A solar engine circuit is used by this amazing robot which will be powering a small car in a large plastic sphere as demonstrated in the video below. It has its roots on the old BEAM Miniball and the power is stored in a capacitor which is a small battery-like storage device since a small solar cell by itself does not have the power to move a motor. When enough power is stored, the circuit provides useful work by releasing the power in a burst to the motor.

Standing for Biology, Electronics, Aesthetics, and Mechanics or BEAM, its robotics technology uses minimal electronics and simple mechanical design. A geared motor is contained in the original Miniball and moves as a counter weight around a fixed shaft inside the plastic ball container. The ball starts to roll in the forward direction as the motor tries to move the weight. This project spins the ball forward as it runs because it uses a motor with wheel as shown in the image below.

As shown below, the mechanical parts needed include paper clip, rubber wheels, motor mounting clip, high-efficiency coreless motor, and transparent plastic sphere. The electronic parts will consist of signal diode, voltage trigger, transistor, tantalum capacitor, 2.5V capacitor, solar cell, and twisted red/black wire.

Soldering all the parts to the solar cell is the first thing to do. The free-forming instructions for building a solar engine circuit can be found when a Solarbotics solar cell is not used because a circuit board ready-to-use comes on the back side of each Solarbotics solar cell. The instructions on the printed circuit board should be followed and the various components will go to the marked labels. The circuit shows how the positive lead of the capacitor is prevented from contacting the diode through isolation with the use of the breadboard wire sleeve.

Two smaller wheels can be made from one large wheel through cutting. A sharp blade is used to slide along the object to be cut as shown below. A wheel holder for both wheels will be created from a paper clip and the guide for the wheels will come from breadboard wire to prevent from sliding too far. In order for the wheel not to fall off the axle, the guide can be simply closed as seen below.

The motor will be mounted using a fuse holder which can be obtained by using pliers to squeeze the fuse holder’s legs over the wire to stay in place while soldering to the frame of paper clip as shown below. The frame needs to fit inside the ball by bending it along the contour of the shell as the center of gravity is lowered. When inserting the wheel onto the motor, a piece of wire sleeve is taken and inserted into the shaft to create a snug fit with the rubber wheel since the inside hole in the rubber wheel is too large compared to the motor shaft.

The motor is clipped into the fuse holder to complete the frame in the photo below before placing the whole assembly inside the half sphere which signals the mounting of solar cell. The wheel assembly is mounted to the solar cell by soldering the frame to the fat metal strip on the back of the PCB. In preparing the ball, the tabs are cut and removed using the snipping tool.

The project is done once the robot is placed into the plastic ball while making sure that it rolls without friction. A long paper clip rod that comes close to touching the top of the plastic ball can be made to prevent the robot from flipping upside down as shown below.