bike103a.jpg (4376 bytes)

View from  the front left of the completed drag racing motorcycle

bike106a.jpg (4978 bytes)

View of  the right side of the completed drag racing motorcycle

bike105a.jpg (3917 bytes)

View from  the underside of the model - the RCX unit provides lateral support of the frame

bike102a.jpg (4788 bytes)

Closeup  view of the rear assembly - note the driver footpeg and control near the  rear wheel and the drag pipes

bike101a.jpg (5586 bytes)

Closeup  view of the front assembly including the fork assembly, support wheels,  supercharger scoop and seat

This is the first of two motorcycle models using the Lego Mindstorms robotic construction sets. This robot uses the RCX brick from the invention set while the other model will use the Scout brick from the discovery set.

The first consideration for this design was to keep the center of gravity low to improve balance. This was accomplished by constructing the frame using the two longest structural member lengths on each side and linking them together with a short structural member and attaching pins where they meet. The entire frame is then attached to the bottom of the RCX unit. The RCX is mounted with the IR receiver pointing forward to allow programming since the rear of the RCX is blocked by the mounting position of the drive motor.

Directly behind the RCX is one motor. The motor is coupled to the rear axle using belt drive. We originally used a medium pulley on the motor and a small one on the rear axle, but during testing we found this did not provide enough torque to get the model moving without a push. This problem was solved by changing to a medium pulley on the rear axle too, creating a 1:1 drive ratio. This gave acceptable speed and allowed the model to start easily by itself.

The front fork assembly is rigid and does not rotate to steer the robot. In the picture at the left you can see that half-width supports were used at the point the axle attached. In a previous design a regular width structural member was used all the way to the wheel, but too much drag was placed on the axle so this was changed to the current design to improve the speed of the motorcycle.

We selected the supporting wheels by trial and error using different sizes and styles of wheels and different attachment points. These hold the model upright and assist in keeping it from turning while in motion. Structural strength is improved by the axles and spacers at both ends of the motorcycle, and the handlebars. We added an axle with spacers in the middle of the fork assembly to improve rigidity.

The final step was to add a few components to improve the realism of the motorcycle. We created a supercharger scoop using the green triangular pieces. Axle coupling spacers were used for handlebar grips and footpegs. A foot brake and shifter lever were added at the rear, and a hand clutch and hand brake were constructed using the long black connecting pins. Small gears and right angle axle adapters were employed for the speedometer and tachometer, and flexible tubing was attached directly to the RCX for drag pipes. Finally, a seat along with backrest was mounted on top of the RCX unit.

Several programs were uploaded to the RCX. One does the "tire burn" -- racers will preheat their tires before racing by spinning them on the pavement. This is copied by having the robot move forward quickly for a short time, then reducing power and backing up to the start line. We also created two racing programs. One turns the motor on for a short period for racing indoors and the other for a longer time when racing outdoors. For each program a short delay is used before execution commences to avoid the need for using the sensors to start execution.

What's next? We plan to build another bike using the discovery set and then race the two robots. We may try to scavenge the toy box looking for riders. Who knows?