Quick Steering Question (hopefully)

[aminnich]

Hey guys,

I am wondering if when you have more than one axle steering you have to have different steering angles... If they are the same does than mean that the truck/ crane/ vehicle just wont be able to turn as sharp as if the vehicle had different turning angles..

I hope that makes sense

EDIT:

also when doing crab steering, do all of the axles have to steer, or can some be fixed?

Edited September 21, 2015 by aminnich

[dhc6twinotter]

Ideally, yes, you would want all steered axles to have varying amounts of steering. If the axles steer at the same angle, then the axle with the most weight on it will probably be the dominant steer axle (I think).

For crab steering, you would want all axles to steer, and steer at the same angles.

[Milan]

If you have same steering angles on all the axles, and your vehicle, or in your case - crane :) - is long, tires closer to the center of the vehicle would tend to stay straight. Ideally, you would want to make different steering angle for every axle, to minimize tire wear and increase efficiency and smooth operation.

For crab steer, all the axle steer the same. However, some big older cranes have the option to lift the middle axle(s) off the ground, while the rest of the tires turn all in the same direction.

For your question, it is best not to leave any axle unsteered in crab mode, as it will drag and bend and cause problems during crab steering.

[aminnich]

So what you are saying is that it would be tough to do "true" regular steering for a crane and "true crab steering on the same Lego model. But it could b done in a no so true manner?

[Vectormatic]

So what you are saying is that it would be tough to do "true" regular steering for a crane and "true crab steering on the same Lego model. But it could b done in a no so true manner?

Doing it entirely true, might require mindstorms/S-brick programmable controllers and servos or mindstorms motors, i think a purely mechanical linkage facilitating both multi-axle multi-angle steering and crabbing would be extremely complex.

The only real way i can think of doing it mechanically would be with two sets of cogs on the steering racks and being able to enable/disable them with clutch gears, but working out the proper gear ratios for several axles to steer correctly might just be impossible with the limited set of cogs we have. And this mechanism probably is so complex and has so many gears, all with a tiny bit of play, that depending on how many axles you want, it might not work at all.

You can probably do 2 steering front axles and 3 "locked" rear axles, where a clutch would make the rear axles steer as well, allowing a vehicle to both turn and crab, but the problem of different steering angles on steered axles remains, and is fundamentally incompatible with crabbing

[aminnich]

I have a great concept idea to do both crab and regular steering, it is the different steering angles that are the problem.

[Milan]

So what you are saying is that it would be tough to do "true" regular steering for a crane and "true crab steering on the same Lego model. But it could b done in a no so true manner?

As answered by vectormatic, yes. Best to do in such case (not practical for you now) is to build 2 axle crane. That way you can have regular steering and crab steering, with two steering motors and simple setup.

We had topic that covers your questions, but as i remember, it did not solve the issue of regular and crab steering on multi axle crane.

[Vectormatic]

As answered by vectormatic, yes. Best to do in such case (not practical for you now) is to build 2 axle crane. That way you can have regular steering and crab steering, with two steering motors and simple setup.

We had topic that covers your questions, but as i remember, it did not solve the issue of regular and crab steering on multi axle crane.

http://www.eurobricks.com/forum/index.php?showtopic=114469&hl=nooteboom

That trailer does 7 indepent angle steering with servos, i imagine adding a servo for the 8th axle plus the needed programming in the control unit would allow for both turn and crab (although the truck obviously wouldnt)

[Milan]

http://www.eurobrick...69&hl=nooteboom

That trailer does 7 indepent angle steering with servos, i imagine adding a servo for the 8th axle plus the needed programming in the control unit would allow for both turn and crab (although the truck obviously wouldnt)

No, not that topic. this two:

http://www.eurobricks.com/forum/index.php?showtopic=88810

http://www.eurobricks.com/forum/index.php?showtopic=100596

[aminnich]

This is kind of a tangent (haha im doing dealing with tangents on my calc homework ) anyway........

how can i get the sharpest turning angle??

EDIT: basically how did the noteboom get all of it turning angles.

Edited September 21, 2015 by aminnich

[dhc6twinotter]

If you are already using a 9L rack, you can use larger gears on the steering rack. However, using a larger gear on the rack means the servo has to work harder, so this may not be ideal for your 5 axle steering setup.

Using a shorter steering arm will also sharpen the steering angle, but your steering arms are already 3L on the front axle, and this is as short as you can go (you could try 2.5 though).

I think your only option is to use a larger gear on the rack, and if the servo can't handle it, switch to an L motor.

Or, you could build a truck to pull the trailer, and just have the servo connected to the front axle of the truck. The trailer could then have self-steer axles, or no steering axles at all.

[aminnich]

I'm using the 13L gear racks that r found in the 42009 for steering. I'd rather use the servo so that I have a true return to center

[dhc6twinotter]

Sorry, I meant 13L steering rack (I always wished for a 9L one though!) You can try putting larger gears on the steering rack, but I don't know that the servo is powerful enough for this. You could also try gearing up the servo, which would have the same effect as putting larger gears on the rack, but this adds slop, and slop isn't something you want with a servo.

I think it will take some trial and error to figure this out, but that is part of the fun.

[aminnich]

Ik LEGO is a huge experiment trying to get things to work. I just wish I didn't have as many experiments haha

[Jeroen Ottens]

In this topic you can find the solution I made to get a steering setup with both crabsteering and normal (Ackerman) steering on a multi-axle setup:

http://www.eurobricks.com/forum/index.php?showtopic=89963

I still have to finish that boom...

[bonox]

http://www.eurobrick...69&hl=nooteboom

That trailer does 7 indepent angle steering with servos, i imagine adding a servo for the 8th axle plus the needed programming in the control unit would allow for both turn and crab (although the truck obviously wouldnt)

that trailer is ingenious but actually very simple. You only need one servo - the rest are just for power. There is no programming either - he's cunningly used the servo control mechanism of the rechargable battery box. THe trailer is a great example of mechanical multiple steering radii setup, but won't help for crab variation or electric control.

( for reference, so says the creator at post #38 of that thead)

many multiple axle vehicles have one or more non steering axles for simplicity when the scrub is minimal. For the trailer, the non-steered axis is mostly at the centre of rotation of the whole assembly.