Coursera, MATLAB, robotics, and 3D printing

Posted by Erica on Feb 10, 2013 in Education, Making |

The Heterogeneous Parallel Programming course at Coursera is more or less wrapped up. There were so many problems with the grading system that any “final resolution” has not been made as far as grades, and it is a little anti-climactic. I did very well on the assignments, but don’t know exactly what we get as far as certification, if anything. The final lectures were on a less interesting topic, and I skipped most of them. Overall though it was a great learning experience.

I did find some odd bugs. While on vacation, I was unable to access the Amazon cloud instance. No one else seemed to have this problem. I eventually discovered that if I VNCed into our corporate servers back in Maryland, I was indeed able to reach the instance. Apparently there is some sort of geographic filtering going on, perhaps to prevent multiple people from using the same Coursera or Amazon account? At any rate it did spur me to complete our corporate VPN.

There were some errors in the course material. This is inevitable and not a big deal. However there is so much noise in the discussion forums that it was hard to communicate with the staff. For obvious reasons the people with misgraded assignments or stuck on a problem were the loudest.

To a certain extent I am seeing similar greatness and problems in the new course I am taking, Control of Mobile Robots. The professor is engaging and this is wonderful material. However, one of the key summary slides has a serious error. For part of it, v is used as a linear velocity, then vr and vl are introduced — but they are angular velocity! This is never stated explicitly and does not make much sense. Since this is the reference page I’d normally use once the class is over, it’s a very annoying bug. Other students noticed it as well. However, it turns out that the TA lecture to walk people through doing the quiz also had an error, and far more people were screaming about that, and long story short I don’t think the slide will ever be fixed. Yet another misleading document to live on forever online…

That said, the material is marvelous and perfectly timed. This week included a broad overview of a robot behavior called “Go To Goal”, aka dead reckoning. This is exactly what I need to get FireCheetah going in a straight line when there is no wall to follow.

I am also taking Grow to Greatness: Smart Growth for Private Businesses, Part I which arguably is the most relevant to my real life. That, however, will be audit only. It is interesting but extremely verbose. One difficulty with streamed video lectures is that one can’t easily fast forward through the fluff. And this one has quite a bit of fluff.


It turns out that as a Coursera student (free enrollment), you can get a student evaluation of MATLAB for only $99, including several toolkits. This is an amazing bargain, as this software package can easily run over $1,000. MATLAB can solve math equations, plot data, and do many other useful tasks.

I have used Mathematica in the past, but the learning curve is quite steep and it’s easy to forget, so I never made much use of it once my thesis was done. With MATLAB installed, I see why it has become the default in the corporate engineering world. It has an easy to use GUI with lots of help, and they have some excellent introductory tutorials on their site. The command-line is there with all of its power, but you are not forced to use it all the time. This makes playing with data very, very easy.

For more details. see this page. (You may have to register for the course first.)

3D Printing

One of the biggest headaches on the hardware side of robotics is finding parts that fit perfectly. If you are not building from a kit, you generally wind up with special orders or hand-machining. I’ve acquired a few tools over the years for this, like the Dremel, a drill press, and vertical band saw; but I don’t have a mill or a lathe (they are heavy and a little dangerous with kids around). I recently took a course to use the Nova Labs laser cutter and that is a great tool for cutting out flat parts. But my machining in general is time-consuming and limited.

A few weeks ago I attended a DC Robotics meetup on hardware prototyping. And I was captivated by their 3D printer. This is a machine that extrudes melted plastic in a precise way to build a computer-designed model. If you can design it, you can (within limits) print it out. I have seen many 3D printers before, but this was the first time I could see the practical applications. Gears, shaft holders, brackets, all easy to create at home.

The printer at the meetup was from the best-known company, MakerBot. They have a very slick ad on YouTube:

My initial intent was to go out and buy one. However, after talking with more knowledgeable people and researching online, MakerBot has a poor reputation — partly because they have portrayed their machines as easy to setup and use. They are not. 3D printing is still experimental and requires extensive initial configuration, MakerBot more than most.

However, the latest generation of machines are at least stable once you have them setup. And then the printing is straightforward. It turns out that Nova Labs is doing a group build of the Mendel Max 1.5, and with the bulk purchase it will only be $750. Low price and expert help, who could ask for more? So I have signed up for it. No date yet but at the end I’ll own something like this:

MendelMax 3-D printer

MendelMax 3-D printer

FireCheetah update

The new drivetrain is working very well. I’ve increased the clearance and FireCheetah is happily running on thick carpets all over the house, at only half the available power. Eclipse with the Arduino plug-in is working extremely well and certainly beats the old Notepad method.

I found a simple solution to the XBee crosstalk during Arduino updates. Since I don’t need any remote control for the robot this time, I simply hook up the Arduino transmission to the XBee reception — but not the reverse. No need for reconnecting wires or using a switch.

But I am the most excited about the software changes. Improved navigation is the key to success. If it works, that will be a post of its own, because I have found little useful information online.

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