Tuesday, July 16, 2013

The Necessity of Prototyping

One of the core reasons why we build our parts out of wood for testing is to be able to see from an early point on the weaknesses and flaws in our designs. Instead of complicated stress modeling with computers, we simply cut our designs in wood and subject them to physical stresses.

In this case, the precaution paid off, as the magic finger jointed footrests failed.

The Necessity of Prototyping

Although the final construct would be made of 0.25” thick aluminum and not wood, it allowed us to see the bending stresses in the structure and how it might lead to repeatedly failure over time.
Thus, we decided to take a different approach to the footrests.

Presenting the Mark II – Now 9001%* less likely to fail!
*Not an actual calculation.

In the previous footrests (which we shall posthumously dub the Mark I), we saw the issue of a large bending moment arise. To solve this in the Mark II, we used a spare section of the 80/20 we had lying around to form a single long footrest bar. Then, we cut out another 2 sections of 80/20 to lower the footrest from the frame.

Attached to Celeris’ mainframe

After doing some preliminary fitting, we cut off the excess length of 80/20 from the footrest bar, and secured it firmly to the mainframe. It now feels significantly beefier – and certainly reassuring for the driver.

More crucially, however, the front axle holder was destroyed during testing. As the holes did not fit the bearing casings perfectly, that little bit of wiggle room meant that the shaft would lean backward, pressing upward on the lower plate, causing the rupture.

Rupture View 1

Rupture View 2

In lieu of this, we decided to replace the standoffs in front with an 80/20 bar, which should provide additional resistance against bending and hopefully prevent another rupture.