Project of the week – Lego Wedo Swinging Monkey
This week, Liam has used Lego Wedo 2.0 to make a monkey that swings along a rope. It’s powered by the Lego Wedo motor, with a geared arrangement to create the swinging action. The inspiration for the project comes from Yoshihito Isogawa’s 2016 Wedo Monkey.
This project can be easily coded using the Lego Wedo app or the Scratch coding platform. When Liam was testing the monkey, he switched between platforms depending on which device was close to hand.
Yoshihito Isogawa’s projects
We’ve recently discovered Yoshihito Isogawa’s YouTube channel, which is filled with incredible Lego projects. His projects aren’t your typical Lego models – he does a lot of work with Technic, Mindstorms, Wedo and Boost. With just a quick scroll through his videos, you can find almost any invention you can imagine.
Yoshihito doesn’t just do videos either. He is the mastermind behind The LEGO TECHNIC Idea Book series – Simple Machines, Wheeled Wonders, and Fantastic Contraptions, as well as seven other books. You can see them all at the top of his YouTube channel, or on his website.
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.
Liam’s version of the Lego Wedo Swinging Monkey
Liam has the hub, motor and sensors of the Lego Wedo core kit, but not the gears, axles, bricks or plates that make up the rest of the set. Instead, his set has been built up from a combo of parts. The parts list for a core kit guided the gears and axles he needed, but as we built his set we added other useful bits and pieces. At the same time, we didn’t get Technic plates, mostly because we didn’t realise the need. As a result, sometimes there are parts missing from Liam’s kit that would normally be in the core kit. In some ways, it’s a good thing, because it gets him thinking outside the box and figuring out substitutions.
There are also variations with the monkey because Liam isn’t working from an instruction book. He watched the video of the monkey in action, and then got stuck in.
Working with gears
The original Lego Wedo monkey uses a LEGO Gear Box for Worm Gear (see Brick Owl for what these look like). We didn’t have one, so tried several variations to find something that worked.
Substituting different gears
The first task Liam dealt with was the worm gear. It has the x-shaped core to fit Technic axles, but it doesn’t grip tightly. That meant it needed to be secured at both ends to keep it in one place. A little spacer block was used at each end of the axle to hold the worm gear.
The second component of a gear box is a 24-tooth gear. That would usually pop into the gear box and align perfectly with the worm gear. To get the same effect, Liam needed to work out the height of bricks and plates he would need on either side to secure the 24-tooth in the right place. It took a lot of trial and error to get this part right, and it was modified several times.
Keeping the gears in place
When the motor was running and the gears were driving the arms, the rotation of the 24-tooth gear pushed the worm gear along its axle towards the motor. This happened even though the spacer blocks were each side of the worm gear. Then, the 24-tooth would let go of the worm gear and the monkey’s arms stopped moving. Liam needed to find a way to prevent the worm gear from sliding. He actually saw the solution really quickly for this – he popped it all apart, added more spacers onto the axle to fill the space, and reassembled it. On the next trial, the worm gear didn’t slip at all. Nice job Liam!
Once the worm gear was fixed, the 24-tooth gear started showing problems of its own. With the worm gear secure, there was a lot of pressure on the 24-tooth trying to drive the arms round. When it got too much, the structure either side of the gear, holding its axle, popped apart as the 24-tooth gave up. Once again, it stopped the arms moving because the worm gear and 24-tooth gear were no longer connected. Liam worked through several different structures at this point, trying to find the most secure option for the axle.
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. Some of the main ones include 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.
Code for the monkey to move forwards 
Code for the monkey to move backwards
Making the monkey swing along the rope
Adjusting the arms
While the arms moved really well with no weight on them, they didn’t perform so well when supporting the monkey. The arms are pinned in just a couple of places, and need to be fairly free-moving to work with the gears. But when the monkey’s weight is transferring from one arm to the other, the gap between the arms widens. When that happens, the second arm can’t hook back onto the rope. The uneven distribution then puts pressure on the motor, and the monkey stops working.
To fix it, Liam needed to find a way to keep the arms a bit tighter above the monkey’s head. Because securing them at additional points would restrict the movement, he got out a rubber band to fix between them. A rubber band is definitely not part of Yoshihito Isogawa’s Wedo monkey, but it worked! Extra pins were added to the outside of the arms, for the rubber band to loop around, and Liam tried a few different placements of the band to see what would work best.
If you’re keen to get stuck in and make your own Lego Wedo Monkey, you might need to do this too. Make sure to try several options and see what works best for you.
Modifying the monkey’s hands
To go alongside the challenge of the arms, we also found that the monkey’s hands struggled to reconnect with the rope after each swing. The original hands are formed with two diagonal bricks which guide the rope back to the centre of the V. With the arms widening, the hands couldn’t get far enough across the rope to catch on.
The solution for this was to modify the hands. Liam found that adding another diagonal brick below the first didn’t work, because there wasn’t enough clearance for the arms to pass one over the other. So, the hands needed to be longer, but no deeper than the original design.
A combination of bricks worked well here. A longer curved brick extended the hands while maintaining the V shape, and fitting an arch on the end tidied up the appearance.
Reducing the weight of the Lego Wedo smarthub
We had an issue with the weight of the monkey. With rechargeable batteries in the base of the smarthub, the hub is very heavy. The motor had to work very hard to turn the gear while all that weight was hanging off the arms. The weight of the smarthub was a key factor in the issues we had with the arms and the gearing. When we changed the base of the smarthub to the plug-in rechargeable base, it was so much lighter. Half the challenges Liam had been facing went away immediately. If you have the opportunity to do so, I strongly recommend a rechargeable base for the smarthub.
Have you done this project?
Have you made the Lego Wedo Monkey? What challenges did you face, and how did you solve them?
Let us know in the comments below, we’d love to hear how you got on with this project.
What’s next?
If you liked this project, check out Liam’s Lego Wedo Inchworm, also inspired by Yoshihito Isogawa. It’s quick to build, and so much fun!
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