Identical Hydraulic Cylinders Overdefining Assy (part 2)

[drillrig]

Hello esteemed colleagues,

This question is a follow up to thread559-150787.

As recommended in that thread, I deleted the limit distance mate in my hydraulic cylinder assy. There are two instances of this cylinder in my top level assy. The barrel ends are connected to a common weldment so that they can rotate (i.e. a "pin connection"). The rod ends are also "pin connected" to another common weldment that itself is also free to rotate. My assy is analagous to the shovel of a front end loader.

Here's my problem:

I have each hydraulic cylinder set to flexible in my top level assy. I can click and drag and the motion is fine (albeit that the piston can just fly through the barrel due to the lack of a limit distance mate). However, as I work on other parts of the top level assy and do rebuilds from time to time, I notice that the hydraulic cylinders seem to "flip around" sometimes. It seems there are two "solutions" to the cylinder's orientation: one with the rod inside the barrel as it should be and another with them completely separated and opposed to each other. I can't seem to figure out how to keep it at the correct "solution".

I've tried several different things to try and get this figured out but to no avail. Any thoughts?

Thanks in advance.

- Chris

 

[josephv]

Hi Chris,

Try using two (2) different configurations for each cylinder.

Technically speaking SolidWorks should not require different configs for this to work, but it is worth a try.

Cheers,

Joseph

 

[drillrig]

Joseph,

Here's what I've tried so far to no avail:

A) Two configurations with identical mates (no limit distance mate).
B) Two configurations, one with limit distance mate and one without.

It seems the cylinders "flip around" when I drag and move a completely different component in the same top level assy, and/or during a random rebuild.

- Chris

 

[JMirisola]

Chris,
I used to have almost the exact same problem a couple of years ago. It's been a while but, if I recall correctly, you should be able to have one in there fixed while you're doing work elsewhere.
Another thought: I'm guessing that you have a concentric mate between the shaft and the barrel and some sort of parallel mate for the barrel ends to keep them aligned. You may want to try adding a parallel mate between a plane from each. This may lock it down enough to allow for movement within its "normal" stroke.

Jeff Mirisola, CSWP
CAD Administrator
SW '07 SP2.0, Dell M90, Intel 2 Duo Core, 2GB RAM, nVidia 2500M

http://designsmarter.typepad.com/jeffs_blog

 

[SolidAir]

What version of SolidWorks are you using?

 

[gatz]

I'm kinda new to SW, but have a few thoughts about this.

Sounds like the rod and cylinder are not fully mated except, of course, for the linear relationship that you want to see as movement.
What is keeping the cylinder and rod in mate?
If not already done, can you mate the axis of the rod and cylinder (of each instance, or do it in the suba'y) to keep them from flippin away from each other? What about their respective Top/Rt planes? (Or Front/Top)
If these are mated, you should be able to apply the limit mate(s).

I've noticed that when parts are not fully mated in an assembly (on purpose--so that one can see the part move such as what you have described) and you use the "Rotate" feature to grab a part corner for instance to rotate, some of the parts go nuts and go all over the place but within the planes where mates don't exist.

Usually, I tie the parts down by mating so that the part is fully defined, then Suppress the mate relative to the movement I'd like to see. This mate I establish last, or if already in place, move it to the last postion in the Mates list so that it is easily seen.
When I want to return to the initial condition, I Unsuppress that mate to bring everything back to starting postion.
One assembly containing numerous parts that were inter-related in their movement was quite a challenge to get "nailed down"
It was crucial as to how the parts were mated and in what order in the FT. This was also an issue when making a Rotary Simulation which included a Gear Mate.

Also in SW2006 as I understand it, if you've Mirrored a part, the new part needs to have mates applied to it, they're not automatic. Not sure if 2007 is the same in this respect.

Gatz

 

[drillrig]

Jeff:

I will try what you suggested.

SolidAir:

I am on SW07x64 SP1.1. I was using SW06 32bit and saw the same problem so I don't think it's a 64 bit issue.

Gatz:

I have a concentric mate between the rod and barrel, and a parallel mate between the rod clevis and the barrel clevis. This gives me the movement I want (albeit that the piston can fly through the barrel body, as I said before). I haven't mated any axes or planes yet because I didn't think I needed to, but I will give that a try. I don't see how that will keep them from flipping away from each other, however.
I don't want to go anywhere near using a limit mate in the hydraulic cylinder assy, because once I do that and rebuild the top level assy I get red and green errors all over the place saying that the assy is overconstrained etc. When I delete the limit mate all the errors go away.

- Chris

Chris Cheeseman, Mechanical Engineer
SW07x64 SP1.1
Dell 490, Xeon Dual Core, 8GB ram
Nvidia Quadro FX3500