Max,
Attached is a model similar to what you posted a few days ago. This version does not use the "through curves" feature; it is pretty stable for reasonable size changes. The model was created in NX 9. I hope it gives you some ideas for your own model.
It's a bit of a grey area. Students who pop in and say something like: "What's the answer to this homework problem?" are sure to be red-flagged. Others may show up with a question such as: "I don't understand my professor's explanation of [some question], can you help me understand?" may get a great explanation or a red flag (depends on how trigger happy the eng-tips members are that day).
Max did identify himself as a student; however, I think he had a good question. He could model the linkage for a particular configuration, so if it were a pure "do my homework" type of problem, he would not have posted. Instead, he was essentially asking "How do I make this model more robust?". Personally, I see no problem with chipping in some ideas to a student who is taking the initiative to improve his modeling skill set.