Simulation and temporarly grounding an object

[Anonymous]

Hi

I have an assembly in a dynamic simulation and I would like to temporarily ground it for a few seconds until the motor within it spins up to maximum speed. Can any one think of a neat way of doing this? I have thought about applying imposed forces on the assembly from several angles to prevent it from moving but ideally I would like to ground it or perhaps add brakes that dissapear after a specified time.

Thanks

Roger

[JDMather]

Depending on the mechanism - you should be able to use some input on the Input Grapher to hold it until a specified RPM is reached.

Can you attach the assembly here?

[Anonymous]

Hi

Thanks for the reply, unfortunately I can't attach it as its currently patent pending. But I can describe it; imagine a chasis that sits on 4 free  to spin wheels that in turn sit on a track. The spinning of the motor creates a forward force, causing everything to roll down the track. What I would like to do is somehow ground/brake/lock the wheels/chasis until the motor has reached maximum RPM, then I want to release it.

I guess a more simple example is a marble at the top of a sloping track that is held back by a gate, after say 4 seconds the gate is removed allowing the marble to roll down the track.

Hope that helps and thanks again

Roger

[AndrewSears · Accepted solution]

Hey Roger,

In DS make sure that you have a joint defined between the track and wheels.  Now edit that joint by going into the imposed motion.  Choose to edit position in the DOF you are trying to restrict using the input grapher.  While in the input grapher you can select the initial and final times with an imposed motion as zero.  At the final time, where you know when the motor gets to the RPM you are looking for release, make the positional imposed motion a free condition.

What should happen is that your motor will start from 0 RPM to some RPM within some time.  When that time is hit, the imposed motion restricting the motion will be set to the free condition and the object will start reacting to forces now.

Andy

[Anonymous]

Hi Andy

That sounds very promising indeed 🙂 I will try this and report back

Roger

[AndrewSears]

Let me know if you have any problems.  Simple models are a good way to prove a concept when learning DS.  If you can, create a simplified model that can be shared without giving away any of your patent pending details.

Andy 

[Anonymous]

Ah yes, I have come across a problem. I have definfed the wheels on the track using the rolling cylinder on plane joint which is not a standard joint, has no degrees of freedom and therefore can not have an imposed motion...any suggestions how I can get around this?

Roger

[Anonymous]

Actually I may have found another standard joint that I can apply the imposed motion on...

Roger

[Anonymous]

Yep that did the trick, one cylinder joint was enough and even better this has fixed the problem I was experiencing with the prototype 🙂 I'll see whether I can remove enough of it so that I can post it here

Roger

[AndrewSears]

If you are unable to share with the world, feel free to email it to me.  

andrew.sears@autodesk.com

Andy