Solar BEAM Marble Machine
Introduction: Solar BEAM Marble Machine
Ladies and gentlemen, I present to you, my marvellous "Solar BEAM Marble Machine"! A brass marble machine with a solar powered, solenoid actuated, lever lifting mechanism!
This machine uses capacitors to store energy from the sun and, once charged, dumps all that energy into a coil, pushing away a magnet, and lifting a small steel ball through the use of a lever.
In previous BEAM related Instructables there was some confusion surrounding my use of the term BEAM. I don't think it is such a common concept anymore. How I understand it is that BEAM is a hobby electronics movement from the late 90s to early 00s that focused on turning found or common components into analogue circuits and robots. https://en.wikipedia.org/wiki/BEAM_robotics
The circuit used here is a type of very common BEAM circuit called a solar engine which stores charge from a solar cell (or other low current power source) in a capacitor until there is enough usable energy (i.e. the capacitor voltage is high enough) to do some meaningful work. This is normally used to run a small motor in short bursts even when the sun is not strong enough to power the motor directly. It is especially helpful in this particular machine as there is no way a solar panel of this size would be able to provide the current necessary to drive the coil while capacitors have no trouble. Furthermore, even if we had the necessary power, we would not want current running through the coil at all times.
For this project, the word BEAM works on two levels, one being for the electronics style, and the second being that the main lifting mechanism is a lever or... a beam =D
Note: In the past I have tried taking all photos on a white background but I found, with the work I do, it often gets dirty too quick. I have tried a black background here, let me know what you think.
Step 1: The Lever
One of the most important parts of this design is the lever as the coil and magnet creates a rather strong force but only when the magnet is close. Hence, we can use a first order lever to translate a strong force over a short distance into a smaller force but over a much larger distance
Step 2: The Solar Engine
The other important part of this design is the solar engine which, as mentioned in the introduction, stores energy from the solar panel in some large capacitors until there is enough to do some useful work. 780
I used a SunEater I solar engine which you can read more about here http://faq.solarbotics.net/suneater/suneater.html with some slight tweaks to work with my coil. In the past I have only used a simple FLED based solar engine however they are always finicky to get working correctly and especially with a coil dumping so much power. So I opted for the slightly more complicated, but much more robust SunEater!
You will see on the left of my schematic we have 2x 4700uF caps in parallel, these form the bulk of our energy storage. I used low ESR, 16V capacitors. The low ESR lets the capacitors discharge quicker and I would have preferred 25V as if something does fail and the solar panel is in full sun it can get quite close to 16V and potentially damage the capacitors however I could not find 25V low ESR capacitors this large at my local electronics store. You will also notice a 100uF capacitor which I use to help provide the initial burst of energy as its ESR will be much lower than that of the 4700uF. I'm not sure if this capacitor even helps in this particular build however it has helped with similar circuits in the past so I keep including it. I also have a small, 10nF capacitor across the power supply as without it, sometimes the circuit would lock up and oscillate.
I also swapped out the green LED which is used as a voltage reference for when the circuit should trigger and replaced it with an 8.1V zener diode. This means the circuit doesn't trigger until the capacitors get to around 8.3V which I found is the right amount for my circuit. If you were to build something similar you may have to experiment to get the right value. In fact, in my final design, I left this diode replaceable for future adjustment.
I also expected high current to flow through the final PNP/coil path and although in testing the final design, it seems I could have in fact gone with a smaller transistor, I opted to use the TIP32 power transistor as it should be able to better handle large currents.
We also need a flyback diode across the coil to drain any excess power created by the coil's magnetic field collapsing on itself which could potentially damage components. 552