ASC Meeting July 11th, 2023

Just gonna drop my notes here for future reference.

STEERING FEEDBACK

The hydraulic steering system is generally alright, the key thing to look into is the feedback we get from the system.

In a regular rack and pinion, the wheels can influence the rotation of the pinion directly. The worry is that the compressibility of the hydraulic fluid in the steering system adds some “slop” which takes away some of the responsiveness from our system.

This could be similar to minimizing the number of U-joints implemented in a typical system. So we may be able to pull a quantitative “slop” comparison.

SLIP ANGLES

I have been doing the math for our steering directions disregarding slip angles. After the call it makes more sense.

The slip angle of our tire is the difference in the direction it’s pointed and the direction it’s moving. When I was doing that math for where our tires need to point, I ignored slip angle. However, the actual approach is to find what lateral force is required for our most difficult scrutineering case (the figure-8) and based on the cornering stiffness chart determine the slip angles required to generate that force. I’ll need to dig into the datasheets to validate this, but it does mean there’s a risk of “widening” the cutout for the wheel.

On more of a tangent, the widening of the cutouts can be mitigated by the reduction of the wheelbase from the trailing arm changes. This would impact ribs and we’d need to double check where the chassis will fit in the aerobody.

HIGH MISALIGNMENT BEARINGS

Related to the slip angles, the extra range of motion required may require us to find new bearings for our upright. This will take away from the DFA we have in using the same bearing everywhere, but we need the car to go. Specifically the name of the part is a high misalignment bearing.

ZERO BUMP STEER GEOMETRY

There is something called zero bump steer geometry. It is best to implement it since the guys from ASC can’t 100% say what an acceptable range of bump steer is (~1 degree at highway speeds still might be if-y). No impact on the rest of the car, just designing the steering system.

INTERNAL RETAINING RING

Where we house our bearings we’re allowed to use internal retaining rings. They’ll cost less and save some weight on the car, specifically looking at the upright.

PEDAL SYSTEM REINFORCEMENT

Just bulk up the pedal assembly so that “panic” braking won’t break the system. Might be useful to dig into some impact failure theories and keep them in mind as we design things around the pedals.