Mechanical Brake Assembly

Matthew Balafas holds his completed master cylinder braking assembly.
Matthew Balafas holds his completed master cylinder braking assembly.

Matthew Balafas just completed his freshman year at the University of Minnesota, Twin Cities.  In addition to this, he joined the Solar Vehicle Project and completed the design, analysis, material sourcing, construction,  and assembly of the braking system for our team’s new vehicle.  The fluid braking system features two master cylinders linked with a balance bar.  The balance bar can be adjusted so that one set of brake calipers locks up before the other.

The design quickly evolved from a two-wheel braking system to a four-wheel system when calculations indicated that the coefficient of friction between the tires and the road would prevent the car from stopping in the required distance.  In addition to this, it is dangerous for the rear wheels to lock up before the front wheels.  If the rear wheels lock up first, the car can fishtail, which is dangerous for the driver.  Therefore, a balance bar was added to the design.  Once installed on the vehicle, the brakes will be adjusted so that the front wheels lock up first.

The bracket that holds the master cylinders and pedals was cut out of aluminum and welded together.  The team machined some of the internal parts for the balance bar, and also assembled the pedal and pad in-house.

Check back in as we make more posts about the construction of Eos!

A closer view of the Eos master cylinder assembly.
A closer view of the Eos master cylinder assembly.

 

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.

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