Create parameter based on measured variable distance

[schnautza]

I've got a situation where I have a chain going over a pulley which causes the parts at both ends of the chain to move in different planes (90 degrees different) with the same distance in translation. Is there a way to set a parameter that the distance through the chain (not modeled) can be constant? This would be a vertical dimension, 1/4 of the pulley circumference, and then the horizontal dimension. I thought that the easiest thing to do would be to set up a parameter that could measure the current position of one end and then I could use a constraint to have the full length of the chain minus the parameter...but this doesn't appear to be possible. Any suggestions? I want to be able to drag the horizontal piece and have the vertical component move with it the same distance, different direction.

[wimann]

What you're talking about is quite possible. However the idea of being able to "drag" one end of the chain freely and have the other react does complicate it a bit. You'd probably want to sketch out the chain path and use a pattern to determine your total length of chain around the curve. That's probably the easiest way.

I've attached a simple example of how this could work. Please feel free to open and dig through it and let me know if you have any questions about how I approached the issue. I kind of did it in a hurry so I hope that it's not too confusing.

Hope this helps.

NOTE: You'll find in mine that instead of being able to click and drag the first link, you'll have to edit an offset dimension in the sketch path. This will, however, move all the links along the path and maintain the full length (Number of Links x Link Length). If you want to be able to pull the link and have the pattern follow, you'd need to project a point from the first link into the path part so that it becomes adaptive. I've attached a couple of word documents I made some time ago to help my co-workers through the same process.

Sorry this explaination isn't more thorough.

[johnsonshiue]

Without seeing the actual model, it is very hard to comment on specifics. Is it possible you can create a sketch on the plane of motion and then project geometry and create a driven dimension? In this way, the driven dimension will be captured as a parameter.

Thanks!

[schnautza]

I would attach images for you to look at, but I cannot get this website to load properly on my work PC... don't know if the firewall settings are screwed up or what, but I have no text formatting options or image/file attachment options. And every new paragraph gets crammed together with the previous one. Very frustrating. Anyhow, the solutions provided have not worked for me. I don't know if it is because of the assembly hierarchies in my model or what. I will do my best to explain in words, bear with me. I have a fixed set of rails in an assembly. On those rails, I have a sort of a cart that moves back and forth, controlled by an actuator. This cart is also an assembly. There is a place on the cart that a chain will mount to. There is a pulley on the rail assembly where the chain takes a downward turn. Suspended from this chain is another assembly...so when the cart moves away from the pulley, the suspended assembly will raise (1:1 ratio). When the cart moves towards the pulley, the suspended assembly lowers. I have attempted to build a separate part that is adaptive with a sketch and parameters like you have suggested, but if I project anything from the other assemblies, then everything that should be able to move becomes fixed, despite the adaptivity of both the part and the sketch. If it is easier, I can email some images or maybe the assembly.

[johnsonshiue]

Hi! I did have similar problem uploading files using Internet Explorer a while back but it seemed machine dependent. I am able to upload files to the forum without an issue using Firefox.

Regarding your dataset, please feel free send them to me (johnson.shiue@autodesk.com). I would like to take a look and understand the requirement better.

Thanks!