WPBD vs. K'nex

                West Point Bridge Design is a great program to help you get started when first designing bridges.  However, I feel that it is very different from using K’nex pieces to build a ‘real’ bridge.  Both WPBD and using K’nex help you to be creative, learn what works and what doesn’t and you can experiment with different sized trusses on either apparatus.

                Although West Point Bridge Design teaches you the fundamentals of bridge designing, it is a relatively easy process that involves ‘connecting the dots’.  When using K’nex, you cannot simply ‘connect the dots’.  You actually have to measure the lengths and angles of each piece you want to use and try to fit them together.  A design may work out perfectly on West Point, but it may not be possible to build using K’nex pieces.  Your design will have to be flexible to meet the restrictions of the piece lengths, widths, and angles of the ‘gusset plates’.  In West Point, you can have long rods of material that crisscross each other, but when using K’nex, you need to use smaller pieces and put a gusset plate in the middle of the intersection.  In other words, West Point is not a completely realistic design experience that conveys accurate products and results. 

                West Point Bride Design allows you to fairly easy erase something and add something somewhere else.  When using K’nex, you have to break things apart and put them back together to make your design perfect.  Another difference about the two ways to create bridges is that the weight that a bridge can hold is going to be significantly different.  K’nex pieces do not relate to real life loads and are a scaled down version.  Also, the costs of the bridges are different because each K’nex piece has a set cost and you can easily predict the cost of the bridge you are building.  West Point has so many different sizes and materials that just don’t relate to using K’nex pieces.  Overall, using K’nex pieces will be a very different experience than designing a bridge on West Point Bridge Design.
                Last week in Engineering Lab we learned a lot about how to construct research for our bridges.  Our guess speaker was very informative and helpful to the research process.  We also got to experience what it was like playing with K'nex.  We were able to use the class to experiment with the pieces and see what works best. For next week we have to design a bridge and draw a blue print of it.  We will then collaborate our designs and choose which one our team likes best.  In class we will start building our bridge.  I hope to  design a cost efficient bridge that holds a lot of weight.  I also hope that my teammates have some good ideas that we can all combine to make a really efficient bridge.

WPBD vs. Knex

To begin with, both systems for the bridge design are effective in their purpose, which is to get an idea of the different aspects that should apply into analysis when trying to design a bridge; especially one that satisfies the given guidelines and evolves under certain priorities.  However, yes both approaches are effective, but each in different ways assigning each other advantages and disadvantages for the creation of this model.

For example with the WPBD program each student is given a great amount of information about their own design that the student might not even have thought of him/herself when they were trying to come up with that design.  This could include factors such as size, material, overall cost, durability and reliability.

On the other hand, with Knex, the student gains an understanding for designing bridges, but through a more physical/experimental approach that might even facilitate the concept and illuminate the student on the several aspects to have in mind as well while they create their model of a bridge.  In this case, it will most probably involve the angles and their resistance depending on the shape and geometrical characteristics of a given design.  It seems as though in engineering, being able to see, and use our senses as we create a model is key to understanding the science behind it, and this could apply to all levels of difficulty to a given design or creation.

-  Ana M. Franco

WPBD vs. Knex

Last week, our class learned about the apparatus that is going to be used to test our bridges. I took note that the Knex bridge design we test needs to have a flat surface on the top of it in order for the apparatus to sit evenly across the bridge. Mr. Jay Bhatt came in to speak to the class and showed us some very useful resources that I will use to learn more about bridges as my group and I continue to improve our designs. Towards the end of the class period, my group mates and I discussed ways to use the Knex to design a bridge that would be strong when compared to its cost. We all decided that the best thing for the group would be for each of us to design Knex bridges separately and compare our design results. This week we will talk about the ideas we had behind our bridge designs and, out of the three of our design, which one we think will be the best.

As we transition from using West Point Bridge Designer on the computer to actually building our designs using Knex, there are going to be a number of differences. Primarily, I must point out that WPBD had a set number of connections for the road surface of the bridge. Not being able to move these connections or change the number of them affected the designs of the bridges. Additionally, WPBD allowed chords of any length to be created, their materials to be changed, and their diameters to be altered. Using Knex, we will be limited in the sizes which will affect the strength of the bridge, the shape of the bridge, and the size of the bridge. Only certain triangular patters will be able to be created. Because the longer pieces are more slender, it will be very important to leave them out of the design. The more slender a member, the weaker it may become as weight is added to the bridge.

- Melissa Wetzel

A2 - WETZEL

The goal of my design was to have a low cost and high strength. Never having designed or tested model bridges before beginning this class, my best idea was to use shorter chords as members of the bridge. Although joints each cost at least $1,000, I decided that their use in between short chords would help make the bridge stronger and tighter once weight was added. By tighter, I mean that I am imagining as weight is added to the bridge's load, the chords will push into the joints and the displacement of the joints will be towards the center of the bridge. As the members move towards the center like so, the stronger, shorter chords will lean into the joints, tightening the joint sections.

Elevation and Plan for the Knex bridge design.

I made sure that the web of the truss was composed entirely of triangles--most of which, in my case, happen to be right triangles. I am hoping that these hold up as well as equilateral triangles may have. My prediction is that if the right angle of one triangle does not have support backing it, it will give out before other parts of the bridge. This is something that I will pay close attention to so I know what the best angles are to use as the groups approach the drafting of their final designs. Something I purposely did not do was make the plan of the bridge out of triangles. I figured that the weight-bearing members all ran vertically, so I did not want to add dead weight to the bridge or raise its cost by webbing its ceiling.

The Truss Bill of Materials

I did my best to keep my design simple so that there would be no useless chords or joints in the price, but I am not yet sure that each chord that I've left will make the bridge strong enough. I was both surprised and glad to see that the total cost of my first Knex bridge design was below $200,000--a price I'd been trying to get my bridge down to in West Point Bridge Design.

A2-O'CALLAGHAN

When designing this bridge, I knew I wanted to have the truss structure on top, as opposed to underneath the bridge.  I also knew that I wanted it to be somewhat of an arc shape.  Through research, I found that this was most effective and could hold the most weight. 

 

Bill of Materials - Knex Pieces
Part Number	Description	Unit Cost ($)	Nr. of Parts	Cost ($)
1	1.25" long chord	$500	52	$26,000
2	1.125" long chord	$1,000	52	$52,000
3	3.375" long chord	$1,500	32	$48,000
4	5" long chord	$2,000	0	$0
5	7.5" long chord	$3,000	0	$0
6	chord splice	$1,000	0	$0
7	45 degree gusset plate	$1,000	0	$0
8	90 degree gusset plate	$1,000	0	$0
9	135 degree gusset plate	$1,000	12	$12,000
10	180 degree gusset plate	$1,000	28	$28,000
11	180 degree grooved gusset plate	$2,000	0	$0
12	360 degree gusset plate	$1,000	18	$18,000
13	360 degree grooved gusset plate	$2,000	0	$0
		Total Cost		$184,000

Upon creating this bridge on a scrap piece of paper, I changed a few things about it.  At first, I was going to make the arc come to a taller position, but to cut down on cost I didn’t want to have to use any long K’nex chords.  I also knew that it had to be at least eight inches flat on top and this was interfering with my design a little bit.  However, I opted to have a ‘flat’ arc instead of one that came up to two points at the top like my original plan.  Otherwise, my design was pretty much how I envisioned it.  

This bridge gave me an idea of what it is going to be like working with K’nex kits.  I had grown used to using West Point Bridge Design and it’s just not the same when you have to translate it to real pieces.  When using K’nex I had to think about what types of gusset plates were going to work best and the angles I was able to use.  I also had to think about the length of each chord piece and if I wanted long ones or many short ones.  I hope that when we get to start building our bridges in class my design works well and everything fits together.  It is quite hard to imagine a bridge that will work when you can’t play around with the pieces since they are not in front of you.