Chris Kouba
Supporter
I just couldn't walk away... After being 0.2s off the course record last year, it was gnawing at me. When I did the math, the difference was about 8 feet at the finish line (less than 3 meters for you other people). If I was ~8' ahead of myself, I would have broken the record. I know I can do that.
So I entered again.
The compromise this year, with all the other things I have going on, is that I would recycle the car. I am re-entering the car from last year, with a few changes under the skin.
What might those be? The car pushed heavily through the Learning Curve. It was easily the worst handling car I had built (of like 7 or 8). It pushed so hard that I actually used the brakes into the Learning Curve, even on the final run (albeit ever so slightly). That's probably where I lost 8'. If the car handled like the others, it would have gotten around the curve without scrubbing so much speed and I would have been able to carry it across the finish line.
I did some investigation at the front end, and it turns out that I don't think I had enough Ackerman in the geometry. I cranked the steering (like I was going down the course) and rolled the front inner tire over a pair of greased up panels. The inner tire ended up pushing the free-floating panel in toward the center of the turn, which to me indicates that it wasn't turned sharply enough to compliment the outer tire. To this end I tore out the steering from the outer tie rods back to the steering wheel and completely re-did it.
I had a few geometric constraints, and when I tried for a center pivot bellcrank, the angles ended up creating a toggle mechanism, basically locking up the steering once I got the desired travel. That clearly wouldn't work. Back to the drawing board, I went old school and tied the two uprights together directly, and then connected a bellcrank to that. In the proof of concept stage of the design, I revisited the greasy panel test, and this time the floating panel was pulled outward from the center of the turn, indicating a bit of excess Ackerman. I assume this will not be as detrimental as the push from the original geometry and that it will also require less steering input to negotiate the corner now. Time will tell.
In other news, I also have a new pusher, Brandon, and we had a practice session this past weekend. A good start is 10+ MPH after the 10 yards, and he was able to consistently get at least 12+, including several mid-13's as measured by GPS. This bodes well.
So not a lot of pics for the build thread this year, but still looking forward to an exciting day of the hill. My dad will be in town for it as well and I'm sure he'll have a great time. If anyone is local (or just passing through), it's all day long at Mt Tabor on the east side of Portland on August 19th. If you make it to the park, you won't miss it. The heats are supposed to start around 9, but usually run behind schedule. There is no admission and food and beverages (yes, beer) are available in the park. It's quite the day!
Chris
So I entered again.
The compromise this year, with all the other things I have going on, is that I would recycle the car. I am re-entering the car from last year, with a few changes under the skin.
What might those be? The car pushed heavily through the Learning Curve. It was easily the worst handling car I had built (of like 7 or 8). It pushed so hard that I actually used the brakes into the Learning Curve, even on the final run (albeit ever so slightly). That's probably where I lost 8'. If the car handled like the others, it would have gotten around the curve without scrubbing so much speed and I would have been able to carry it across the finish line.
I did some investigation at the front end, and it turns out that I don't think I had enough Ackerman in the geometry. I cranked the steering (like I was going down the course) and rolled the front inner tire over a pair of greased up panels. The inner tire ended up pushing the free-floating panel in toward the center of the turn, which to me indicates that it wasn't turned sharply enough to compliment the outer tire. To this end I tore out the steering from the outer tie rods back to the steering wheel and completely re-did it.
I had a few geometric constraints, and when I tried for a center pivot bellcrank, the angles ended up creating a toggle mechanism, basically locking up the steering once I got the desired travel. That clearly wouldn't work. Back to the drawing board, I went old school and tied the two uprights together directly, and then connected a bellcrank to that. In the proof of concept stage of the design, I revisited the greasy panel test, and this time the floating panel was pulled outward from the center of the turn, indicating a bit of excess Ackerman. I assume this will not be as detrimental as the push from the original geometry and that it will also require less steering input to negotiate the corner now. Time will tell.
In other news, I also have a new pusher, Brandon, and we had a practice session this past weekend. A good start is 10+ MPH after the 10 yards, and he was able to consistently get at least 12+, including several mid-13's as measured by GPS. This bodes well.
So not a lot of pics for the build thread this year, but still looking forward to an exciting day of the hill. My dad will be in town for it as well and I'm sure he'll have a great time. If anyone is local (or just passing through), it's all day long at Mt Tabor on the east side of Portland on August 19th. If you make it to the park, you won't miss it. The heats are supposed to start around 9, but usually run behind schedule. There is no admission and food and beverages (yes, beer) are available in the park. It's quite the day!
Chris
