Tutorial on how to install and run Java on Lego Mindstorms EV3 using Eclipse on Mac OS X

This is tutorial on how to install and run Java on your LEGO Mindstorms EV3 using Eclipse and LeJOS.

We will be installing Java and the Eclipse Integrated Development Environment (IDE). This will allow us to develop your LEGO Minstorms EV3 software in Java and running it on the EV3 using LeJoS. Please let me know in the comments if you encounter any problems. I will try to keep this tutorial up to date.

You will need:

This tutorial will only get you started and you might want to dive much deeper into Java development for the EV3. These books might be useful for you:

My personal favourite for building amazing mechanism is Sariel’s book:

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LEGO Compatible Medium Sized Thrust Ball Bearing

LEGO’s turn table has considerable friction and rotating a model at an exhibition for a whole day would ruin it. A thrust ball bearing is necessary to decrease the friction. I previously 3D printed a large bearing for my Unikitty. For this year’s exhibition I needed a smaller thrust ball bearing so I designed a new medium sized ball bearing. It includes liftarms to hold a worm wheel which results in a rotation ratio of 1:78. You can download the model from A360 and GrabCAD.

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LEGO compatible thrust ball bearing

To rotate an axial load LEGO developed the turn table. For light loads this works great but the friction increases dramatically with heavy loads. This thrust ball bearing uses standard LEGO balls to transform the friction into rotations. This allows the two disks to easily rotate. The balls and an additional rim keep the two disks in place.

A motor can be attached on the inside to power the rotation. Even the smallest LEGO motor is sufficient to easily rotate this 2 kg load. This thrust ball bearing is fully LEGO compatible and even allows studs to be attached to top half. Standard 14.2 mm LEGO balls can be used. The bearing measures 20 studs across and is three bricks high. This should be big enough for even the biggest crane or MOC display.

The 3D data is available from the Autodesk Gallery and GrabCAD.

 

Review Dexter DLight for LEGO Mindstorms

Dexter Industries offers the DLight for LEGO Mindstorms. It allows you to control four full color LEDs through a sensor port of your EV3 or NXT. The first thing to do is to set the toggle switches on each LED to a unique address, so that you can control each LED individually. In the NXT-G environment you can still decide to control all of them at the same time if desired. The biggest nuisance is that only the first LED can use its red component. The other three cannot show any red light. Dexter acknowledges this bug in its forum and offers refunds. It is ridiculous that Dexter does not warn its customers on its product page, in particular since they do not intend to fix this problem.

WordPress errors

Askimet is a very excellent tool and it protected me from a whopping 80.000 spam comments  on  my WordPress based web site. That is for October alone. Those spam comments completely filled up my SQL database beyond the point where I could repair it following these instructions.

It was a classical Catch 22. To empty the database I had to “optimize” it, which does take some additional space. Which I did not have because the database was full. Askimet has just released their 3.0.3 update which might have solved the issue. Or it could have been my webhoster’s support worker I called that finally had mercy with me and hit the optimize button on his side.

In any case, getting from a “Warning: Creating default object from empty value in wp-admin/includes/post.php on line 567” error to the conclusion that my SQL database is full due to comment spam that Askimet caught was a rather interesting journey. And it only took me two days to figure it out.