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What's up, figured I'd make an account on this forum... Seems like a great place to get ideas for a cafe build.
I'm a senior aerospace engineering student at NMSU, and I just picked up a 1979 Honda Hawk 1 (CB400T) for free. I'm doing a full rebuild of the engine and some modifications to the frame. I've attached some pictures of the bare frame and a preliminary sketch of my design. To accomplish the frame modifications, I'll need access to some high power machinery that I don't have at my house, so I'll make use of the student project center machine lab on campus. To gain access to the equipment, I have to write a design proposal and do some force/stress analysis to show that it has something to do with school. I'll probably end up posting some of that technical stuff on here for whomever is interested. This will be my first ever motorcycle, and my first ever build. But I have plenty of experience designing aircraft, so it shouldn't be so hard. I'm on a budget too, so stay tuned, this build will be going for some time...
Solidworks 2013 With the analysis package. I have to prove to the shop director that the new design is safe, for liability purposes So far, the modelling has been pretty accurate. I'm trying to keep the dims within 1/16". Its more about getting the gist of the stress distribution...
Here is the (almost) final assembly of the frame. The rear suspension springs will be simulated, so I don't have to actually model them. Soon, I'll upload the results of the FEA on the stock frame. Then, onto the frame modifications anaylses...
Today I set out to measure the spring stiffness of the rear suspension springs. For anybody out there looking to know how to do this, or looking for the stiffness of the Honda 1979 CB400T rear shock springs, here are my result:
I first removed the spring and measured its length. Using a cinder block as a loading plate, I started stacking dumbbells onto the spring. With each weight that I added, I measured the length of the spring. I subtracted each length I measured from the uncompressed length of the spring. Then I plotted the Displacement vs. Weight Curve. Using a curve fit, we can find the spring stiffness as the slope of the linear curve.
Data:
Uncompressed length: 8 3/32" (This is about 1/8 off of OEM recommendation)
Force Length
0
8 3/32
35
7.75
95
7 5/16
145
6 7/8
185
6 3/8
This data was used to plot the attached linear trend.
From the spring curve we can see that the spring stiffness for this spring is 112.4 lbs/in or 1350 lbs/ft. I'll use this spring property to do a finite elemental analysis.
Similarly, I will measure the stiffness of the front suspension springs. To do this, I utilized a similar technique of loading the springs. Attached are the pictures of the apparatus, and the results of the loading displacement curve.
From these results, I attained the equivalent stiffness of the two springs as 1260 lbs/ft. Because their are two springs instead of just one, the actual stiffness per spring is 630 lbs/ft (see attached diagram).
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