The period of the pendulum is T (secs) = 2 * pi * sqrt( L / g) in either metric or english systems. g is the gravitational constant at earth surface or 9.8 meters/sec^2, or 32.15 ft/sec^2. Notice the period is independent of the mass. Mass does affect how quickly friction slows it down, so how much energy needs to be supplied on each pass. The amount of energy imparted on each pass does affect how wide the pendulum swings, which does affect its period, but is a lesser effect than the length. Cool circuit and demonstration! Out of curiosity, why does the circuit kick about 25 times per pass instead of one big kick and then quiet until next? Also, does the polarity of the pulse need to switch on each pass, as first north pole is arriving followed by south, then the reverse on the returning pass? Or is this why the circuit kicks many times per pass? How does that work magnetically--isn't the same alternating field operating on first the north pole and then the south on each pass? How does this translate to a preferential kick each way, or one of the directions? Seems like a good next video!
Thank you for your interest in this experiment and your questions: Your first question. Why the 25 kicks as opposed to one big kick? This is interesting. If no oscillations occur, then as the armature magnet passes over the coil; Q1 & Q2 turn on hard and REMAIN ON even when the magnet is no longer over the coil. However because the oscillations occur (a type of relaxation oscillator), the Q2 collector voltage falls to ground potential (in fact a negative potential due to back emf) upon completion of each oscillator cycle. If the armature magnet has passed over the coil then there is no way to retrigger the circuit. Thus it remains off. A bit difficult to explain. Your second question. Yes in fact the polarity of the emf generated by the armature magnet indeed reverses polarity depending on swing direction. In this build. A right-to-left swing generates two negative peaks and a single positive peak. A left-to-right swing generates two positive peaks and a single negative peak (Lenz's law). Clearly seen in the video in the case where the circuit power is off. The positive going pulses trigger the circuit (once the circuit is powered of course). Thus right-to-left generates a single pulse train of 25 pulses and the left-to-right direction generates two pulse trains of approximately 25 pulses each. Three pulse trains per pendulum period. This can be clearly seen in the Slow Motion clip in the video where the LED lights to show 3 pulse trains. If one were to orient the armature magnet in the vertical plane relative to the coil then I believe a different pulse sequence would result? Yes I think the same alternating field is operating on first the north pole and then the south on each pass, however the 'feedback' magnetic field is switching (perhaps)? For sure there is much food for thought and opportunities for experimentation here. Of course there are many circuit topologies that can achieve the objective, but I found this one particularly interesting. It would be very interesting to also model the behavior of the mechanical system in LT SPICE! Model the pendulum equation. Now there's a challenge. Thank you.
Nice demonstration Dick. To change the frequency would you change the length of the pendulum only? OR (depending on the frequency) Both the length of the pendulum and the circuit? This would make great Makers Fair Demo.
Many thanks for your kind comment Rick. The pendulum period can be changed by varying the length of the pendulum armature. The circuit 'kick' will simply follow with no circuit adjustments needed, since it's action is stimulated by the emf generated as the armature passes over the coil.
I apologize but I am traveling with limited internet access. For the electronics parts please refer to the schematic shown in the video. For the mechanical parts these are parts you can find or adapt easily. I used a bearing mechanism from an old stepper motor. The armature is a skewer. The magnet is from an old hard drive. An opportunity to use your own creativity!
The period of the multivibrator = 584uS at a rail voltage of 3Volts and 513uS at a rail voltage of 2Volts. The pendulum period will likely change with rail voltage variation also since the duty cycle of the energy supplied changes.
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Very neat Richard!
Thank you!
The period of the pendulum is T (secs) = 2 * pi * sqrt( L / g) in either metric or english systems. g is the gravitational constant at earth surface or 9.8 meters/sec^2, or 32.15 ft/sec^2.
Notice the period is independent of the mass. Mass does affect how quickly friction slows it down, so how much energy needs to be supplied on each pass.
The amount of energy imparted on each pass does affect how wide the pendulum swings, which does affect its period, but is a lesser effect than the length.
Cool circuit and demonstration!
Out of curiosity, why does the circuit kick about 25 times per pass instead of one big kick and then quiet until next?
Also, does the polarity of the pulse need to switch on each pass, as first north pole is arriving followed by south, then the reverse on the returning pass? Or is this why the circuit kicks many times per pass?
How does that work magnetically--isn't the same alternating field operating on first the north pole and then the south on each pass? How does this translate to a preferential kick each way, or one of the directions? Seems like a good next video!
Thank you for your interest in this experiment and your questions:
Your first question. Why the 25 kicks as opposed to one big kick? This is interesting. If no oscillations occur, then as the armature magnet passes over the coil; Q1 & Q2 turn on hard and REMAIN ON even when the magnet is no longer over the coil. However because the oscillations occur (a type of relaxation oscillator), the Q2 collector voltage falls to ground potential (in fact a negative potential due to back emf) upon completion of each oscillator cycle. If the armature magnet has passed over the coil then there is no way to retrigger the circuit. Thus it remains off. A bit difficult to explain.
Your second question. Yes in fact the polarity of the emf generated by the armature magnet indeed reverses polarity depending on swing direction. In this build. A right-to-left swing generates two negative peaks and a single positive peak. A left-to-right swing generates two positive peaks and a single negative peak (Lenz's law). Clearly seen in the video in the case where the circuit power is off. The positive going pulses trigger the circuit (once the circuit is powered of course). Thus right-to-left generates a single pulse train of 25 pulses and the left-to-right direction generates two pulse trains of approximately 25 pulses each. Three pulse trains per pendulum period. This can be clearly seen in the Slow Motion clip in the video where the LED lights to show 3 pulse trains.
If one were to orient the armature magnet in the vertical plane relative to the coil then I believe a different pulse sequence would result?
Yes I think the same alternating field is operating on first the north pole and then the south on each pass, however the 'feedback' magnetic field is switching (perhaps)? For sure there is much food for thought and opportunities for experimentation here.
Of course there are many circuit topologies that can achieve the objective, but I found this one particularly interesting. It would be very interesting to also model the behavior of the mechanical system in LT SPICE! Model the pendulum equation. Now there's a challenge. Thank you.
Nice demonstration Dick. To change the frequency would you change the length of the pendulum only? OR (depending on the frequency) Both the length of the pendulum and the circuit? This would make great Makers Fair Demo.
Many thanks for your kind comment Rick. The pendulum period can be changed by varying the length of the pendulum armature. The circuit 'kick' will simply follow with no circuit adjustments needed, since it's action is stimulated by the emf generated as the armature passes over the coil.
Come on, how long ago was galileo alive?
He just watched a chandelier and worked it out.
Can you list the components you use in the video ?
I apologize but I am traveling with limited internet access. For the electronics parts please refer to the schematic shown in the video. For the mechanical parts these are parts you can find or adapt easily. I used a bearing mechanism from an old stepper motor. The armature is a skewer. The magnet is from an old hard drive. An opportunity to use your own creativity!
Do you know whether the stable frequency of the system changes as the battery voltage drops?
The period of the multivibrator = 584uS at a rail voltage of 3Volts and 513uS at a rail voltage of 2Volts. The pendulum period will likely change with rail voltage variation also since the duty cycle of the energy supplied changes.
@@N4HAY thanks for that! So, if the input voltage is kept well-regulated, it should make for a very stable oscillator indeed.
There will be variants as a result of other influences such as Temperature variations, bearing friction variations, wind currents etc.
Excellent...
Thank you
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Thanks cheers