Trailer Graphic Design Competition!

The University of Minnesota Solar Vehicle Project acquired a new trailer in the past year. The team is looking for submissions for the design of the trailer, which will be vinyl-wrapped using printed vinyl from 3M. The deadline for submissions is Friday June 12th, which leaves pleanty of time to get designing! In-depth requirements and team logos can be found at z.umn.edu/SVPTrailerContest, and questions can be directed to svp@umn.edu. The winning design will be announced on June 15th, and the designer will be credited on the actual trailer.  This would be an excellent addition to any graphic design portfolio – as this is a large, real-life application of graphic design.  We look forward to seeing your submissions!

Our Sponsor Board for the American Solar Challenge 2014.
Our Sponsor Board for the American Solar Challenge 2014.

The sponsor board above shows a sample of how many sponsorships our team holds during a two-year design cycle.  There will be a space on the trailer to display a graphic like this one, which will be changed out every two years.  Thank you once again to all the generous sponsors who supported us on our way to placing 2nd place in the American Solar Challenge 2014!

Suspension Testing and Layups

On this beautiful spring day, team members are concurrently working on testing our previous car and constructing our new car.  Tests of solar cell efficiency, stress and strain in suspension members, and pull-out strength for our carbon fiber chassis panels have been running smoothly.

Mechanical team member Chris Torres sets up a test on Centaurus III's suspension.
Mechanical team member Chris Torres sets up a test on Centaurus III’s suspension.

Suspension testing is focusing on finding stress and strain in the a-arms, which connect the upright to the chassis.  The strain experienced by the members can be used to find the forces acting on the tire at the contact patch with the ground.  The team currently designs its vehicles for a worst case senario of a 4G bump, 1G turn, and 1G braking load.  These tests will give the team knowledge of the actual loading seen by a vehicle driving down the road.

A strain gauge is numbered and attached to the upper a-arms of Centaurus III.
A strain gauge is numbered and attached to the upper a-arms of Centaurus III.

In addition to suspension testing, Aero team was in the shop today to complete a layup for a removable array panel.  The panels are made of fiberglass to avoid shorting the solar cells.  Carbon fiber is electrically conductive, so the team is careful to ensure that all electrical components do not have direct contact with the carbon fiber shell and chassis.

Core is laid out for a removable array panel.
Core is laid out for a removable array panel.

The team laid up sharp offsets into the shell, so that panels, doors, windows, and other openings can be filled with separate panels.  Those separate panels have a better chance of having good seam lines than if the team just cut out the doors from the shell.  This is important for aerodynamics!

A team member cuts off excess fiberglass from a panel layup.
A team member cuts off excess fiberglass from a panel layup.

Our molds have endured the trip to and from the Delta composites shop, and are now being put to more use for laying up our panels.

Stay tuned for updates as we manufacture Eos!

Molds and Layups at Delta Aircraft

Last week our team began the process of building the Aerodynamic shell of our vehicle.  We had the opportunity to us the Delta Tech Ops Composite shop at the Minneapolis/St.Paul Airport.  The week started off rough, with both molds cracking during transport due to thermal shock.  We will be sure to find a functioning heater for our trailer, next time.  However, we got to try out our new winch and it worked great!

Once at the Composites shop, we unloaded our molds and repaired them. There was a well-ventilated sanding area and the Delta employees supplied us with extra tools as we needed them.  We are very grateful for the use of their shop.  They are allowing us to come back for another week, because we were unable to finish all of our lay-ups due to the cracking of our molds.

We lay the first ply of carbon on the shell of our new car, Eos.
We lay the first ply of carbon on the shell of our new car, Eos.

This week has been a great learning experience for a young team.  The completion of our first wet lay-up took patience and trial and error.  Along the way, everyone got a little sticky, and everyone had fun!

Aerodynamics Team is fun to be around!
Aerodynamics Team is fun to be around!

The composites shop has a large Autoclave that we were allowed to use to cure our part in.  Just for reference, our mold base is over 6′ across and 16′ long.

Everyone helps push the mold into the Autoclave for curing.
Everyone helps push the mold into the Autoclave for curing.

Once the wet fabric is laid on the mold, the part is vacuum bagged and all of the air is sucked out of it to push the fabric against the surface of the mold.  The mold was then baked in the autoclave for 12 hours to cure the epoxy resin and hardener, which formed a hard plastic interwoven with carbon fiber fabric.  Composites like these are often used on aircraft and spacecraft, and are extremely strong for their weight.

Posted in Eos

Eos Battery Bracket Manufacturing

This year, the team is using 18650B type battery cells.  The batteries will be held together with ABS plastic brackets.  The team chose to manufacture the brackets by milling them out using the CNC machine in the University of Minnesota mechanical engineering student shop.  This involved using featureCAM to create tool paths and G-code to run the machine.

A FeatureCAM screenshot of the program to cut four brackets simultaneouskt,
A FeatureCAM screenshot of the program to cut four brackets simultaneouskt,

A jig was also created so that the blanks could be bolted to a plate and then milled out, four at a time.  Despite streamlining the process by creating a fixture, the parts will take the team over two weeks to fully machine because the student shop is only open during business hours, and most team members are full-time students.

Battery brackets on the CNC bed.  They are held down with 4 bolts each.
Battery brackets on the CNC bed. They are held down with 4 bolts each.

The battery pack will be assembled by welding nickel shim onto each of the batteries through the bracket.  The nickel is highly conductive and easy to weld.  Soldering the batteries could damage the cells if they got too hot.  The team built a spot-welder which was used on Daedalus and will be used again on Eos.  Below is an image of the cutting of the nickel pieces, donated by Diamond Metal Products in Ham Lake.

Nickel Shim is laser cut at Diamond Metal Products.
Nickel Shim is laser cut at Diamond Metal Products.

There were some difficulties in cutting out the nickel with the laser, but they were overcome by using a backing material when cutting out the fragile pieces.

Look for another post in about two weeks regarding the rest of the manufacturing process for our battery!  Below is a closer image of a completed bracket.

 

Completed Battery Bracket!
Completed Battery Bracket!
Posted in Eos