Steering with Pitman Arm.

[MCoach]

That's exactly the car I'm thinking of. Excuse my previous post, it's not their electric motors, it's the entire chain drive system...

[Z]

This "two idler" steering is similar to what I (edit: and Doug) was getting at back on page 3. This system has its idlers pivoting around longitudinal axes, but a similar system with idlers on vertical axes would be better IMO (better Ackermann, and less bump-steer).



Again, the biggest advantage here is that it allows a lower footbox with a flat floor for the full length of frame, which gives a significantly lower CG and easier build (as ECU have proved!).

Z

[BillCobb]

See the USA in your 1914 Chevrolet Baby Grand. Check out the steering reveal.

[MCoach]

http://49.media.tumblr.com/ad52e511d...uqcio1_500.gif

[tromoly]

Bill, correct me if I'm wrong, that system looks very similar (the same?) to what current Sprint Cars use for their steering systems.

[BillCobb]

And to just about every vintage farm tractor. Looks like a bit of casual tire rub on the old drag link.

[Charles Kaneb]

CWA,

TAMU used to use roughly 10" steering wheels (250mm). Obviously, that will increase force required and per-inch-of-hand-movement response by 50%. If a vehicle is "too responsive" for a driver - you either have another vehicle dynamics problem (unstable rear toe, parts dragging on the concrete, excessive rear brake force, a rear wing that has just exited stage right) or you need to build or get a faster driver. You're looking for someone who can win a shifter kart race in intermittent rain.

At East Lansing Kart Track speeds without the wings range from 7.5 m/s (17ish MPH) to 23 m/s (60ish MPH). This is roughly equivalent to my FSAE experience.

-CPK

[Charles Kaneb]

After reading what Z had to say about power steering, I have a question for the professionals in chassis engineering.

With full analyses of K&C for the car, dynamic analyses of response & input, performed as part of the design process, then extensive testing with pro drivers at real proving grounds with good instrumentation - why does every power steering system I've ever driven on a passenger car suck?

Quantifying that assertion - examine system backlash on-center (<5 deg at the wheel for manual systems, >5 deg at the wheel for typical PS systems, for ~10N at the wheel), examine the force gain (a manual rack has increasing force with increasing lateral acceleration in an understeering car until self-aligning torque drops faster than the increase due to mechanical trail, but hydraulic and electric systems barely change effort when you go around corners faster - maybe 20% extra force for 100% more lateral acceleration), and ESPECIALLY examine lateral vibration response (Picture a car rolling along the road. Feed in a sinusoidal lateral forcing function at the front of the tire of a given amplitude, then sweep frequency from 1/10 hz to 100 hz. Measure the magnitude and phase shift at the wheel. Then do the same thing at the front of the rear tire).

I can't tell what's going on at the front wheels of my 2013 Fiat anywhere near as well as I can in my 1991 Honda, and it's not an FCA issue - a 2013 Honda is just as bad.

[rrobb]

Charles,

I'd guess that what you and I call "suck", the average car buyer actually prefers.


Cory

[BillCobb]

After reading what Z had to say about power steering, I have a question for the professionals in chassis engineering.

With full analyses of K&C for the car, dynamic analyses of response & input, performed as part of the design process, then extensive testing with pro drivers at real proving grounds with good instrumentation - why does every power steering system I've ever driven on a passenger car suck?

Quantifying that assertion - examine system backlash on-center (<5 deg at the wheel for manual systems, >5 deg at the wheel for typical PS systems, for ~10N at the wheel), examine the force gain (a manual rack has increasing force with increasing lateral acceleration in an understeering car until self-aligning torque drops faster than the increase due to mechanical trail, but hydraulic and electric systems barely change effort when you go around corners faster - maybe 20% extra force for 100% more lateral acceleration), and ESPECIALLY examine lateral vibration response (Picture a car rolling along the road. Feed in a sinusoidal lateral forcing function at the front of the tire of a given amplitude, then sweep frequency from 1/10 hz to 100 hz. Measure the magnitude and phase shift at the wheel. Then do the same thing at the front of the rear tire).

I can't tell what's going on at the front wheels of my 2013 Fiat anywhere near as well as I can in my 1991 Honda, and it's not an FCA issue - a 2013 Honda is just as bad.

Write yourself a detailed simulation of hydraulic or electric power assisted steering control and answer your own questions. Don't forget consideration for 'Lumpy Steeering' effect from poorly designed or poorly installed u-joints in the intermediate shaft. AND, some of your statements are not true. Try to keep in mind the purpose of 'power steering' and go from there. Your lateral excitation is called lateral runout. Another manifestation of it is 'high speed shake'.

Perhaps your own built in torque sensors need some more experience, calibration and higher sensitivity to rim force.