NX5:Assembly mating conditions

[adrag]

I have several models of engine blocks where I create an assembly with the crank, a rod, and piston. Once, they're mated properly, I can rotate the crank and spin the assembly virtually to check clearances and other things. I would also like to add a camshaft and have that turn as well when the crank is turning. Is there a way to drive the cam somehow with the crank? It obviously needs to spin at half crank speed and I have to time it to the crank somehow. I can't see how I can apply any of the mating conditions to drive a parallel shaft.

Al

 

[JohnRBaker]

For something like that, you'll have to move to a true kinematic solver, such as can be found in the 'Motion Simulation' module of NX where you can define relationships like parallel shafts with gear ratios, etc.

John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[hudson888]

adrag,

In the animated engines that I have shown on my website and elsewhere we have the same problem. If you try and articulate the thing using the piston then the crank reaches top dead centre and won't go over-centre. The trick is to turn the crankshaft so that the pistons are force to go full circle, mating conditions do fine to translate the linear piston motion. For geared or chain drive mechanisms you'll define the ratios with formulae linked to the rate at which the crankshaft rotates I'd imagine.

To run all of this you can use angular mating condition between datum plane along the crankshaft and another fixed datum in the assembly file.

This does not deliver everything you need for full kinematics but for most engine design work and clearance checks it ought to be quite sufficient.

Best Regards

Hudson

www.jamb.com.au

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