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Caster and force feedback - Printable Version

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Caster and force feedback - LBodnar - 07-27-2011

I have to piggyback on this thread because I can't open a new thread. It says "no post mode spcified" when I try to post.

I can't seem to find if caster provides an input to steering wheel force feedback.

It should be roughly along the lines of

Code:
Feedback = Mz - My * WheelRadius * sin(CasterAngle);

I have only found

Code:
Feedback = Mz

Caster is massively important in providing self-centering forces, Mz is OK but it will go to zero and even turn negative at some point.

I have no idea how to pull all data into one place - caster is defined in suspension, radius is in tire. All these definition scopes and other "::" nonsense! Plain C and FORTARN were the pinnacle of my high level languages skills before I slipped back into Assembly.

Anyway, I have hard- coded the caster details and it feels much better.


Update:
It's not exactly sin(CasterAngle) because this assumes that the wheel steering axis projection onto the wheel plane passes right through the wheel's centre. It should be caster distance but I don't know how to calculate it from suspension geometry. E.g. open wheelers usually have caster [distance] between 10 and 20 mm.

[Image: castor.gif]

- NaN - 07-28-2011

Quote:I can't seem to find if caster provides an input to steering wheel force feedback.
It is not implemented. I'll have a look asap.
Issue: https://github.com/VDrift/vdrift/issues/25

- LBodnar - 07-28-2011

NaN Wrote:
Quote:I can't seem to find if caster provides an input to steering wheel force feedback.
It is not implemented. I'll have a look asap.
Issue: https://github.com/VDrift/vdrift/issues/25

Thank you!

I am slowly snailing through the code.

It looks like there was an attempt of bringing in the full double wishbone suspension geometry (coordinates of body attachments and hub point) but that was abandoned, still even though this is great and will help determining accurate wheel hub position still wheel axis is not necessarily at the centre or even on the centreline of the hub.

So maybe sin(caster angle) x wheel radius is good approximation which can be overriden with something like "caster-distance=0.015" in suspension section?

Some racing chassis manufacturers spare engineers from tedious calculations and just quote caster distance in a manual.