Solar Powered Miniball Wannabe

This miniball project has its roots in the old BEAM Miniball kit published by Solarbotics. It's still a cool kit, so we're going to show you how built a simpler version. This project is spearheaded by Mr. Jerome Demers ( aka Robomaniac ), our intern at Solarbotics!

This robot uses a solar engine circuit. A small solar cell by itself generally doesn't have the power to make a motor move, so you have to store this power up in a capacitor, which is a small battery-like storage device. When the circuit sees that there is enough power stored, it releases it in a burst to the motor, getting useful work.

With this project, our solar engine will be powering a small car in a large plastic sphere!



This technology of using minimal electronics and simple mechanical design is call BEAM robotics.

The Miniball itself was originally invented by Richard Weait of North York, Toronto.The Miniball is a amazing robot - it uses a simple circuit and the robot itself proves to be very capable, rarely getting stuck. The Miniball is mechanically complex and electronically simple. (But don't worry - the mechanical part is still pretty easy)

In this case, we aren't going to build the original Miniball, but a smaller, more basic wannabe version. This robot is extremely simple and can take a beginner less than 2 hours to build.

The original Miniball has a geared motor that moved as a counter weight around a fixed shaft inside the plastic ball container. As the motor tries to move the weight forward, the ball starts to roll in that direction.

In our case we have a motor with wheel, which spins the ball forward as it runs.

Imagine this like a hamster in a ball - it's almost the exact same thing! But in this case, we're feeding our hamster with photons!

Step 1: Parts You'll Need

Mechanical Parts
1 - Transparent Plastic Sphere (80mm - get from craft store or hobby shop)
1 - High-efficiency Coreless Motor (Solarbotics part #: RPM2)
1 - Motor Mounting Clip (Solarbotics part #: MMFC)
3 - Rubber Wheels on Nylon Hubs (Solarbotics part #: RW)
2 - Paper clip

Electronic Parts
1 - 37 x 33mm Solarbotics Solar Cell (Solarbotics part #: SCC3733)
1 - 0.35F 2.5V Capacitor (Solarbotics part #: CP.33F)
1 - 6.8uF Tantalum Capacitor (Solarbotics part #: CP6.8uF)
1 - 3904 Transistor (Solarbotics part #: TR3904)
1 - 1381 Voltage Trigger (Solarbotics part #:1381C)
1 - Signal Diode 1N914, 1N4148 (Solarbotics part #: D1)

1 - Length twisted red/black wire

Tools Required
- Soldering equipment (soldering iron / solder / cleaning sponge) (HVW tech soldering tools)
- A pair of Needle-nose pliers (HVW tech part #: 43060 or 43061)
- A pair of Flush Cutters (HVW tech part #: 43040)
- Safety Glasses - VERY important when clipping and snipping! (Solarbotics part #: 5330)

We made a parts bundle of everything you you need to build this project (not including the plastic ball and hand tools). You'll have all the mechanical and electrical components to start making this neat lil' robot!

Click this link to get the bundle.

Step 2: Making the Circuit

The first thing to do is solder all the parts to the solarcell. If you are not using a Solarbotics solarcell, you will have to find the "freeforming" instructions for building a solar engine circuit.

Solarbotics solar cells all come with a circuitboard ready-to-use on the backside of each cell.

Step 3: Solder the Circuit

Follow the instructions on the printed circuit board - there are labels that mark where various components go. Note how we used the sleeve of a breadboard wire to isolate the positive (+) lead of the capacitor, preventing it from contacting the diode.

Step 4: Make Two Wheels From One

What we do here is simply cut one large wheel into two smaller wheels. It's a way to recycle and save parts at the same time.

This is how you do it:
Take a sharp blade and slide along the object you want to cut. Roll with the wheel and press down at the same time. You'll cutting through easily. Don't press too hard. Roll it back and forth 4 or 5 times with gentle pressure to make a nice cut.

You can use this technique on metal tubing too! It works very well!

Step 5: Wheel Holder

We're now going to take a paper clip and bend it, creating a wheel holder for both wheels. Just cut at the last step.

Step 6: Wheel Guide

Use breadboard wire to make a guide for the wheels. This will prevent the wheel from sliding too far.

(Check the next step if this doesn't quite make sense yet...)

Step 7: Closing the Wheel Guide

Simply close the guide so that the wheel doesn't fall off the axle.

Step 8: The Motor Mount

Here's a clever way to mount a motor to your robot - these pager motors are really small, and they fit perfectly in fuse holder.

We'll use a fuse holder (included in the parts bundle for this project) to mount our motor. Don't solder directly to the motor - this is pretty difficult, and you can ruin the part.

I used pliers to "squeeze" the fuse holder's legs over the wire, so that the wire stays in place while soldering it to the paper clip frame.

Step 9: Bend the Frame

Since this will go into a ball, we need to make the frame fit inside of it. We'll bend the frame run along the contour of the shell, and lower the center of gravity.

It is best to have your sphere on hand to you can play with the wire's bend geometry.

Step 10: Inserting the Wheel Onto the Motor

You've probably noticed that the inside hole in the rubber wheel is too large compared to the motor shaft.

This is a neat way to insert the wheel to motor shaft. Just take a piece of wire sleeve and insert in onto the shaft, creating a snug fit with the rubber wheel.

Step 11: Clip the Motor to the Frame

Here we clip the motor into the fuse holder, completing the frame. Place the whole assembly inside the half-sphere.

Now you're ready to mount the solarcell to the frame!

Step 12: Mount the Wheel Assembly to the Solar Cell

We are now ready to attach the wheel frame to the solar cell. You can do this with glue, but solder is much better!

I will solder my frame to the fat metal strip on the back of the PCB, but it is covered by a green coating. Scratch the surface of the PCB (like in the picture) to create an exposed patch where you can solder on a breadboard wire.

If you want, epoxy your wire here instead. DON'T USE HOT GLUE! Hot glue will get soft and melt in the warm insides of the clear ball, especially in sunlight!

Step 13: Preparing the Ball

Take the plastic ball and cut the tabs. Be very careful with your cutting here, as you don't want to break the ball.

Use the snipping tool and slowly cut in a circle until the tabs are removed. Start clipping far out, and work in. Snipping too close to the sphere's edge might crack it!

Step 14: Insert Robot Into Ball

Take your robot and put it into the plastic ball. Et voila, you're finished!

Be sure that the robot rolls in the ball without friction. You might need to bend the paperclip to make the robot work perfectly, with no rubbing.

Now go try out your new robot!

Here is a quick test, make your robot roll into a wall...

You will probably realize that it flips over in the ball. It goes so fast, that it flips itself over and is now stuck upside down!

Check next step to fix that issue.

Step 15: Statbilization Improvement

To prevent the robot from flipping upside down, you can make a long paper clip rod that comes close to touching the top of the plastic ball.

Just like in steps 6 & 7, take a paper clip, add a rubber wheel at the end, and then solder everything to the bottom of the paper clip frame. All done!

Step 16: What Is Next...

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