Presentation 1 Powerpoint

9/21-9/28

This week has been spent preparing for the first round of presentations, and working on CAD models. There are a lot of parts that need to be designed with how many changes are planned. It is our attempt to procure as many off the shelf parts as possible to avoid custom machined ones, however with the size of the bogie and the compact nature of it, it is turning out to be difficult. Figure 1 shows an early picture of the bogie thus far.

Figure 1. Bogie Structure

 From the picture, it can be seen that the largest change so far is that there will be three wheel instead of two wheels at the bottom of each bogie. This is in order to keep the bogie perpendicular to the track at all time, independent of one another.

Figure 2. Cross Section of members with thread inserts

Figure 2 shows the new design for mounting the support wheels on the bogie structure. Last year they used a threaded rod that went through the length of the member, this year we will mill threaded inserts that will be welded into place and the wheels will be on should bolts that will have some kind of bushing to allow for free spinning. 

Figure 3. Initial Joint design for Bogie Connection

Figure 3 is the initial design that has been done for the joint between the bogie uprights. It uses should bolts, brackets, a center shaft insert, and middle x joint to allow for 2 DOF for traveling up and around bends. 

Figure 4. Off the Sheld Bearing Unit

Figure 5. Start of Custom Bearing Unit for Main wheel

Figure 4 and 5, are an example of issues with off the shelve purchase parts I am currently having. I would like to be able to buy a full bearing unit for the main wheel, however, The ones available are too wide, and won't allow for the wheels to be aligned with the current track config. This means I need to design a custom one that will need to be machined. Not shown in figure 5, is addition bearing retaining plate that will also act to position the wheel in the correct location.  The bearing is required because Propulsion is planning on integrating the drivetrain onto the main wheels. This is going to make fitting everything difficult, so this is currently one of the top issues in my mind. 

Lots more work needs to be done. 

This week I spent my time doing some initial hand calculations for sizing the joints that connect the two bogie uprights to one another. I created an excel spreadsheet that can be used to calculate the shear and bearing stresses that bolts and brackets would see. The excel spreadsheet can be seen in figure one.

Figure 1. Bolted Joint Calculations.

Along with this, I started hand writing out position equations for the steering mechanisms. The lower steering arm is going to be treated a four bar mechanism with a driving diad that will be connected to some kind of actuator. The upper steering arm is slightly different in its current configuration, and may require some deep redesign to optimize the linkages for a rotary input rather than the linear one used in the full scale. Tomorrow we are going to work on creating an excel document where all of the equation will be in variable form to which we can change infinitely to try to optimize the design. 

I have also been working on the bogie upright structure. The old CAD models were difficult to work with, and we have enough changes to justify develop a new design from scratch. Most of the mounting points will remain the same, however, some things will be shifted around. The current upright can be seen in figure 2.  

Figure 2. Current Development of Bogie Upright

I am so far pleased with the development of the our design. We know for a most part what we need to do, and we are beginning work to make it happen.

9/7/2016 - 9/14/2016

9/7/2016-9/14/2016

A large part of this week was spent reviewing previous reports from the summer 2016 group, and trying to come up with clear design specifications. From the reports completed prior, it doesn't seem like there are clear requires for components such as time for steering to switch or weight values for cabin and suspension. These are important values because they dictate the strength requirements for the members. This Wednesday will be used to come up with clear design requirements. From there, the work load will be split between us to complete the goal.

In addition, to reviewing the old design, I had to complete some tasks as president of Superway. I completed the recognition application as well as looking into funding for the project. I wanted to get a polo shirt design together in order to have something for people to wear to events such as maker fair.

Design work that was complete this week was a discussion of how to model the steering system in order to come up with the equations that will define the input speed requirements for our actuators. The discussion of what kind of actuators also took place. Currently, the debate is between a linear actuator and a high-torque servo.  There are advantages and disadvantages to both, but the defining variable that will more than likely determine it will be the speed requirements for steering changes. Linear actuators are in general slower with the faster ones have a much large volumetric footprint. This could be a problem for us. The solution could reside in a servo motor to actuate the movement. We are also currently planning to have two actuators running with one a slave to other to actuate the upper and lower steering mechanisms. The distance between the two is too great and would a require a complex linkage system that would have long members that would either need a lot of mass to be structurally sound or be quite thin and may buckle.

Another design decision that has been made is to create a three wheel system for the lower rail. Currently, there are two wheels lying in a vertical plane with each other. This allows for rotation to occur about the rail which is causing binding in the upper guide wheels. The three wheel system would counteract this rotation and in conjunction to a 2 DOF of freedom jointed bar between the two bogies, would allow both bogies to be perpendicular to the rail, but independently of each other. This is an additional solution to the current binding issue.

We also plan on adding springs to the guide wheels at the top in order to take up some of the manufacturing tolerances that are currently a problem and creating some rotation perpendicular to the rails. It would also produce some give in the curved corners.

A redesign for the steering system is currently in talks as well. The lower steering arm was dropper down relative to the rail in the previous design, without being modified. The previous teams solution was to place the wheels of the steering arm on long rods in order to put them in the right position. A redesign of the arm could extend them and have a cut out for the lower wheels and place the wheels in the right position without the long rod. All the wheels should be on bearings or at least shoulder bolts that have shoulders with the right length for the wheels to rotate freely. The current design doesn't allow for some of the wheels to rotate freely.