For the FIRST LEGO League 2016-2017 Animal Allies we prepared an attachment for lifting the robot. The idea of the attachment is to show how you could lift the whole robot with a system of gear wheels, levers, and scissors constructions.
Built mainly from LEGO Mindstorms EV3 parts but could probably be constructed from NXT sets.
This material requires a subscription to one of the following plans:
- FLLCasts Personal B One Year
- FLLCasts Team Six months
- FLLCasts School
Building instructions delivered to your device by 3DAssemblyInstructions.com
- 20 Mar 2017
- LEGO MINDSTORMS
- EV3, FLL 2016, Gears, Math, Methodology, Construction, Attachments, FLL, Classes with students
- K.Mitov, D.Staykov
To construct this you will need
- LEGO Mindstorms EV3 45544 Education Core
- LEGO Mindstorms EV3 45560 Education Resource
Bill of materials (Parts list)
The final way for lifting our box robot is by using a scissors mechanism. In this Episode, we would discuss the benefits and advantages of this mechanism.
In the previous video, we found the correct answer for our task and it is 18.75, or is it?
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.
Connect the attachment to the box robot and find the correct number of rotations of the middle motor that would bring the robot up and forward and would attach it to the mission model.
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.
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"
How great is the great attachment for lifting that we built in this course? How many times can it lift the robot without making an error? How great are your attachments and how could you test them? - the answer is simple. Just try 10 times and they should work at least 9 of them as our attachment is.
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.
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.