Getting to and from the train is not an enjoyable experience. Train stops are not always conveniently located, scooters are not a practical transporter as it is hard to fit a scooter in your bag, and bikes are not allowed on trains forcing riders to risk having their bike be stolen. So, we set out to create an enhancement to the T riding experience that was fast, compactable, and lighter than the existing ways of getting to and from the train. From the beginning, we intended to create a device to enhance the T, what we believe is an already existing and functioning mode of transportation. We had no intentions of creating a device to replace the T riding experience. With this in mind, we set out to design the Transit-Wheel.
In the preceding two weeks, we spent the bulk of the time designing the outer shell of the transit wheel and searching for a motor, during this two weeks we started designing the wheel, but also incorporated feedback and returned to heavily modified the body design
We spent a lot of time redesigning the body of Transit Wheel. It used to have a rounded top with organic looking curves on the wings that met to make a handle. We had a design review at SPI. We talked about a lot of things, like the wing lock and the body design. The engineers there told us that the wings and wheel cover would be difficult to make and very expensive. We decided that that wasn't realistic to fabricate so we shifted approach. Now the wheel cover has three edges on the top to make a trapezoidal shape. The wings match the shape of the wheel side, and when they are folded up all the edges meet. The edges on the wings are folded up to increase the strength of the metal. Since the handle is no longer attached to the wings, it's fastened to the wheel cover.We also decided to use steel instead of titanium because of money, steel is also a lot easier to work with. When we went to SPI we talked a lot about the wing lock, many ideas were talked about, but we decided that just screws are the mode reasonable approach due to time.
When we started working on the wheel we had to think about a couple of things. First, we had to figure out how to reduce friction when it turned. The most obvious way to do this was bearings, the problem is that bearings that are as large as we need are either too expensive or don't exist. The next problem was fastening the two wheel halves together. If we used screws the two halves could move slightly and get out of aligned. We decided that using screws and a small locking mechanism on the edges where the wheels meet.
A critical aspect of the wheel design are the gears, which transfer and amplify the torque from the motor to the wheel. Since our gears need to fit inside the wheel, with the motor, we decided to use a planetary gear system. Planetary gears are known to be suitable for high-torque, compact applications. The struggle with gear design started with finding suitable software in which to design them.
I tried multiple different software to design the gears I started using gear generator. I stopped using that because it does not make accurate teeth and there is no good way to import them because it uses polylines instead of curves. I started looking at Solidworks add-on for gear generation that got good reviews. I found a software called Eassistant through this site calling the best gear generation tool. I found out after doing more research than I should have had to that Eassistant does not do gear generation. In the past I had used the Solidworks toolbox I knew that they had gear model but did not think they were customizable I found through a video that you can customize the pitch multiplier and tooth count. Getting the proper gear ratio was challenging I thought we would need a much larger ratio to get enough torque. I made a 3 layer planetary gear set with 2 caked gears stacked and an annular this took a long time to get to this solution. When David and I calculated the gear ratio we realized that we only needed a 2 layer gear set with one set of planets and annular gear.