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  • 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.

  • Fabrication:

    We started the fabrication process by water jetting the wheel side and wing. This was good and bad. We found a lot of little problems that we had to fix, it helped us find problems in our design and fix them. It was bad because the wheel side and win that we cut are not perfect. We then started to design for fabrication. The wheel halves were hard to fabricate due to undercuts and poor designing. We simplified the design and changed both halves to be symmetrical. We also changed the right wheel mount. It was previously too big and wasted material. We refined the design to make it smaller and cleaner.

     

    PCB:

    There are many different electronics elements in Transit Wheel. To connect them we have the main PCB. The PCB holds the Arduino, two analog to digital converts, a gyroscope, an accelerometer, a compass, two level shifters and voltage monitor. This allows us to manage all the sensor on transit wheel in a compact way.

     

    Pressure pad:

    To measure the amount of forward or backward lean that the user provides, we have pressure pads on the wings. We spent a lot of time looking at sensors but could not find one that was long enough for our purposes. We decided to make the sensors ourselves. We are using velostat, a material that is more resistive the more pressure put on it. We will have strips of that glued to a flexible PCB with the other surface touching the metal of the wing. This will allow us to measure the placement of the person's weight to see how much they are leaning.

     

    Gear Box:

    The gears had to be held in place using two gear mounts, one on either side. The Planetary gear set has two layers of three gears. The Gears have bearings that ride on three rods. The two gear box halves have to be attached somehow. We had to add three extra rods to hold the gearbox halves together. We can't put screws through the gear shafts because the process of drilling and tapping them would make the shafts bulge and not be as precise as we need them.  The gearbox is attached to both wheel sides. This is for two reasons. First, the gearbox will align the wheel halves, it also disperses the force evenly along the two wheel sides.

     

  • 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

    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. 

    Wheel:  

    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. 

    Gear design:

    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.

  • 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.

    Lock

    To make the lock mechanism we first started by sketching multiple ideas and designs. The first one that we looked at used something that stuck out from the wheel side and held the wing down. We decided that that would take up too much space in the wheel. The next design that we looked at was a piece inside of the wheel that hooked onto the wing and prevented it from moving. The next design involved a piece sliding down into slots in the hinge. This would prevent the wing from moving by locking the barrels in place. The final design works very similarly to this except it locks from the inside of the wheel side.

    Handel

    We decided to redesign the handle because all of our previous ones didn't work as well as we wanted them to. The new design is built into the wing and the wing and the handle are one piece. The Wing now sticks out from the wheel side and bends up. When the two wings are folded up the wings meet. There is a hole at the tip of the wing creating a handle. When we first made the handle design there was a lot of wasted space. The hole was moved down and the flat part was majorly shortened.

    Motor

    We spent a lot of time trying to find a motor that met the specifications we need. We looked at  high torque low rpm pancake motors. We found two companies that make them Kollmorgen and Printed Motor Works. We originally contacted Printed Motor Works in a previous studio and the quote they gave us was too high at the time. We contacted them again and asking for a motor with a gear box. And they quoted us 700 usd we then realised that putting their gearbox on it didn’t make sense because we would need our own gears on top of that. We were about to contact them again and then realised that they were advertising their motors as a drop in replacement for Kollmorgen motors, so we started looking at those motors. We spent days pouring over datasheets and found the ideal motor for us. We called a distributor and found called them they got back to us and said the motor would cost 1400 usd and would have 12 weeks leed time. So we will from Printed Motor Works. All that work was for nothing.

    Pressure pads

    When we started to find ways of controlling the speed of the transit wheel we looked at two forms. The first was an exeloromater and the second were pressure pads. We decided that pressure pads were a better way to go. The problem was that all the pressure pads now are all too small and not precise enough. To fix this we used velostat and custom PCB The velostat would be sandwiched between the wing and a custom flexible PCB. We would have strips of velostat that would act as pressure areas. There are going to be eight pressure areas arranged in along the foot.  This would be able to sense when there is a change in pressure on your foot and where the change is so it will move.

    In the future, we will actually order the motor because we need to design the inner wheel around that motor and that is a lot of work we haven’t even started on. We wanted to work on that this week but there were complications with the shipping and we don’t know if the motor has been actually ordered yet. We need to finish the pcb design for the pressure pads and the main controlling pcb. We need to figure out how we are going to manufacture the wings because creating complex curves like that is not easy. We need to decide what buttons transit wheel will have and where they will be.