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making assemblies move

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rollin45

Senior Member
making assemblies move

Sorry to ask and take up space here with a newby question, however, I've tried everything I can think of, and I'm not getting anywhere.

I've drawn several parts , assembled them with corresponding holes and shafts. I assembled them by inserting an axis through the centerline of a hole, inserted an axis for the corresponding shaft, then aligned the two axes. I've checked for interferences and all seems to be good. I've gone into the configuration dialogue and made constraints flexible ( I think :roll: ) but when I try to rotate any of the pieces, entire subassemblies move and don't seem to be constrained by the aligned axes. I do have the base of the entire assembly anchored and presumably the other parts will rotate around this anchor.

If I examine each subassembly separately, things work as expected, but on the final assembly it seems to lock up. The geometry is correct as far as I can see as I modeled this after a working mechanism and simply copied the dimensions.

I'm hoping my verbal explanation is clear enough for someone to give me some ideas, as the actual model is pretty fair sized.

regards
rollin'
 
schenman

schenman

Member


Select the sub-assembly in the Design Explorer and click on "Make Flexible". This should take care of the problem.

Schenman
 
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anthonyws

Member
Should is the operative word. I've been using Alibre for several years and the performance of assembly constraints is very inconsistent. I have the same problem with sub-assemblies, some simple and some more complex (>10 parts). I've had great results on the first try with some assemblies and with others I've spent hours trying various things-order of applying the constraints, variations on anchoring and the ever unsuccessful 'make flexible' option. The latter seems to wreck havoc more often than not. your example of rotating a sub-assembly is a perfect example of the uselessness of 'make flexible'. The whole thing falls apart kind of as if to say it's not fully constrained, I'd prefer an error message because the undo button is useless as well. The constraint issue seems to be a weak spot for Alibre. I'm loosing interest. In desperation I've just given up and brought each part into the main assembly window and constrained everything in as logical an order as I can, this seems to work most of the time although it defeats the purpose of being able to import /insert sub-assemblies. I'm really not sure what causes this, even in the case of a simple hydraulic actuator with 1 sliding piston and 2 clevises I usually have to "build" it in the main assembly. Tedious at best when trying to assemble several cylinders into a mechanism.
Sorry for the rambling, but I've spent most of the day grappling with this very issue.
 
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david.beale

Member
I agree with all the comments about the flakiness of the whole constrain/animation area. I have had one complete animation destroyed by V11.1, at least one other which causes the whole thing to freeze needing a PC restart no less to resolve. Like another contributor I am losing the will to use this whole area which is one key reason I bought into Alibre in the first place. The constraint system is so inconsistent, sometimes it works as expected and many other times makes a total mess of my assemblies. I have one simple flywheel on a shaft in a simple bearing on a small supporting tower which works fine when the flywheel is rotated in Assembly space but when a motor is applied the whole model flys apart!! I have never seen anything like this before....
 
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MilesH

Alibre Super User
I have one simple flywheel on a shaft in a simple bearing on a small supporting tower which works fine when the flywheel is rotated in Assembly space but when a motor is applied the whole model flys apart!! I have never seen anything like this before...
Click to expand...

David,

Can you post the file for this?
 
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david.beale

Member
Miles,

I don't have the original files as I got so fed up I dumped them!! What happened was a component - a flywheel with a cranked arm - was constrained in a bearing hole in a simple tower - one constraint only for testing. The flywheel spun in place as expected but when it was animated by driving the constraint the flywheel jumped to an another location and began to rotate about an odd place in space! I redrafted the whole thing and its been OK since but I have seen this before so need to understand what I did wrong (probably).
 
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david.beale

Member
I have just recreated the problem - imported the parts as SAT files from IronCAD, made the assembly and applied motion and the same thing happens. Its a problem with the source files I am fairly sure - the X-Y-Z axis are all shifted about 90 degrees relative to Alibre's view of the world! Alls well when the assembly is made and I can spin things as expected but Motion must be getting some incorrect information from the SAT files I guess. I really need to watch this one as I have a lot of existing models I was hoping to use. All OK unless I animate I guess.
 
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david.beale

Member
I can't send one file because its too big! .... and I can only add 3 files!

I shall send the SAT instead. I think the problem is something to do with the different World-View between IronCAD and Alibre. I suspect IronCAD....
 

Attachments

  • try.AD_ASM
    71 KB · Views: 87
  • pylon.AD_PRT
    1.5 MB · Views: 84
  • fly.sat
    63.4 KB · Views: 80
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david.beale

Member
I have investigated this further and can confirm that IronCAD's view of the "World" is different to Alibre and all other CAD systems I have access to!! Their view has the Z axis where the rest have Y. The resultant mess is most likely down to this I fear....
 
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