After building my original DominoBotNXT I was not happy with the need for it to backup each time a domnio was placed. (see link for details on this). The stanard NXT system provides only 3 motor ports. On DominoBotNXT, 2 were used for the drive wheels and 1 for the domino placement gate. This resulted in the need to tied the domino conveyor that carries each domino to the gate to be driven directly from the left drive wheel. When placing a domino, the distance between each was too wide, so it would have to back up each time one was placed. To fix this, I needed a 4th motor and a means to drive one. So, how do you do this with only 3 motor ports you ask??? Good question, I’m glad you asked as that is what this page is for….
The Motor Multiplexer from Mindsensors attaches to a single sensor port and allows the NXT to drive an additional 4 motors. In my case, I only needed 1. Using RobotC, I was abled to write (with some help from Dick Swan and Nitin Patil – thx guys) code that would allow communication with the IC2 interface on the sensor to control the 4th motor. So, in the programming environment, I simply had another motor port and use it in a similar way to the 3 core ports on the NXT. It only took a little bit of code to get this working. Now, DominoBotNXT can continue to drive forward while placing domino’s – making it much faster at its task. For info and a video on this, visit my DominoBotNXT2 page.
Results:
I am happy with the way this sensor works. I was working with a pre-production beta version that had some glitches (one port did not work), but I have been assured that the production units have this addressed.
Construction:
The sensor uses a standard NXT cable plug to interface the unit with the NXT. It is not encased in any plastic or bricks. Instead, it provides standard width Lego mounting holes to integrate with studded or studless beams and connectors.
Have a sensor or add-on that you want reviewed? Drop me a line. 
May 2006:
Update: DominoBotNXT has been enhanced. See DominoBot2.
For those who do not know about the Lego Mindstorms Developer Program (MDP), back in January of 2006 Lego was seeking assistance from the Lego community on their next generation Mindstorms product (NXT). Approx 9600 people applied to become one of the 100 MDP’s. In late February, I received an invitation to participate and of course jump at the opportunity. For a few months, the group of us were under an NDA (Non-Disclosure Agreement) where we could not talk, show or discuss anything about what we had been working on in the MPD. Now that May 1 has passed, we can now open to discuss some of what we have been up to. 
We all had an opportunity to participate in different areas of the testing/development process areas from software to Bluetooth to building robots. Initially, I wanted to get involved in more than one area, but time was limited, so I decided to focus on building only. I wanted to try and re-build my original DominoBot robot to see if I could make a better, more efficient version of it. I also wanted to test the new motors’ built-in rotation sensors – as I needed this functionality.
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This page is dedicated to the further enhancements that I have done to DominoBotNXT. For more info on the original DominoBotNXT, have a look here. 
One of the drawbacks of the original was that due to the 3 motor limit, it had to backup to properly place dominos. This was because the domino-placing component was tied directly to the drive wheels. So, as it drove forward, a domino would make its way to being placed in the holder mechanism. Doing this caused the robot to move forward approx. 4 inches. Since this is too far for domino’s to actually cause any chain reaction, the robot had to move each newly placed domino back to be within 1″ of the last placed one.
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DominoBot 2 was my take on re-creating my original DominoBot. After I had finished the original,
I found ways to make it more efficient and better at what the original did. I also did not have the limitations of the parts supplied with the RIS and UBS sets.
One of the parts that needed re-designing was the mechanism used to force domino’s out of the chamber. The original tended to have difficulties at times. I devised a mechanism using rack plates (3 – 1×4’s). It is driven by the same motor that moves the loader arm, but the method does not allow slip-up or misalignment. A touch sensor at the full-out and -in positions ensure that Dbot2 knows exactly when a domino has been pushed out and when the rack has reset.
Check out newer versions of DominoBot (NXT).
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Having participated in the creation of this book, I have to admit some bias to the review. 10 Cool Lego Mindstorms Ultimate Builders Projects contains 10 original Lego Mindstorms creations. The model I submitted is DominoBot. It was a great challenge to build and create the building instructions for this model. The book contains step-by-step instructions on how to build each of the 10 robots. The book should challenge the intermediate enthusiast and contains some great ideas on building techniques. If you are interested in this book, it can be obtained by most retailers including Amazon, Chapters, Ingigo, and the publisher Syngress. I have also included building instructions in the Instructions section of this website.
It had been a few months since I built my last robot (Climber). During the early summer of 2002, I received an email from Syngress. 
They had indicated that they were going to create a series of “10 Cool Lego Mindstorms Robots….” books, and invited me to produce a model for one of them. For some time I had the idea of building a robot that could mimic the activity of laying down dominos on a pre-determined path. It was the perfect opportunity and hence DominoBot was born… Given that I was in the midst of assisting with wedding plans, and moving our business, I had a busy summer already. But, I was not going to pass up this challenge. This is something that I had hope for since I began building Technic creations in my young days.
Update: View my NXT version of DominoBot.
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