Thursday, September 19, 2013

Current FSAE Work

My work on the MIT Motorsports, or Formula SAE Team has changed scope quite a bit since the last time I updated. I have worked quite extensively on the Accumulator Enclosure for the electric race car. The enclosure must securely hold the batteries in case of a collision, and be able to maintain its rated strength in the case of an electrical arc or electrical fire. This is a crucial component on the car, and its required that we verify our calculations and that the enclosure meets the prescribed rules. If the team is not able to prove this in a way that is satisfactory to the judges, the car will fail E-scrutineering and be disqualified from competing in the dynamic events. Our enclosure is going to be a kevlar composite layup with a nomex honeycomb core that contains several threaded aluminum inserts to bolt to mounting tabs on the frame. Natalie and I performed several destructive tests on composite beams to determine the material properties of our layups for use in design calculations. A short report of our work can be found here, but here are some picture of our test setup
The test piece is mounted so one can load the AN4 bolt in shear, and assess the strength of the aluminum insert embedded in the layup.

The above 2 pictures are of the test to assess the force required to push the aluminum insert out of the composite layup.
 The test specimens are 2 ply kevlar fabric coated in epoxy resin on either side of a nomex honeycomb core. We tested both 1/4" and 1/2" thick core layers. I also made Aluminum inserts on the manual lathe in the N52 shop in varying diameters to embed in the layup to simulate mounting points. These inserts were etched prior to insertion in the layup. All of these layups were vacuum bagged for at least 8 hours while the epoxy cured and used roughly a 50:50 mix of epoxy resin/hardener to kevlar fabric by weight. Natalie and I made a short video of our layup process of the tests to determine an effective elastic modulus of our layup.


The next project that I am hoping to finish is a small 12 Degree of Freedom (DoF) Hexapod. The frame consists of 12 HXT500 5gram Servos, lasercut acrylic, and the hardware to hold everything together. I plan on entering this in an instructables contest before October, so keep an eye out for it. I am doing a custom circuit board with a high current power supply, a "Master" Microcontroller, and a "slave" mcu that acts as a serial servo controller. I am eventually going to release all the design files under a Creative Commons license when I iron out more of the bugs, but for now here is a sneak peek.

 The CAD files were all done in Solidworks, with many iterations of test parts cut to find the optimal size. I currently have the schematic and about 10% of the board layout done, and the entire mechanical frame constructed.

Hexapod with tiny Fedora. The green PCB's are Pololu Micro Maestro Serial Controllers I was using to test.

Underside of the Hexapod

Close up of the leg mechanism.

I was going for a Jake and Elwood Blues color scheme, and am going to use the Fedora to cover up the finished PCB. I know that the leg joint design could be improved greatly by replacing the cantilevered limbs with better supported ones, but I am currently focusing on ease of assembly and economy. I think that this could be  packaged as a kit for the amateur roboticist, as a lower cost alternative to current hexapod chassis. The only tools required to assemble the final version will be a soldering station, needlenose pliers and a hex key.