Video tutorials -

• Gears

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• LEGO MINDSTORMS EV3

In this tutorial, we add another mission to our current program. This mission is - hanging the Gecko from the FIRST LEGO League Animal Allies. 

We calculate the number of rotatios when a gear system is involved. The driving wheel will have to do a number of rotations for the driven wheel to rotate to a desired number of degrees. In our specific case when the driven gear wheel is rotate to about 90 degrees the legs will lift the robot.

This is a teacher's note about the math behind calculating gear ratios with for our lifting attachment. It math model we build in previous tutorials is not exactly correct and here is the explanation why.

The task in this tutorial is to execute the program 10 times and to do it yourself. If you have your attachment then use it. If you have our attachment then use it. But execute the program 10 times and make sure that it works. 

Sometimes the answer that you get by calculating seems not to be right. Is it the calculation that is wrong. Probably it is not the calculation, but something is happening with the robot. 

Calculate the number of rotations you have to do with the motor to rotate the final small 8 teeth driving gear wheel to 1.25 rotations?

What should you as a teacher know when the students are trying to achieve a program and robot attachment that could reproduce their behaviour 9 out of 10 times. 

If you've done the calculation following the previous tutorials you would arrive at a result of 18.75 rotations. But this is not the correct answer. The calculation is wrong, because the math model that we've built, although kind of obvious, is not correct. When experimenting the correct number of rotations would be 37.5. This is a large difference. Two times larger. Exactly two times large. Something should be happening here - and this thing is "planetary mechanism"

What should you do as a teacher when the students are calculating the gear ratios and number of needed rotations?

In the previous video, we found the correct answer for our task and it is 18.75, or is it?