Introduction: Walker the Robot
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Walker is a little robot who gets around in his own waddling fashion. He is solar powered, but does not need bright sunshine to become active. His "brain" is a solar engine which enables him to store up energy, and when there's enough, to energize his motor muscle and move on for a bit.
Walker moves by inching himself along on his arms - or legs. Each one is a little more than long enough to reach to the floor as it rotates around to the vertical. This slightly raises his torso and pivots it a bit forward. Then the arm on the opposite side comes around and does the same. And thus he sashays along.
One leg was purposely made longer than the other to constrain Walker's excursions to a small circle in one corner of the living room. That way we know more or less where to look out for him when we are walking around.
There is a short video showing him in on one of his afternoon waddles.
Step 1: CSS555 Solar Engine
The solar engine with which Walker has been endowed is shown here as built on a DATAK Experimenter's I. C. Protoboard (No. 12-607). The SIP sockets allow plugging in the solar cell (top two), the motor (next two down), the photodiode (the close pair off to the right side), and the storage capacitor (the two right next to the IC). The circuit for the engine is very simple as shown in the schematic. The CSS555 Solar Engine Instructable describes the components and circuit operation in detail.
Step 2: Walker's Motor Unit
Walker's "muscle" is a solar type motor driving through a 60:1 gear train unit. The gear box is from a kit for motorizing various toys and models. It is called the "2 in 1 Gearbox Kit" and sold by a number of sources. It comes with a battery type motor, but those kinds of motors are not suitable for being powered through small solar engines. However, the frame of the gear box is easy to cut and bend to accept a solar type motor.
Step 3: Walker's Base
Walker's base was made from three pieces of wood. His "foot" is a 2-3/8" dia. disk cut from 3/32" thick plywood. The base block is a piece of soft wood glued to the foot. The upright (Walker's breast plate) is also 3/32" thick plywood.
Step 4: Lower Assembly
The motor unit is mounted on the breast plate with machine screws.
The solar engine circuit board is held in place by wood screws into the base block.
Step 5: Construction Details
The head block of Walker is a piece of balsa wood glued to the motor. It has a groove on the underside to clear the terminals on the motor and provide a conduit for the wires from the motor and solar cell.
The solar cell is an RU6730 which has an advertised rating of 6.7V and 35mA. These outputs are in full sun - output is less of course in the lighting conditions to be typically found indoors. Now the solar engine with which Walker is equipped turns on when the voltage in his storage capacitor reaches about 3.5V. The solar cell unit easily supplies this voltage throughout the day just from the incident light that enters through our windows. Even on quite overcast days, Walker goes for his strolls - it just takes him longer to recharge between walks when it is cloudy. If he happens to stop in a rather heavily shaded area, he will usually still eventually become active (in fact the CSS555 Solar Engine is particularly adept at dealing with low light situations). During his saunters, Walker slows down little by little as the voltage in his capacitor runs down. It turns off at around 1.9V bringing Walker to a sharp halt.
Walkers arms are lengths of 1/4" square wood drilled to be a tight push fit on the gear shaft. The arms are about 3" apart. The "cut and try" method determined the best lengths for the arms. The longest one protrudes about 3/8" below the base. The other arm is cut shorter to give the size of the circle in which Walker is desired to promenade - which in our case is about 15". Our Walker marches on a hard floor, but he also works on carpet if we let him. If we had thicker softer carpet, his arms would probably have to be longer. The arms are set at about 90 degrees to each other for a waddling gait, but setting them in line gives an amusing hobbling gait.
The capacitor shown in the photographs here and in the video is 0.22F which allows almost a full circle of travel in each waddle. He goes around several times when equipped with a 1F cap, but of course it takes correspondingly longer to charge up between jaunts.
Step 6: Walker Senior
Actually, we refer to the Walker just described as "Walker Jr." because he is the baby brother to the original Walker. The two of them are shown here together. Walker Sr. has been parading around here at home for a number of years. We don't know exactly how old he is, but he is pictured in our Easter Solar Engine Instructable which was published in 2010. And he was around some years before that because as pictured there, he is sporting the RU6730 solar cell. Originally, he had an "indoor type" solar cell which was amorphous silicon on glass. With this he was able to gather energy under very low lighting. But alas it was broken. If memory serves, it was on a day when we had several young visitors who were having a great time playing with Walker Sr. At one point, he was placed on the kitchen table by a well meaning adult for fear that the children might bring harm to the helpless robot. Then the children, and everyone else, turned their attention elsewhere...until much later when we heard a tiny crash. Walker Sr. had taken up enough energy to waddle right off the table!
That wasn't his only trip to the robot hospital. Parked somewhere on the floor during the evening hours, he got accidentally kicked every now and then. For a while, a blinking red LED was mounted on his breastplate so we would know where he stopped after his last tramp of the day (the flasher circuit described in the Electronic Paperweight Instructable is ideal for this warning beacon). It was removed during one of his repair operations and never replaced for no good reason. Because of all the injuries and repairs, Walker Sr. was showing his age, so it was decided recently to make the new more colorful Walker Jr. Now we have the two of them moving around on the floor!
Both creatures have the same muscle unit, but Walker Sr. is set to a lower gear ratio, namely 76:1, so the older guy moves a bit slower. This suits him just fine because his solar engine works in a lower voltage range. He has an Easter Solar Engine set to turn on at 2.6V and off at 1.5V. The lower voltage makes it possible to use a simpler storage capacitor. He now has a single 1.5F capacitor rated for operation up to 2.75V which keeps him going for a good long time - once he does get going!
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