A builder asks: I want to pick your brain about pendulums. I'm thinking of Organic and Flight. Organic is perfection, the way you dropped the center of gravity and curled the pendulum around. I understand the bob at the top to adjust the timing and how critical the weight is.
Then I moved to Flight. When you sit down to design that pendulum, other than cutting out a trial pendulum and weighing it, how else can you begin to predict how much that pendulum will weigh, and therefore work? Or do you just empirically keep working at it until it does?
I see that you keep the center of gravity low, by expanding the lower pendulum leg from the pivot point.
I know the length of the pendulum with the Bob creates the 2-second cycle.
Thanks,
Eric
More Compound Pendulum Physics as related to Escapement Efficiency
The mass of a well balanced horizontal pendulum is, within reason, almost irrelevant if one keeps in mind that it is easier to push a child on a swing than an elephant. Moving the mass of the horizontal pendulum is the job of the clock's drive weight, gear train, and an especially important consideration is the efficiency of the escapement itself.
Take for example the SwingTime (or Mantis or Flight) and Organic, all of which have compound pendulums. The SwingTime (or Mantis or Flight) clockworks cannot be driven by hanging drive weights using the usual one inch diameter drive pulley barrel. There is simply not enough torque produced from the pulley barrel's 1/2 inch of leverage to be transmitted through the gears into that inefficient escapement to run the clock. SwingTime requires that it be driven by a motor arm transmitting its torque through the large center wheel...and it must be a relatively large center wheel diameter, too, to create a large enough lever. I tried running a clock with SwingTime's escapement with a smaller diameter center wheel and even after adding significant additional weight onto the motor arm, it still did not have enough torque to run that particular clock. A long lever is required.
The picture above shows what kind of lever one might need to move an elephant.
On the other hand the Organic has a very efficient escapement and using this extended lever motor arm on the already large diameter center wheel almost overpowers that clock design. Organic is almost unstoppable. I have to stick a pencil in the gears to keep it from starting on its own.
So the mass of a horizontal pendulum, again within reason, is more a consideration of the type of gear train and escapement that one uses to drive the pendulum.
Once a horizontal pendulum, of pretty much any reasonable mass, is perfectly balanced, it takes very little force to keep it in motion once set into motion. (Organic is so efficient that it doesn't even need to be set into motion ~ it starts itself.).
The beat or timing of the pendulum is created by the relative masses above and below the horizontal pendulum and their location relative to the pivot point. Those are the upper and lower bobs, one of which is fixed and the other adjustable, depending upon the clock's particular design. SwingTime, Organic and Flight all have adjustable upper bobs and fixed lower bobs. Mantis has a fixed upper bob (the antennae) and an adjustable lower bob.
You may enjoy going back and reading my Pendulum Physics blog post on compound balance pendulums of 09 04 2022. The above information is explained again in that Blog post somewhat differently than I have explained here. https://claytonboyer.
So why do I design with the inefficient escapement of the SwingTime, Mantis and Flight? Because I love seeing that excessively huge, beautiful pendulum swing that it produces. The escapements inefficiency imparts a magnificently exaggerated movement to the pendulum. Anyone who has stood in front of Mantis or Flight knows how relaxing and mesmerizing that huge, slow pendulum swing can be, and what a delight it is to watch each of these mechanisms displaying their dramatically exaggerated pendulum kinetic joy.
