The LEGO MINDSTORMS HoopRover History

The LEGO MINDSTORMS HoopRover model was first created back in early 2006 while I was part of the LEGO MINDSTORMS Developer Program Group (the MDP). It was also the first complete model I created with the NXT set. As part of our development process LEGO wanted the group to create some interesting models by combining the (then new) LEGO MINDSTORMS NXT Robotics Kit with existing production sets and elements. Several models were showcased on the MINDSTORMS main webpage and other places. I've always been interested in the robots and machinery of the Star Wars series and actually returned from my Dark Ages with the little LEGO Speeder Bike set #7128. When LEGO produced the Star Wars Hailfire Droid set #4481, I was thrilled. Specifically, the awesome gear wheels could be and were extremely useful in LEGO MINDSTORMS Robotics. I went for the challenge to use them during the MDP and was successful. The outcome was a graceful mix of minimal parts with awesome functionality. I wanted to create something with the wheels while I was stuck in rover making mode. I felt the hoop wheels provided a very “space rover” look together with the NXT elements. The main challenge of building with the hoop wheels is creating a precise LEGO drivetrain position for proper wheel/gear control. The hoop wheel‘s inside diameter gear and slot configuration made it difficult to render a perfect motor and grapple structure. But, the arrangement of the HoopRover is elegant and very efficient. The pBrick and chassis can roll over 360 degrees without falling away from the hoop wheels while also maintaining the proper gear mesh. It operates very smoothly and is very robust. While, the simple structure is strong, my objective was to save weight using the least amount of elements possible. 

The HoopRover can easily become a Hailfire Droid and although it does appear to be an NXT Star Wars Hailfire Droid, the plan was something entirely different with a different meaning. The truth is, my plan was to create a rover with the hoop wheels closer together at the top and a wider stance at the bottom. This angle was inspired by "MurderBall" the documentary film about the evolution of this extreme sport and the sportsmen who play full-contact rugby in Mad Max-style wheelchairs - overcoming unimaginable obstacles to compete in the Paralympic Games in Athens, Greece. The very rugged wheelchairs have wheels angled outward at the bottom for stability. I did create the proper angles with studless beams for this wheel position but felt that the operation would be impaired somewhat for my MDP rover effort. So, to have a more similar Hailfire Droid look...some repositioning of the wheel/slot grapple structure, guide wheels, and alignment/drive gears would be needed. I was surprised at how well it works. Resistance and sound within the drive/wheel support system is barely evident when operating. I planned to add some suspension or flex into the design. Below, I included a picture of an early design with the hoop wheel...the NXT MonoWheel. While it works and can drive, it cannot balance. This was a “just for fun model”. I have been interested in monowheel vehicles since I was a kid. Thank you for stopping to read about history of these creations. Robotics has been a favorite of mine and I hope I have inspired you and other robotics developers to create some wonderful marvels.

Here is the original NXT HoopRover and NXT MonoWheel... 

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This is the revamped HoopRover dressed in the EV3 hardware and a CAD wireframe version... 

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A picture from LEGO Magazine of Astronaut Dr. Daniel Barry with my HoopRover floating above his head like a space station. With a screen grab from the LEGO MINDSTORMS Website.

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