Knex review - Hudson

Looking back over my post from last week I agree with everything I wrote. Working with knex more made me realize how much more they need a larger variety of pieces at different angles. Some things are just not possible with knex and that makes no sense when you're trying to make a scale model of a bridge you want to build.

The knex also break in strange ways that the bridges can't actually break. Pieces of bridges won't just slip out of the joints, which is one major project with knex. A real bridge might not break in those places. Bridges made out of knex also flex together and apart which real bridges wouldn't do. Overall it's still a really good medium to work with your hands when you're modeling your bridge, like I said in my last post.

I think the difference between knex and designing a real bridge would be the ways the bridges break and how they can be constructed, along with the materials, like I said last week. The materials only come one way with knex, which makes it difficult to judge how weak you can get a certain beam before it breaks. Steal is also a lot less flexible than the plastic knex so they aren't entirely accurate when it comes to how the bridge behaves under stress, much like the WPBD software overexaggeration of how the bridge would bend.

Building a real bridge out of steel would be a lot more realistic, even if you were just making a scale model. You could weld the pieces together and do tests on them that would work better since you're making it out of the same materials that you're making the bridge out of, though you can't just snap the pieces apart if you do that. You have to be fairly certain of your design before you start to construct it, so it requires a lot more initial planning.

For this week I hope to see the ways in which our bridge breaks and improve on it from there. We can also get a base model for the strength vs cost ratio that our final design might follow.

For next week I want to improve on our bridge and make it stronger, while also understanding how knex interact with each other so we can try to fix how they go together. That might stop the beams from sliding out of the grooves or we could make the design better so that it isn't even a possibility that the beams slip out.

Knex Process - Lester

In my previous entry, I discussed the advantages and disadvantages of using K’nex pieces to build a bridge. The points I made still stand. It would be much more convenient if there was more variety to the pieces, with more sizes instead of only the ones provided. Yet despite this, K’nex allows artistic freedom that is not present in the West Point Bridge Designer. K’nex has the option to be asymmetrical or changing cross-section styles. However, there were some factors that I did not take into account. K’nex bridges can stay intact until many pounds of weight without the pieces separating. In the same way, it takes a lot of physical effort to disconnect certain support members. While building the model my hands got very sore and it was stressful to take apart. Also, during lab periods, many people were building bridges so certain crucial members ran out and were no longer available. These issues never arise when building with the WPBD: there are unlimited available supplies and taking the bridge apart is as easy as pressing “delete”.

WPBD is more related to designing a real bridge than making a K’nex model. Real bridges are designed with similar software that virtually tests designs for structural problems and can automatically calculate cost. When a real bridge goes up it must be perfect. There cannot be multiple weight-testing trials until breakage, like with K’nex models, because building real-scale models is extremely expensive not to mention time consuming to build.

This week we constructed the first physical K'nex model that we will test in Week 6 lab. Next week our group will further analyze our K’nex bridge. During week 6 we will load weight until the truss breaks then fill out spreadsheets with information on cost, triangle angles, and trigonometric values of the design. If any beneficial alternatives are found then the bridge will be updated accordingly. Beneficial alternatives include options of removing certain members to cut costs or adding more angles for better 

K'NEX Design vs. Real World Design- Durkin

After reading over my post from week five I agree with all the differences listed, I have not found any new differences since then. Last week during class we came up with new bridge designs built from K'NEX and we since have tested those designs.  At no point during this process did we discover new differences. There are many differences between the design of a real bridge and the bridge built out of K’NEX.  As with the difference between WPBD and real bridge design K’NEX also lack the range of joint options that a real bridge design would offer.  K’NEX do offer a wider range than WPBD but there are still not as many possibilities as there would be in the real world.  A K’NEX design also differs from a real world in the same way that K’NEX differs from WPBD in that WPBD and the real world both offer different options in thickness and material, K’NEX do not.  K’NEX also lack some lengths of members whereas in the real world and WPBD nearly any length is available.  K’NEX joints also tend to be somewhat fragile and snap under pressure; real world joints would not break as easily.  The cost calculations may also be somewhat off from real world prices, the costs assigned to the pieces also may not properly account for labor costs.

            This past week collaboration on a group bridge design began and new ideas were brought up that had not previously been considered. Next week this discussion will continue as well as hopefully testing one of the bridges that we built during the last class.  The bridge we built last class was very compact and hopefully very durable.  The cost of it was considerably low which suggests that if it is stable it will have a low cost to weight it can hold ratio. Next week we will test this bridge which will give us a better idea of how we need to adjust our bridge to make it more stable.