[MOC REVIEW] Grove GMK6400 Mobile Crane

[jantjeuh]

Take Blakbird's BrickStock inventory, subtract the inventory of 42009 twice, remove all the PF parts and all parts with negative or null quantities, et voila.

Edit: well, because I'm such a nice guy I did it for you [link removed].

Edited April 20, 2018 by Jim
Link removed. Warnings about malware.

[Blakbird]

Now I'll talk about the boom luffing mechanism. This system uses an L motor to drive a pair of parallel linear actuators geared down 5:1 as shown. Even though the boom is quite heavy and the mechanical advantage is poor, the system seems to have ample power to lift the boom.

The only problem with this system is that the travel of the linear actuators is far too short to properly mimic the range of motion of the real machine (approx -1.5deg to 82 deg). Gerger has partially addressed the low maximum boom angle by eliminating an interference by moving a pair of 11L double bent liftarms forward one stud (as shown in this prior post). This works well enough at the cost of some strength in the aft part of the boom. As the image below shows, the real Grove GMK6400 attaches the actuators much further forward, nearly at the front of the cab, and uses a very long stroke. It may be possible to use an aftermarket actuator to mimic this attachment point and stroke.

The other issue with the main boom and superstructure is that it simply needs MUCH more counterweight and/or a longer arm on the counterweight. You can see the turntable straining visibly when the boom is lifting, and if your turntable is not tight it might pop apart. The guide wheels that Gerger added help a lot with this. If you again look at pictures of the real crane, you can see that the counterweights are not present in the roadable configuration and only get added at the site. The way the model is currently built is in the scale roadable configuration so it really doesn't represent the counterweights at all. It might be possible to simply clip something on, much like the real thing, when using the main boom. Note that if you change the attach point of the actuators to the boom such that you get maximum elevation, then the balance of the superstructure is OK. It is when the boom is at a lower angle that there is some trouble.

I also decided that the model needed a boom rest for when the boom was stowed, so I just added a couple of Bionicle teeth to the roof of the cabin. It works very well to center and support the boom during transport.

[Blakbird]

I decided to do a quick test to see what kind of fictional actuator it would take to make the boom motion realistic. By moving the rotation point forward to the furthest axle hole on the superstructure and moving the attachment point to the boom to a scale location, the following pictures show the ideal actuator. It would be about 50 studs long and have a stroke of at least 15 studs.

Of course there is no such actuator so it was just an exercise. On the other hand, I thought I would see what it looked like with a Firgelli actuator. It would actually work almost perfect, albeit with a low boom attach point. However, this solution would eliminate the need for one of the L motors and the associated gearing.

Any solution that moved the rotation point of the actuators forward like this would also greatly increase the stiffness of the raised boom.

[nychase]

Its worth mentioning that if you mounted two firgellis (not sure how easy it would be) that had the internal gear train swap then they would have a combined 66lbs of lift force. I built the 3 section boom for Han's 8421XL and just one with the geartrain swap was plenty strong. I mention two incase someone wanted to mount a 4 section boom...it could certainly be lifted.

I am seriously considering converting my 8421xl to this...still wouldn't be cheap!

Eric...Did you investigate if the top-back of the boom had the clearance to be at an 82 degree angle? It was a big hassle with the 8421xl and still somewhat a problem in Jennifer's Demag to get the lift angle I wanted. If its simple on this then the firgelli might be the way to go for people (like me) who are sick of these pathetic OEM booms that are in serious need of a little blue pill.

Edited September 8, 2014 by nychase

[Milan]

I also decided that the model needed a boom rest for when the boom was stowed, so I just added a couple of Bionicle teeth to the roof of the cabin. It works very well to center and support the boom during transport.

AT mobile cranes, such as this Grove, have rubber mounted carrier cabin. So resting the boom on the holders on the cabin is not realistic. Instead, the boom is resting on the separate support that is attached at the front of the chassis, and usually have triangular shape.

[Blakbird]

Its worth mentioning that if you mounted two firgellis (not sure how easy it would be) that had the internal gear train swap then they would have a combined 66lbs of lift force. I built the 3 section boom for Han's 8421XL and just one with the geartrain swap was plenty strong. I mention two incase someone wanted to mount a 4 section boom...it could certainly be lifted.

Considering that this is a scale model, I'd only want to use a single actuator because that's what the real Grove uses.

Eric...Did you investigate if the top-back of the boom had the clearance to be at an 82 degree angle? It was a big hassle with the 8421xl and still somewhat a problem in Jennifer's Demag to get the lift angle I wanted. If its simple on this then the firgelli might be the way to go for people (like me) who are sick of these pathetic OEM booms that are in serious need of a little blue pill.

I have not measured the angle, but with the modification of moving the 1x11 double bent liftarms the boom can rise to the position shown in the picture as long as you have a long enough actuator.

AT mobile cranes, such as this Grove, have rubber mounted carrier cabin. So resting the boom on the holders on the cabin is not realistic. Instead, the boom is resting on the separate support that is attached at the front of the chassis, and usually have triangular shape.

Yeah, I know. The boom rest was a practical consideration for the model, not a scale detail. With no boom rest, the boom bounces all over the place while driving. Whether or not to use it is a personal decision.

Balancing the boom on the cabin in a real vehicle would be a terrible idea. The poor driver would have to endure the pounding of that massive boom.

[JDC]

Blakbird, which Firgelli actuator did you use in the above drawing?

[DoGoods]

Has it been considered to use a string LA like here: http://www.eurobricks.com/forum/index.php?showtopic=86857

I have been attempting to make it work but I'm not very good, I need some instructions.

[Blakbird]

Blakbird, which Firgelli actuator did you use in the above drawing?

The long one.

[JDC]

Blakbird, based on your fictional actuators above, this is what I had in mind using efferman's actuator with the L Motor. Of course, I had to make a rough representation of his 3D printed part. The cylinder is supposed to have a 3 stud diameter, but the length is about right. I think it's about 30 studs long. The whole thing would pivot where your fictional ones do.

Here is the idea at Bricksafe.

http://bricksafe.com...jpg/640x139.jpg

Edited September 9, 2014 by JDC

[nachtlegobauer]

Hey Guys!

You knows this thing?

http://www.bricklink.com/store.asp?p=Eezo

Greets

Thorsten

[gerger]

On the other hand, I thought I would see what it looked like with a Firgelli actuator. It would actually work almost perfect, albeit with a low boom attach point. However, this solution would eliminate the need for one of the L motors and the associated gearing.

Any solution that moved the rotation point of the actuators forward like this would also greatly increase the stiffness of the raised boom.

Very interesting. I leave the superstructure as less changes as possible because they are performing reasonable ok until reading the review. Tempting to get a Firgelli...

I just downloaded the Firgelli LDraw models to test around (this won't go into instructions) and noted that it takes some spacing for cable attachment behind the pivot, a bit tricky to brace it firmly.

[jantjeuh]

I hope the final instructions will still use Lego parts exclusively

[Blakbird]

I hope the final instructions will still use Lego parts exclusively

I have no intention of changing the instructions to reflect any of my brainstorming ideas. These are just thoughts as I go through each function.

[Blakbird]

The simplest feature on this huge model (apart from the lights) is the slewing of the superstructure. The below image shows how an M motor is geared down 22.2:1 through a worm gear. Use of a worm gear is useful not only to give a large gear reduction in a single stage but to prevent the whole thing from swiveling under any sort of external loading (like wind, or pets). The ring gear of the turntable is fixed to the carrier, so the rotation of the 8 tooth gear on the superstructure causes the superstructure to rotate. The 8 tooth gear protrudes out the bottom of the superstructure along with the upper half of the turntable, but the whole thing snaps easily onto (and off of) the carrier.

This function works very well and I have no complaints. The M motor has plentiful power for this application. The slew rate is probably a bit faster than scale, but close enough to look good.

[JDC]

I agree with the "LEGO parts exclusively" sentiment. Everyone can participate. The rest are just ideas to toss around for fun, and done at an individual's discretion.

[Kladovec]

I´ve made XLS part list for this beauty. Hope will help to someone.

https://mega.co.nz/#!c8ZVRbiR!3xs1dO58M0PhdJMUq5o_jkvjIum0pQLjc-b_4zE4n-k

Edited September 12, 2014 by Kladovec

[kandykop]

I just finished building this one. It looks great but barely move and steering is poorly working. Otherwise great build.

[Leif]

After a single stage 12:20 gear reduction, a longitudinal axle then runs the entire length of the vehicle taking the torque to each axle.

Maybe nitpicking but isn't it true that for a proper drivetrain a differential between each pair of wheels is needed?

Just like you need a center diff on 4wd.

[Blakbird]

Time to explain the final 2 features. The main winch is driven by an M-motor through a clutch gear. The total reduction is only ~5:1, but the cable is still pretty slow which is probably realistic (you lose half speed because the cable is doubled down to the sheave. It seems to have plenty of power, though I have not tried to lift a load with it because I do not think the boom could support the weight when fully extended.

The last feature is the telescoping boom. The mechanical part of the mechanism is simple enough, but it is cables that allows the 3 stage telescoping to occur. This function is driven by an L-motor through a fairly convoluted gear train. This is necessary to allow the power to pass through the boom pivot. The worm gear drives a rack at the end of the middle stage, and the 3rd stage is driven by cables. Per other suggestions, I also added a return cable to assist in getting the 3rd stage to stow without gravity. It all works very well, although routing the cables was tricky.

[Kladovec]

Is there any video of this crane? Is moving really so bad?

[jantjeuh]

Yeah, that's kind of a bummer to hear. What's your opinion on the crane's moving and steering, Blakbird?

[JDC]

Will you show the cable routing for the return cable in the instructions?

[Blakbird]

Is there any video of this crane? Is moving really so bad?

Yeah, that's kind of a bummer to hear. What's your opinion on the crane's moving and steering, Blakbird?

Who said it was bad? You can read my impressions of the moving and steering in my review. Apart from some axles falling out sometimes, it works great.

Will you show the cable routing for the return cable in the instructions?

What I post will just be the output from LPub. The cable routing is well documented in another thread (pun intended), but I have a feeling afol1969 will be adding all that stuff in his quest for perfection.

[Blakbird]

Having finished describing all the functions, now I can move on to the part of my review dealing with the actual build. Here's the real life finished model:

I'll say one thing: the build was not quick. I acquired the parts over the course of about 4 months once the parts list became available, and then I had to get a bunch of additional parts when gerger made design changes. The loose parts filled two big IKEA bins without the panels or PF parts. With such a big project, I felt that parts really needed to be sorted. This is just a tremendous amount of parts. The PF parts alone cover the whole back of the table, and the pile of panels is unprecedented.

I was working with a rough draft of the instructions, and at this point I was still waiting for some last minute parts so I decided to build out of order and start with the boom. I was anxious to see how big it was.

From there it was time to do the 6 axle assemblies. With every axle driven and 5 axles steered, you might think this would be pretty repetitive. While there were similarities, I found that every axle was unique and therefore the build experience was varied. The axles are build in pairs, first the front two, then an outrigger box, then the middle two, then the back two, then another outrigger box. The front and rear outrigger boxes are not identical either.

Front axles with drive motors:

Outrigger box added:

Middle axles added:

Rear axles added: (this is still not the whole length, we have to add another outrigger box!)

At this point I was able to put on the tires and try out the chassis. At this weight, it drove and steered very well and I played with it all day.

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. Again, I have to say that the performance was very good at this weight, but this was when I first had an issue with the 2L axles falling out.

The only thing left to do was add the superstructure, and the boom was already built. Still, look at how many parts remain in the background of the above picture. The superstructure assembly took only one (long) evening.

It is hard to explain just how large this thing is, but my daughters were impressed.

I had a really good time building this model. It looks great in any position. Some performance suffers due to the weight, but I think it performs admirably given that factor. With all that being said, I did make a couple of minor modifications to strengthen things here and there, and I'll talk about those next time.