Project of the Week – Lego Wedo Crab With Dance Moves
This week, Liam has built a Lego Wedo crab with his kit. He found this project on YouTube when looking for how to build a bird, and it looked like fun. The crab uses the Lego Wedo smarthub, the motor, and three gears.
What is Lego Wedo?
Lego Wedo 2.0 is Lego’s entry-level robotics & coding kit, designed for the education space. The core kit comes with a smarthub, motor, tilt sensor and motion sensor, plus a range of gears, wheels, axles and bricks to create a wide range of projects. As you would expect, it’s compatible with all the standard Lego and Technic components.
Alongside the kit comes the Lego Wedo 2.0 app. The app contains instructions for heaps of Wedo projects, and an image-based coding platform that communicates with the smarthub via bluetooth. For us, a big benefit of having the project instructions within the app is that they’re all in one place, and they can’t get lost or damaged. The app is a very big download, just under 500MB, but once you’ve got it installed, it’s very easy to set up and get started.
Building the Lego Wedo crab
The body of the crab is built on the Lego Wedo smarthub. With the smarthub light facing forwards, fix the motor on top towards the back of the hub. Attach a 4-long and a 12-long technic brick directly in front of the motor. Insert a small axle through the centre hole of the technic brick and into the motor. Then, add an 8-tooth gear to the end.
At the back, a pulley wheel fixed to a short technic brick lifts the smarthub and helps the crab move side to side.
The 24-tooth gears need to be free-spinning in order to work properly. To do this, put a cap-ended axle through the centre of each gear. Check where the gears will need to be aligned so that they interlock with the 8-tooth. Thread the axle through the right hole in the technic brick, and secure it on the back. At this point, connect your smarthub to Scratch and run the motor. This helps you to check that all the gearing is spinning at it should.
When you’re happy with the movement of the motor and gears, you can start building the legs, pincers and eyes.
Building the crab’s legs
Use an 8-long technic brick and a 7-hole technic beam for each leg, plus three non-friction pins. Pin the end of the brick to the main 12-long brick, and the end of the beam to a hole in the 24-tooth gear on the same side. At this stage, don’t worry about which hole you use on the gear. This will change as you create different dance moves. Then, use the final pin to fix the beam and brick together, like in the image below.
Pincers
For the pincers, you can get creative here. If you’re working with the full Lego Wedo kit, you’ll probably find these a bit easier than Liam did. Liam used a combination of angles and arches to get the shape he wanted. To fix the lower claw to the upper, use a technic brick at the bottom of the main claw with a friction pin attached. That will let you fix the lower claw on sideways.
Head and eyes
The head and eyes are pretty simple. Start by building up a head shape with blocks you have. The important part is the modified plates on the bottom with the socket joints. These will carry the ball joint on the base of the eye stem.
For the eye stem, fix one end of an axle into a technic brick and the other into a type 1 angle connector. A non-friction pin works well to join the eye plate to the angle connector.
With the head and eyes built and connected, go ahead and fix the whole unit to the top of the motor.
The finished Lego Wedo Crab – ready for dancing
Liam is sooo happy with his completed crab. Have a look at the video above if you haven’t already – the crab’s eyes spin when he moves.
Using the Ledo Wedo 2.0 app vs Scratch for coding
The Lego Wedo 2.0 kit comes with an app for pictorial coding, which lets you get your projects up and running quickly. The platform is very simple to use, with blocks aligned side-by-side in the sequence you want your project to execute the instructions. A range of inputs can be used, including from the tilt sensor, motion sensor, noise sensor (from your devices microphone), or from the ‘go’ button. In terms of outputs, the motor can activate, a display can show on your devices screen, or the colour of the light on the smarthub can change.
There is limited complexity that can be achieved within the Wedo app, as it’s designed for simple instructions and getting started. If you want to start coding more complex actions, consider using Scratch instead.
Scratch is a block-based coding platform, which has the ability to integrate with a wide range of hardware options including Lego Wedo, Mindstorms and Boost, BBC microbit, and Makey Makey. Importing the custom blocks for Lego Wedo lets you combine them with standard Scratch blocks to extend what you can do.
Coding the crab’s dance moves
We prefer to use Scratch for coding the Wedo smarthub, because it allows for greater control. Have a play with the motor speed and direction to see what suits your dancing crab. Liam set the motor speed to 80 or 100, depending on what he was creating.
For a sequence that you want to repeat, try using a forever loop like the one below. By turning the motor on and then changing direction every 1 second, the crab gets a great boogie style.
For more Lego Wedo projects…
Have a look at these projects for more Lego Wedo ideas:
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