In reverse order. I made some excellent bruschetta tonight. Not bad for a first shot. Threw in some roasted red peppers. I was kinda weak, went with the bruschetta spread in a jar, but it's got all the essentials. Plus the roasted red peppers, plus fresh mozz, on ciabatta bread and toasted at 450F. Not bad. Plus I endorse Smithwick's as the official adult beverage of suspension design. Or I guess Coors Light if you're still doing FSAE.
Been throwing together some basic spreadsheets... weight transfer numbers... sprung natural frequencies, wheel rates, all that fun crap. Referenced Matt G's tech tip's at the OptimumG site. Good stuff. Think he's still working in Colorado... smart guy.
One of the kinda screwups we did at CU Racing was throwing a ridiculous amount of spring at the car, for no real reason. No downforce and on bias tires where you don't really get any advantage from "locking" the suspension with spring. 120 lb/in wheel rate on a 460lb car! The car does not necessarily respond quicker with more spring. Either the tire or sprung mass is a limiting factor. Think about putting F1 tires on a minivan, or minivan tires on an F1 car. The handling would not be good. The two have to be matched up.
In any event, starting at a guess of 43/57 static mass split F/R, and 2.0Hz front sprung mass natural frequency, the wheel rates come out to be pretty low. Much lower than I'd be able to get away with using a Cane Creek damper and anywhere close to a 1:1 motion ratio.
- 2.0 / 2.2 Hz split F/R :: 88 / 141 lb/in wheel rates
- 3.0 / 3.3 Hz split F/R :: 198 / 318 lb/in wheel rates
- 4.0 / 4.4 Hz split F/R :: 352 / 565 lb/in wheel rates
2 comments:
Nice, Matt G is indeed a smart man. His papers have helped many an FSAE team.
Just a quick question - why the concern over getting a 1:1 motion ratio? Or is there another concern, not just packaging?
Cheers, Pete.
In the CU Racing days we used a 1.7 MR to get the spring and damper rates to work out. It works.. it's not inherently bad.
But my thought is if I can get a little closer to 1.0 it decreases the mechanical hysteresis in the system, the friction in the damper seals etc isn't then as amplified at the wheels.
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