Weight Drawn Rotation - How To?
JBWolf
Posts: 405
Wasnt sure exactly where to go with this question...
I want to rotate what basically looks like a 2ft tall ferris wheel. Weight about 5lbs, very low friction as it will be well balanced on skateboard 'speedbearings'.
The idea is to put magnets on the 'ferris wheel', and around it.... stationary, custom wound coils... so it is now a generator.
To drive the wheels rotation, I want to use gravity.... Just like a cuckoo/grandfather clock.
So my question is... how can I create a gearing system to translate roughly 10lbs to 300rpm with an estimated time to drop of 5feet in 24hrs?
I do not know how to determine rotational torque to drive the wheel or drag coefficient of the bearings or any other equations....
The wheel weighs approx 5-6lbs, planning to use fastest and lowest friction skateboard bearings I could find = 'Bones Swiss Ceramics'.
The weight and rpm are completely fabricated, I do not know yet exactly what RPM I need and there is not a predetermined weight... looking to determine that as well (best weight for this wheel).
I believe it would be best to have the highest rpm possible... but, initial manufacturing methods will be lower tolerance which will reduce the stable max rpm
I just cant figure out where to start on this one... I did some research on clocks and the pendulum method was about the closest I could find... but I believe that would cause an unstable rotational speed (constant rpm).
hoping there would be a simple gear reduction box I could make, but theres just too many variables involved for me to figure out.
I'm more than willing to do the math and research... but I need guidance.
Thanks in advance
I want to rotate what basically looks like a 2ft tall ferris wheel. Weight about 5lbs, very low friction as it will be well balanced on skateboard 'speedbearings'.
The idea is to put magnets on the 'ferris wheel', and around it.... stationary, custom wound coils... so it is now a generator.
To drive the wheels rotation, I want to use gravity.... Just like a cuckoo/grandfather clock.
So my question is... how can I create a gearing system to translate roughly 10lbs to 300rpm with an estimated time to drop of 5feet in 24hrs?
I do not know how to determine rotational torque to drive the wheel or drag coefficient of the bearings or any other equations....
The wheel weighs approx 5-6lbs, planning to use fastest and lowest friction skateboard bearings I could find = 'Bones Swiss Ceramics'.
The weight and rpm are completely fabricated, I do not know yet exactly what RPM I need and there is not a predetermined weight... looking to determine that as well (best weight for this wheel).
I believe it would be best to have the highest rpm possible... but, initial manufacturing methods will be lower tolerance which will reduce the stable max rpm
I just cant figure out where to start on this one... I did some research on clocks and the pendulum method was about the closest I could find... but I believe that would cause an unstable rotational speed (constant rpm).
hoping there would be a simple gear reduction box I could make, but theres just too many variables involved for me to figure out.
I'm more than willing to do the math and research... but I need guidance.
Thanks in advance
Comments
The only concrete thing I can get hold of here is that the end result is that it should be a generator powered by falling weights.
Interesting idea. What is missing then is an ide about how much power this generator is expected to produce? With out that information it is impossible to even start to think may be required in a solution.
Coincidentally, I was in the Berlin Science Museum a few days back. There I saw a big old church clock mechanism, you know, three hundred years old and made of cast iron. It was powered by some big rocks tied to a rope hanging down from it. The two meter long pendulum controls it's speed through a complicated looking escapement mechanism. So certainly one can get power from falling weights over 24 hours, we have been doing it for hundreds of years! Speed regulation is pretty good. You are not going to get much power out of such a thing though.
Jim
One could probably regulate that with a pendulum or other escape mechanism. Sounds pretty fiddly and complicated to make and probably would not last very long before wearing out if any significant power is wanted out of it.
One could gear the thing down a lot and drive a generator, a motor in reverse, by having a load on the motor the rate of fall would be slowed. One could measure the speed and vary the load on the motor to regulate it. Perhaps not very efficient.
lets start over:
How can I make a 10lb weight turn a shaft at a continuous 300rpm via gearbox so the weight can be redrawn every day?
If accuracy is not so important one speed regulator I saw in a wind up musical box used air resistance to limit the speed of spinning. Basically a shaft had some vanes on it that had to work against the air as the shaft was turned. Simple, reliable.
How far can this weight fall? Two meters perhaps?
What is this for actually?
This isn't a microcontroller problem?
You would need a clock movement made of wood. I know I have seen instances of them on the web.
EDIT: This looks like a nice find.
https://wooden-gear-clocks.com/
Here's a grasshopper escapement.
https://wooden-gear-clocks.com/tranquilityclock/
A typical good old escapement has some kind of wheel driven by the power source. Be that weights on a rope or a spring. That wheel has some kind of teeth on it that engages with a mechanism that let's it "tick-tock" around. That mechanism is often using a pendulum to get the timing right.
So, what if we throw away the pendulum and drive the 'tick-tock' mechanism from a micro-controller? Whose timing is maintained by a nice accurate crystal.
So basically what we have is a micro-controller system that is "harvesting" the energy it needs to run from the energy stored in the suspended weight. Presumably via some moving magnet pushing electrical energy into a coil. In return the micro-controller is providing the accurate timing and speed control.
And perhaps there is energy left over for this whole gizmo to drive something else. Which might even make it useful.
In short, perhaps we can state the problem as: How can we power a micro-controller from a falling rock ?
You could dispense with the wheel altogether and couple your coils and magnets to the pendulum itself.
-Phil
Only my suggestion was to do away with the mechanical pendulum and use the crystal "pendulum" of a micro-controller.
I don't have a sensible suggestion as to how that could be done yet. I'm just hoping it could simplify the mechanics and make it a lot more reliable and accurate.
Like I said, an MCU powered by a falling rock!.
The weight delivers a force, and force cannot deliver constant angular velocity.
You can eventually get to some terminal velocity, when the system forces plus air-resistance equals your injected force, but at that point, you can extract no energy yourself.
Adding stuff like escapements, waste a lot of energy.
On the contrary, those are actually the ideal way to provide that balancing force needed to regulate the RPM.
As the generator extract energy, it provides a reverse torque-by varying how much energy if extracts, you can vary that torque.
Generators are velocity driven, but you do need to keep well below air resistance losses, so that it is you that extracts the energy, not the air.
ie the focus should be on the lowest-speed generators.
Did you look at Washing Machine motors ?
You can work back, from the energy you actually need.
Taking some rounded metric numbers, a 51kg weight moving 2 metres, delivers ~ 1000 J (J=watt-second)
Put another way, that is 277mW for one hour, or 11.5mW for 24 hours. (100% assumed, for this sanity check calc)
Those are sounding quite low, and if you seek to extract that level, clearly the 'spinning power' your setup requires, must be well under that.
You can probably experimentally determine the 'spinning power' aka system losses, by coupling a tiny DC motor and plotting power vs each fixed/stable rpm operating point.
That system loss power will set an upper limit, on the falling time you can hope to push to.
So, acceleration = Force / mass
Here we have a constant force due to gravity and a constant mass. Ergo, we have a constant acceleration. The thing runs faster and faster until limited by friction. Or something breaks!
Question is do you have a way to harness that energy? And regulate it?
10 pounds falling 5 feet is 50 foot pounds.
divided by 86,400 (Seconds in a day) = 0.0005787037 foot pounds per second, or 0.00078462 watts.
Unless you do this in a vacuum, you will lose all energy to air resistance at much less than 300 rpm, even if the wheel is perfectly smooth and polished.
Of course, to top it off, the efficiency of a step up arrangement is poor, especially at this huuuuuge ratio. (if your windlass is 5' in circumference, thats a ratio of 1:432000!!)
But, to answer the original question, with the windlass making one revolution, you need three stages of gearing at 1:60.plus one stage at 1:2
A 24" diameter "ferris wheel" turning 5 revs/second is a fan, dissipating energy. It's its own governor at that speed, like a music box. No escapement required. You'll need to power it with an electric motor to move it that fast. A weight dropping 5 feet in 24 hours? Not even close enough to reality to be called futile.
It goes without saying that you won't be generating any power off it.
So, what you will have accomplished is a very time-consuming, lossy way to do all of the work yourself anyway.
Lots of energy there. Row boats and super tankers will rise and fall the same amount.
But yes, I think it would need a pretty big rock to get the job done as described.