Unexpected jamming an offset assembly

[John MunroeParticipant @johnmunroe13164]

Hi all,

I have a small assembly with a disc (clear) spinning on its own axis and turning a rod (pink) that is connected to a L-bracket. There is a fixed outer ring (clear-blue) that limits the L-bracket and a fixed oval slot (blue) for letting the shaft of the L-bracket (yellow) slide up and down. The L-bracket presses on a block (green) whose axis is vertically offset. My issue is that the mechanism is jammed at the current position prohibiting further anti-clockwise turning of the clear disc. Here's a video:

Clearly, the black wheel is being pushed against the outer ring, but shouldn't the yellow shaft be consequentially pushed upward shortening the distance between the yellow shaft and the pink rod? By pushing the L-bracket down, shouldn't the other side be lifted up (and thus, pushing up the yellow shaft)?

I was expecting some kind of see-saw effect, circumventing the jam. I wonder if there's a way to modify it?

Any help appreciated.

 

Thanks

John

 

 

Edited By John Munroe on 11/03/2016 16:31:24

Edited By John Munroe on 11/03/2016 16:47:34

[John MunroeParticipant @johnmunroe13164]

[Mark CParticipant @markc]

John, at first glance it looks like the mate relations might need addressing? Are you using advanced mates (cam etc)?

Mark

[John MunroeParticipant @johnmunroe13164]

Hi Mark,

Do you mean the mate relation between the yellow shaft and the blue oval slot? It's a Slot mechanical relation there.

Thanks

John

[Mark CParticipant @markc]

John, it is hard to see in the video but the way it stops and the relative movement make it look as if the mates are getting into position that is indeterminate for the software. I assume you have tried moving it by pushing other bits of the mechanism after it locks up?

The normal problem is mates wanting to "flip" over in this type of arrangement. You might have better luck creating a plane or other reference geometry to mate. You can always hide it so it is not on show if it is a demonstration for something.

Mark

[John MunroeParticipant @johnmunroe13164]

Hi Mark,

I've now uploaded a clearer version. I've tried nudging the yellow shaft and all, but nothing budges (beside moving back in the clockwise direction). I'm trying to get it to move further anti-clockwise.

Is your suggestion that a slot mate shouldn't be used but use a parallel mate with a plane instead?

Thanks

John

[Mark CParticipant @markc]

John, I looked at it again and the problem looks to be the green box at the back. It looks like you have the grey spigot concentric with the half circular top section of the outer housing – the grey spigot is clearly concentric to something or is on an intersection etc. I think if you suppress the green thing or its concentric mate the assembly will then work. You could also reduce the width of the green thing or increase the clearance some other way and that should allow it to turn over.

Mark

[MWParticipant @mw27036]

The trouble is if you don't know then why should we know any better? If theres a jam then something in your mechanism is either too big, or your housings too small.

Michael W

[Mark CParticipant @markc]

Michael,

I am trying to read that as constructive but it certainly does not come over as such.

John is simply asking a question, if he knew the answer, he probably would not have asked. As a reasonably competent user I don't mind taking a guess at the problem for him and perhaps he might find my replies of some use. Understanding assemblies in Solidworks (or any other 3D cad) can often be challenging when it does not behave as expected.

Mark

[Jeff DaymanParticipant @jeffdayman43397]

I think the green block may be jamming it, you could try suppressing the green block and try and rotate again. Is the black roller supposed to follow the arc shape in the purple part? doesn't seem to be, if so. JD

[Ed DuffnerParticipant @edduffner79357]

Just my beginner input, after watching the video a few times.

The pink crank pin is moving sideways and downwards in an arc. As the orange L bracket makes contact with the green block it slides the L bracket toward the fixed outer ring where the black wheel then makes contact. The pink crank pin is still trying to move in two directions, but the black wheel is by then pressing against the fixed outer ring.

I think if you were to lower your pink crank pin in the clear disk so that's it's past the arc of the black wheel as the black wheel makes contact, then the crank pin is only travelling in the downwards and opposite sideways direction.

You might need to add a dog leg into your pink crank pin so that the point where it enters the clear disk is further on around it's arc.

Hope I made sense there.

Ed.

PS. I just thought, how about a spring loaded black wheel to allow for the compound arc?

PPS. Another way of putting it. The black wheel needs more room to travel sideways until the point where the orange angle bracket is horizontal and the black wheel can then move away from it's maximum sideways travel.

Edited By Ed Duffner on 11/03/2016 23:17:07

Edited By Ed Duffner on 11/03/2016 23:31:50

[John MunroeParticipant @johnmunroe13164]

I've now simplified the simulation to just this:

Basically, it's just a wheel with a pin turning a bracket that slides over a block on an offset axis. The wheel turns on its own axis.

Strangely, the wheel still gets stuck even when the bracket can freely slide along the block and its lateral position w.r.t. to the block is not constrained. Here's a video:

Essentially, the problem is that, at the current position where the red rod hits the end of the slot in the bracket, the wheel can no longer turn anti-clockwise. I find it counter-intuitive because the bracket should be able to slide along the block. If the bracket is manually shifted such that the rod no longer hits the end of the slot, the wheel turns.

Does anyone know why this is happening?

Any thought appreciated.

 

John

 

Edited By John Munroe on 21/03/2016 06:45:42

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