The Old Bike
The Old Bike is the main test platform of the Cornell Autonomous Bicycle Team. It is a converted folding bicycle developed by Andy Ruina's lab. Built in 2016, this bicycle is currently the only working Autonomous Bicycle in the Western Hemisphere.
Mechanical Components
Front Motor Assembly
The assembly sitting on the front of the bike is one of the main components of the bike. The assembly steers the bicycle by turning the front wheel, much like a human. However, instead of using handlebars to apply a moment to the stem, the assembly is directly attached to the fork. The motor notably must be in line with the axis of the wheel.
The current motor enclosure was created by welding a circular steel plate to the intersection of the head tube, top tube, and down tube. This acts effectively as a base for the entire assembly. The welded plate supports all of the weight of the assembly as well as any produced torque. The leveling of the head tube, from the inclusion of the steel base, allows for direct access to the fork. In lieu of a stem, a rod was placed inside of the exposed fork and bolted at its end to prevent rotation. The insert is threaded on its bottom end to interface with the fork, and is connected to a coupling at its top. This coupling connects with the drive shaft of the motor. This allows for the power from the motor to be translated down to the fork and effectively control the bike's direction.
The motor is a large 24V, 80W motor found in Andy Ruina's lab. The motor speed is then stepped down by a 3:1 gearbox to increase torque and decrease speed. There are plans to replace this motor, as it has been described as "jerky". The backup motor awaiting testing is a VEX Robotics BAG Motor stepped down with a 36:1 gearbox. The lessened power and increased gearing will allow any motor coasting to affect the steering inconsequentially as well as create more reliable, precise movement of the front wheel.
The surrounding components of this assembly are also important. An orthogonal plate is placed directly above the original base plate to correct any offset from the fork caused by the placement of the steel base. This plate is connected directly to the base plate with nuts and bolts. Proceeding this is a plate that was added to stabilize the encoder, and two more were added to constrain the motor. Between these plates, four long threaded steel rods and an assortment of nuts were used to connect the plates to mesh the system.
Rear Motor
The rear motor is a 24V electric hub motor. While the manual is long lost, the principle of the motor is simple. The hub is static; it attaches to the dropouts with nuts. The motor revolves the wheel around itself using nothing more than a controllable DC current.
Fall Protection
When bringing the bike on a test ride, one of the main concerns of the team is fall protection. While there have been previous attempts to attach a Landing Gear-like device near the bottom bracket, the mainstay of bike protection are removable cushions that attach the length of the bike on either side. These assure that the sensitive electronics don't break in the case of a fall by absorbing much of the impact.
Electronics
Electronics Box This is the clear plastic box that sits on a seat-tube mounted rack. It holds and protects the PCB and any of its peripherals as well as the battery. This is the most fragile part of the bike and required additional protection from impact and water. Main Article: Cargo box
IMU The Inertial Measurement Unit is the sensor located nearest the center of mass of the bike that measures the bike's real-time dynamics. It relays its measurements to the PCB and ultimately is crucial to keeping the bike upright. It is currently protected by a 3D-printed box. Main Article: *Controls, make one!*
Bicycle-Specific Components
Wheels The wheels are 16 inches in diameter and have 28 spokes per wheel. The wheels are the primary driver of the bike as they convert the rotational motion of the motor to linear translation.
Tires The tires provide the inner tubing of the wheel an added layer of protection. The tires on the bike are mountain bike tires and give the bike added gripping strength for stability. They are 16 inches in diameter and have a width of 1.75 inches. The recommended pressure for mountain bike tires is between 25 to 35 psi.
Frame The frame of the bicycle is that of a folding DAHON Classic III. The Classic III frame is short and heavy built with a steel frame. Due to its intended use as a portable bike, the small frame of the bike sacrifices its weight for its size. It acts as a liaison for all the assemblies and components of the bike.
