Follow-Up- 12/12

December 12, 2013

Deliverable: Final Report

Our bike stand project is done and done; the final report is submitted, we showed off our design at an engineering open house, and I believe the only thing left to do is complete a survey about the class.

Our final design did not work, which is a bummer. We splayed the two frames out to the side and incorporated support triangles onto each of the four corners. Although we could screw in the top of the hypotenuse to the design, we had to epoxy the bottom corners, so we should have realized this plan wouldn't work.

When we tried out the design, our bike stand fell apart at the seams (no thanks to you, epoxy!).

Problems abound. First, it takes two people to mount the bike on the stand. One person has to lift the bike, while the other has to position each side of the bike stand and simultaneously make sure that no gears or brake wires are caught in the bike stand. Second, during our process of prototype refinement, we didn’t foresee the extent to which stress concentration points would affect the usability of the bike stand, which resulted in the bike stand tipping to the side almost immediately after the rider got on. Third, the chainstay support doesn’t completely support both sides of the chainstays. The weight is distributed unequally which causes the bike to tip back and forth. Fourth, the screws that come up from the bottom create an uneven surface- the screw heads create a slight but significant decrease in stability. In short, it was unrealistic to expect screws to be a practical mechanism to adjust for different bike sizes, and perhaps more importantly, to remain tight against the pressure of riding the bike on the stand.

If you'd like to read our final report, here's the link. Even though we didn't produce a working bike stand for our partners in Nicaragua, we made good progress on designing a better bike stand. I hope that engineers in the future will be able to use our report to help eliminate some options that don't work, or see what we have and improve.

If you have any questions we'd be more than happy to answer them in the comments. Other than that, thanks for reading! 

Fail Early, Fail Later, Fail Always- 12/8

December 8, 2013

Deliverable: Project documentation and prototype refinement. 

We got our welded model on Thursday, and to the chagrin of everyone involved, our bike stand can hold a bike quite well and even support the weight of bike + rider, but once the person starts pedaling, what we want to happen fails in several places. First, the two sides of the bike do not assume equal weight of the bike, and inevitably the bike stand, with bike and rider on top, starts to tip towards one side. Second, because the bike is tipping, the wheel, which should be comfortably suspended and spinning between the two sides, tilts far enough to one side that it catches the posts of the bike stand, preventing the wheel from spinning.

Although our final project is due on Monday, we're going to spend the class period (a) adding to the design, and (b) finalizing our project report. For the design, we're going to try to add triangles to the bottom of each of the four corners in the hopes of added stability. That will cause the legs to splay away from the bike, so we will have to cut leg posts about 10". As for the report, if we can fix our design we'll base our report off of the new final design. If not, the theme of our report will be "We tried really hard," and hopefully our documentation will help future groups perfect the design.

Waiting... 12/2

December 2, 2013

Deliverable: Rough draft of final report

Our welded model isn't quite welded yet. We're on high alert for when it's ready for us to test- we'll get an email sometime before Thursday, and then we'll test the bike stand. Unfortunately for us our timeline prevents us from building a second welded model, so what we get for Thursday is our final product. Luckily for us, it's a pretty slim design, and I have high hopes that it'll work.

Today we're working to produce a rough draft of our final report, for Amy to read over at the end of today. We have until next Monday (12/9) to edit.

Welding Request- 11/25

November 25, 2013

Deliverable: Submit welding request

Today our mission was twofold- improve our adjustment mechanism and submit our welding request. We want to have a welded model by next Monday.

As a reminder, this is our "working" prototype from last class:

Absolutely stunning.

We started the class by brainstorming ideas to change our adjustment mechanism:

This design was having leg posts in different places. One option would be having a pair on either side of the bottom bars; another option would be having one pair of leg posts in the middle

This design would have only two leg posts, instead of two pairs of two leg posts. These legs would swivel on the screws.

Alex's design also incorporates a rotating leg post. She also drew pictures of a man with one central leg, and also a baby.

We talked to Machine Shop Larry and got his opinion. He suggested that we put the leg posts on the outside of the trapezoid, instead of the inside.

We decided on our final design, which is to have one leg per side that swings around on a bolt, and also has a slit in the middle of each leg to be run through a screw that is secured on the other side. We decided to eliminate the top bar of the trapezoid, and put the chainstay supports directly on the two side bars, which turns our design from a trapezoid into a triangle. I know that doesn't quite make sense, but you'll see the pictures soon enough.

Pictured: our new triangle (not trapezoid) frame.

We chose not to cut new pieces of metal for our welded design. Instead, we disassembled the parts from our working model. For our second welded model (if we have time) we'll cut new parts of metal.

In order to get a clean welding line, we filed down the edges of our side bars in order to get an angle that can be attached to the bottom and top bars:

Debbie used a protractor to determine the angles that we needed to shave off.

We shaved off some bits of both sides of the side bars.

We drilled holes through the sides of the side bars for the adjustment mechanism, and away we went. We submitted a request to Machine Shop Larry to weld our design.

These are the pieces of metal that will be used in our bike stand. It's not much, considering the bulk of our last approximately six designs.

A final write-up of our design, including lengths of the pieces.

Since this week is Thanksgiving week, today (Monday) is the only class period we have this week. Next Monday (12/2) we'll be waiting to see if our design got welded, and the Monday after that (12/9) our final model and project write-up is due.

Happy Thanksgiving!

It lives! Part 1- 11/21

November 21, 2013

Deliverable: Working Prototype

Thank you, good St. Eligius, patron saint of metal workers! Today we tested our prototype, failed miserable, fixed some things, tested again, and our design worked!

We first started the day by attaching the chainstay support to the top of our stand. The epoxy with which it was fastened didn't work, and so we resorted to duct tape and twine.

We put the bike up on the stand, and while it did not collapse, the bike did not fit in the stand. The ends of the top bar hit the gears, so the bike didn't sit flat:

We decided to quickly shorten the top bar, basically making it only as long as it absolutely needed to be.

We started to unscrew the top bar from each sides, which worked well except for one screw. Using our mighty strength we had accidentally secured it too firmly, and we couldn't unscrew it. We tried unfastening the screw and nut using a: screwdriver, wrench, hammer, metal cutter, pliers, and hand saw. This process took about 45 minutes. Finally, Amy tried to use the mini band saw we have in our lab, which didn't work. We then went to the machine shop, where Amy used the bigger band saw. She sawed through the screw, which was good, but she also incidentally welded our drilled hole shut, so we  had to drill another hole. Basically the whole ordeal ate up an hour of our time for something that should have taken approximately 10 minutes. Lesson learned: never trust your time estimates.

With our shortened top bars finally in hand we drilled new holes and reassembled the stand, complete with reattaching the two chainstay supports that had broken off during the kerfuffle. Here is our new, improved bike stand:

We tested the bikes in our classroom, and look at this magic:

Our bike stand works! It successfully holds a bike. Alex tried getting on the bike. She managed to cycle for about two seconds, enough to blend a blueberry, before the structure started to tip over and collapse. We're going to chalk that up to our necessitated screw joints, and when we weld the structure it will be more supported and less likely to buck off the rider.

We talked over our design and looked at things we could improve. On Monday we're going to talk to Larry about the following ideas:

-Completely eliminating the top bar, and having the two side bars reach up and be welded to the chainstay supports.
-Changing our adjustment mechanism from a slitted bar and a screw to a sort of graduated stair case adjustment that would click in place, or another idea.

Working Prototype II- 11/18

November 18, 2013

Deliverable: Working Prototype

Today we began by sharing with the class our progress since the last design review. One of our biggest pain points was how the angle iron had failed to stay attached to the tubing from last week. Epoxy has failed us! In response, Amy suggested that we bolt the angle iron onto the top surface of the base tubing. 

Katie and Alex drilling away...

... and TA DA! The base is complete.

For our working prototype, we decided to bolt the angle iron shut so that we can test the bike in our classroom and see if our prototype does what it is supposed to do -- withstand the weight of the bike, support the chainstays at the right location, and stay upright.

With the base complete, we epoxied the chainstay supports onto the top tubing.

Before we placed the bike onto our stand, we noticed that the chainstay supports were too far apart. We went back and re-adjusted the angle iron to the narrowest possible fixture (i.e., bolted the angle iron together at the innermost holes), but even after this change, the supports were too far apart. We could not make the bike stand any narrower without sanding off some of the angle iron -- it was the only way to make the angle iron slide along the base without it getting stuck at the intersection between the tubing. Alas, we went to Larry, who kindly agreed to help us. He used a machine similar to the drill press, which shaved away the unwanted chunk of angle iron; the machine could be adjusted along multiple directions.

Larry showing us how to sand off extra bits of the angle iron.

Thanks to Larry, we now have a working prototype that can be adjusted for width. Our goal for next class is (1) to use mini clamps to clamp the angle iron into place, (2) and to finally test our prototype. Before Thanksgiving, we hope to file a welding request.

Working Prototype- 11/14

November 14, 2013

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.

Scroll down for more pictures, but first: We learned two main lessons today:

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?