Daily Archives: June 29, 2014

What I’m doing on my Summer Vacation on a Wreck-Free Sunday

I’m just east of the Hudson river in a tiny burg called Pine Plains this week and the next two weeks. Tiny and mostly isolated (no cell service on my carrier for miles around the town and dozens of miles east) but they do have the Internet here. There is a Wi-Fi hotspot down the road that operates on a limited schedule, and where I’m staying has ethernet broadband (but only one socket) so I can get Internet here when the owner is not using it or I can make sure I have a full charge on the laptop battery and wander down to the park and get Wi-Fi when it’s on. Later there should be a Sprint Cup race on the tube and then after that we will have a big dinner.

Even though I won’t get any chance to build it I’m still working out ways of building the Sprint T Bucket. I think that is one of the drawbacks to being a follower of Hephaestus: you either build things or you plan to build things and constantly refine your plans until either build it or can’t improve it any further and have to start planning something else. Anywho, I was trying to figure out how to make the car lower to lower the center of gravity so I decided to abandon the triangulated 4-bar to move all the suspension links out from under the passenger compartment. That created a whole other packaging issue in that the front mount for the 4-bar would have to be outside the body instead of under it. Meaning the frame would also have to move outside the body and yet maintain triangulation around the passenger compartment. I figured out 2 ways of doing that. One way would be to use channel and sheet metal to move the frame connection to the lower mount out from the side of the frame under the body to beside the body and then run two diagonals from the rear rollover hoop to the upper side of the front mount for the 4-bar. Triangulation would be maintained but the frame would be slightly heavier. Plan two involves moving the uprights on the front hoop out to match the rear hoop so that most of the actual frame is on the outside of the car like some Supermodified racers. This keeps the weight the same as the triangulated 4-bar and slightly increases the torsional stiffness, which is a desired trait. Esthetically I’m not real “sold” on either idea because I think the suspension links should be completely hidden inside and under the body, but it solves so many other issues that I think I might be able to live with it. For one thing I could mount a small step on the top of the front mount and drastically reduce the step-over height for getting into the car.

Another solution that had occurred to me was to drop one of the top links and go with what is called a 3-link rear suspension because that would get the suspension out from under butts and not require major changes to the external appearance of the car, plus the 3-link is a thoroughly “scienced” design that is well-understood and easily tuned. The downside is when combined with the low ride height and 24″ tall body of the T-Model Ford body there would be no luggage space forward of the rear axle because of the height required to make the rear mount of the upper link work out (the lowest ready-made mount I could find on the Internets yesterday was just over 9″ above axle centerline, with most being between 11″ and 14″). So that solution was discarded because I have to be able to carry things in the trunk and the trunk space would essentially end at the back side of the rear axle, leaving only whatever space was left over the safety fuel cell behind the axle.

Getting away from the triangulated 4-bar caused a minor secondary issue of locating the rear axle laterally as the triangulated lower links performed that function and defined the rear roll center at the intersection of the extension of the links, or somewhere in the vicinity of the axle mounts when there was no intersection. So I’m either going to install a Panhard rod (track bar in NASCAR terminology) or some kind of Watt’s link. There are advantages and disadvantages to both with the tradeoffs being opposites, so to say. The Panhard rod has the advantages of being simpler to design and build, and less likely to puncture the fuel tank in a rear end wreck, the disadvantages are the rear axle will move slightly from side to side as it goes through its travel. Flip those over for the Watt’s link: more complicated and more likely to puncture the fuel tank, but keeps the axle in the same centerline as it travels. Keeping the axle on the centerline gives the exact same handling in left and right turns, but with the limited amount of travel on the bucket combined with running the Panhard rod from the top of the bottom frame rail to a bracket that just clears the frame rail when the axle droops there should be little detectable variation in handling between left and right turns.

And I’m getting told I need to wash up for dinner since I was out in the sun moving furniture closing down a yard sale and got all sweaty and dinner will be ready in half an hour. So Y’all be careful out there, and I will resume sorta normal posting starting tomorrow.

PSA, Opus