[MOC] Small 4-axle mobile crane - finished!

[ludov]

I managed. After a lot of iterations on the concept shown above, I realised I was overcomplicating it. I moved the driven gear that extends the outrigger to the other side, put a idler gear on the far outside (where the driven gear used to be), and then the synchronisation is trivial:

The 3L pins are end-stop that prevent the outriggers from falling out. The total extension is a bit over 5M, including the extension of the 2nd part.:

The yellow axle will linke the front outriggers with the rear ones (once the loose u-joint is connected), so in the end one control extend all four. As you can see, I also fitted an engine, and routing the outrigger link under the turntable and past the engine and past the steering (the tan gears in the top-left of the picture) was a real pain.

I think the overal length is still good, but the 16z gears of the front outrigger extension will end up in the cabin... no seats, probably:

I'm short of a few 5M levers in LBG (for the outriggers).

Next steps: add cabin and engine cover.

You can find more photo's here https://bricksafe.com/pages/ludo/small-crane. Feedback is appreciated! 

[Jeroen Ottens]

Interesting and good that you found a compact solution. One question though: Why don't you use the 7L gear rack with 12T gears? Adding a beam above it (oriented sideways so that the curved edge acts as a natural guidance for the 7L rack when it is extending) should then be enough to limit the tilt of the outrigger... Or do you need the space above the 8T gears?

[ludov]

1 hour ago, Jeroen Ottens said:

One question though: Why don't you use the 7L gear rack with 12T gears?

I considered that, but the 7M gear rack only has 3M of teeth, which allows only 2M of extension. I thought that too little. This solution uses the maximum amount of extension possible given the width of the vehicle (minus the space taken up by the outrigger mechanism, which is 1M).

I tried a solution with the 13M gear rack, but it has the holes in the wrong places and I couldn't manage... A 9M or 11M intermediate size would be nice to have!

[1gor]

Outriggers solution is great 

[ludov]

Update time again. Yes, I build really slowly 

This it what it looks like now (note: still missing some LBG parts for the outriggers):

Everything is connected now and starting to be covered up. I'm not sure yet how to finish the cabin... Not sure if I'm happy with it's size, but I'll see how it turns out when done. I'm definitely not super happy with the seats, but I don't see an alternative at this moment. The exhausts do the steering by the way, as you can see in this picture below (you can also see how uncomfortable the seats are )

The outrigger control is done by a double bevel gear on the back:

Not too satisfied with it though: it sticks out from the back, and the 8L axle with stop is really easy to pull out. It's on the other side are a 16z and 8z gear, but those have really little friction for some reason. I could put a 9L with two half-bushes, but then it sticks out even more... Any ideas?

Feedback and comments welcome! 

[Jeroen Ottens]

27 minutes ago, Ludo Visser said:

The outrigger control is done by a double bevel gear on the back:

 

Not too satisfied with it though: it sticks out from the back, and the 8L axle with stop is really easy to pull out. It's on the other side are a 16z and 8z gear, but those have really little friction for some reason. I could put a 9L with two half-bushes, but then it sticks out even more... Any ideas?

Feedback and comments welcome! 

The 16T gears have a huge variation in friction. If you have an older version (with the four round holes in it) you should use that, they typically have much more friction. For the newer style 16T gears there is a difference between the older ones (very low friction, almost sliding on the axles) and more recent ones, which have reasonable friction. So it worth testing a couple to see which one has the highest friction.

[ludov]

On 5-6-2018 at 10:41 PM, Jeroen Ottens said:

The 16T gears have a huge variation in friction. If you have an older version (with the four round holes in it) you should use that, they typically have much more friction. For the newer style 16T gears there is a difference between the older ones (very low friction, almost sliding on the axles) and more recent ones, which have reasonable friction. So it worth testing a couple to see which one has the highest friction.

I'm not a fan of relying on particular molds, even though I have a lot of the older 16z gears. I'd like to think that someday I might make instructions and someone might use them and then I don't want to this very hypothetical person to have to worry about which gear to use. Hypothetically.

So I solved it with a 9L axle with two half-bushes locking the 16z inside in place. The 12z on the outside has more friction and stays on even when I pull the whole thing by it.

 

And I finished the cab! I took @Erik Leppen's advice and raised the cab two studs. The roof only one. What do you guys think?

As always, feedback welcome! 

[1gor]

Just one question - is it possible to put V6 instead of V4?

Cab is relatively good

[dhc6twinotter]

Great looking model!

 

[ludov]

Thanks! I guess it's time to start on the upper structure.

17 hours ago, I_Igor said:

Just one question - is it possible to put V6 instead of V4?

I initially was considering a V8 at the smaller scale, like the new Mack Anthem has. It fits, but I wasn't happy with its robustness and playability. I like how @Thirdwigg puts small 2- or 3- cylinder motors in his MOCs and took inspiration from that when I decided for a regular V4.

[1gor]

6 minutes ago, Ludo Visser said:

Thanks! I guess it's time to start on the upper structure.

I initially was considering a V8 at the smaller scale, like the new Mack Anthem has. It fits, but I wasn't happy with its robustness and playability. I like how @Thirdwigg puts small 2- or 3- cylinder motors in his MOCs and took inspiration from that when I decided for a regular V4.

I see...

[Thirdwigg]

@Ludo Visser I'm happy to have a little bit of influence on your build. Keep it up, I like where this is going.

[ludov]

Still working on it 

I made the boom:

This tool me a lot longer than I expected. I really wanted the boom to be 4x4 or 5x5 in cross section. I tried many solutions based on the "old" 2M worm gear on a gear rack (often used, e.g. by @Erik Leppen here (design by Anko) and recently by @jwarner in his small 5-axle crane. But I didn't like how the axle joiners rub on the gear rack. Also, LDD wouldn't allow the construction, so I searched on. I found two solutions that I was reasonably happy with:

The front one uses an idler 8z gear (kind of hidden) and has the gear racks sort of on the side of the boom. The back one uses the new 1M worm gear, which fits nicely into the space at the end of the 3x11 curved panel. I like that solution the best for its symmetry so I developed it further. Here's a close up of the final implementation

I also spent a huge amount of time figuring out the geometry of the actuator. Being an engineer and all, I dusted of the cosine rule and try to optimise the placement for horizontal boom when the actuator is retracted and maximum elevation angle when extended.

Spoiler

Here is what I did (maybe already figured out by the experts among you )

• The length of the linear actuator when retracted and when extended are given, so the only free variables are the relative position of the mounting point of the actuator with respect to the hinge point of the boom (2 coordinates: a and b) and mounting point of the other end of the actuator along the boom (d).
• I restricted the variables to have half-stud resolution, otherwise it will be very difficult to build
• To visualise all the options, note that a,b are almost restricted to a circle with a radius equal to the length of the actuator (almost, since you have d to play with as well, so you can deviate from the circle).

Here's a plot that shows the maximum elevation angles for a subset of a,b: I choose this subset based on having a near-horizontal position (0 degrees) when the actuator is retracted and at least 70 degrees elevation when extended.

I then choose a solution based on the following criteria:

1. a, the horizontal distance between the hinge point of the boom and the mounting point of the actuator, should be as large as possible for the mechanical advantage.
2. b, the vertical distance, should be at least 2, so that the actuator is parallel or below parallel to the boom when fully retracted (above parallel the actuator wouldn't be able to lift the boom), and you need some space to actually fit the actuator (the actuator itself is about 2 studs in diameter).
3. d, the distance of the actuator mounting along the boom, should not exceed 16, otherwise it would collide with the cabin of the carrier
4. at least 70 degrees of elevation, preferably 80.

I settled for a=2.5 and b=3, which gave d=14.5 as optimal for a maximum elevation of 79 degrees (solid lines are the boom, dashed line the actuator):

If you know what a jupyter notebook is, I can share some code, but in the end it's just geometry 

The final solution shown above has 79 degree elevation, and I'm happy with that 

I will finish it some day. Hope you like the progress!

[suffocation]

Love this build - so much going on in so little space, and it looks great.

I think I'll steal your boom idea and turn it into a custom actuator

[1gor]

Nice progress, but I hope that someday 4 X 4 section Crane will be working properly. I would like to have 3 studs wide crane...

[Magical Duck]

I've been following this topic for a while... glad to see the boom taking shape! Nice job 

[Boulderer]

Only just seen this topic. Great content and really interesting to read about the project development. 

Love the geometry lesson ?

[Yevhen]

16 hours ago, I_Igor said:

Nice progress, but I hope that someday 4 X 4 section Crane will be working properly. I would like to have 3 studs wide crane...

It's possible when using old beams. Perhaps you have to add several thin liftarms to make the boom more robust.

[1gor]

2 hours ago, Yevhen said:

It's possible when using old beams. Perhaps you have to add several thin liftarms to make the boom more robust.

That is probably the only way but crane should be short ?

[Yevhen]

21 hours ago, I_Igor said:

That is probably the only way but crane should be short ?

Why does it make you sad?

Ludo Visser, so your boom is still 5 studs wide?

In my opinion many Technic designers make the same mistake when building such wide booms in cranes and excavators.

In reality those parts are pretty slim!

Edited August 17, 2018 by Yevhen

[1gor]

47 minutes ago, Yevhen said:

Why does it make you sad?

Ludo Visser, so your boom is still 5 studs wide?

In my opinion many Technic designers make the same mistake when building so wide booms in cranes and excavators.

In reality those parts are pretty slim!

Actually it makes me worry (please look above). In reality I plan to make small telehandler, but there is only light bluish gray and red gear rack that I can use and no black. Real booms are indeed very slim. Perhaps instead curved panels 11 X 3, ordinary panel 11 X 3 would be more usable; this one

https://rebrickable.com/parts/15458/technic-panel-3-x-11-x-1/

 

[ludov]

13 hours ago, Yevhen said:

Why does it make you sad?

Ludo Visser, so your boom is still 5 studs wide?

In my opinion many Technic designers make the same mistake when building so wide booms in cranes and excavators.

In reality those parts are pretty slim!

Yes, it is 5x4 (5 wide, 4 high). I agree that f it were a scale model it should be about 4 studs wide, but I prefer playable over scale in this case.

 

13 hours ago, I_Igor said:

Actually it makes me worry (please look above). In reality I plan to make small telehandler, but there is only light bluish gray and red gear rack that I can use and no black. Real booms are indeed very slim. Perhaps instead curved panels 11 X 3, ordinary panel 11 X 3 would be more usable; this one

https://rebrickable.com/parts/15458/technic-panel-3-x-11-x-1/

 

Good idea! I didn't think of the regular 3x11 panel, as I don't have them in yellow. But you could indeed make it 3x4 with those:

Obviously, 4x4 would be trivial, just add a layer of beams in the middle.

Maybe I need to reconsider my design

 

[Yevhen]

The last 3x3 scheme is very good, but you have to turn it upside down to make the boom stronger.

Or use additional beams to staple the panels. But in this case the boom will have a 3x4 full size.

Edited August 17, 2018 by Yevhen

[Ivan_M]

Panels 3x11 are indeed very good for it, here is how I did it back in the day on my excavator:

IMGP4971 by Ivan Moc, on Flickr

You have to add at least one layer of plates to hold technic brick together. I have used two bricks side by side, one plates layer on bottom and one on top.

Edited August 17, 2018 by Ivan_M
better pic

[ludov]

Guess what, it's finished!

Here are two quick photo's I took; I'll try to make some better ones in the coming days during the daytime.

In the back of the upper structure is a small gearbox. When you engage the red switch and then rotate the knob for the hoist, the boom is extended (or retracted) with the same pace as the spool, so the hook stays at the same relative position; no need to first drop the hook, then extend the boom, extend the hook again, etc. I'll try to make a small movie of it.

I'd love to hear your opinions!