Product Idea |

Technic Search and Rescue Double Arm Grabber


Although my project has been entered into the Lego ideas Technic construction competition, please comment, I thought many kids would enjoy playing with their own version if I managed to get enough votes.


My futuristic remote controlled entry is a ‘search and rescue’, demolition or construction double arm grabber.

This has the following playable features:

Through a rear vertical gear clutch lever a single ‘cream’ gear on top controls through the turntable either the opening or closing of one of the grabbers, or the lifting up and down of the grabber arm.

The black knob controls the horizontal movement of one of the arms through 90 degrees.

The above is mirrored to create twice the play on the same area as a normal tracked base.

Designed to be as compact as possible for ease of transportation and to keep the brick count at around 700 using half of two 42006 Lego sets and some spares.

Each half can be played with separately so they can independently search and rescue, or split to go around obstacles and re-join afterwards!

Expandable in-between each half with two motors, one to control each set of tracks and above 3 functions using a 2nd clutch lever.

My main aims are to demonstrate:

Getting three gear paths to work through lots of thinking, trial, error and simplifying, which perform the above functions which make the idea original”. I've put a video here 

show them in action.

In this project, one gearing path goes through a bottom turntable and the other through a top turntable, which I haven’t seen done before.

A vertical (which I have never seen before) clutch system, which is far simpler than the usual Lego manuals to encourage others to use more clutches in their MOCs, together with actuators (my favourite modern pieces).

Compactness to keep the allow others to rebuild their own similar versions, and make a commercial version viable at the mid-price technic level.

1 Concept & design brief (talking)

My entry started out trying to replicate the two arms and pincers/grabbers found in underwater exploration vehicles. I soon realised that these needed to be simplified otherwise the arm becomes too heavy for the end support to hold. But I needed to keep the grabber, and move the arm through both a horizontal and vertical plane.

To allow transporting of the grabber arms a tracked vehicle seemed the most fun option, resulting in a ‘search and rescue’, recovery vehicle, with the arms to be used to lift fallen debris to find survivors underneath, or pull down unstable walls. So need to able to reach out as far as possible to cover the full horizontal and vertical view of field. The arms needed to be tucked away as close to the track as possible so that it can be as compact as possible to fit into 1, or split into 2 standard containers to be shipped to the disaster region.

Most importantly, to be able to rescue after all that transporting and searching, the grabbers needed to be able to independently hold and then lift small separate objects, or two grabbers working together to lift a larger single object.

2 Practical problem solving (building)

The grab was straightforward as just needed to modify the pincer and actuator of one of my favourite Lego sets, excavator 42006 (which seems to be the only set with 4 pincers).

This also had instructions on how to use a gear box to control 3 different gearing paths through the boom. However, this was way too complicate to replicate, the boom was too heavy and needed the whole base with all the gearing to rotate making a double turntable impossible unless you pinned two 42006s together (but the size would be way too heavy and large with 1400 pieces).

As I just wanted a small arm to move I followed the far more simpler and often repeated truck crane mechanism of feeding the rod controlling the grabber through the centre of the turntable but this only gave 1 gear path (as needed to be dead centre), whereas I needed to also have lift. So I put a 2nd turntable on top upside down to give a 2nd gear path to allow lift through a large actuator.

I don’t think anyone has done this before and took days to get both paths to work cleanly while still looking polished and professional. The top turntable also had a side benefit of helping to support the weight of the arm, and made rotating the arm from the top ‘black’ knob, using a gear against each turntable a lot more fluid and stable.

As it is difficult to turn the gear underneath the bottom turntable, these two gear paths meet at a gear box, allowing a single top 2nd ‘cream’ gear wheel to control either path through the flick of the rear red gear switch. As well as interesting to watch the red gear barrel mechanism move up or down, as far as I am aware no Lego set has ever had a vertical red gear barrel mechanism?

A mirror image of all the above was then repeated for the other side.

3 End result (playing)

When playing with the two arms and tracks reminded me a bit of a famous tracked movie robot. 

The main thing you notice is that with  no cab or piston engine you free up a lot of space, so you can have double the functionality on the same double track area. This is not as sci-fi as you may think, search for double-front work machine, which also has grabbers rather than shovels.

I don’t think any Lego set has achieved the repeated triple functionality within the confines of a standard double track area before?

However, what is sci-fi is this tracked grabber vehicle can split into two halves, so each sibling can have an equal share in the build, and they can each have one half to play with or co-operate and play together with the joined toy.

4 Future refinements (further talk, build & play)

From the front, the two grabbers remind me of two Lego-people hands, but unlike these hands I did not include wrist rotation as I found only possible if you sacrifice either horizontal or vertical movement (which seemed more important to keep). Please let me know if you find a working solution including all 4 gear paths, although to fully replicate the human hand in Lego you need to ideally move onto hydraulics (search for on line videos).

The design was purposely built in two halves so that they can be split to allow an extra 4 studs to be added in-between for the new Bluetooth battery box (or train power function box), to control a left motor, which with an extra gear box mechanism can then be used for the left track and corresponding 3 possible gear paths for the left arm. Similarly, the other battery lead socket (or 2nd power function IR sensor socket) can control a 2nd motor for the right track, and right arm triple movements through a 4th gear box mechanism. I still need to work out all the detail.

There are no digital instructions, as there was only one way of making sure the above gearing worked through trial and error.

Thank you for reading to the end, please vote and comment if you found this project interesting.

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