I am looking for a complete robot kit which includes encoders for the
wheels. All of the kits I've seen omit this feature. Of course, price
is an issue for me (defintely under $300).
The reason I was looking for a complete kit, was that I am weak in
regards to programming. If I can get a complete kit, I figgure that
there will already be some instructions about including the encoder
information in the programming.
Can anyone suggest one?
Thanks for the link. I had not come across their page before. It is
based off the Parallax Boe-bot, but adds their own controler and does
include wheel encoder sensors. But, most importantly, it seems to be
well documented in every aspect of the computer (both hardware and
At $300 for the base model it at the top end of my budget. The actual
hardware of the robot probably less than $50 of that cost. Their
"brains" board is certainly very complete, but I suspect the majority
of the cost is going towards their development of the educational
It's not that hard to add the encoders if you need them. Nubotics makes
an after-market product called the Wheel Watcher that works with
servo-based robots. Their standard product interfaces to those colored
plastic injected wheels that are popular, but they also sell an adapter
to allow for use with just about any wheel. The Wheel Watcher uses
quadrature encoding, and they provide programming examples for various
Encoders are not a universal requirement. A line follower doesn't need
them, for example. So it just adds to the cost, and when budget is a
main consideration, the extra $$ for a pair of encoders could be used
for something else you might be looking for, like a gripper or an
In my case, I have good electronics knowledge, so physically adding the
encoder is not a problem for me. However, it is the software
integration to the programming which will challenge me. This is what
makes a complete kit so attractive to me.
In my case, some of the future applications I have in mind will require
accurate navigation. I hope to eventually include some beacon type
method to provide an absolute location. But, most beacon methods seem
to require some time to establish a location. Also, they will
occasionally be blocked from the robot's view, so they need to be
supplemented by the encoders.
I hope to eventually make a vacuum attachment so it can vacuum my
house. Since a true vacuum (not just a sweaper) is power hungry, it
can't afford to just bump around the room hoping to cover the entire
room. So, it needs to track the areas it has been. The Boe-bot based
robot is obviously too small for this. But, I imagine that I can start
with that kind of kit and then re-build a larger new robot using more
The link you provided to www.roboticsconnection.com was a great one.
They seem to have a lot of choices in hardware... especially a variety
of encoders. They also seem to provide some help integrating them into
the user's robot. Their $140 Botster is a Robot base kit that does
include encoders, but no "brains", but possibly if you buy their
"brains" it will include some documentation about using the encoders.
Since I am writing about my robot plans, perhaps I can take the
opportunity to go into more detail. I think I would like to eventually
make a differential drive base, but rather than two motorized wheels, I
would like to use the "dual differential gear" method. This allows one
motor to drive both wheels forward without them getting out of sync
with each other. A second motor (probably a lower-power one with a
worm gear) provides the steering ability.
For a controler, I would like a PC based one, either as an onboard
laptop, or preferably remotely via a 802.11 or bluetooth.
Then you probably don't need quadrature encoders and you can go with a
much simpler design of a single vaned/slotted/striped disc. See the
ARobot at robotics.com for the design principles.
You don't mention the microcontroller you want to use but assuming it's
a common popular one, you can get sample code all over the Internet for
attaching encoders to it. Some controllers like the BASIC Stamp isn't
fast enough to handle both inputs of two quadrature encoders
simultaneously, but products like the Wheel Watcher (which I have
nothing to do with, BTW) do the decoding for you, simplifying the
You should probably go about this the other way around: decide what
microcontroller you want to use. Then see if there's example code for it
that handles the type of things you want. From this stage, getting
compatible hardware is the easy part.
To get the ball rolling, check out the OOPic-R at oopic.com. This
controller has built-in objects for dealing directly with a wide variety
of common robot hardware, incuding un-decoded quadrature encoders (that
is, channels A and B in quadrature). The OOPic has a very active Yahoo
user group, and there's a book by Dennis Clark that supports it. Dennis'
page: http://users.frii.com/dlc/robotics/botlinks.htm .
You might also check out this page for expanded OOPic-based robot
controllers: http://oricomtech.com/oobot40.htm . The software's the same,
but the board has more than what comes on the standard products from
I had looked at that system a while back, but dismissed it after
trying to research the technical details. It seemed to be a relatively
closed system because of the lack of technical information. But the
lack of information may have been because of its newness.
I've spent a few hours researching the NXT system again. I found
more information, but still nothing about the servo motors themselves.
But, I am getting a feeling that they are not servo motors themselves,
but rather just a motor and encoder, with the driver electronics inside
the NXT brick. I wonder about the torque and weigth capabiliy for the
motors when directly attached to wheels.
I seem to have widened my field of choices. While my ultimate goal
is more elaborate than the Boe-Bot or NXT system, I was thinking of
them as my first robot. Then I would build another, larger and more
elaborate one, from purchased components. But now I might consider
jumping in to the deep end of the pool! My choices are;
Lego NXT system; $250 [complete - including bluetooth and USB]
RoboticsConnection.com 's Traxster Robot Kit, $185 + Serializer
Controler $140 + serial Bluetooth $80 + Encoders $60 = $465 [more
poserful motors and base, more expensive system, I don't really like
HobbyEngineering.com 's Scribbler Robot [Completely assembled, but no
encoder or provision for one] $80
zagrosrobotics.com 's 12" Dia base kit $180 + Controler [Includes Motor
controler, I really like its robust construction, holds 35lbs and can
carry a laptop. But almost a build-from-scratch situation]
Irobot's Roomba, a surprise last-minute entry into my choices, and
probably the way I will go. It seems to have everything I want,
including encoders. $100 + $100 for Bluetooth [from
http://www.roombadevtools.com /] = $200 total. Processing would be on my
PC. I will post on this on another thread.
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