --> shoulder_z_joint --> humerus --> sphericalJoint --> act3_humerus --> act32
     --> sphericalJoint --> act3_base --> actuator3 --> act31
Cheers

TomDelaney
Posts: 22
Joined: 31 Jul 2022, 19:48

Re: Multiple motor actuation

Post by TomDelaney »

Hey,

Thanks for your help! However I still have a couple issues with the simulation.

The first one is after applying your solution I experience a movement at the begining of the simulation without applying any force to either joints. I suppose it is because of the positions of the dummies, however I do not know where to place the dummies in order to solve this.

The second one is I would like the actuator's base to be fixed so that it applies force in a straight line. I was wondering if there was anyway, that I could make this possible.

As always thank you for your help, also I uploaded the updated file. I would be grateful if you could take a look at it.

coppelia
Site Admin
Posts: 10339
Joined: 14 Dec 2012, 00:25

Re: Multiple motor actuation

Post by coppelia »

When you have 2 dummies linked together with a dynamics, overlap constraint, they will try to overlap each other at the beginning of a simulation. You should always try to have the two dummies in the exact same position and orientation before simulation, in order to avoid that kind of problem.
Additionally, you have one additional pair of linked dummies, that is to related to the task. Finally, you have a huge inertia for the auxiliary shapes, and a too small mass for them. Make sure to carefully read the dynamics design considerations 7-8.

Cheers

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