Sunday, September 21, 2014 A Quick How-To

Below are 5 steps to getting the most out of ROS Answers, and hopefully giving the most back to the community in the process:

1. Don't be afraid to ask a question

The name of the site may be "ROS Answers", but there is no point in having answers if there are not questions. Often I find that people comment on old questions, or post answers to old questions, hoping to get help for a possibly related problem. Your comments will probably be missed by anyone who did not previously participate in that question/answer thread, and posting an answer with a question is just bad etiquette. If you have a question, open a new question!

2. But before you ask a question, check to see if someone has already asked and answered the exact same thing!

There are over 15,000 18000* questions on ROS Answers. There is a good chance that if you have a common problem, it has already been asked, and probably answered. The average time between posting a question and getting answer is probably several hours, however, if you spend just a few minutes searching the site you might find your answer immediately.

3. If you ask a question -- try to make sure other people will be able to find it some day by adding appropriate tags.

That search thingy in #2 depends on questions being properly tagged. Adding a few (useful) tags will both help get you an answer faster, as well as making sure that the next person with the same question can find your question and the answer to it. "ros" is probably not a useful tag, the name of the package, node, or command in question would be good tags. Including tags for the specific hardware you might be using could also be useful (for instance "kinect" or "pr2")

4. Close button is evil. Karma is good.

This is probably the most misunderstood aspect of ROS Answers. People frequently post a comment saying "thanks, that works" and then click the "close" button on the question instead of selecting an answer. Please don't do this! Instead, click the checkmark next to the question to select the answer to your question. You can only select the answer on questions that you asked, however, if you find an answer to someone else's question that helps you, you can give a little Karma by clicking the "up arrow". The answer to the right here has been upvoted 26 times -- it must be pretty good.

The answers website really depends on Karma. New users have restrictions (unable to post links, images, etc).  New users NEED Karma to become more effective users. Power users need Karma to be able to moderate the site, like retagging those questions where people didn't get the tags right.

5. Finally, make sure somebody can actually maybe answer your question.

Good answers require good questions. If you get an error in the console, certainly include that exact error into the question. A summary of the error, or "I got an error" are not substitutes for the actual error or traceback. Tells us exactly what commands you ran. Other things you probably want to include: what ROS version, operating system, and robot you are running -- and if you aren't running from up-to-date debs from the OSRF apt repo, you probably want to point out how you installed ROS.

* I started writing this post a few days after the 15000th question was posted. I finished writing it 3000 questions later....

Saturday, September 6, 2014

Intel NUC for ROS

This post has been a long time coming -- I think I promised it to several HBRC members at the July SIG...

I've frequently been asked "what computer do you use on your robots?", usually from someone looking at a variety of sub-$100 ARM boards. ARM processors have come a long way, but for a ROS computer, they are not the easiest choice. Austin Hendrix has done a lot of work to get a buildfarm up and running for ARM processors -- but there is still a long way to go and many things will not work "out-of-the-box".
So my choice? Well, it's not under $100, but it is a very fast, fairly low power machine (here, I define low-power in the sub-15W range). The latest generation of Intel NUC (Next Unit of Computing) modules offer quite a few options for small Intel Core-based computers. I'm using the 4th-generation i3-based D34010WYK. This offers quite a bit of compute power for ROS, especially when you consider that early TurtleBots ran on a single-core Atom. I've used 35W TDP i3 processors on a number of mobile manipulation problems and been able to run the OpenNI/OpenNI2-based drivers, the navigation stack and MoveIt! without much difficulty. If you're looking for a bit more processor, there is an i5-based version for $100 more.
Intel NUC (image from Intel NUC website)
These computers are sold as either a board (somewhat hard to find for sale) or as a kit which includes the case. Either option requires memory, hard drive and wifi card to be added. My setup is:
  • 8GB Crucial Ballistix Sport SODIMM. Whatever you choose, be sure it is 1.35V RAM -- the newer NUC models work ONLY with 1.35V RAM (many modules are 1.5V).
  • 120GB Crucial mSATA SSD. Intel offers a larger case version of the NUC that fits a standard 2.5" drive, but the smaller versions only take an mSATA drive.
  • Intel 7260 Wireless-AC Card. This card will work best with Ubuntu 14.04, older versions will need an updated kernel (at least 3.13) to get working drivers. No need for antennas as they are already in the case.
These boards take 12-24V DC input, but are probably most efficient at 19V. I'm powering mine off a 12V battery connected to a Pololu 5A Step-Up Regulator that is configured to output the desired 19V. My batteries will never get even close to 19V even when fully charged, and so the regulator should not have any issues.
I would recommend installing Ubuntu 14.04 and using ROS Indigo for these machines. If you want to use an older Ubuntu distro, you should definitely make sure your wifi card is compatible, because the Ethernet port will not work with the drivers present on the 12.04 installer and you will have to connect to to update somehow. Another alternative is to look for a NUC based on the 3rd-generation Intel Core processors, but these might be hard to locate.