42042 - Crawler Crane - Mods and improvements

[kolbjha]

I really like this set, and even it has IMO a great gearbox, one of the first things I was thinking of after completing the build, was how to make it RC.

I guess most of the six functions are straight forward, but operation of the claw is obviously more tricky. I tried to figure out if it was possible to operate the claw by the hoist string. I realized that it is possible to transfer motion to a pulley in the claw simply by pulling the string on one side of the pulley, and letting out on the other side. The claw should then in theory be kept at the same level, and the motion transfered to the pulley could be used to drive the m-LA. To achieve this, I have used two reels, each of them connected to the ouputs of a subtractor (geared down 1:3 with Z12 and Z36 double bevel gears).

If using tracked vehicle implementation of a subtractor as a reference, the "drive" part is done with a M motor driving a worm gear that in turn drives a Z8 spur gear. The "turn" part is done by a XL motor, directly driving the differential housings. I probably could use a L motor as well, thus avoid the coasting of the XL. The string I have used, is simple string for packing purposes. I guess it is better (and more puristic) to use the thick LEGO string, as it looks better, is more solid and no twisting. Problem is, can I get a thick LEGO string that is long enough?

Please don't judge from the aesthetics, the main goal for me at this stage was to demonstrate the idea, and I have not put a lot of effort in the looks, or making it compact.

Link to video:

Here is my own judge for the idea:

Pros:

1. IMO it looks more clean than a hanging motor with it's supplying wires.
   
2. Both hoisting and claw operation may be done simultaneously.
   
3. Able to operate two functions with a simple string.
   
4. Adding mechanical complexity to the model, something I like.
   

Cons:

1. The torque delivered to the m-LA is limited, so the grip of the claw is not very strong.
   
2. It should be apx. equal amount of string on both reals, to achieve claw operation without changing the level of the claw.
   
3. Claw operation is depending on friction between the string and the claw pulley. If the the claw is resting on the ground or the object it should lift, it will not work.
   
4. Probably not real-life-like implementation of claw operation.
   

Another idea I have, still not tested, is to convert the hoist string into a closed loop. the claw implementation is the same, with a pulley driving the m-LA. On the tip of the boom, there is a pulley, driven by cross axles from the super structure (the reason for location on the tip of the boom is to reduce length of the string, and number of pulleys, to reduce friction). The hoist may then be done by two pulleys pulled along the boom, towards the super structure. One of the advantages of this implementation, if it works, is that "Con #2" above is eliminated. I don't know if this description makes sense to you, I will try to test this version also. Main problem is, how to make a long, closed loop of LEGO string, without any bumps.

I appreciate any feedback, including cons. And I also hope to inspire some of you to come up with a better solution.

PS: Somebody who knows how to embed a "visual" youtube link, like most of the others do (I didn't figure out)?

Edited August 7, 2015 by Alasdair Ryan

[MaxSupercars]

Hmm... very good work... I like that you have not copied that stupid ideas with motors etc...

Max...

[SNIPE]

I Think this is a good idea, how do the two spools counter rotate?

[kolbjha]

I Think this is a good idea, how do the two spools counter rotate?

The two spools are connected to the two outputs of a subtractor. A subtractor is mechanism that combines two input movements into two outputs. It is often used for tracked vehicles. The claw up/down is done by the "drive" part of the subtractor, while open/close claw is done by "turn" part of the subtractor. Sariel's book "The unofficial LEGO Technic builder's guide", chapter 18 "Adders and subtractors" explains this subject very well.

[lcvisser]

I like this! I think it is a quite elegant solution, better than the alternative you're proposing at the end of your post.

The whole idea would probably work better with a heavier claw, as that would increase the friction on the pulley and also make it easier to keep the claw level during opening/closing. If you have one, maybe you can add one of the Technic counter weights (like the one on 8868) to the claw. It seems silly though to add weight just for that...

[Cumulonimbus]

That is a nice idea, did I understand correctly that you use the grapple cable to power the mLA in the grapple? Why not simply connect the grapple cable to the closing mechanism of the grapple? I'm working on a similar MOD and this is how I solved it:

Instead of a subtractor, I use the gearbox to couple the two spools. Simply said it works like this: If you select the hoist function, the grapple function is always powered as well. So if the grapple is lifted, the grapple closing cable is winched in the same amount, so the grapple stays in the same position relative to the lifting cable. If you want to open or close the grapple, only the grapple spool is powered. The demonstrator I have built works relatively good. There are some drawbacks though: the cable powered grapple lacks pinching force, the cables and spools of both functions have to be of equal size and thirdly I still have to find a way to attach both cables closer to the centre of gravity of the grapple.

[Jurss]

Good work.

[shineyu]

good work, thanks for sharing

[Jeroen Ottens]

That's really clever...

Maybe adding some thin rubber tire to the spool will help to increase the friction? Something like this: with some guiding elements around it to make sure the string doesn't fall off.

If you remove the s from https your videolink should embed (and maybe you'll also have to add before and after, I always forget)

[Victor Imaginator]

Wow! Magical solution. Just incredible)

Using worm gear instead of pulley will increase friction, but at cost of limited range of operation.

[thomol]

Why not simply connect the grapple cable to the closing mechanism of the grapple?

Do you mean something like this? http://blug.es/eng/productos/tongs/pmb-300-pi10

Only problem I see is that the grapple is too light in respect to the friction in the pulleys. When pulling the grapple string the whole grapple will probably be lifted instead of closed. Maybe that can be solved using a weight brick.

[Cumulonimbus]

Do you mean something like this? http://blug.es/eng/p...gs/pmb-300-pi10

Only problem I see is that the grapple is too light in respect to the friction in the pulleys. When pulling the grapple string the whole grapple will probably be lifted instead of closed. Maybe that can be solved using a weight brick.

Yes, that is what I meant. You're right about the pulleys, that is why I didn't use any pulleys and connected the cable directly to the central linkage of the grapple. But even then the closing force is small.

I added a central liftarm where the mLA used to be to reduce the degrees of freedom and make the movement smoother. This is how it looks at the moment: (the central grey liftarm can slide up and down)

[thomol]

Yes, that is what I meant. You're right about the pulleys, that is why I didn't use any pulleys and connected the cable directly to the central linkage of the grapple. But even then the closing force is small.

I think you need at least one pulley on the bottom of the central linkage. Let the cable go down, round the pulley and then up and connect it to the outer frame. When you pull the cable it will then pull the inner part upwards and the outer part downwards, closing the grapple. The closing force should be somewhat proportional to the weight of the outer frame, which is what's holding the grapple down to the ground.

Hm, just realised you need to balance the claws to stay open when you release the grapple cable, otherwise it will be impossible to pick anything up...

To bad I'm away from my Lego, I would like to test this myself.

[kolbjha]

PS: Somebody who knows how to embed a "visual" youtube link, like most of the others do (I didn't figure out)?

Alasdair, thanks for embedding my video in my initial post

[kolbjha]

That is a nice idea, did I understand correctly that you use the grapple cable to power the mLA in the grapple?

I use no dedicated grapple cable. There is only one string that simply goes from one reel -> boom tip -> pulley in the "claw module" -> boom tip -> other reel. The two reels are driven by the two outputs from a subtractor. The inputs are one motor for hoist and one motor for claw operation.

I'm working on a similar MOD and this is how I solved it:

Instead of a subtractor, I use the gearbox to couple the two spools. Simply said it works like this: If you select the hoist function, the grapple function is always powered as well. So if the grapple is lifted, the grapple closing cable is winched in the same amount, so the grapple stays in the same position relative to the lifting cable. If you want to open or close the grapple, only the grapple spool is powered. The demonstrator I have built works relatively good. There are some drawbacks though: the cable powered grapple lacks pinching force, the cables and spools of both functions have to be of equal size and thirdly I still have to find a way to attach both cables closer to the centre of gravity of the grapple.

Sounds like a very interesting idea, and I like the simplicity of it. And it is probably closer to real-life-solution. Perhaps it is possible to make the claw in such a way that the grip is getting stronger the more weight hanging in the claw, almost the same way as a bat is hanging. I will try to experiment with your idea also

[kolbjha]

That's really clever...

Maybe adding some thin rubber tire to the spool will help to increase the friction? Something like this: with some guiding elements around it to make sure the string doesn't fall off.

If you remove the s from https your videolink should embed (and maybe you'll also have to add before and after, I always forget)

Thanks for the feedback!

Here is a few pictures showing some more details:

Her you can see the pulley (3L diameter) and 6 small rims (the same as your posted picture, only without the rubber) to keep the string in place. the two uppermost pulleys (you see only one of them) are there for securing the string, and also to make distance between the entrance and exit of the string. This to avoid too much rotation of the claw, and also twist of the string.

The claw pulley is driving a Z36 double bevek gear, which in turn drives a Z20 bevel gear, driving the m-LA.

If I understand you correctly, you suggest to use rubber on the pulley to increase friction, and thus the torque transfered to the m-LA before slipping? Perhaps it is possible to use two 3L diameter pulleys with rounded rubber tires (the same as the front wheels of the 42033 Record Breaker) tightly together, and place the string in the groove between them? That will certainly give a lot of friction.

[Jeroen Ottens]

Thanks for the feedback!

Here is a few pictures showing some more details:

Her you can see the pulley (3L diameter) and 6 small rims (the same as your posted picture, only without the rubber) to keep the string in place. the two uppermost pulleys (you see only one of them) are there for securing the string, and also to make distance between the entrance and exit of the string. This to avoid too much rotation of the claw, and also twist of the string.

The claw pulley is driving a Z36 double bevek gear, which in turn drives a Z20 bevel gear, driving the m-LA.

If I understand you correctly, you suggest to use rubber on the pulley to increase friction, and thus the torque transfered to the m-LA before slipping? Perhaps it is possible to use two 3L diameter pulleys with rounded rubber tires (the same as the front wheels of the 42033 Record Breaker) tightly together, and place the string in the groove between them? That will certainly give a lot of friction.

I just realized that my example will require an axlehole in the wheel and not a pinhole , so yeah, having two 3L pulleys with tires will be a better solution. Just make sure that the rope is thick enough so that it doesn't slip inbetween the two pulleys.

[kolbjha]

Wow! Magical solution. Just incredible)

Using worm gear instead of pulley will increase friction, but at cost of limited range of operation.

Using worm gear instead of pulley in the claw will give more friction, but also smaller lever.than a 3L diameter pulley, thus lower torque for the same tangential force of the pulley/worm gear. Anyway a really nice idea, and very compact, I didn't think of that

[Victor Imaginator]

Another idea for increasing torque

Yellow #1 connector in the middle should be new 1L beam. Or regular 3L beam)

Tan 5L axles is mounting points for claw mechanism.

[efferman]

victor, this does not increase the torque

[Alasdair Ryan]

[Victor Imaginator]

Sorry, i mean friction, not torque)

[D3K]

That has nothing to do with Victor Imaginator's idea.. However this principle is indeed used in the 42042 out of the box, on the boom lifting mechanism

EDIT:

By the way, I like the idea!

@Victor have you tried to build this in physical bricks?

Edited August 8, 2015 by D3K

[Victor Imaginator]

Nope, most time now i spent at my job, Here's no lego( i'll try this at home, if i find a time... 7th day without weekend

[Richard Dower]

here is a rope mod is saw on YT: