Correct me if I'm wrong but a truck with true Ackerman steering would not be a good candidate for crab steering as well?

Crab requires wheels at same axle to be parallel at all time.

So how does a mobile crane alternate between the two?

Edited September 24, 201410 yr by Leif

It was a challenge for me years ago, I learnt it is imposible, for me, with gears and racks I suppose real ones use independent steering in each axle with electronic coordination for each case.

I would imagine as they use hyrdraulic pistons to steer they have one for each side and simply re-routing the fluid will alternate between ackerman and parallel steering

or just maybe they never have ackeraman to begin with?

Edited September 24, 201410 yr by Rockbrick

If you have a mechanism with a feedback - AKA servo, than electronics can do wonders for all kinds of steering configurations. Purely mechanical solutions are rather too complex if not impossible.

Well, it seems like an idea down the drain...

rack and pinion is not part of the solution since they need to be of different length, ackerman vs parallell.

something with LA but how the heck gear them for different speeds and different direction. anything is possible but it would take a huge amount of motors to administer the settings.

anyway, a 4x4x4 where Ackerman may be disregarded could have crabbing, just reverse second axel. could be good enough for a smaller crane!

-ackermann between axles is no problem

but with full ackerman i have no idea

Could maybe attach 1 server per wheel and use the new sbrick with a custom profile to control

You should check out how Huib de Van hart at lifting bricks does it. It is pretty amazing! (I'll put the link in later)

You would need to power each steerable axle independently with a servo or m motor and have each servo/motor on its own channel for the remote. This will allow you to steer crab or ackermann. Lots of different motors and remotes for a simple function, but that is my advice.

-ackermann between axles is no problem

but with full ackerman i have no idea

That's a really cool idea. Could you post some pictures or an LDD file

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=442099

these are all pictures i have

I thought about this for a while and came to the conclusion that you het do something with midstorm motors and have profiles set on the brick. But then most cranes are built with those (I don't know the number for them) wheels in 42009, which would take up a lot of space. Hmmm...

I thought about this for a while and came to the conclusion that you het do something with midstorm motors and have profiles set on the brick. But then most cranes are built with those (I don't know the number for them) wheels in 42009, which would take up a lot of space. Hmmm...

exactly. every wheel has to be steered independent. so that is one motor per wheel, and profiles and such. maybe do a mindstorm invest in the near future..