Well with the Niken it’s the fact that it’s got two wheels up front but can still lean. That’s as opposed to the Can-Am Spyder which is an old school trike.
The mechanics of turning are one of those things that seem simple and mundane at first but become increasingly more interesting the more you analyze them.
Actually train stability is way more subtle than that. Even the "stable" one has a critical speed at which it will become unstable. This is called Klingel motion or "hunting". It is caused by the effective damping from the contact reducing as train speed increases.
Caster and trail are interesting concepts which make it so the steering automatically returns to straight. It is confusing that the casters on office chairs use trail, not caster. It should be intuitive why one can ride a bike hands free, but good luck on a bird/lime.
The 6-wheel diff video starts a bit late and misses some details. They first start talking about 6-wheel diffs here: https://youtu.be/LwZBnMQ40rI?t=248
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
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.
As a boy I'd always wanted a small car that I could drive. I pestered my father for years with plans from various magazines until one came up for a kart ("go-kart"). He got interested and bought some scrap mild steel. My job was to cut everything to fit and assemble it. We paid a welder to weld it.
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.
a competition kart with a single solid rear axle has a different steering setup from the car. the wheels also dig into the ground to lift one of the rear tires up, which allows the cart to actually turn. otherwise they understeer under enough throttle.
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.
Our kart had a live rear axle with power to both wheels and slicks on the rear. Top speeds was < 60 mph so standard Ackerman geometry was fine.
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.
shifter karts are faster, but the one i modified for a project only did 60mph. you still needed to lean. you were probably still seeing a great deal of slip.
take a look at the steering on a pro kart - the wheels are deeply angled around the kingpin and dig into the ground.
My first exposure to this term and concept was back in the early-mid 90s when building and racing RC-10s. Ackermann was something we could adjust, and it, combined with caster, made a big difference in how the vehicles steered especially in the dirt.
Hobby-grade RC kits have to be one of the most useful educational "toys" you can give children, even today.
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.
28 comments
[ 3.0 ms ] story [ 65.9 ms ] threadFor 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
https://en.wikipedia.org/wiki/Hunting_oscillation
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
[1]https://en.m.wikipedia.org/wiki/Missile_vehicle
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.
https://rigtriv.wordpress.com/2007/10/01/parallel-parking/
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.
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
https://news.ycombinator.com/item?id=21143135
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.