The ground moves in mechanism design

[SW]

I am trying to model a mechanism consisting of a gimbal
attached to a potentiometer slide, like that shown in the image below. Even
though the base plate (shown in blue) is the ground, when I drag or run an
analysis of the mechanism, the ground part moves. If I just try and move the
slide it works fine, but trying to drag or run an analysis of any other feature
makes the ground part move and the whole thing jumps about in an unpredictable
way.


View attachment 566








The same thing has happened before and I got round it by reassembling
the whole mechanism, but I can

 

[SW]

My mechanism went balls-up again, so I re-defined it and again it works
fine. Has anyone had similar problems, or am I ignoring a requirement
in the modelling of mechanisms?

 

[SW]

Its done it again. I re-defined the mechnism to consist of two
sub-assemblies and it has been working fine for the last few weeks.
I've just re-booted the computer, opened the assembly and now its all
on the piss when I try drag it. What is going on?

 

[infinidof]

Hi Sam.


What constraint(s) are you using when assembling the base plate? Is the base plate the first component in the TLA? I haven't come accross this problem, but it looks as though there is a constraint between the slider and the base plate. Perhaps creating a sub-assy with the base plate and the slotted block, and another sub-assy with the gimble and slider, then a TLA with those two sub-assy's using sub-assy level datum features for mechainsm constraints. In addition to this, perhaps constraining the slider to the slot block instead of to the base plate, using sub-assy level datum features, will improve stability.(same method we've been discussing for the potentiometer.) Also, snapshots canhelp to retrieve initial states from one day to the next with a shutdown in between. i.e.assemble the mechanism, go into mechanism application, click drag, take a snapshot without dragging anything, close drag window, go into standard application and then save. (i'm being verbose only for clarity of my reasoning). A planar orient constraint in the "Place" tab when assembling, then changing to "Connect" tabcan also help (it's a mystery to me as to why, but the orient seems to stick in the background even after it has been replaced/superseeded with "Connect" constraints).


Anyway, I hope this helps.


Cheers.

 

[xcad]

it is difficult, especially for a mechanism, to give a solution without the real part indeed...


is it able to send me the assembly to study it for you ?

 

[tinag]

Hi,


i also have this problem when trying to render the animation of a moving mechanism.. The grounded part always seems to move aswell as the other parts.. Is there something i am doing wrong ?

 

[xcad]

OOOppssss...


Mr Tinag good question in a wrong topic...


This is a bug...


wait until i have more info

 

[infinidof]

Hi Sam,


How goes the progress? As with xcad, if you'd like to send a model, I'd like to have a crack at it.


Cheers.

 

[xcad]

here i am, direct from PTC :


) Mechanism Design and Design Animation capture and encode animation files using MPEG-1, an internationally standardized means of compressing a series of digital image frames into an efficient video format. This standard approximates the perceptual quality of consumer video tape (VHS) and meets the quality, bit rate, and file size requirements needed for mainstream engineering design communication. The MPEG-1 standard is optimized for encoded image sizes of 352x288 (pixels) at 24-30 frames per second (fps). Software decoders, such as Windows Media Player, are tuned for these settings and may skip frames or adjust the displayed frame rate in order to accommodate an acceptable data transfer rate. Although it is possible to capture images of a larger size for improved resolution and detail by increasing the playback capture width and height, larger images will require higher data transfer rates. This can have an adverse effect on the quality and smoothness of your animation, depending on the sophistication of the media player used and the graphical performance of the hardware in use.

2) The real-time duration of an MPEG captured using Mechanism or Animation is dependent on the number of captured frames. Mechanism Design and Design Animation capture MPEG files with a fixed 24 fps setting. To create an animation file that plays in real-time for a desired duration of seconds, make sure that you capture an appropriate number of frames in your animation or analysis definition. For example, you would capture (2sec) x (24 fps)=48 frames to create an animation that plays for 2 seconds. Pro/ENGINEER Wildfire contains additional options to create MPEG files with frame rates of 25 fps, 30,fps, and 50 fps if desired.

3) There is a direct relationship between the aspect ratio interpreted from the specified image size height and width for captured MPEG files and the aspect ratio of the model window (excluding the model tree, message areas, and toolbars). It is imperative that you specify a capture aspect ratio equivalent to the aspect ratio of the model window. For example, if the model window is square, then a square aspect ratio (e.g. 300x300, 400x400, or 500x500 will create an MPEG of good quality. If the model window is rectangular, then you may need may need to approximate or measure the model window obtain an appropriate capture aspect ratio. In Pro/ENGINEER releases 2000i through 2001, the primary cause of distorted animation is a result of inappropriately specified height and width values. In Pro/ENGINEER Wildfire height and width values are automatically adjusted to avoid distortion due to aspect ratio mismatch.

4) Whenever possible, use a uniform background color for the model window when capturing animation to MPEG. Encoding a stream of images into a compact animation file requires optimization of graphical color and detail. Minimizing background color variation can help minimize any unnecessary distortion or blurring.

5) Avoid overlapping the Pro/ENGINEER model window with windows or dialogs from other applications, and disable monitor power save standby or screensavers while an MPEG is captured. Image data is captured from the model window and compressed into MPEG format. Any disruption to the model window display can have an adverse effect on the animation quality.

 

[xcad]

about this topic.... (moving round)


i think this is a bug..


with a tan id: 124456


reported in code 2001, datecode 2003120


and solved in wf2, datecode 2003400


which version are u working at?
Edited by: xcad

 

[tinag]

I am using 2001 date code 2004010. and unfortunatly we are not upgrading.


But thanks for the info


Ms Tinag.

 

[SW]

Thanks very much, it seems to be the bug that was causing the problems.
Re-setting the view to defualt as suggested by the TAN solves sorts the
mechanism out - although I should probably install the latest
datecode...