The Snatcher

The Snatcher from the Discovery Book

This autonomous robot finds, grabs and lifts objects, and it is featured in Chapter 13 of the Discovery Book. The robot is heavily popular among MINDSTORMS builders. It is especially used frequently in robotics competitions because of its versatile grabber design.

The Snatcher grabs and lifts objects with just one motor

Building and Programming this Robot
Instructions for building and programming this robot are included in The LEGO MINDSTORMS NXT 2.0 Discovery Book. It can be built with just the pieces in the NXT 2.0 kit.

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54 Responses
    1. Every programming step comes with illustrations that you can replicate to make it work. If you’re having trouble doing this, you can also download the programs from here.

  1. Luis

    Hi i´m from Peru and its hard to buy the discovery book because i don´t know how to shipping it. So my question is if there is another way so see how to build the snatcher because is the only robot that i want to build and i can´t do it by myself. Thanks and excuse my bad english.

      1. Michael

        Thanks! And I wasn’t telling you so you would post it on your website I just wanted you to see it. I actually that was my own mechanism I didn’t even look at how the Bobbot was made before this 🙂

  2. mtndew

    Hi Laurens,We followed the instrutions from book and built the snatcher and the program, but it didn’t work as it was supposed, it alwsys trys to grap something else which wasn’t there; finally I loaded your program, it still won’t work, and it did same thing. We couldn’t figure out what went wrong, could you give some directions where to check.


    1. Use the View menu to see if the sensor on port 4 can detect the object you want it to grab. Also, the object cannot be too far away or the sensor will not see it. That will help you determine whether the problem is in the program or not.

  3. Bob

    Hello Laurens, I’ve seen The Snatcher a couple of times now around the internet and I want to build a robotic arm out of Lego Technic and Mindstorms. So I think the ‘claw’ of The Snatcher is the most suitable for my project. The problem is, I don’t want to buy the whole book, only for the claw. Is there any way to get the instructions for the claw itself only? Thanks in advance, Bob

      1. Tony Tajiri

        I’m also having problems with it and it has to be the program since the ultra-sonic works, the servos work, the touch sensor works, the color sensor, but the program doesn’t. All it does is lift it’s claw up and stop without scanning at all.


    My child snatcher assembled in Chapter 13. Children will not be able to put together a program still small. I do not know what do I enter a number I want to download the program there.
    Please tell me how I can understand a child can not be confirmed at this fine eye disease now.

    I do not know how do I enter a number or character download site but also Uchikomeru digits can be displayed.

    We have created a site in question translation

  5. Bob

    Hey, is there a way I can buy only the instructions of The Snatcher? I like it very much, but I can’t buy the whole book. Thanks!

    1. If you’re having trouble programming the robots, you might want to read the first chapters first and move on to Chapter 13 later 🙂

      You can also just download the programs (Use the menu at the top of this page).

  6. Legomindstormsgeek

    I was making my snatcher with my brother but at the end we had a problem the claw closed when it was down
    And opened when it was up we need some help

    1. Check out the illustration on page 224. It’s important that everything is aligned exactly as shown in that sideview. Note that the claws are opened (not grabbing something) in that side view.

  7. legomindstormsgeek

    I’m 99% sure I programed my snatcher right but it only spins around and dose not move closer or try to grab or ANYTHING

    1. Nxt7

      It does not matter if you programmed it right. You need to have built it right. If one if the gears is 90 degrees off that what it would be then the arm is reversed. So sadly, you need to go back and rebuild the arm again carefully. If it does still now work then check the troubleshooting page in the book.

  8. Samuel

    I built the Snatcher (from the NXT 2.0 Discovery Book), and have run into a problem I can’t seem to fix. It goes through the motions of finding the object (a colored paper tube), but never seems to actually recognize it, completing 2 180 rotations and dropping its arm at a random location. Upon cross-referencing my code with the sample your website, I found that both programs were identical, and the official program encountered the same problem. Any ideas from people who have built it would be greatly appreciated.

  9. Lhester

    hi good day im trying to assemble the snatcher out on you tube and
    your site is there any possible that i can bet a copy on how to assemble the snatcher thank you and good day

  10. LIAM

    Hello Mr. Valk I am programming my robot and i an stuck on the figure 13-10 on the snatcher i could really use your help understanding it

  11. Carlos Almeida

    Hello Laurens,
    I think the Lego NXT GrabBot – To Louie is your creation. Do you know where do I get the building instructions?
    If its not yours, do you have any idea who can help me?

  12. Robo-Cat

    Dear Mr. Valk,
    I built and programmed the snatcher and followed the instructions in the book exactly. But somehow the snatcher only puts up the arm and then turns round and round all the time, without recognizing any objects. I’ve already used View to test the ultrasonic sensor, and it works perfectly.
    Could you please help me finding my mistake?

    Thanks in advance!

  13. Tony Nguyen

    Hi Laurens,

    Do you have an edition on ev3 home edition?

    If you have, could you mind show me where is it?

    thanks a lot


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