Machination Mode

[Guest EricFoy]

... And I think it's just me.

 

But, I dunno... it doesn't seem like what I want to do should be this hard. EXCUSE ME WHILE I VENT FOR A MOMENT!

 

Okay, I feel better already. So here's the deal: Trying to do some work in mechanism mode. Is it just me, guys, or are the constraint thingys hard as hell to figure out? I'm a pretty smart guy, but this all seems pretty non-intuitive. I would expect first to be offered a list of global constraints, such as, "This part is a concrete block poured into bedrock (it caint move 'tall)." Then, "This part can move linearly along the [X][Y][Z] axis." Then perhaps, "This part can only rotate about [user specified] axis." Then I would expect to add the inter-part and inter-assembly constraints.

 

I'm sure that the constraints offered are all one needs to fully describe a mechanism, but the documentation I've been able to find says scarcely any detail about them. What are the various modes all about? What exactly does "Relaxed Mode" relax? What's "Rigid?" Rigid generally means "constrained," so I'm really at a loss here, guys.

 

What I need is some instruction that translates all the constraining mechanisms into terms I'm familiar with, such as, "This is a pin-connection with these mating thrust surfaces," or "This is a slide which rides inside this raceway."

 

And how do I know if the part or its parent assembly is being constrained? Mechanism mode seems to pretty much obfuscate this information.

 

Does anybody feel me here? Is there a tutorial I don't know about? Any help?

 

Thanks

 

[edits]: After my morning coffee, I felt better, and thought I should remove some of the gratuitous vitriol.

Edited February 13, 2008 by EricFoy

[Cary OConnor]

Well there are two types of thoughts. CAD constraints - Fixed, Collinear, Mate, Align, Concentric, etc... and there is the Simulation which is more along your thoughts (Motors, fixed directions, etc).

 

If you are using the CAD method, you need to think in those terms. Fixed means fixed in all directions. The others should be understandable.

 

The Solving modes are different ways that allow the mechanism to move. Rigid - Rigid body - meaning more items will move as a group. Localized would be in a case like a robot arm. If you wanted to only move the fingers and not the entire arm, you would use localized. Relaxation allows more items to move (so in the case of the arm a lot more would move). There was an example that showed this when the mechanism mode was released. Maybe Kevin can find it and post it.

 

As for the structure levels....the mechanism mode is different than IronCAD's solving since it support simultaneous solving. It means that dimensions are applied at the same level in the structure. For example: If you have a dimension from a part (not in an assembly) to a part under an assembly. In IC, it will try to solve this situation. In the Mechanism mode, it will change the association to be at the part and the assembly level since they are at the same level in the structure (so the assembly moves not the part below the assembly). Really this is more logical if you think about it (in most cases). Take a door with a handle and hinges. You could think of this as one assembly and the door frame as a different part. You would not create a constraint between the door handle and the door frame to position and move the door. The door, handle and one side of the hinge move as a unit and are constrained to the other side of the hinge and door frame.

 

Hope that starts to clear it up a little, I'm sure more can be explained. Maybe Kevin has a good tutorial.

 

Cary

 

[Guest EricFoy]

Cary:

Thanks for your speedy response.  I have a bunch of questions now...  I'll number them to make the discussion easier.

---

A) Modes of Operation

1. So if I hear you correctly, the Mode of operation (Rigid, Relaxation, etc.) simply changes the "character" of your "grasp" on the model when you click and drag, by introducing a Spring or friction weighting to the joints within a given range of your "grasp" point...?


2. Would it be accurate to say that the various Modes will all behave the same if your mechanism is completely determinate in structure? 


3. Are the Modes provided in order to provide an ad hoc way of changing the behavior of the model without the user having to explicitly add springs and dampers? 


4. Does each Mode act by "imposing" some degree of "soft determinacy?"


5. Am I correct in assuming that (in the robot arm, for example), if the stanchion base is fixed (however one would properly constrain it -I don't know), then it will never move, regardless of which Mode you are running in?

If all of my above assumptions are correct, at least essentially, then I think I'm getting it.  But if a "fixed" constraint can become more or less unfixed, then I have a lot farther to go toward understanding how to use the tool.

---

Structure levels...

1. When you say, "In the Mechanism mode, it will change the association to be at the part and the assembly level..."  Does this change the model once I exit Mechanism Mode, or will my IC model remain as-is, structure-wise?

---

C) The help file sez:

In addition to these constraints, a Fixed in Parent Constraint can be added by right-clicking on a selected shape. This will lock all degrees of freedom for the shape which will disallow all movements. The shape is fixed in the parent space which means that the parent shape can move and the fixed shape will stay in its current position with respect to its parent.

1. Is this a necessary step to keep my assemblies from flying apart?


2. Since the drag functionality appears to always happen at the Part level, will I be unable to drag a Part that is fixed within its parent assembly? (It seems like I have seen this, but it could be due to something else I'm doing wrong).

---

D) Other questions

1. Does "Aligned" mean coplanar?


2. What are the various types of "Coincident?"


3. What is the difference between "Tangent" and "Follower/Cam?"


4. How do I tell the system, "This part is a concrete block poured into bedrock"?

[Guest EricFoy]

*UPDATE* *UPDATE* *UPDATE*

 

Okay, guys, apparently, unless I'm severely internally arcing, and I don't think I am, then Mechanism Mode has some pretty severe misbehaviors when asked to work with assemblies containing linked instances of parts. The reason I couldn't understand it was because it was not working.

 

Once I replaced all these assemblies with single part entities, the thing worked beautifully. It works like any rationally thinking, reasonably intelligent, non-incontinent engineer would expect. See? I'm not crazy! I am sane! I am sane! [*wrings hands with grin*]

 

It's really not all that non-intuitive at all.

 

It's really a pretty marvelous piece of software.

 

I really like it.

 

I'm gonna take it home and show it to my mom!!!

---

Thanks, IronKev, for the extra-mile-style phone support!

 

P.S: After I'm done with this project I'm currently working on, I'll do some testing and enter a formal bug report.

Edited February 14, 2008 by EricFoy

[swallis]

Eric,

 

I had all the same reactions that you stated, good and bad, about the mechanism mode. I have gotten some good results but also lots of frustration, mainly due to the lack of documentation. It's great that Kevin was able to get you on the right track. It's a shame that the help he gave you isn't printed somewhere. I also found that keeping things simple with individual parts helps a lot, but I need to be able to move assemblies also. Post any tidbits of advice you can.

 

I am surprised that by now software can't just automatically use the part surfaces as constraints and allow assemblies to be grabbed and moved like the real thing. Maybe there is some high-end package that does that now, I haven't researched it in a long time. Then again maybe it's impossible, in which case it may be a couple more years before we have in IronCAD.

 

Scott

 

 

[Cary OConnor]

Just a note... You can change the selection filter while in the Mechanism mode to select Parts and assemblies. Maybe that is what you are looking for.

 

Cary

[swallis]

Just a note... You can change the selection filter while in the Mechanism mode to select Parts and assemblies. Maybe that is what you are looking for.

 

Cary

20680[/snapback]

I did not know that. I will have to try it out when I get a chance.

It would be great to have some sample files to download so we can see what should be achievable, and get ideas for how to set up constraints in complex assemblies.

 

Thanks,

Scott

 

[Guest EricFoy]

Just a note... You can change the selection filter while in the Mechanism mode to select Parts and assemblies. Maybe that is what you are looking for.

 

Cary

20680[/snapback]

Yes, Cary, I think this probably had a great deal to with my early frustrations. If this selection toggle isn't set on Assembly/Part, then assemblies just kind of drift apart when you drag them, whether their components are locked within their parents or not. This seems kind of strange, as I'm unsure what use the other mode would have.

[Cary OConnor]

Well in most cases (I think), the mechanism is part within an assembly. So the default is set to part to drag the parts to see the mechanism move. If you have a mechanism of a series of assemblies, then you need to change the filter.

 

Cary

[Guest EricFoy]

"Ohhhhhhhhhhhh..."

he said, in a long, descending tone, as one suddenly awakened to a state of quasi-total enlightenment in an epiphanic trance.

 

I get that.

 

Seriously, I never thought I could be this dense. As a consolation, I'm clinging to the hope that one day my hard earned age and treachery will prevail over some kid's youth and skill.