2008/8/6 Nicolau Werneck <nwerneck@gmail.com>
Hello fellow players. I am still with that idea of mine, of trying to
build myself a small robot using just CMUCam3 and EZURiO WISM for the
whole processing part. This project has some obvious difficulties,
partly regarding robotics as a whole, and partly regarding player /
stage. I am hoping other interested researchers can give me a hint or

My robot will probably be based on DC engines with velocity control,
what I believe is similar to a great number of robots around. I
believe it will have odometer readings too, plus the camera. My
problems and inquiries are:

1_ What difficulties should I expect to find when creating a Stage
model for my robot? What are the essential parameters I must measure?
2_ Regarding motion control: I have already "played" in stage with
simple velocity control avoiding obstacles, and with the VFH module.
In my robot I don't plan to have the range readings required (isit?)
by VFH, but I would still like to have some form of "proxy" control
algorithm on top of the velocity, to follow some kind of smooth track.
This is, of course, one whole world of research: what tools do I have
available (in Player and in general) to apply in this new and unknown
robot of mine, other than VFH?

I think all of the obstacle avoidance methods in player rely either on a ranger type interface (IR, Sonar, laser) or on a prebuilt map, so you would probably need to either adapt or create your own method for this. (feel free to correct me if I am wrong, there are a couple of new drivers that have gone in recently...)

3_ If I turn out to be able to reliably detect wall positions with my
camera, I could probably create a form of range device. What would be
the best way to implement it in player, just like it were any other
array of range sensors?...

The point cloud3d interface was designed for this sort of thing. The challenge then is working out what to do with the data :) if you can post process it to produce a 2d set of information you could use it as a psuedo ranger device and therefore use vfh...

4.1_ What is our experience with problems in controlling robots using
Player through a Wi-Fi network caused by delays and limited bandwidth?
What is the minimum amount of local processing I should expect to need
to perform in the robots instead of in the mother-ship-computer-box?
How much does a wi-fi network resembles R/C?

This all depends on the stability of your controllers, and the amount of precision you want (and the speed you are travelling). For slow speeds I would suggest your velocity control loops on board and you can get away with the rest off board. If you need higher speeds your motion control may need to be onboard as well, and if you want very high precision on your final position, all your sensor processing and so will need to be onboard as well (fair simple to work out, speed * maximum delay in wifi = potential error in final position as it can travel that far between sending the stop command from the 'mother-ship' to the on board)

4.2_ Does anybody know the bandwitdh consumed by a basic Player
program controlling a standard robot (e.g. Pioneer)? Is a 115kbps
UART-bottlenecked connection enougth to send motion commands and range
sensor and odometer readings back and forth?
It will all depend on the amount of sensor data, if you want to send large sets of extracted points from the camera over that interface then 115kbps could get used up reasonably quickly. One of those things where you just need to do the math... packetsize*frequency=...

I am sorry again if I am bordering off-topicness, I hope some list
readers might identify with some of these problems. And I feel like
asking too much sometimes, wanting my own fully functional robot
from-night-to-day, but wasn't it much more difficult 10 years ago?...

I would like to talk to other robot researchers who identify with my
dissatisfaction with small, simple mobile wireless robots in the
market. We must unite!...  BTW, the Surveyour Philippe found seems
great, but I grew quite attracted to this idea I started to develop. I
have this feeling a whole new generation of small (100mm?), simple,
smart and speedy mobile robots will start to emerge at any time!!...

Looking for it, I compiled a list of 14 "branded" mobile robots, from
Pioneer (440mm length) to e-puck, which has a 7mm diameter. But from
all of these I still like the looks of CMUCam's spoonbot more. :)

See you, and thanks for the support.


Nicolau Werneck <nwerneck@gmail.com> 9F99 25AB E47E 8724 2F71
http://www.lti.pcs.usp.br/~nwerneck EA40 DC23 42CE 6B76 B07F
Linux user #460716

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