Leif

@Jeroen, do you have some info or LDD about the mechanical block you have to prevent steer mode switching when not in straight mode? I would really appreciate some insight there!

Good to hear about progress! Yeah I think I have been studying too hard on steering geometry for each and every automobile so I forget that it really doesn't matter all the time to pinpoint all those darn angles I built a big beast superstructure 8x8x8 using Unimog tires and on this one I actually did Ackermann as well, and what do you know - I can drive and turn on a thick turkish carpet, even with the superstructure and big boom on top! so little skidding, next to noe http://www.eurobrick...opic=100552&hl= It is satisfying to see all those calculations pay off from time to time! But current build will be more or less exactly like yours, different steering angles for every axle, normal + crab (If I solve all issues) and we go for "Ackermann light". I will also use the 42009 wheels + more so skidding will not be such a big issue as the Unimog tires are, especially with portal hubs as well.. Now down to the man cave and look into new crab solution! keep us posted!

Holy Moly that was a big machine! did he ever finish the beast? A really interesting concept with double gear racks for steering, I will steal with pride Don't wanna bash the guy, and he confirmed in the last post as well, there is no Ackermann in this setup. But that's alright, we cant win them all! not without hydraulics...

lol at "crapsteering" Yeah I got another machine 8x8x8 with PGA - Pretty Good Ackermann... Slack is always an issue with our gears, I am pondering on using worm gear after each diff, that would remove the slack for the rack and pinion part. Issue in that case is of course that I alter the gear train by 90 degrees so I have to build a new setup in order to get to the gearrack, so the hits keep on coming..

Alright, got it, but how can you have identical angles on four axles in crab mode if you have different gear on different rack? I browsed through your flicker, and that's a good machine you building there! do you have any more detailed pics about the steering? Oh and btw, yeah slacking is always an issues with the gears we have..as few as possible and as few perpendicular as possible as well, that's what we have to aim for! My concept build in this thread can of course be optimized at a few places and the crab gears do not really slack, it's the normal turn side that slacks, but I have some ideas. perhaps divide with two engines and of course no gearing up to fourth axle, that was just a lazy and quick thing!

You have some good ideas there but I wonder, with your 2diff system, do the pair of axles turn the same degrees? In crab all axles turn the same degree, but normal steering, inner axles (2 and 3) should turn less than outer axles (1 and 4) in order to get as little tyre rubbing as possible, even without Ackermann. My system with 4 diff takes this into consideration. perhaps you didn't see it from my pic but I gear down for axle 2 and 3 and gear up again for axle 4, for normal steering..! see this pic, two options:

That is a really nice usage of really old school gears! I didn't know anyone else but me still had those..

Yep, I will be there! Looking forward to it no matter how much or less technic.

I am not sure I understand completely. 4 axles, 1 servo motor for the first 2 axles, and 1 servo for remaining 2 axles? Or another setup? Remember, during normal steering the 2nd and 3rd axle do not turn as much as 1st and 4th, but they all turn the same length when crabbing. Generally speaking, servos will of course help to auto-center, before switching steering mode. That is a question of taste; jerky steering with servos (or train remote), or smooth steering with medium motors...

Thank you for your kind words. You may be correct but I cannot see that issue as it is now. The motor locations are temporary and they should of course drive via worm gears in next version.

As so many of my builds this is a crude mockup of an idea that I have been pondering about and had to get out of my head, down to the table! This steering setup supports 4 axle steering and crab steer as well. Naturally Ackermann went out the window but I think we can make it at least this time What I have done is that the feed is from the first or the second motor, to differentials - backwards use of differentials so to speak - and output from differentials will support rack and pinion steering. Note that the two middle diffs are geared down in order for proper radius thinking when turning, but all diffs turn at the same speed and direction when crabbing. 8x8x8 will set you back 8 differentials but that's another story

I am in London last weekend of November. Brick 2014 runs at the same time and naturally I will attend for at least some hours during saturday. I have found some notes that the Volvo 42030 will be there, along with a real Volvo(!) Besides from this I haven't really found any Technic events at Brick 2014, or maybe they do not post that many news? I think the Netherlands Lego show is more or less one of the best, how does Brick 2014 stand in comparison?

Milan, Is there any chance you can measure the pressure as well, using the Lego Gauge?

Found it! Good discussion and nice options. http://www.eurobrick...8 And here I was thinking I had invented something new for the world

Brilliant! I am on the right track. Yeah, the machine gets a lot tougher, but counterweight is still needed for proper build. As a matter of fact, heavy lifting with my crane bends the entire substructure of truck as well, but turntable stays together..

Recently I built some POCs (Proof of Concept) for Mobile Crane ideas and I "invented" double turntables as an idea for sturdier support of crane superstructure. Of course we all know that a crane superstructure needs a counterweight in order to be able to lift any kind of load. Still, there are many situations where a counterweight is not, or is not the only, solution. Difficult to balance weight according to load and so on. We also have other machines with turntables, diggers and such. However, having said that, which is, I know that counterweight is always the answer(!) I came up with this idea for a more stable turntable, which will never snap and which adds a lot of strength and balance to superstructure and turntable 'nuff said, here are the pics, I have built it as well. This is my first creation in LDD Just a concept, not the Nobel prize! Gentlemen, start your opinions!

In the high prestige competition "Daughters and Mobile Cranes" I hereby submit my contribution Given the crane is a WIP and I only have one daughter I do not expect to win the contest, but I might at least be runner up!

So far the Lego L.A. s really have no problems lifting. Homemade LA will of course require a whole new superstructure so that is another story to put together.. Thank's a lot

Crane in place! At this moment I basically added the Ultimate 42009 superstructure with a few changes. along with afol1969 boom, with some reinforcements by myself. The big change and a new idea, double turntables.. One turntable inside the substructure where the protruding beam is attached to lower part of turntable, and after that attached inside crane superstructure. Are you still with me..?.. This idea really stabilizes the superstructure to the extend of more or less bending the chassi rather than the "classic" near-popout of turntable! And some pics of the crane from different angles. the 8x8x8 still passes the carpet test and has a pretty good Ackerman geometry If this MOC continues the superstructure should of course be rebuilt to match scale! Right now it is just Proof of Concepts (POC) of different ideas! So what's next? I don't know really. I am not really into cosmetics, just a rough edged builder.. I should build outriggers of course, but then I have to extend the chassi some in order to fit them between the wheels and that would require more or less a whole tearing apart and rebuild.. If I build outriggers I can promise they will be powerful and stable! Drivetrain is still sufficient but adding one more PF XL motor would not hurt. There are some grinding gears when driving on an extra thick carpet so I though of have another motor at the other end of the drivetraing in order to offload some. We'll see, still - first MOC in approx 30 years

just my 2 cents, I'm pretty sure you read most of the posts at the forum, but my boom, a modifed version of afol1969 is pretty strong. At least 1.2 kilogram without extending boom, and at least the unimog cab while fully extended details here: http://www.eurobricks.com/forum/index.php?showtopic=85388&st=400#entry1996084 I am all for stronger, bigger stuff so please let me know your progress and if anything of my build is good input for you!

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..

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!

Yeah I know! I have 5 XL motors on the shelf som I am ready to add Naturally I will also sooner or later build a larger superstructure, to match scale!

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?

thanks a lot! Can you point out where to reinfoce drivetrain? first pic of drivetrain is old, first version, and not is use, 2 last pics are current and it feels quite strong? The truck is still a skeleton so reinforcements will be done, for example around worm gear for steering. funny thing is clutch wheel disengage long before any beam pushing so no dealbreaker... I would like to clarify that I meant gear ratio to 2nd and 3rd axle steering, rack and pinion - not the drivetrain if anyone thought so