Robot kit that includes wheel encoders?

Hello Joe, Look around the "

". Their intelliBrain-Boe is a complete kit. They seem to have good tutorial and docuement. The prgramming language is Java.

-Pandit

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 software).

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 content.

Joe Dunfee

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 common controllers.

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 accelerometer.

-- Gordon

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 robust hardware.

The link you provided to

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.

Joe Dunfee

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 interface.

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:

You might also check out this page for expanded OOPic-based robot controllers: The software's the same, but the board has more than what comes on the standard products from oopic.com.

-- Gordon

You'll still need a controller and motor drivers.

You could try the new Lego Mindstorms robot (NXT). Encoders are integrated in the motors. ...And it just fits your price.

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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 tank treads])

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

= $200 total. Processing would be on my PC. I will post on this on another thread.

Joe Dunfee

you can print your own enocoders if you have access to a laser printer

dan

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