Ackermann Steering Geometry
en.wikipedia.org
en.wikipedia.org
For instance:
How do trains turn if the outside wheels can't spin faster than the interior wheels? - https://www.youtube.com/watch?v=Ku8BOBwD4hc
How do you create stable train wheels? - https://www.youtube.com/watch?v=agd8B-31bjE
How do automotive differentials work? - https://www.youtube.com/watch?v=85CA4_cgZ5U
How do 6 wheel truck differentials work? - https://youtu.be/LwZBnMQ40rI?t=261
And on and on down the rabbit hole
The question about train wheels reminds me of one of my all-time favourite videos, where Feynman explains how trains follow their tracks: https://youtu.be/q5PAJ4tEIsM
But the steering geometry was the beautiful part. We knew about Ackerman's work and also about camber, caster and toe-in/out but had never done any design. So I had to read up on steering design/geometry. I already had a strong interest in auto sports. My geometry class turned out to be quite useful. FWIW on a kart with no suspension the geometry problems are simpler.
That kart is still in the family, still running and never had a structural failure. It's worn out a number of engines and been a blast for all involved.
http://yospeed.com/wheel-alignment-explained-camber-caster-t...
when a car goes fast enough you actually want anti-ackermann. the slip angles and not the actual angles are what matter, and the inner wheel has a different load which means it needs to turn less rather than more in order to still grip.
On a track or flat parking lot you could throw the wheel hard left or right even at max speed with no controllability problem other than the aforementioned slight "washing out" if the surface was slick. It would go into a very nice predictable controlled slide.
I miss it! It was great training for later driving a car. I never had the urge to do anything foolish in an automobile b/c the kart was always far, far more exciting. Driving a car was dull in comparison.
take a look at the steering on a pro kart - the wheels are deeply angled around the kingpin and dig into the ground.
My childhood street had a circle of boys who regularly did RC stuff together, our bedrooms overflowing with kits, parts, tools, it was borderline obsessive. But as we became young adults, it was very apparent that we had learned a whole lot of valuable skills the kids whose parents refused to spend money on the relatively expensive toys lacked.
I remember like it was yesterday a friend letting me take one of his disassembled kits unfamiliar to me home without the instructions so I could put it back together "blind" for the fun of it. It was just a box full of tiny screws and parts, such a great puzzle, with only the box exterior photos to go from. It was a Kyosho Lazer ZX-R, I coveted that kit.
They actually have pretty aggressive negative Ackerman, which is why they can do stuff like reverse entry drifts
But you gotta know that the lot has no interior curbs.
Control Schemes of Steering System of a Multi-axle All-wheel-steering Robot
This steering configuration would seem to also require very large wheel wells.
The problem this addresses is facing each front wheel the correct direction when turning.
Imagine fixing a pair of bicycles together at the bodies. When you want to go around a corner, the inner bicycle will have to turn more sharply than the outer one (which in turn has to go faster). That means that the front wheel needs a higher angle of deflection on the inside than the outside.
The same dynamic exists in a true 4-wheel vehicle, except that there is a mechanical linkage that allows you to steer both front wheels together instead of independently. The problem this linkage geometry solves is the problem of getting the inner wheel to deflect further than the outer wheel, by approximately the right amount. (iirc, this geometry doesn't get that perfect, and modern cars use a variant that's a bit more accurate. But that's a small optimization compared to the improvement this provides over just making the wheels both turn the same angle.)
The problem a differential solves is allowing the wheels on the outside edge to spin faster even when sharing an axle with the wheels on the inside edge.