Skip to main content
P
ptc-46314451-Visitor
1-Visitor
March 6, 2019
Question

Tips on shortening mechanism run time

  • March 6, 2019
  • 1 reply
  • 5548 views

Hi -- I am having issues with long run times in mechanism dynamics. I am driving my mechanism with a velocity servo motor at 1750 rpm. There are 15 bodies and about 15 connections. The dynamics analysis runs quickly when I drop the motor speed to 2880 deg/sec (480 rpm), but when I try to run at 960 rpm, the program runs fast at first, but then slows down to a crawl at about 55%, and finally stops. On the "Mechanism Settings" I have the "Graphical display during run" un-checked, I do have some parts in assemblies not fully constrained. These are round parts where I have not defined their rotation. Is that a problem? I am trying to make only 1 revolution, for the sake of the graphs, For instance, 1200 rpm would have a duration time of .05 seconds. I can live with the slower rpm's, but feel the real rpm would be more accurate.

Any suggestions would be appreciated.  Thanks

1 reply

C
ChrisKaswer16-Pearl
16-Pearl
March 6, 2019

You will need to define joints on all your parts (along with density/mass) AND you will need to make sure you constrain the motion of each body (lock them down if you don't need to consider them in the solution). If you leave it up to the solver to determine unconstrained bodies positions/velocities, etc., you'll chew-up compute time.

 

Hope this helps,

 

Chris

P
ptc-46314451-VisitorAuthor
1-Visitor
March 6, 2019

Thanks for the tips. What I can't understand is why the program runs great at low rpm's, but can't handle the high rpm's. If I had errors in my connections, etc.,wouldn't that show up at any rpm? Is the issue with the short duration time? When I attempt do reduce the frames, it automatically jumps to a higher number.

C
ChrisKaswer16-Pearl
16-Pearl
March 7, 2019

My guess is that it's because the solver has a more difficult time calculating where the unconstrained bodies want to move given higher accelerations - don't forget, this is what a dynamic analysis is trying to solve for - the movement of all the bodies in your model under whatever input conditions you've set-up. If you run the study at low speeds, it should have an easier time calculating positions, velocities and accels of all parts...even when they're not constrained. My first rule of thumb is always treat your set-ups as disciplined as possible, and you will never have an issue. This means assign mass, proper constraints and create joints formally (only between two bodies) to every part.

    Terms & ConditionsCookie settingsAccessibility statement