25 October 2012

Challenge On!!

NASA has announced the Sample Return Robot Centennial Challenge is ON for June 2013. It is again a Worcester Polytechnic Institute. The rules appear to be basically the same as the June 2012 challenge. Prizes are similar but there are $500 awards for showing up with a competitive robot and another if the robot picks up the cached sample. I'll read the rules more carefully to see if anything else is changed.

Now I have to decide if I can do this on my own. The registration deadline is 7 January 2013 which gives me ten weeks to answer all the open questions.

I did order a Dagu Wild Thumper 6WD from the Robot Shop. Should be here next Monday.

I have two Pololu Simple Motor Controllers that I bought during a sale last November. I worked with a Pololu Maestro Servo Controller with my iRobot Create so have the basic Pololu control protocol working with a C++ Maestro class. In the last couple days I added a PololuSimple class, and a PololuBase class to generalize between the Maestro and new class, and can now talk to the Simple Controller. Those two controllers will go onto the Thumper. Their amperage rating is marginal for those motors but should be okay as long as there aren't any sudden reversals in direction.

I will probably use the Maestro to handle servos either for the picker or positioning cameras.

Oy vey! Lots to think about in a short period of time.

The more I looked at the Thumper the more I liked the idea of a swarm based on it as the platform. I added some additional analysis tonight to the swarm section and have at least one more page to finish on communications. I am focusing on a swarm of two searcher and five collector robots. There is a lot to recommend this, as some of the analysis shows, but it does introduce some complexity by requiring communications and replicating that many robots. A big advantage in using the Thumper is removing the basic locomotion capability from the design.


21 October 2012

Thinking About the Challenge - Hardware


Continuing my summary of thought over the last few weeks, I'll consider the hardware platform. This is not the final platform for the challenge. There are two major issues that need to be settled:

  1. Swarm or singleton,
  2. Picker and, related, storage of samples on the robot. 

Despite those uncertainties I need an outdoor capable platform to start work on the software tasks discussed in the previous article. One of the interesting ones I'd like to accomplish is proceeding to a potential sample. Keeping the vision processing on the sample while driving the robot is, hopefully, non-trivial but requires a lot of detail chasing. The work on the vision processing should help my understanding of how to locate samples.

The requirements for the robot are:

  • Capable of driving in a park type setting, e.g. no major rocky areas, some obstacles like trees and benches.
  • Large enough to carry:
    • One or two cameras, possibly on a 1-2 meter tall mast,
    • A PC class system with Wifi,
    • A prototype picker (thinking ahead a bit.),
    • Sensors for orientation and obstacle avoidance.
  • Drive at 2 meter / second since that is a possible speed during the challenge.
The robot may not need to carry all of the items listed above at the same time since some are only needed for specific experiments. For example, only a single camera may be needed when used to guide the picker toward acquiring a sample. 

I've gone through various vendors and reached a tentative conclusion on what to get. I rejected the simple 4 wheel platforms mounted on a solid box chassis. Most are a little smaller that I liked and while they do well for scampering around a yard I have my doubts about them in an environment with tree roots. Specifically, I don't think they will be sufficiently stable for testing when working with the cameras. Ground clearance might also be a problem.

I considered a tracked platform such as the Lynxmotion Tri-Track because it is so neat but it suffers from the same problem as the square platforms. 

The platforms I mention on the hardware technology page are very appealing but just cost to much for a platform that is only for experimentation.
Wild Thumper 6WD

I am strongly inclined toward the Dagu Wild Thumper 6WD (wheel drive) available from many shops - Robot Shop, Pololu, and SparkFun - to name a few. One reason for naming all of them is the documentation on the platform is different on each site. By checking all of them I got a better idea of the capabilities. 

The Thumper is a good size (16.5" x 12" x 5") without being gigantic, i.e. it fits on a workbench and can be handled by one person. The suspension and ground clearance (2.5") look good. The carrying capability is 11 lbs so it should handle the devices listed above. Its speed in the 1:34.1 gearing is 7 km, which is around 2 m/s. That is probably unloaded but close enough it will give me a feel for the problems of controlling a robot at that speed. 

After considering it, I started wondering if it wouldn't make a good platform for a swarm using it and maybe  its little brother 4WD version in combination. Since it weighs 6 lbs and can carry 11 lbs for a total of 17 lbs, there could be 10 of them in the swarm and still meet the total weight limit. Not that I can imagine setting ten of them loose for the challenge. The organizers would probably shoot me for requiring the ten judges to keep an eye on each robot. 

Thinking About the Challenge - Software

Despite nothing appearing here for awhile I have been thinking about the SRR Challenge. I had a week in Mexico and a week with a cold that kept me from writing. Now I am back to making some progress. I'll summarize some of the thoughts, possible plans, etc. No additional analysis, but there are some things that need to be looked at based on my thoughts.

As I look at hobby robot builders web sites I've concluded that most build a nice piece of hardware that doesn't really accomplish anything real. I've seen some beautiful robots that are the delight of machinists. But there is no mention of any software driving them that makes them meaningful. As I looked at the robots from the 2012 SRR Challenge competition I wonder how many of them spent many hours on the hardware and let the software go until the last minute.

I know from experience in embedded systems development that the hardware is always late. Since there are limits to what can be accomplished in software when you don't have even the preliminary hardware that makes the software late. (And software gets the blame for the project being late!)

I am going to avoid this trap by focusing on the software first. Still, I need some hardware to make progress but that is for the next entry.

I've thinking about the actions the robot needs to accomplish. Some of these are trivial, some need a lot of detail chasing but are straightforward, others are challenging, and still others are possibly beyond my capabilities.

If there are any of the last group I probably cannot enter a credible entry into the challenge. I won't know until I try. A prime example of this is using the vision processing to identify samples at a distance.  Another is maintaining the location of the robot in the search area so (1) all the area is searched and (2) the starting platform can be located so samples can be returned properly.

The trivial items are the basics of controlling the robot:
  • Controlling the motors to drive where needed,
  • Read sensors to determine orientation (gyroscope),
  • Drive servos for positioning the picker or cameras,
  • Etc.
Detail chasing items are:
  • Drive to a potential sample that was located,
  • Etc. (Which means I haven't identified these.)
Challenging items...well, I'm not sure yet. More analysis is needed to identify these. 

03 October 2012

Another NASA Rover

CREDIT: NASA/Ames Research CenterView full size image
Stumbled on this NASA rover in this article on an Lagrange L2 point space station being considered. NASA Ames is using the rover to test teleoperation. A station at the L2 point would be directly behind the moon from the earth. Astronauts could use teleoperated robots to study the backside of the moon.

[Lagrange points are stable locations caused by the gravity fields of an object orbiting another object, in this case the Earth and Moon. An object at a Lagrange point is held in place by the gravity fields. See Wikipedia for more details.]

Anyone have more information on this rover?