Analyze a LEGO WeDo 2.0 Model – Helicopter

Recently I found an interesting LEGO WeDo 2.0 model on YouTube. It is a giant helicopter model in terms of its size. It uses most of the parts in one LEGO WeDo 2.0 set. What is more amazing is that it uses one single motor to drive three components – the top propeller, the rear propeller and the wheels. Let’s check how the model looks like.

You could find the original YouTube video here.

As shown in the above video, three components could turn simultaneously. Since the YouTube video has provided step-by-step instruction, I will not show it again in this post. I will mainly explain how the motor power is transferred to different components.

The Gear Train

Removing some parts on the top, we could see that in the middle body of the model is a gear train which consists of three gears. The uppermost 20-tooth double bevel gear is connected to the output axle of the motor, so it is the driving gear in the whole model. The driving gear drives the other two straight gears which are aligned at the lower part of the model.

Drive the Top Propeller

In the above section, I introduced the driving gear. Since it is a double bevel gear, it could pair with a yellow 20-tooth bevel gear in a perpendicular position and change the rotation direction. The output axle of the bevel gear then drives the top propeller.

Drive the Rear Propeller

The gear train transfers the rotation power from the driving gear downward. The 24-tooth gear, which is located in the middle of gear train, connects to a long axle as show in the below illustration.

The long axle then connects to a pair of bevel gear to change the rotation direction. The output axle connects to a piece of elastic band to drive the rear propeller.

Drive Wheels

When I explained gear train in the above section, I mentioned that the 24-tooth gear transfers the rotation power to the rear propeller, while the 8-tooth gear, which is located at the lowest position of the gear train, connects to a gear worm in the transparent gear box (in red circle). The output gear of the gear box then drives the two wheels.

Program

This is a sample program. Feel free to design your own program to make the model alive.

That is all for the brief analysis of this complicated model. Although LEGO WeDo 2.0 has only one motor in one set, it could drive multiple components through arranging those gears cleverly, but all those components have to move simultaneously. In another word, you could not use one motor to control those components independently. That is based on the mechanical principle.

If you would like to control components separately, one way is to add another motor and connect it to the smart hub. It will make the whole model heavier, but could achieve better flexibility.

Another problem for this giant model is the driving power. It is a big load for a motor to drive three components. Even using the biggest motor power of 9 in the program, the model’s motion is intermittent sometimes due to overload.

Finally, enjoy the design and have fun!

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