howitzer

[WIP] Telescoping boom excavator

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While excavators are long-time favorite of Technic, I recently saw something new in a construction site nearby: an excavator which had a boom that telescoped and rotated around its axis, instead of articulated jib. I then learned that a company called Gradall makes those, here's an example:

 thumbnail-slider-hero.png

So I set out to build one, though I make no attempt to replicate the looks exactly as some parts of this machine are next to impossible to replicate in Lego, at least in reasonable size.

The first problem was the triangular cross-section of the boom, but very soon it became clear that it's not feasible so I settled for squared cross-section. Considering the functions of axial rotation, luffing and telescoping it also became clear that the motor driving the telescoping action would have to be located on the boom, and hoses for the pneumatically operated bucket would have to run the length of the boom and exit at the back so that there would be room for extension. I wanted to extend it as much as possible, and some 11-12 studs seems to be reasonable maximum. Here's a photo of one stage:

JS0Xahq.jpg

Next in line was an attempt to build a superstructure which would support the batteries, pneumatic controls and gearbox for the axial rotation and luffing. At this stage I didn't even think of full motorization or remote control, I don't have PF parts for that and it was already complex enough. I got it as far as testing the motorized boom functions which more or less of worked, but I wasn't satisfied with the performance and there was a lot of problems with the gearing anyway. Here's a photo:

LiZcya8.jpg

At this point I was at sort of a crossroads: take apart and rebuild the superstructure to fix the aforementioned problems with gearing and try to finishing the thing OR make it even more ambitious with the Mindstorms Robot Inventor set that I just recently bought. It would have 4 additional motors (to complement the two PU medium motors I already owned) and hub with 6 outputs which could be controlled much better than what PF allows, enabling perhaps full RC control with proper programming.

I chose the latter so that's what I've been doing recently. And it hasn't been easy.

First I needed to decide how to use my motors and how to connect them to the functions. With motorized drive (2x tracks) and slewing in addition to the boom controls (axial rotation, telescoping, luffing, bucket switch and pump) there are more functions than the hub has outputs so some sort of gearbox would be required. The 8043 Motorized Excavator acted as an inspiration with its 6 functions for 4 motors, and I decided to try similar gearbox solution where 4 two-position selectors are moved with one motor at the same time so that in one position you can drive and slew and in another position all boom functions can be operated. I also stole the coaxial drive mechanism for tracks from the same set.

Here's where I'm now in photo:

u4VdEgy.jpg

And in digital model:

2X33fGY.png

I recently realized that it's almost impossible to use the angular motors in driving the boom extension, so I ordered a C+ L motor for that purpose and I'm waiting for that now. I also ordered a new type of pneumatic switch, so that it's easier to operate with motor.

Some problems at this stage: Is there any way to make the boom support narrower? The problem is the gearing for axial rotation, which seems to be pretty much impossible to fit in between the turntables in any narrower configuration than this:

fk6ayeo.jpg

Another problem is the gearbox construction, how to route all the functions to their places while still having the gearbox to be properly supported and smooth so everything works fine. Especially the axial rotation seems to be hard to achieve as there is a lot of resistance in the thing. With the earlier PF iteration I tried routing the gearing to both sides so that both turntables would rotate and while it sort-of works it of course introduces a lot of gears and friction. Turning just one turntable would have the force directed through the boom to the other turntable and that requires a lot of force too so it's probably not feasible.

And of course I haven't even touched the programming side of things with the RI hub yet, but I suspect that'll be much easier.

Any thoughts or tips?

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Challenging project.

Maybe looks and functionality is possible to achieve with mechanics, not pneumatics, using the same principle as on 42009 leg(or what it is called) extension. OK, not triangular beam. That would be really hard.

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Why not scale it down a bit and use the Arocs rack as the basis for a boom? Not everything has to be massive.

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16 minutes ago, Maaboo35 said:

Why not scale it down a bit and use the Arocs rack as the basis for a boom? Not everything has to be massive.

I thought of that, but it wouldn't help in any way to make the pivot mechanism smaller so not much point as the boom telescoping works fine as it is.

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Now here is a challenge :laugh:.

I see you use a waveselector in the function gearbox. You can put four driving rings around that. With the servo ability of the Control+ (and I guess also the RI-motors) and a small lever with an endstop you can select eight different functions in sets of two. So you'll need in total three motors to drive eight functions. I used this kind of setup in my WIP Spaceshuttle and to be published Backhoe. It works like a charm and is super compact. I do use a lot of 20T clutch gears in this setup for picking up the different functions from the gearbox. If you want I can put some pictures on Flickr.

For the rotation of the arm I think I would try to drive the turntables with wormgears instead of a 12T gear at a 90 degree angle. That complicates the whole connectionjoint but the forces in the drivetrain will be smaller and that hopefully will result in smoother performance.

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12 minutes ago, Jeroen Ottens said:

Now here is a challenge :laugh:.

I see you use a waveselector in the function gearbox. You can put four driving rings around that. With the servo ability of the Control+ (and I guess also the RI-motors) and a small lever with an endstop you can select eight different functions in sets of two. So you'll need in total three motors to drive eight functions. I used this kind of setup in my WIP Spaceshuttle and to be published Backhoe. It works like a charm and is super compact. I do use a lot of 20T clutch gears in this setup for picking up the different functions from the gearbox. If you want I can put some pictures on Flickr.

For the rotation of the arm I think I would try to drive the turntables with wormgears instead of a 12T gear at a 90 degree angle. That complicates the whole connectionjoint but the forces in the drivetrain will be smaller and that hopefully will result in smoother performance.

Thanks for your thoughts!

I considered using the four (or three) possible positions of the wave selector but using four motors (plus boom extension which is separate from the gearbox) will allow using the whole boom without needing to switch gears. Of course it would be possible to program the gear selector motor to switch gears whenever another function is needed but that would introduce significant delay so I think I'll stick to the two-position gearbox with 4 sets of functions. Hopefully I will be able to build the gearbox in a way that it's properly braced.

My earlier PF-driven build indicated that it's possible to drive the boom functions with bevel gears, but I have thought about using linear actuators for luffing the boom instead of driving the turntables directly. I experimented with it earlier but finding the correct geometry proved to be a challenge so I stuck with driving the turntable. Maybe I should give LA's a second try though.

Additional thought with the above: reducing number of motors with gearbox design would allow the connection of RI sensors like colour sensor, which could be combined with colour-coded turntable base so that it would detect the amount of rotation and stop where commanded. I'm not sure what use that would be though, because similar functionality can be done simply with motor position sensing...

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I have a much less detailed response...

THAT is what TECHNIC should look like!! Hundreds of cogs, and turntables and gear selectors... i'm going to go back and have a proper look, but i was compelled to reply. I love what i see!!  (..and not a system brick in site!!)

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15 hours ago, howitzer said:

 

Some problems at this stage: Is there any way to make the boom support narrower? The problem is the gearing for axial rotation, which seems to be pretty much impossible to fit in between the turntables in any narrower configuration than this:

fk6ayeo.jpg

 

In order to make it narrower, I'd actually invert it, so that the turntables that currently control the axial rotation become the bearings for raising and lowering, and the other turntables become the axial rotation. I'd then have a single shaft driving both axial turntables, you can get that by meshing the 12z gear and the turntable with an offset. I think that if you had a shaft right beside the black beams, you could do it.

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This comes right when we had a post that queried if we have ran out of good ideas for Technic models.  Great pick!

I actually tried to do this a few years back.  My problem was with hose control because I was using pneumatics.  I will post pics when I have the chance.  

I do know this was done successfully a while back by another user.  Forgot their name.  But the only problem was the end shovel/bucket was manual, which I think negates the true challenge of the project...

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7 hours ago, Saberwing40k said:

In order to make it narrower, I'd actually invert it, so that the turntables that currently control the axial rotation become the bearings for raising and lowering, and the other turntables become the axial rotation. I'd then have a single shaft driving both axial turntables, you can get that by meshing the 12z gear and the turntable with an offset. I think that if you had a shaft right beside the black beams, you could do it.

Hmm, I'm not sure what you mean, any chance you could make a quick model of your suggestion?

14 minutes ago, nerdsforprez said:

This comes right when we had a post that queried if we have ran out of good ideas for Technic models.  Great pick!

I actually tried to do this a few years back.  My problem was with hose control because I was using pneumatics.  I will post pics when I have the chance.  

I do know this was done successfully a while back by another user.  Forgot their name.  But the only problem was the end shovel/bucket was manual, which I think negates the true challenge of the project...

Would be great to see the solutions in yours and the other build!

---

Last night I couldn't sleep so I got up to do a major redesign: I turned the gearbox 90° relative to the boom, which appears to enable much more balanced and compact build. This requires some changes to the motor configurations, but I believe it's still much better than the original. Here's a couple of photos:

Rp8YrJz.png

x7UMHp5.png

The white collections of beams act as placeholder for the motors as there's no models for either Spike or C+ motors and the same goes for the dark azure battery box acting as RI hub. The pneumatic switch is similarly a placeholder and also built wrong here, but please ignore that :D

Few things of note:

- I got rid of the worm gear driving the boom functions and decided to use spur gears instead in several downgearing stages. This way friction losses should be smaller and there are no perpendicular axles so bracing should be easier. 

- There was a lot of juggling involved in positioning the slewing gears and gearbox controller motor and I'm not entirely satisfied with them yet.

- I put a banana gear ring here to gauge the size of the machine and to see if it will be needed for greater support than what the large turntable can provide. A lot probably depends on how the boom and the motors balance out, though the larger slewing ring might be useful in any case as the superstructure is going to be pretty heavy.

- I'm yet to design any bracing and that will probably be pretty hard to do, especially in a manner that is actually buildable. The cable and hose routing must also be figured out, though it shouldn't be too hard.

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Very cool project! For whatever reason, that is the most popular excavator for road work where I live, albeit on a tracks instead of truck chassis. 
All that looks somehow familiar (My Mecalac), but even more complex. My only advise is to start testing in real bricks and with real motors as soon as possible. You cannot guess what amount of torque and what level of bracing you will need. And that can change a lot in the build. Couple of times I had to scrap the entire superstructure because I haven’t tested it in real life. 
I agree with @Jeroen Ottens on using the worm gears to drive turntables. Bevel gears in that configuration are very hard to brace properly. Worms don’t skip and easier to control, since the reduction is much higher. 

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46 minutes ago, proran said:

Very cool project! For whatever reason, that is the most popular excavator for road work where I live, albeit on a tracks instead of truck chassis. 
All that looks somehow familiar (My Mecalac), but even more complex. My only advise is to start testing in real bricks and with real motors as soon as possible. You cannot guess what amount of torque and what level of bracing you will need. And that can change a lot in the build. Couple of times I had to scrap the entire superstructure because I haven’t tested it in real life. 
I agree with @Jeroen Ottens on using the worm gears to drive turntables. Bevel gears in that configuration are very hard to brace properly. Worms don’t skip and easier to control, since the reduction is much higher. 

I could drive the luffing of the boom easily enough, but what about the axial rotation? In my current design it works because the axle driving it is located at the center of the turntables on the sides but if I replace the bevel gear with worm gear, there's no way to route the drive there, or at least it will be very ugly and inefficient.

But yeah, I'll start building in real life soon, with maybe a little more thought put into bracing in the CAD model. Besides incorrect bracing, it is very easy on computer to design structures that are impossible to build in real life.

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1 minute ago, howitzer said:

I could drive the luffing of the boom easily enough, but what about the axial rotation? In my current design it works because the axle driving it is located at the center of the turntables on the sides but if I replace the bevel gear with worm gear, there's no way to route the drive there, or at least it will be very ugly and inefficient  

Okay you are right about the axial rotation. And you won’t have much load there anyway. I was mainly thinking about boom elevation. If I am reading the renders right all the weight of the boom will transferred to the gearbox, keeping under the stress all the time. And what will happen if you disengage it? Won’t the boom fall? Please disregard, if I am reading it wrong. I am sure you’ve thought that through. 

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8 minutes ago, proran said:

Okay you are right about the axial rotation. And you won’t have much load there anyway. I was mainly thinking about boom elevation. If I am reading the renders right all the weight of the boom will transferred to the gearbox, keeping under the stress all the time. And what will happen if you disengage it? Won’t the boom fall? Please disregard, if I am reading it wrong. I am sure you’ve thought that through. 

I thought about the backdriving issue, and that was the reason I originally planned to use worm gear, but in the first version I was able to balance the boom well enough that combined with the high gearing it should stay where it's put. I might be wrong though, in which case I will have to resort to worm gears after all.

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Interesting project. When I saw name of this thread I thought you plan to build UDS (Univerzální Dokončovací Stroj - in English Universal Finishing Machine) on Tatra chassis but then I understood that there are similar excavators from different manufacturers. Anyway for inspiration this is our Czech classic:

1f32e1ea84748be81386def25c2d9935.jpg

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So the very first image is not showing up for me.   I now see your target machine is a little different than the one i had in mind. Still, here is a version, tracked with clamshell buckets instead of shovel by one of our own ( or at least used to be part of the forum).

 

years ago i attempted this myself on Antos smaller excavator.  Here is the thread.  

pics are  gone because MOCpages died but of i can find the original ones ill put them up here.  I got things to work fine but could not figure out how to manage the pneumatic hoses.  

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5 hours ago, nerdsforprez said:

So the very first image is not showing up for me.   I now see your target machine is a little different than the one i had in mind. Still, here is a version, tracked with clamshell buckets instead of shovel by one of our own ( or at least used to be part of the forum).

 

years ago i attempted this myself on Antos smaller excavator.  Here is the thread.  

pics are  gone because MOCpages died but of i can find the original ones ill put them up here.  I got things to work fine but could not figure out how to manage the pneumatic hoses.  

WOW. Tthis moc is awesome, two motors withe many function!! :thumbup:

 

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8 hours ago, nerdsforprez said:

So the very first image is not showing up for me.   I now see your target machine is a little different than the one i had in mind. Still, here is a version, tracked with clamshell buckets instead of shovel by one of our own ( or at least used to be part of the forum).

<snip>

years ago i attempted this myself on Antos smaller excavator.  Here is the thread.  

pics are  gone because MOCpages died but of i can find the original ones ill put them up here.  I got things to work fine but could not figure out how to manage the pneumatic hoses.  

Very cool, I love both!

The first one was especially great with its modular construction and ingenious solutions like the function selector and support for superstructure stability. The bucket operation would indeed be a difficult thing to achieve remotely in that one, even if the manual version leaves a lot to be desired.

But yeah, my machine is of somewhat different type, though in many ways similar too.

10 hours ago, Tomik said:

Interesting project. When I saw name of this thread I thought you plan to build UDS (Univerzální Dokončovací Stroj - in English Universal Finishing Machine) on Tatra chassis but then I understood that there are similar excavators from different manufacturers. Anyway for inspiration this is our Czech classic:

<snip>

Actually, Gradall has also similar models, an excavator mounted on a truck chassis. I contemplated that too, but I believe tracked version is easier to make, so that's what I'm going to do now. Truck version would be nice future project though.

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Just a quick photo update on how the latest redesign is coming along:

iihw3ZX.jpg

Right now I'm waiting for my BL order to arrive, in order to get the new pneumatic switch so I can start thinking of hose routing. I'll also have to give some thought to wire routing so that they end up placed cleanly and with minimal hassle when it's time to recharge the hub.

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