Deliverable: Working Prototype
Today we started class by showing our prototype to Amy and getting ready to test it out on real live bikes! Then we found out that our bottom posts broke off and spent the majority of class trying to epoxy them back on. Twice. We were actually holding two pieces of metal together, praying for the epoxy to bond, right up until the end of class:
Pictured: human clamps.
Epoxy:
Last time we worked in the lab we tried to use epoxy to connect the parts that we couldn't bolt. The epoxy comes in little packets with two separated gels, and you mix the gels together to get a really firm bond. I tried using epoxy to glue two little pieces of angle iron to make the chainstay (the brackets have a name, we've learned) supports, but after three hours the epoxy still wasn't dried. We then tried using Superglue and hot glue, and nothing worked. We also used Superglue to glue the bottom posts to the bottom legs, and it proved less Super than one would expect. Amy explained that the way I was using epoxy (putting a thin line of one material on one piece of metal, and a thin line of the other material on the other piece of metal) wasn't mixing the two enough, so know we know how to use epoxy. Lesson learned: know how to use your tools, or else you'll be fruitlessly waiting over 48 hours for two tiny pieces of metal to bond together in order to be ready to test out your prototype on Thursday without doing last-minute repairs.
Difference between bolted prototype and welded prototype:
Amy said that it's okay that our bolted prototype and the welded prototype we'll have soon are differently constructed. We have to arrange our strips of metal differently in order to get two sides of the metal that can be bolted, but when we submit our design for welding Machine Shop Larry will be able to weld two sides together that we couldn't bolt together. Lesson learned: sometimes design consistency doesn't matter.
Today:
Today we drilled holes into the angle iron, so we have a fully working prototype that can be used to test whether it can withstand the weight of a bike.
Our first metal prototype, from the side.
We drilled holes in the bottom posts to use as a pseudo-adjustment mechanism until we get the welded version, which uses one big slit per side instead of three small holes.
We use screws and bolts to fasten the legs together (the legs are not attached to the posts in this picture).
Our chainstay supports are glued to the top.
Chainstay support from the side.
Oh look! A Zehra in the background!
From the top, with the adjustment mechanism extended slightly.
This is one of the four joints that will be supporting most of the weight.
Our epoxied chainstay support.
Next class period: test a bike on our metal prototype. Maybe submit the welding request. Who knows, at this point?
Congratulations ya'll, your prototype looks GREAT! For your final model, would you consider making the two horizontal bars that will hold up both sides of the bike adjustable? If these bars could slide up and down the vertical metal bars and be secured at different heights, then you might be able to better accommodate bikes with bars that are different distances from the ground.
ReplyDeleteHi Mackenzie,
ReplyDeleteThanks for your suggestion! Ideally we would have ways to make both vertical and horizontal adjustments, but you'd be surprised at how difficult making an adjustment mechanism is. As we've spent sooooo many hours learning, adding an adjustment mechanism essentially doubles your materials needed and complicates the building process, and also potentially weakens joints. At this point we're shying away from anything that is more complicated than a screw, and even with screws we're trying to minimize the number we use.
hahaha awesome, love this.
ReplyDelete