Ackermann Steering Geometry. What a big long confusing looking term. In this tutorial, I plan to put this term into simple understandable terms. I've divided this into 3 sections.
1)What is it?
2)Why use it?
3)How to build it
So let's dive right in, and get started!
1) What is it?
Ackermann Steering Geometry is a system for steering devised to solve the problem of the inside wheel having to turn in a smaller radius than the outside wheel. As shown below:
It was invented by the German Carriage Builder Georg Lankensperger in Munich in 1817, then patented by his agent in England, Rudolph Ackermann (1764–1834) in 1818 for horse drawn carriages.(Info from here)
This is achieved by shorting the connecting steering linkage. The two photos below show parallel steering linkages vs the Ackerman geometry ones.
Parallel linkages make a rectangle when the steering is straight.
Ackermann linkages make a trapezoid.
2) Why use it?
So really, why do you need to use Ackermann Geometry on your steering? Well a couple reasons are that if you use Ackermann Geometry, the wheels will turn better, and your creation will be more efficient. It also reduces wheel slip around corners. Wheel slip is
when the outside wheel turns on the same radius as the inside wheel, and the outside wheel slips sideways when turning.
3) How to build it!
The part you have been waiting for. How to make Ackermann steering.
First of all, let me state that true Ackermann steering is harder to make in lego, but not impossible.
This is how you make true Ackermann steering. First of all, true Ackermann requires that the two angled sides of the trapezoid can be extended back, and come to a single point above the center of the rear axle. As shown above, the red pieces are the 'V' made by extending the trapezoid sides. the dark grey piece on top of them would be your stationary bar, and the light grey would be your moving steering bar. To make true Ackermann, you have to make sure these both line up with the red pieces.
A side view of the 'V'
This is another true Ackermann. The yellow piece would be the steering bar. As you can see the yellow bar is pretty far from the grey bar. This leads to a bulky big and inefficient steering system. So the solution to make a Ackermann steering system better suited for techinc is to just make sure you have a trapezoid for your steering arm.
I actually didn't design this one. It came from Sariel It is designed for a large scale vehicle.
I am not sure, but I think this is the same or similar steering/suspension system that Ingmar Spijkhoven uses on his heavy trucks.
It features a simple pendular suspension attachment via this pin, and the steering rod.
Now you may be saying, this is good and all for solid axles, but I want to add Ackermann geometry on my independent suspension. Well look no further, I have designed this system which is really simple.
I simply took the design for the snowmobile suspension, and move the steering arms in. The picture below shows the trapezoid.
I moved each steering arm in one stud.
The inside wheel turns sharper, thus achieving Ackermann steering.
Minus the wheels.
Ok, so now you know how to build Ackermann steering, I'll leave you with a few tips.
1) It's hard to add a rack and pinion to Ackerman steering. My advice, stay with gears, or the yellow knobs.
2) When making Ackermann steering, make sure the moving arm is shorter, and toward the rear of the vehicle. You can put the moving arm on the front, but it must be longer than the solid arm, and it makes thing complicated.
3) Trapazoid, thats all you need to know.
LDD has both steering systems.
Thanks for looking. Did this tutorial help you? Please give me some feedback so I can make the best tutorials. Tutorials are all about you, the readers!
Thank you very much for your comprehensive guide to the theory of Ackermann steering! I am working on my first large scale Model Team/Creator style car and was about to give up the idea of a working steering. But studying your tutorial I was able to build in an easy but still smooth steering system. Thank you so much!
arrey yaar..its good but I need the techniques that will help me to decide steering arm lengths and tie rod lengths for a given turning radius and track width for a good ackerman .Plz help me in that :)
Quoting 2ror ornot2ror
How's your video and the next steering/suspension tutorial coming along.?
Video for this one is done. Next steering tutorial is on hold for a little, I had to build my turret for my WWII half track. I'm itching to post it, but still waiting on parts. I think I'll work on the tutorial tonight. Thanks for asking :)
Quoting 2ror ornot2ror
I,m adding 2 comments in a row 'cause I said enough in the last comment. Probably the next step in steering geometry is total steering geometry. What I mean is caster, camber toe in, and out angles.
Thanks for your comment. Id be happy to see your ackermann design. I think my next tutorial will be return to center steering, maybe I'll cover all the steering terms in that one.
Quoting jmmy avila
exelent suspension design! i have been developing a brushless mottor powered R/c car out of legos and seeing how you made the suspension for the sway bar makes me want to re think my design.
Great tutorial George! I already before this tutorial designed an ackermann steering system BUT, it needs some perfecting. Did you know that all you need to do to get a simple compact ackermann steering system is just to take the pieces that you use for regular ackermann seeing and put the 2 pinhole 1 axle hole pieces on the stub axles for the wheeles on the outside of the steering hubs? This is the way my ackermann steering system works.I'l probably put it on moc pages.