Compound lever mates

nolan_krisher

Hey guys,
 I cannot figure out what I’m missing-this compound lever won’t move, no matter what combination of mates I’ve tried. Please help!

https://cad.onshape.com/documents/5b35d934acc2dd898d6b2875/w/ef9a72600071b952f0121a52/e/26ea46bc371cfc77b960e051 

owen_sparks

Hi @nolan_krisher

Sorry about the link, I'll look at that in a minute.

As for the model, it's acting exactly as the real parts would in that situation, that is to say locked solid.

If we want it to move then we need a way to allow that centre pivot point to operate.

This is one method to achieve that.

You'll see I've:-
(a) Added a slot in place of the hole
(b) Used a tangent mate in the assy to control the movement of the pin in the slot
(c) Set some realistic limits for the left hand pivot.


We can now manipulate the handles and have the assy behave as we wish.

https://cad.onshape.com/documents/2e940bd95636ed4298b7c9ad/w/92fe59991cba4b3dbc41464f/e/c4bb8c269a318765d794a326

Make sense?

BTW are you a designer / hobbyist / student that I just did their assignment for?  Am I about to get shouted at by @brian_brady ?

Cheers,

Owen S.

owen_sparks

Hmm.  A few things going on here.

(1) You have a slider mate where you need a revolute.

(2) I think your pin location in the grey parts is off.  You can mate everything else and it works fine but this last mate breaks it as the holes don't quite line up.

Also a couple of observations if I may?

(a) You've made this waaaaaaaaay harder than it needs to be by modeling all the parts in separate part studios.  Onshape excels at designing multiple parts together in one studio.  You'd have all the parts fitting together in a tenth of the time, and any errors are much easier to find.

(b) Much easier to communicate if you name your parts.  You have multiple "Part1's" and saying "the blue one, no not that one the other blue one" isn't too precise.

Hope that helps,

Owen S.

nolan_krisher

Hey Owen,
 Thanks for responding. This is only my second model, and my first multipart assembly, so there’s a lot of things that took more time and effort than necessary.  Thanks for the suggestions.

1) there are no slider mates used in this sketch, so I’m not sure if you meant the cylindrical one? If I use revolutes for all 3 pivot points, it gives me the error of “mate overdefines the assembly”.

2) I thought that might be the case, also. I have tweaked dimensions until they measure exactly the same from Center to Center, and while the position of the handles moved to parallel, it still remains immobile. Maybe it’s still not exact enough? I’ve been using the measurement function in the assembly view-is that the most accurate way?

owen_sparks

Hi @nolan_krisher

If that's your 2nd model then you're doing really well, nice!

Re 1) Yeah, sorry after I'd changed your mate in my copy  I think I'd not remembered what it was.  Either way you need revolutes for all of them. 

With regards to the "mate overdefines the assembly" error imagine two parts, one with a pair of holes 1 inch apart, the other with 2 holes 2 inches apart.  Now you could mate the part together on either of the holes one at a time, but not both at once.  I believe that is what's going on with your assy, the holes don't line up.  To see what I mean zoom in on the hole through the 2 grey parts.

I modified your drawing and deleted the holes through the jaws and then put in a new location that lines up. (Part Studio Owen S), and then made a new assy (Assemble Owen S) with new revolute mates. 

**Edit - Links broken and model has changed anyway so link deleted - OS

However you'll see that although the mates do not conflict they do not allow movement.

If you go back the the studio you'll see a sketch with two circles centered around the 2 outboard pivots.  These represent the path of the centre pivot point if the handle or jaw are moved..  I believe this shows that the pivot points will only line up in the closed position.  Opening the handles is not possible as it's trying to rip itself apart.  That centre pivot can't follow both circles at once.




Does that make sense?

Owen S.

nolan_krisher

Hi Owen,
 Interesting. So, there is no way to create a movable model with a compound lever? I can’t open the link in your reply, for some reason. It’s says server not found. Maybe it’s because I’m on the iPad app version?

owen_sparks

Hi @nolan_krisher

Sorry about the link, I'll look at that in a minute.

As for the model, it's acting exactly as the real parts would in that situation, that is to say locked solid.

If we want it to move then we need a way to allow that centre pivot point to operate.

This is one method to achieve that.

You'll see I've:-
(a) Added a slot in place of the hole
(b) Used a tangent mate in the assy to control the movement of the pin in the slot
(c) Set some realistic limits for the left hand pivot.


We can now manipulate the handles and have the assy behave as we wish.

https://cad.onshape.com/documents/2e940bd95636ed4298b7c9ad/w/92fe59991cba4b3dbc41464f/e/c4bb8c269a318765d794a326

Make sense?

BTW are you a designer / hobbyist / student that I just did their assignment for?  Am I about to get shouted at by @brian_brady ?

Cheers,

Owen S.

nolan_krisher

Hey Owen,
 Now it makes sense! I see what you were trying to explain all along.   Thank you so much! And you shouldn’t be getting yelled at-I’m none of the above mentioned. Just a lowly tinkerer trying to make something unique in my shop, and not wanting to waste a bunch of metal with trial and error. Little details like this are exactly why I wanted to build a digital model first-it seems logical now, but didn’t occur to me before.

brian_brady

owen_sparks said:

BTW are you a designer / hobbyist / student that I just did their assignment for?  Am I about to get shouted at by @brian_brady ?

Not one of my students. They know I am on the forum often enough to catch them.

owen_sparks

nolan_krisher said:

Hey Owen,
 Now it makes sense! I see what you were trying to explain all along.   Thank you so much! And you shouldn’t be getting yelled at-I’m none of the above mentioned. Just a lowly tinkerer trying to make something unique in my shop, and not wanting to waste a bunch of metal with trial and error. Little details like this are exactly why I wanted to build a digital model first-it seems logical now, but didn’t occur to me before.

Hi Nolan.

You're welcome, it was an interesting exercise.  BTW there is nothing "lowly" about tinkerers, without them we'd not have the aeroplane, the jet engine, the light-bulb...  The world need more tinkerers.

Happy CADing,

Owen S

owen_sparks

brian_brady said:

owen_sparks said:

BTW are you a designer / hobbyist / student that I just did their assignment for?  Am I about to get shouted at by @brian_brady ?

Not one of my students. They know I am on the forum often enough to catch them.

Hi Brian.

I'm going to be serious for a minute.  When I was at school I was very bad at asking for help.  (High pressure environment / much "parrot fashion" learning / needing help perceived to be sign of weakness / socially awkward nerd etc.)

Skip a few years ahead into the working world and a good foundation from school is great but only 50% of the story.  The ability to problem solve, identify what you don't know, know where to find out new information and quickly formulate a plan makes up the other 50%.

I wonder if finding forums and constructing clear courteous requests for help / collaboration is just as valuable an exercise as learning how the CAD features work?  I'd be tempted to throw in an extra credit question that requires a visit here...

Just a thought.

Owen S.

brian_brady

@owen_sparks I encourage my students to find help; whether from me or the forums or elsewhere. In fact, I told them that there were a lot of people like you who could answer questions for them on the forums. They just know I am watching, so they won't try to get somebody else to do their work, just assist and point the right direction.

I do like the extra credit idea. Maybe have them tag me when they ask a question. One extra credit question per semester. I already offer extra credit if they export and 3D print a simple collaborative keychain assignment.