Building Sim For Finding Deltas

[J.R.]

So, I'm trying to figure out which steering angle I'll need to cause a certain slip angle. RCVD, P. 169-170 is the bicycle model. Since I don't know how to make a four wheel model yet I thought that I could take two bicycle models and place them next to each other and calculate rough estimates. I assumed that the inner bicycle model was going around a 25' radius (inside of skid pad) and the outside model was going around a 25'+ 46" (our front wheelbase) radius. To estimate beta (vehicle Side slip) we need an alpha_rear value. At the advise of our Faculty Advisor, I picked the max force slip angle, since we're talking steady state cornering. I then determined the front slip angle from the maximum force that our tyres are capable of producing given a camber (from roll) and load (from Load transfer calcs).

Now that we have beta, Alpha_rear, and Ackermann steer angle (from wheelbase/Radius), and Alpha_front, we should be able to calculate delta very easily (EQ. 5.50, RCVD).

Inputs of a negative Ay (LHT) give me outside positive steer angle, and very slightly negative inside steer angle. (Sorry no numbers, I used the TTC data so IDK if it's allowed). So positive steer angles on a LHT means that I'm turning away from the turn, therefore oversteer car, I think. Checking the basic calc for K, stability factor, gives me two positive, but very small, numbers (understeer/NS car).

My questions are:
* Can I assume that the two halves are 'basically' operating independently of each other at SS? All WT has already occured, and all variables should be defined.

* Countersteering in an FSAE vehicle seems crazy. I have the car set up to transfer a ton of weight in the rear (Solid Axle), so this is moving the car in the oversteer direction, but my stability factor says that we're not. Has anyone else ran into this?

* Also, my beta values for the two models did not match, and I would expect that they should to get accurate results. Anyone have any insight on this? I was thinking of taking an average of the two I attained, and then re-running the calcs that way. I got what seem to be extremely high beta's (10 and 20 deg, inside and outside respectively), which I guess wouldn't be so huge for a car that is sliding/ contersteering. Any thoughts on these values?

* Does anyone see anything else in my assumptions that could give me funky results?

* Also, tyres tell me they want anti-Ackermann, but common knowledge on the forum says we want to run regular Ackermann due to the tightness of the course. Is there a mathematical way to figure out a compromise, or is it just testing?

Thanks for the input, it's always appreciated!

[J.R.]

So, I'm trying to figure out which steering angle I'll need to cause a certain slip angle. RCVD, P. 169-170 is the bicycle model. Since I don't know how to make a four wheel model yet I thought that I could take two bicycle models and place them next to each other and calculate rough estimates. I assumed that the inner bicycle model was going around a 25' radius (inside of skid pad) and the outside model was going around a 25'+ 46" (our front wheelbase) radius. To estimate beta (vehicle Side slip) we need an alpha_rear value. At the advise of our Faculty Advisor, I picked the max force slip angle, since we're talking steady state cornering. I then determined the front slip angle from the maximum force that our tyres are capable of producing given a camber (from roll) and load (from Load transfer calcs).

Now that we have beta, Alpha_rear, and Ackermann steer angle (from wheelbase/Radius), and Alpha_front, we should be able to calculate delta very easily (EQ. 5.50, RCVD).

Inputs of a negative Ay (LHT) give me outside positive steer angle, and very slightly negative inside steer angle. (Sorry no numbers, I used the TTC data so IDK if it's allowed). So positive steer angles on a LHT means that I'm turning away from the turn, therefore oversteer car, I think. Checking the basic calc for K, stability factor, gives me two positive, but very small, numbers (understeer/NS car).

My questions are:
* Can I assume that the two halves are 'basically' operating independently of each other at SS? All WT has already occured, and all variables should be defined.

* Countersteering in an FSAE vehicle seems crazy. I have the car set up to transfer a ton of weight in the rear (Solid Axle), so this is moving the car in the oversteer direction, but my stability factor says that we're not. Has anyone else ran into this?

* Also, my beta values for the two models did not match, and I would expect that they should to get accurate results. Anyone have any insight on this? I was thinking of taking an average of the two I attained, and then re-running the calcs that way. I got what seem to be extremely high beta's (10 and 20 deg, inside and outside respectively), which I guess wouldn't be so huge for a car that is sliding/ contersteering. Any thoughts on these values?

* Does anyone see anything else in my assumptions that could give me funky results?

* Also, tyres tell me they want anti-Ackermann, but common knowledge on the forum says we want to run regular Ackermann due to the tightness of the course. Is there a mathematical way to figure out a compromise, or is it just testing?

Thanks for the input, it's always appreciated!