Force Balance on Multiple Bodies

[JonReynolds]

Hi all,


Picture 2 rotating shafts, such as in an engine with balance shafts, so a crankshaft, with 1 or 2 separate balance shafts running alongside it.


In isolation, I can rotate each shaft and determine the force their out-of-balance masses create on their 'bearing surfaces' or onto the body they would be mounted in (engine block).


But what I want to try and do is rotate them simultaneously as see the overall effect they have on each other.


So for (simple) example, if I have 1 shaft that looks like this:


__p__


thats a shaft with an eccentric mass. If I spin it it will create an out of balance force due to the mass sticking out.


If I arrange another opposite it, so that when they spin in opposite directions, the masses cancel each other out, how can I determine this in Pro/mechanism?


I can set up the rotating shafts, I can gear them together, I can graph the reactions at their constraints (like reactions at their bearings), but how can I get an overall picture? So summing all the rotating forces of all shafts that would be acting on the block they are mounted in?


Phew... thanks in advance.

 

[Kaz Z06]

Jon,


There are a couple ways to do this. One is to create a custom measure that will sum the components of each shaft into one vector sum. The other is to mount both shafts to a common part (block) and assemble the block to another body ('engine mount'), then measure the reaction forces at the rigid joint between the block and the engine mount. This second method will also let you visualize the total reactions with force arrows in an animation.


Hope this helps,


Chris

 

[JonReynolds]

Hi Kaz,

Thanks for the reply. I did it in the end with a custom
measure summing up the individual forces. I did think of
making some dummy bodies to mount them in, but then the
result 'should' be the same as the custom sum.

Thanks!