Old Trafford

This is the second part of an unknown number of reviews of the LEGO 31313 Mindstorms EV3 robotics set. If you haven't seen the first part, I recommend reading that to understand what this set is all about.

Of the five main robots, the second one I built after the Track3r was the snake-like R3ptar. This is quite a cool and menacing looking robot and was the obvious choice to build next, before trying the full sized robots. The use of the IR receiver as eyes and tooth/wing parts give it a great evil look. Mechanically, there are a few different motions:

  1. The whole snake can move forwards or backwards via the large motor in its rear.
  2. The tail can bend left and right via the medium motor at the base of the body.
  3. The head can strike forwards via the large motor in its neck. As it strikes forward, its mouth opens up to bite any unsuspecting sisters.


After building the Track3r robot, this one was a much more involved build. The snake is surprisingly large which definitely improves its coolness factor. However, despite it's size and flexibility it's quite sturdy and easy to carry around. All the remaining stickers get used by this robot (other than my 2nd sticker sheet which was included accidentally!), and all but two of the panels are used.

See all photos at Bricksafe.

The missions are fairly straightforward:

  1. Mission 1 - Slither Like a Snake. This includes building the body/tail of the snake and getting it to roll forward while turning left and right.
  2. Mission 2 - Rattling R3PTAR. This mission completes the build of the robot, and demonstrate it's striking capability.
  3. Mission 3 - Hunting. This program has the snake moving around aimlessly until it finds something worth biting. This is also the first program to make use of a more advanced operation.
  4. Mission 4 - Take Control. The robot is fully under remote control in this program, and has a lot of conditional logic. You will have a good understanding of how to use the remote control after building this one.


One rather obvious thing I haven't mentioned is that you really want to use rechargeable batteries for the programmable brick. I originally used plain AA's and they ran out of juice while playing with the R3ptar, only the 2nd robot to be built from the EV3 set. Unfortunately the 31313 Home Edition set does not come with the rechargeable battery pack that the Education Edition comes with, but hopefully it will be sold separately at some stage.

I tried to stick with the 3D building instructions on the iPad for this build. If you haven't built from 3D instructions before (e.g. LDD), it might take a bit of getting used to. It has advantages in that you can rotate and zoom the model to help you see the correct part placements. However, it has disadvantages too. The most apparent problem to me is that it is not always obvious what size axles you need to use. I also found myself sometimes having to count the holes in technic beams instead of just being able to recognise them on sight. Not a big problem, and with practice it goes away. Besides, the ability to build away from the PC is worth it.

The increase in programming difficulty from the first Track3r robot is not large. There are some more involved uses of conditional logic, and showing you how to run two streams in parallel, but it's mostly more of the same. This is a good thing as it is very important to understand the basics before you can jump in and create the more advanced robots.

While programming this robot, I was struck by how quickly my son was picking it up. This is a great tool for teaching robotics, programming, debugging, and general problem solving to kids. He was trying to understand how something could be done and when he saw my solution, said "Ahh, you put a switch block in the false case" I was a bit stunned :) He picked up the terminology just by using the Mindstorms software, and could at a glance see how to achieve what he was thinking. Combine that with the pure joy both my kids got out of scaring their Mother with the snake, this set is a pure winner!

You can buy this set (and help support Rebrickable) at eBay, LEGO or Amazon. Alternatively, for your country specific links please see the links on the EV3 set details page.

See all photos at Bricksafe.

Click here for the full list of Mindstorms EV3 reviews



  • 6 years, 5 months ago DLuders Level 20 MOC Designer
    Your wife and son will conspire to set up that snake near your alarm clock! :)
    • 6 years, 5 months ago Nathan Level 28 Site Admin ADMIN
      Don't give them ideas! Too late anyway, the snake has now been dismantled and we're building the next one :)
  • 6 years, 5 months ago BertZelf Level 13 MOC Designer
    Great job, well done, Nathan. A small hint. In the 3D building app (at least in the Android one) you can double-click an element to see what the id is, and the length of beans and axles.
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