Comments on: Draw a Square: Using Motors in leJOS EV3

By: Frank Parchim

Frank Parchim — Fri, 06 Feb 2015 16:47:38 +0000

Thanks a lot, Miguel!
This helped me to quicker understand the motor control and gave further ideas … You made my day!

By: HOWTO Calibrate a differential robot: UMBMark Explained ← LEGO Reviews & Videos

Sun, 01 Jun 2014 14:00:14 +0000

[…] article is just a follow-up of drawing squares with leJOS where the problem of calibrating correctly your differential robot […]

By: Miguel

Miguel — Sun, 25 May 2014 08:48:03 +0000

Hahaha. I am having the same problem between my laptop and my desktop. I will have a look at this and write a little side note about it.

By: Michael

Michael — Sat, 24 May 2014 21:43:18 +0000

Thank you! Thank you! This is just the sort of easy learning steps that I need. I have tried both of the previous LeJOS books with very little success. Maybe this time I will actually learn some JAVA programming. I look forward to further LeJOS/EV3 tutorials. Something I am struggling with is how to get finished JAVA programs/projects into Eclipse.

By: Miguel

Miguel — Fri, 23 May 2014 21:42:52 +0000

Thanks. I will edit the code to use waitComplete… I supposed that left would have ended more or less at the very same time than right ( or the robot won’t be moving at a straight line, isn’t it? ) but it doesn’t hurt to add it.

Reading the paper right now.

By: gloomyandy

gloomyandy — Fri, 23 May 2014 18:20:29 +0000

Hi,
Nice, blog. Accurate movement using odometry can be tricky! A few comments…

In your example code you recommend the following sequence:
left.rotate(degrees,true);
right.rotate(degrees);

This may introduce an error because there is no certainty that the left motor will have finished when the right one does (particularly when using different numbers of degrees). If you follow this move immediately by another then leJOS will not complete the partial move instead it will blend the two moves together using the current acceleration setting), which is probably not what you want. It is always best to add a waitComplete call to ensure both motors have stopped.

Secondly if you are going to use a variable number of degrees as the target for the two motors (which you may need to do if one wheel has a larger diameter than the other), then you will probably also want to use a different target speed as well (so that both motors stop at the same time). However if you do this remember to also use a different acceleration factor for the two motors, otherwise one motor will reach the target speed before the other.

Finally if you are serious about calibration of a differential drive robot take a look at the following paper:
http://www.valentiniweb.com/Piermo/robotica/doc/Borenstein/paper58.pdf

Oh and if you want another fun way to evaluate the quality of straight line movement, take a look at:
https://www.youtube.com/watch?v=NJ_6Qm_BNFI

Have fun

Andy