Someone mentioned an app on Twitter that did something I needed, tracking walks and estimating calories burned. So I looked it up at the Google Store and found out the price was right (free) and the basic version did in fact do everything I needed from such an app. So I now have “Map My Walk” installed on my phone.
What I learned is my “short walk” is 3.31 miles long instead of my estimated 2.5 miles I’ve been telling everyone, and that I burned 500 calories on my “short walk”. I’m thinking my “long walk” is closer to 5 or 6 miles than the 3.5 or 4 that I thought. This also explains how my shoes keep wearing out so fast, since I go for a walk almost every day. I’m also faster than I thought but still nothing to brag about.
Also while on my walk I contemplated the one remaining issue I have to solve with the rear suspension: keeping the rear wheels from steering the car under power because the toe angle changes. With the 2D Pratt truss the knuckle could have had enough bending torque to change the toe angle uncontrollably, so I had to make it 3D without adding to the weight or making it take up too much space behind or over the transmission. Thinking the problem through I realized the 4-link was going to be taking almost all of the forces that would be changing the toe, so all I really needed to do was give the 2D truss a fighting chance at using the depth of the structural members to resist toe change by using some diagonals connecting to the vertical member of the last bay before the knuckle, in as many planes as I could so the last bay would be 3D but everything else could remain 2D, only slightly increasing the weight of the truss and not changing the vertical stiffness needed to keep the wheel aligned on the other 2 axis. In doing so I would not be using a true Pratt truss in that the diagonal members will be under compression rather than tension, and the end bay would not have an upper horizontal member or terminating vertical member but would be similar to a kingpin truss in 3 planes, with another triangular bay under the truss from the bottom of the knuckle up to the bottom horizontal member in the plane of the main truss keeping the camber angle constant. I wish my CAD skills were good enough to draw this out and output a .gif or .jpg file to put in the blog, because words are only so good in describing this.
Another stab at it, the plate that holds the knuckle to the truss is going to be rectangular or maybe a right triangle with the hypotenuse facing down and forward and the right angle on the top rear side. Diagonal members will run from all 3 corners of the triangle to the first vertical member of the truss, one from the bottom corner to the bottom of the first vertical member from the bottom, one from the top front corner to the bottom of the vertical member on its front side, another from the top front to the top of the vertical member on its front side, and a last one from the top rear corner to the top of the first vertical member, that diagonal in the plane of the truss. That should be more than enough to keep the forces driving the wheel under control so the toe and camber don’t change. And none of the added members will interfere with the drive shafts or the lateral links of the Watts link that keeps the whole shebang located from side to side. That’s because all of the added structure is either behind or above the knuckle and therefore above or behind the driveshafts and lateral links.
I really need to learn how to use the AutoCAD 360 program I downloaded to the laptop and not just so I can draw pictures of the car to post to the blog. Anyone know of some good tutorials to teach me to use it?
Billed @€0.02, Opus the Unkillable Badass
Witch on a Bicycle 