Hi there, I'm having a bit of a problem building a claw on a crane.

I need it to rotate freely (the claw) and also mechanically... I'll explain better, I want the turntable to rotate freely all the time, but sometimes I also need to custom rotate it.

My problem is that in order to having it rotate I'm pluging it into a motor, and of course then it wont rotate freely

Its actually the same principle as a bicycle wheel, it runs freely until you activate the pedals and then the gears kick in and control it.

Any chance this is possible?

I was thinking of a gearbox to activate/deactivate the gears that go into the turntable but it wont work since it's still connected to the motor and it wont move.

Not sure if I'm making myself clear

Edit: Could I use two turntables one on top of the other? So that the top one rotates mechanically and the bottom one rotates freely? Problem is that the top one would maybe rotate on his own and doesnt rotates the claw.

Edited May 26, 201212 yr by Pedro Antunes

@ Pedro Artunes: Have you seen RJMcNamara's "Ultimate LEGO Technic & Mindstorms Crane Claw"? It HAD both LDRAW and Lego Digital Designer (LDD) Building Instructions, but the links don't work. However, the ONLINE INSTRUCTIONS (at the bottom of that webpage) do work. I saved the entire Online Instructions webpage on my computer's hard drive (by doing a File-->Save As--> Webpage). This

shows it in action:

"The design is based from footage of the Claws used in wrecking and recycling yards to pick-up scrap. This Claw can be used with either your LEGO Technics, or LEGO NXT Cranes. It's the Ultimate Ball Grabber!

"I've been working on-and-off for a couple years now on a reliable LEGO Technics, Crane Claws which will pick up balls reliably. Initially I started of with a two sided clamp type claw with a rounded cage to secure the ball, but this only worked reliably if the claw was directly over the ball. There had to be a better way!

"The design is based from footage of the Claws used in wrecking and recycling yards to pick-up scrap.

"For full project details, including CAD Instructions, please visit http://www.rjmcnamara.com/?p=4265 ."

Edited May 26, 201212 yr by DLuders

Thanks DLuders but that does not helps... you see in that video the claw does not rotates freely (by freely I mean by hand) since its connected to the motor and only the motor action can make it move.

I need it to move both ways... with motor action and with simple inertia, my claw serves to pick stuff and drag it as the truck is moving that's why I need it to move freely, just like a truck trailer for instance.

Since I'm draging stuff I need it to move around just by itself following the truck movement (think of the stuff I'm dragging as a trailer), but I need to rotate it once its in the air before picking stuff up.

Edited May 26, 201212 yr by Pedro Antunes

As seen on The Lego Group's official

below, you can see that the small log grabber can freely rotate. Is this what you mean? If so, you can download the 9397's Building Instructions here to see how it is made. Attach a motor to the 2-long Technic Axle Connector (sticking out of the side of the top of the grabber claw).

Edited May 26, 201212 yr by DLuders

But if I attach a motor to it then it stops moving freely

Are you looking for a grapple skidder grap?

That should be quite easy to build,rotate freely and have the grap open and close.

You can have the drive shaft through the center of the turntable,this way it will not affect the rotation of the turntable.

Edited May 26, 201212 yr by Alasdair Ryan

It depends how free you really want the rotation.

You could use the 24t clutch gear. Using the motor this would drive the claw rotation. When the motor is off, you would be able to rotate the claw by hand but it would not be very loose.

Otherwise, could you fit a small clutch yourself to disengage the motor when not in use?

You may have to consider a Lego Technic Driving Ring setup. As seen on HarupapaLEGO's

, "This video shows the mechanism of LEGO Technic Transmission Driving Ring (P/N: 6539) and [16-tooth] Clutch Gear (P/N: 6542).

The new video is here:

" [2nd video below]

Edited May 26, 201212 yr by DLuders

It depends how free you really want the rotation.

You could use the 24t clutch gear. Using the motor this would drive the claw rotation. When the motor is off, you would be able to rotate the claw by hand but it would not be very loose.

Otherwise, could you fit a small clutch yourself to disengage the motor when not in use?

@Alasdair Ryan

Not that vehicle but the same principle, what you're mentioning is what I already have... what I need it to be able to rotate the claw by RC but also have it rotating freely just by itself.

The claw on that skidder can be rotated by the operator but also rotates on his own when its dragging stuff, that's what I need.

@chorlton

The clutch gear is too tight...

@Dluders

Thanks, that will really help... lets see what I can achive based on that.

Edited May 26, 201212 yr by Pedro Antunes

Would that work?

When in the above position the steering wheel can be moved freely on his own/by hand correct?

If the driving ring gets engaged towards the gear then the motor kicks in and moves it.

(Nevermind the gears used, its just for demo purposes)

Edited May 26, 201212 yr by Pedro Antunes

Yes, your LDD design should work -- you have replicated HarupapaLEGO's

above.

Out of curiosity, to what are you going to attach your claw?

Out of curiosity, to what are you going to attach your claw?

Its a construction vehicle that can pick up and drag large concrete pipes

I'm back from my dark ages and I'm facing a lot of new advancements having just builded 8043 and 8110, my most advanced set before these two was 8829 so you can see where I'm coming from

Thank you for your help.

Little late for the party but...

I think i understand what you are looking for. I made a simple "proof of concept" video about my completely motorized(one motor) solution. I has one big flaw: the motor needs to do a small backwards correction to disengage the diving ring and it can be quite hard if it isn't geared down A LOT. Basically it's an automatic clutch. Output is the darkgray gear in the middle.

That is a interesting idea you came up with,welcome to Eurobrick's.

Yes, skppo's Automatic Clutch concept is interesting:

Or you can use LA for opening claw. It works fine for me

Pedro Artunes, does the claw need to rotate freely only when it is holding the pipe? I'm not quite sure what your project is, but my assumption is that you want to use the motor to rotate the claw so it can be aligned with the pipe while you are picking it up. Once one end of the pipe is picked up, you want to then drag it around with the pipe turning freely as you make your turns. I'm not sure if I'm correct with this assumption, but if so, maybe you could use some sort of weight sensitive gearing system that engages the claw rotation motor when there is no load on the claw. When a load is placed on the claw, it would then disengage the motor.

Pedro Artunes, does the claw need to rotate freely only when it is holding the pipe? I'm not quite sure what your project is, but my assumption is that you want to use the motor to rotate the claw so it can be aligned with the pipe while you are picking it up. Once one end of the pipe is picked up, you want to then drag it around with the pipe turning freely as you make your turns. I'm not sure if I'm correct with this assumption, but if so, maybe you could use some sort of weight sensitive gearing system that engages the claw rotation motor when there is no load on the claw. When a load is placed on the claw, it would then disengage the motor.

Yeah that's it

I am considering a spring attached to the gear shifter so that when the claw is loaded the spring extends and disconnects the driving ring... but I think this is too much complex for the space I have avaiable.

I'm testing several stuff at the moment.

Yeah that's it

I am considering a spring attached to the gear shifter so that when the claw is loaded the spring extends and disconnects the driving ring... but I think this is too much complex for the space I have avaiable.

I'm testing several stuff at the moment.

Yup, that is exactly what I was thinking, although I wasn't sure what scale you were trying to build at. Sounds like a neat project.

Edited May 28, 201212 yr by dhc6twinotter

This is an interesting challenge. Here is a mechanism I just put together that might work for you. The output is powered when the motor is on, and free to rotate when it is off. It's not perfect - it would need some experimentation to get it right.

This is an interesting challenge. Here is a mechanism I just put together that might work for you. The output is powered when the motor is on, and free to rotate when it is off. It's not perfect - it would need some experimentation to get it right.

Ooh, clever. I believe the same sort of mechanism is employed in Zblj's three-speed automatic transmission.

This is an interesting challenge. Here is a mechanism I just put together that might work for you. The output is powered when the motor is on, and free to rotate when it is off. It's not perfect - it would need some experimentation to get it right.

That is one beautiful and simple mechanism. Nicely done. I might include this mechanism in my skidder as well.

tim

Very nice idea there, thank you.

I will try that but I think that my claw weight will offer too much resistance and cause the gears to slip, since the gear that makes that mechanism work is actually "floating" and not fixed to anything.

But it might work!

This is an interesting challenge. Here is a mechanism I just put together that might work for you. The output is powered when the motor is on, and free to rotate when it is off. It's not perfect - it would need some experimentation to get it right.

-snip-

Ha! I just had the same idea a moment ago, though yours is much more simple than what i had in mind. My previous autoclutch was unneccesarily complex.

This is just beautifully simple!

Very nice idea there, thank you.

I will try that but I think that my claw weight will offer too much resistance and cause the gears to slip, since the gear that makes that mechanism work is actually "floating" and not fixed to anything.

But it might work!

Actually I don't think that should be a problem. If there is resistance on the output then the "floating" gear gets pushed harder onto the correct side. I tried to show this in the video. (If the resistance is VERY high in your application then you will want two liftarms, one either side of the floating gear, so that its axle is held more firmly. You might also want to limit the movement of the liftarms so that the gears are not pushed together too hard. Like I said, lots of experimentation needed!)

One potential issue is not enough resistance - in that case it's possible that the floating gear will not engage at all. There needs to be a bit of friction between the drive axle and the floating liftarm to avoid this.