Dynamic Sim, parts going thru each other even with 3D contact applied

[steambc]

JDM, I ordered the "Part 2" book on dynamic simulation that you recommended (I forgot the author's name)  and am eagerly awaiting its arrival tomorrow. Therefore this question should be considered a fairly low priority (to you guys) because I'll probably have my answer when I start studying tomorrow.

In the meantime, tonight I thought I'd play around and see what I could figure out on my own. Here's what I've done:

1) Created an assembly with a simple ball hovering over a plank of wood.

2) Went to the Dynamic Sim environment. Grounded the plank.

3) Created a Spatial Joint between the two parts.

4) Defined gravity direction.

5) Defined a 3D Contact Joint.

        a) Selected 3D Contact Joint from drop-down

        b) Clicked on a ball surface

        c) Used component 2 arrow to select the wood plank and clicked "Apply". No compaints from Inventor.

        d) Ran Simulation. Ball travels down and goes right through the plank.

Am I missing a step or overlooking something obvious? I must say I was delighted just to see the ball drop, as I was quite in the dark about Dynamic Simulation. I followed the above procedure precisely so I'm not sure why the ball would travel through the plank. As an aside I tried to re-apply the 3D Contact joint and Inventor told me that the joint already exists.

Thanks for the help! Again, this is very low priority and just represents my having a bit of experimental fun while I await the book.

[JDMather]

Attach your assembly here.

I just followed the exact same steps and it worked fine for me.

(I added a bit of spin on the ball to make it more interesting.)

[admaiora]

Hi Steam,

as JD said, your steps are right.

I think that or are you missing some selection with the 3d contact or maybe your assembly has  a problem of low inertia (micro mechanism model).

[steambc]

Thanks for looking into it. I'm out in the field right now but will provide the assembly and parts later.

I thought maybe the issue was that the ball was created with a "primitive" (I forget the term Inventor uses), so I created a new assembly with one plank falling onto another grounded plank. I got the same result, the falling plank goes right through the grounded one. I receive no error messages in creating the joints and they do show as existing.

I'll report back later, and thanks to both of you for your help.

[JDMather]

If you did in fact have a Spatial joint and a 3D Contact joint - I am going to guess that the falling part was not in line with the grounded part and therefore would never contact it.  Check from different angles on the View Cube and make sure it will actually contact when dropped.

[steambc]

I'm pretty sure I'm good in that regard because I can see the ball being swallowed up by the floor and the ball is somewhat near the middle of the floor.

I shouldn't be using the term "plank" as it's really a square floor that is 100 x100". The ball is 12".

Perhaps my construction is wrong. The floor is a simple square extruded to 12" thick. The ball is one of the Inventor supplied primitives accessible from the ribbon menu.

Another possibility is my selection technique. I'm essentially selecting a single face on the ball and the upper face of the extruded square. My understanding is that it doesn't really matter which face on the ball one selects. Am I in error about that?

As I mentioned, I also made an assmbly with a smaller plank falling onto the floor. With the plank falling onto the same floor, the face I chose was the short edge that would touch the floor first.mIn both cases, the falling object falls through the middle of the floor making it clear that there would normally be contact.

I'm still at work so will post the files when I get home. Is all in a zip file ok? My understanding is that I need to upload both parts and the assembly.

Thanks again for your interest. I got a text from Amazon today telling me that the book has been delivered, and I can't wait to dig in.

[JDMather]

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@steambc wrote:

....Perhaps my construction is wrong. .....

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Attaching the assembly would have erased all doubt within minutes.

[steambc]

Yes, I just now got home after unexpectedly spending the night on an emergency job. I've been dealing with a huge emergency in-between Inventor sessions even 2 nights ago so things have been inn a bit of an uproar.

After I settle in and have dinner I'll get the project zipped and posted.

I did receive the Younis book in the mail today so I'm looking forward to a weekend of intense study.

Steam

[admaiora · Accepted solution]

Hi Steam,

you can compare your steps with this:

[steambc]

Wow, GREAT tutorial. Thanks so much for posting it. Is this your own YouTube channel or something you found? Subscribed.

Interestingly, last night I decided to create a brand new assembly with new parts and the darn thing worked. The only difference that I could discern was that I did not apply materials to the parts. This assembly was a ball dropping onto a cone which was placed on a floor.

I then created another one with a "wooden" plank, and that worked too, although at the end of the simulation the plank partially submerged itself into the floor. In other words, It reacted with the floor fine after it bounced off the placed cone but when it came to rest on the floor it partially sunk under the surface. I had not set any kind of friction, damping, etc.

It seems to me that the best course of action is to forget my old assemblies and just move forward. That video was great. Not only did it verify the steps needed but also helped me with some concepts of damping & friction.

Thanks again for clarifying!

Steam

[admaiora]

u are welcome Steam. Keep goin with Inventor and your new Wasim book.

[JDMather]

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@steambc wrote:

...It seems to me that the best course of action is to forget my old assemblies and just move forward. ...!

Steam

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I have always learned more from when things didn't go right, than when everything goes off without a hitch.

I am still really curious why your first assembly didn't work and why on another try you end up with one part embedded in another.

I tend to toss the ones that do work and keep around the ones that I haven't yet figured out.

[steambc]

You make a good point. Tonight I'll post both my initial assembly with the ball going completely through the ground and the assembly where the plank eventually settles half-buried in the ground.

I appreciate your interest.

Steam

[steambc]

I've gone so far beyond that initial situation, during which I was almost completely ignorant of how dynamic sim worked, that I'd rather forge ahead and address new issues in the more complex assemblies I'm currently building, if and when they come up.

Everything is working normally now, and I've starting building some significantly more complex systems within Inventor. Thanks for your help, guys.

[JDMather]

Last Thur night my students had a DS test where several had the same problem getting theirs to work.

Then following Tues night I went through the problem step-by-step with the entire class (after practicing it myself in my office).

Everything went fine in my office, but in class - every student had the same unexpected behavior that the few had had during the test.  We didn't figure it out on-the-fly, so I had to put it aside for later.

Last night I took another look at it in preparation for tonight's class and found my mistake.

So simple that I will never reveal it here, but after I show the class tonight - I am sure we will never forget and make the same mistake again.  I will tell them I did it on purpose to see if anyone was awake.

In my experience we (I) -  learn far more from when things don't go as expected and going back and figuring out why.

[amirandaL4VAC]

Hi @JDMather and @steambc I'm hoping you can say what went wrong here. I'm having a similar problem. I tried spatial contacts and 3d contacts, and the dots of contact show up (see video) but it still goes through. It works when I drive things manually, but the second I add the unknown force in it doesn't behave.  I've tried a bunch of ways to get this slot to behave and putting these two fake surfaces at the ends of the slot with a 3d contact seemed like it would be the best answer but still no dice. 

[JDMather]

@amirandaL4VAC 

This is an old thread that has been marked as solved.

Too late now, but it would have been better if you had started a new thread with a link back to this old thread for reference.

On quick inspection it appears to me that your mechanism moves in a plane.  In that case I would use 2D Contact Joint rather than 3D Contact Joint.  Before I did deeper - can you explain why you did not use 2D Contact Joint? 

And I see no need for Spatial Joints.  I suspect that I would need to reassemble the components from scratch to get the correct Joints.  That would be time consuming for me.

Edit: Also, you should mention when you are using an older release of Inventor. iProperties would seem to indicate that you are using 2022.

[amirandaL4VAC]

Hi @JDMather thanks for your reply. When I do 2D contact, I get the following message: Impossible to solve the system. Check the definition of joint "2D Contact [...] (normal orientation)."

I tried it the following way, with the outer profile being a 0.5mm larger diameter.

I tried following your Youtube channel's video on prismatic joints for this. Is it not working because it's not explicitly linear sliding, but instead following a curve?

[amirandaL4VAC]

I finally figured it out, I didn't understand that the z direction was the 3 headed arrow until I re-listened! Sorry about that and thank you for the help!

Update: It works when I play it until I add unknown force back in! Does unknown force not play nice with 2d contact?

[JDMather]

@amirandaL4VAC 

Attach revised assembly here.