[MOC REVIEW] Grove GMK6400 Mobile Crane

[Blakbird]

To finally finish up my review of the Grove GMK6400 crane, I'll show some modifications I made to the superstructure. I was getting a lot of gear grinding sounds when luffing the boom, and it took me a long time to figure out what it was. If you look at the following image, you can see that there are a whole bunch of axles which stick out 1 stud and never attach to anything. The result of this is that the L motor is not supported very well and tends to sag.

At first I thought maybe this meant that the 8 and 24 tooth gears were slipping, but they are actually locked together by a connector so that couldn't be it. Finally I found the problem which is that the 24 tooth gear was scraping on a long pin with stop bush beneath it. I have color coded the image below to show the offending parts in green and red.

I removed the green pin with stop bush and the problem went away, but I still wasn't happy with the sagging motor so I added some parts to support it better.

Here it is with the 5x7 frame attached. At this point it is very solid and I have no further issues. Once I finish adding these couple of parts to the instructions, I'll publish Draft4 and also the source file and others can take it from there.

[kandykop]

To finally finish up my review of the Grove GMK6400 crane, I'll show some modifications I made to the superstructure. I was getting a lot of gear grinding sounds when luffing the boom, and it took me a long time to figure out what it was. If you look at the following image, you can see that there are a whole bunch of axles which stick out 1 stud and never attach to anything. The result of this is that the L motor is not supported very well and tends to sag.

At first I thought maybe this meant that the 8 and 24 tooth gears were slipping, but they are actually locked together by a connector so that couldn't be it. Finally I found the problem which is that the 24 tooth gear was scraping on a long pin with stop bush beneath it. I have color coded the image below to show the offending parts in green and red.

I removed the green pin with stop bush and the problem went away, but I still wasn't happy with the sagging motor so I added some parts to support it better.

Here it is with the 5x7 frame attached. At this point it is very solid and I have no further issues. Once I finish adding these couple of parts to the instructions, I'll publish Draft4 and also the source file and others can take it from there.

That is exactly what I did to the grove....actually ultimate 42009 had same problem but not as severe as grove.

Edited September 22, 2014 by Blakbird
: Removed quoted images.

[Blakbird]

I have completed Draft 4 of the instructions incorporating issues I found during the build. At this point, my part in the instruction creating process will be ended. I've uploaded both the "final" draft instructions as well as the LDraw file to my Bricksafe. The model is buildable and playable as is. However, I know there is a desire to "perfect" the instructions and I believe afol1969 is planning to undertake this project. Good luck! The LDraw file is 7273 lines long and many hundreds of those are LPub meta-commands. The photo below shows my final build incorporating any minor changes I made.

If I were to recommend any further changes to the model in the future, it would be the following:

• 2.5L axles (which don't exist) for the drive axles to prevent them from falling out into the CV joints.
  
• Much longer stroke boom lift actuator (which doesn't exist). Possible non-LEGO options are Firgelli or the new actuator being designed by Efferman.
  
• More counterweight.
  

It has been a great project and this is a great model. I hope everyone has as much fun with it as I did!

Since this review was spread over many pages, if anyone wants me to go collect all the updates and put them in the first post, I'd be willing to do so.

[JDC]

Thank you for the enormous effort you put into this project, so that we could all benefit from gerger's design.

[afol1969]

Many thanks for all your effort and time you spent on this project

So I'll soon start for "perfect" instructions. L2,5 axles can be made easy, and more counterweight will be necessary. Both I'll add to the instructions.

So let's do it, it will be a long work which needs lot of patience, and some more parts I've to buy to build the model. As your CAD file is full of Meta commands, I can learn some more LPUB functions, and I'll try not to make too much changes, as you have already put an enormous work on it.

Greetings

Alex

[jantjeuh]

Thanks a lot for taking the time to do this!

[Kumbbl]

Many thanks from me too!

[Henk61]

Many thanks for me too... I am already checking if I have all the parts to build this MOC.. Thanks again to all of you who spend their time in this project

[Moz]

If I were to recommend any further changes to the model in the future, it would be the following:

I thought the steering was also a problem? Viz, the steering geometry doesn't work so it needs to skid wheels whenever it turns? Working out what steering ratios are needed between the different axles and getting closer to ideal would be tedious and probably difficult, but very helpful. It could probably even be done using Lego parts, so in that sense it's more solvable than the short linear actuator problem.

[gerger]

So I'll soon start for "perfect" instructions. L2,5 axles can be made easy, and more counterweight will be necessary. Both I'll add to the instructions.

So let's do it, it will be a long work which needs lot of patience, and some more parts I've to buy to build the model. As your CAD file is full of Meta commands, I can learn some more LPUB functions, and I'll try not to make too much changes, as you have already put an enormous work on it.

Greetings

Alex

Alternately, the engine could use a small pulley (same size and the lower pulley) which would increase the speed by 3x.

Now it was time to add the aesthetic features of the carrier, which involved a lot more parts than I was expecting. I was able to avoid using the rare black bushings by just using black axles instead.

Alex, if possible, I highly recommend to include Blakbird's suggestion on the above as final instruction such that everyone can build with more common parts, thanks.

[gerger]

You can see in the video...the problem it's the design itself! The angles of steer are absolutely wrong in all axles! you can see the "non steering" wheels tug! Looks like the all crane hasn't a "rotation point" in it's body....normally all the crane have one!

I thought the steering was also a problem? Viz, the steering geometry doesn't work so it needs to skid wheels whenever it turns? Working out what steering ratios are needed between the different axles and getting closer to ideal would be tedious and probably difficult, but very helpful.

Although steering geometry is not as ideal as in real cranes, the 1x5L suspension arm + wheel hubs are wobble enough to adopt any angles varies.

The real challenge is the very long driving and steering train vs weight. When it steers WITHOUT drive, 1st and 2nd axles turn as always and 4th-6th axles turn less than expected because the superstructure is heavy enough to press the rear part of the carrier not moving. Adding more counterweight to the superstructure may cause the carrier steering worse. All axles steering works fine when it drive.

I have some brain storming whether to keep the front and rear drive / steer functions separately, something similar to real grove 12x8x12 arrangement:

the front 1st and 2nd axle:

- keep 1L motor for steer as where it is now.

- keep only 1XL motor for drive and arrange it longitudinally.

the rear:

- remove 3rd axle gearbox and use that space for second XL motor to drive 4th and 5th axles. 3rd axle will not drive or steer.

- remove 6th axle gearbox and use that space for additional L motor to steer 4th, 5th and 6th axles. 6th axle only steer but not drive.

A pole switch can also be added to the rear steering motor such that the carrier can preform crab walking mode!

There is a big question mark whether the above driving and steering setup can result a more even power distribution along the carrier. But I like current 12x12x12 all wheel drive and steering setup as it is very fun to play with.

[afol1969]

@gerger: Boah, a lot of suggestions! I think, at first I build the crane, test it, and then I'll begin to review the instructions. Of course I'll try to use common parts, to avoid that you have to buy exotic/expensive parts.

If I change the pulley with a small one, which rubber belt should I use? I think a smaller one in . And I've to redraw it (I've still not much experience with LSynth....)

And @blakbird: Did you made any changes on the submodels axle1 and axle2? I've already stepped them from the CAD file before. (see instruction example some posts before)

Greetings

Alex

[Blakbird]

I thought the steering was also a problem? Viz, the steering geometry doesn't work so it needs to skid wheels whenever it turns? Working out what steering ratios are needed between the different axles and getting closer to ideal would be tedious and probably difficult, but very helpful. It could probably even be done using Lego parts, so in that sense it's more solvable than the short linear actuator problem.

While I agree that the steering angles are not right, I don't think there is any easy solution. There are no gears with the right number of teeth to allow the right distribution, and you can't just use different length steering arms because there is no room. I think it steers well enough given all the constraints.

If I change the pulley with a small one, which rubber belt should I use? I think a smaller one in . And I've to redraw it (I've still not much experience with LSynth....)

The belt is not synthesized, I just used MLCAD's rubber belt generator. You can just double click on the belt and type in a new diameter for the upper pulley. I had to stretch my belt a lot to install it, so you may not have to use a smaller belt for the smaller pulley.

And @blakbird: Did you made any changes on the submodels axle1 and axle2? I've already stepped them from the CAD file before. (see instruction example some posts before).

I think I did make changes, yes. I can't remember exactly what they were, but there were a lot of little things that were not quite right in the file which I fixed as I went along.

[kungpo]

What an amazing MOC!

Is there a part list on rebrickable yet? Before I embark on this build I want to make sure I have all the bits! So far got 2x 42009, 1x 9398 plus a few other bits and pieces. I think I have all the other PF parts knocking around and I know I need some more curved panels.

[jantjeuh]

The set will be posted as a public MOC on Rebrickable when the final instructions are done (we require MOCs to have instructions). Until then, you can add it as a private MOC (My RB => My MOCs => Add New Private MOC) using the parts list posted by Blakbird earlier in the thread. Then, simply click on 'Build this MOC with your sets and parts' to see if you have all the parts required! Note that this parts list is not the parts list of the definitive version, so there may be changes.

Edited September 24, 2014 by jantjeuh

[kungpo]

Perfect - Thank you! I think I'm almost there with the bits.

[keithleon]

Hi there , just join and look forward to seniors folks here for guidance .

Just had a stock 42009 sitting on my work desk , initially wanted to build a ultimate version with RC , then come across this interesting thread !

So for now I'm just happy that there's another exciting version going on right now right here , guess I'm in the right time @ the right place !

Looking forward for updates from seniors master hobbyist here !

Regards

Keith

[dhc6twinotter]

This is a beautiful model, and all the renders are fantastic! Thanks for all the work you've put into this, Eric. Really nice work.

I'm surprised the L motor is strong enough to lift the boom, but I guess I just haven't played around with the L motors enough to know their true strength.

I'm in the thinking stage of a large crane (AC-700) that I've wanted to build for a while, and there is some great ideas and lessons that I've learned from this build. Thanks!

[afol1969]

News about the instructions:

I come to finish the carrier near the end of the month, I plan to to separate the instructions in a carrier part and superstructure part, with two part lists. Until now I built the submodels like blakbird has made them in his instruction drafts. But some models I'd completely change the step order to make parts more visible. I didn't need to change any parts, only some axles with another length.

Alex, if possible, I highly recommend to include Blakbird's suggestion on the above as final instruction such that everyone can build with more common parts, thanks.

Of course I try not to use very exotic parts, I myself use the parts which I have in my stock. For example I don't have enough LB pins wit stop bush, so I use them in black.

Greetings

Alex

[a_h_adl]

Fantastic model, superb job, thanks guys!

Has anybody built this MOC and has already got another untouched 42009? It would be great to see them side by side.

[jantjeuh]

Ask Blakbird, he has got all past, current, and future sets and MOCs built.

[kandykop]

Fantastic model, superb job, thanks guys!

Has anybody built this MOC and has already got another untouched 42009? It would be great to see them side by side.

[PhyBuilder]

You are a clone of Madoca .

[keithleon]

Hi , is it possible only to use just the front end of the Grove GMK6400 cab and replace the original standard cab of 42009 ? The new cab face of this Grove GMK6400 is stunning !

Maybe I would consider only just to convert the original cab face to the cab face of Grove GMK6400 .. is that possible ?

Edited October 9, 2014 by keithleon

[Blakbird]

Hi , is it possible only to use just the front end of the Grove GMK6400 cab and replace the original standard cab of 42009 ? The new cab face of this Grove GMK6400 is stunning !

Maybe I would consider only just to convert the original cab face to the cab face of Grove GMK6400 .. is that possible ?

Anything is possible, but it won't fit without modifying the backup structure.