Elevation mechanism mysteriously misaligned

massimo_asteriti

I designed a simple elevation mechanism for a drop-down metal basket that's supposed to fit squarely into a compartment of equal size. However, despite making sure all of my measurements are correct, something is somehow misaligned such that the basket itself is slightly askew despite every other component being perfectly in place. I can't imagine what could possibly be causing this and it's driving me insane. Here's the link to my project: https://cad.onshape.com/documents/476aaecb595d495f5f31dd85/w/d685f01f7d8cb82fb3f15524/e/0d1c3e21528d5da6171338ae

dirk_van_der_vaart

After insert of the bottom (misaligned) first fix the part and then insert the other parts with the mateconnectors

massimo_asteriti

dirk_van_der_vaart said:

After insert of the bottom (misaligned) first fix the part and then insert the other parts with the mateconnectors

I tried that, when I insert the part from the part studio into the assembly, it's perfectly aligned just like everything else; however, when I connect it all with the pin slot and revolute mates, then it suddenly becomes misaligned. 

ilya_baran

Use the measurement tools -- on your bottom part, the hole on the right is a slightly different distance from the top than the slot.  I think that's the issue.

massimo_asteriti

ilya_baran said:

Use the measurement tools -- on your bottom part, the hole on the right is a slightly different distance from the top than the slot.  I think that's the issue.

I just checked the sketch and both the slot and hole on the bottom part are exactly 0.25 m from the top, although the slot had a radius that was slightly off which I fixed. I double checked with the measurement tools, but the issue persists.

james_aguilar160

massimo_asteriti

james_aguilar160 said:

What measurements are the red numbers referring to here?

james_aguilar160

On further introspection, I see that I've not added anything to answer your question -- of course if the tops are misaligned the pins are going to be misaligned in the slots too. I wonder if what is happening is simple numerical error on the part of Onshape. With so many parts in sequence, maybe its solver begins accumulating error as it goes? Anyway, what I mean to say is I don't know. According to my inspection, there is already error even by the time you get to the end of the first arm pair of joints. I tried doing things like adding a parallel mate and that overdefines the assembly. Maybe someone else will have some better ideas.

wayne_sauder

@massimo_asteriti

 Study fully constraining your sketches. And maybe part design vs assembly. You should only be modeling one of every part.  

 Some of your circles are off by just a bit. I fixed a couple of issues; if done correctly, it all works out as parallel. I did not complete the whole assembly nor spend time ensuring no interferences.  

https://cad.onshape.com/documents/59c01a756ade521c414c340a/w/6bec8080af27b67a9c5e400a/e/e0d0305ada39d01a7f5bc337

massimo_asteriti

wayne_sauder said:

@massimo_asteriti

 Study fully constraining your sketches. And maybe part design vs assembly. You should only be modeling one of every part.  

 Some of your circles are off by just a bit. I fixed a couple of issues; if done correctly, it all works out as parallel. I did not complete the whole assembly nor spend time ensuring no interferences.  

https://cad.onshape.com/documents/59c01a756ade521c414c340a/w/6bec8080af27b67a9c5e400a/e/e0d0305ada39d01a7f5bc337

Thank you so much! I will look into fully constraining sketches for sure; just out of curiosity, what exactly was off about my circles? I was quite confident I had dimensioned all of them properly, but I guess not. 

wayne_sauder

 I didn't spend much time figuring out all the issues, but if I remember right, you had your midpoint pivot on the part 2 constrained midpoint on a line that went from the center of the bottom circle to the edge of the top circle. The one on part 1 is driven by a dimension. I think this is the issue, but I'm not sure without digging through it a lot more.