Help creating a simulation

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- cad232
  
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posted
20 years ago

Wed, Oct 22, 2003 4:50 PM

I am new to Solidworks, and am currently trying out the 2003 learning edition. I am attempt to try out a design for a pneumaticly operated motion base (like flight a simulator). Since the design is already created in AutoCAD, I am really just trying to see if I can try out the motions in Solidworks, and double check our control system because there are redundant forces which will try to tear the frame apart if the 4th actuator is not the correct length.

The geometry of the part that moves is a rectangle 8' x 10'. There are 4 actuators, each with 20" of stroke, one on each corner. They simply push up on the frame which is free to move. That moving frame is prevented from falling over by an outside rail. I've tried a few approaches, but am running into difficulties. My first attempt was to just create a new part, then;

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- Philippe Guglielmetti
  
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posted
20 years ago

Thu, Oct 23, 2003 5:58 AM

I studied such structures in deep some years ago. Check

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for a SW model of the fastest robot in the world based on such a "parallel" structure. From what I understood, your structure is hyperstatic ("3 of the actuators will be given dimensions, the 4th is determined by the other 3"), which will lead to an overconstrained design if you don't care. The important thing is, SW assembly mates solver operates on parts that are "rigid", or fully determined. You can't expect a "driven dimension" in a part to be driven by the assembly. I can see 2 ways of solving your problem:

1) remove the "Line" from the 4th actuator, and replace it by a driven dimension between its 2 ends in assembly 2) model your actuators as an assembly where the piston can slide in the cylinder, then drive your model with the 3 "distance" mates. e-mail me your model if you need more help.

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- J.
  
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posted
20 years ago

Fri, Oct 24, 2003 1:27 PM

Yes, I was aware of that issue, and did take your approach (i.e. only creating 3 actuators in Solidworks). My difficulty was just in creating that geometry. My first effort to just do it using sketches didn't work, either because of me being new to Solidworks, or because that process is not workable. However, I did succeed by actually creating solid parts and then each actuator had a design table, so that I could choose the different lengths at my assembly.

In fact, my entire purpose was to do a reality check of our control algorithm. I would enter the lengths of 3 of the actuators, and see if the resulting distance for the 4th actuator agreed with what our control system would do.

I think it would have been possible to create a spreadsheet at the assembly where I could have typed in the various possible positions, and got the results there. However, I couldn't figure out how to do it. I ended up manually editing each actuator and assigning its length.

As for the results; our simple control algorithm assumed each actuator stayed perfectly vertical, which was incorrect... but I wanted to determine if it was good enough. We are creating a Boat to be used in a theatrical production. Our actuators are pneumatic and have more than enough compliance to accept the positioning error I measured in Solidworks.

Joe Dunfee