Re: Help needed: kinetic sculpture

"N:dlzc D:aol T:com (dlzc)" wrote in message news:HoRYc.65056$4o.22124@fed1read01...

How about modifying the escapement to be a conical shape. It would unwrap starting at the wide end, and drive your 1:4000 gear set. This would essentially give you a better initial gear ratio, perhaps 1:500. As the device sped up, the cord would be coming off a smaller and smaller diameter, thus increasing the gear ratio significantly. For giggles, you can use a shape other than a cone to produce a more sudden change from acceleration to maintenance.

You are going to have to look at how much force you need to move your sculpture and how much you have available in the weight.

You might also consider using several weights on several cords, rather than just one.

If it were a little earlier at night, it might be interesting to consider some governor style mechanism which would apply energy only if the flywheel was going too slowly.

Michael

David Smith referred this note to sci.engr.mech.

Here's my six pennyworth: Engineering is a numbers game. If you would provide some numbers, you would get helpful answers. Turning things takes power. Not electrical power necessarily, but power just the same.

The number you need to tell us, is the torque needed to turn your zoetrope shaft at a modest clip.

Torque is a force times its distance from the shaft. So if you mounted a temporary pulley on the vertical shaft, and ran a cord from the pulley, over a fixed pulley and down to a weight, you could add weights to the string, untill the shaft began to turn.

The pulley radius and the size weight you used, would be a measure of the power requirement. Give it a try

Brian Whatcott Altus OK

N:dlzc, The bearing I'm using is a high quality ball bearing with metal plates. I don't think it is introducing the bulk of the friction. When I spin the turntable by hand it moves quite smoothly, and slows very gradually. When it does come to a stop, it actually reverses direction for about an inch so I don't think there's much "sticktion". I did think about using a thrust bearing but felt it would introduce more friction than the ball bearing. When I remove the turntable the weight does fall, rather quickly as a matter of fact. Could the bevel gears be at fault? I'm employing a step-up 1:2 bevel gear set (although I don't know that it was designed for stepping-up). Might it be the changing of vertical rotation into horizontal that is causing the excess friction? I believe I will start by reducing the gear ratio at the bevel gears to 1:1, add more weight and go from there. I'm interested in what Brian had to say and will reply to his post as well. Thanks so much,

-Mac

Brian, Thanks for your thoughts. I like the idea of getting back to fundamentals, fundamentals I can understand . I will try your idea and try and get you the numbers you asked for. So, the diameter of the vertical shaft pulley, the diameter of the fixed pulley, and the weight required to turn the table at the desired pace. Anything else? Thanks very much,

-Mac

N:dlzc, The bearing I'm using is a high quality ball bearing with metal plates. I don't think it is introducing the bulk of the friction. When I spin the turntable by hand it moves quite smoothly, and slows very gradually. When it does come to a stop, it actually reverses direction for about an inch so I don't think there's much "sticktion". I did think about using a thrust bearing but felt it would introduce more friction than the ball bearing. When I remove the turntable the weight does fall, rather quickly as a matter of fact. Could the bevel gears be at fault? I'm employing a step-up 1:2 bevel gear set (although I don't know that it was designed for stepping-up). Might it be the changing of vertical rotation into horizontal that is causing the excess friction? I believe I will start by reducing the gear ratio at the bevel gears to 1:1, add more weight and go from there. I'm interested in what Brian had to say and will reply to his post as well. Thanks so much,

-Mac

The shaft pulley radius, the weight motivating it, and the speed at which the shaft turns, is a complete description of the power requirement. Go for it!

Brian W

Dear Mac:

Good.

This is the "backlash", that causes/allows the short reverse motion.

There will be a component of force that is nether coaxial with the turntable, or the host of gears, due to the bevel gearing. It is at the lowest torque position, so it is as small as you can make it, based on where it is in the drive train. But the choice of bearing may have "overspecified" (in some sense) the degrees of freedom. I would recommend that an axial type bearing be used to offset this loading (by the bevel gear-set), and thrust type bearing be used to support the "turntable/zoetrope". You could probably do both with the type of bearing used on the front axle of a rear wheel drive car (tapered roller).

The bearing I was interested in mostly, was the bearing that actually supports the weight. I didn't see another weight on the other end of the same chain, did I? Because there shouldn't have been one...

By the way, please add your response inline, or at the end (as I have adjusted this). We all try to respond to posterity, as much as to you. And it reads better (and appears a little more curteous) this way. I'm not intending to thrash you, just to charge you with 'nettiquette...

David A. Smith (and thanks Brian!)

You need a better turntable/ bearing. You don't just have a friction problem, you have a 'runout' problem.

When the turntable reverses, it's telling you that there's a 'hill' that it can't climb with the available torque. It stops, then it rolls back down.

Your extreme speedup gearing also, extremely, reduces the drive torque that the gravity power unit can deliver to the turntable.

When there's not enough torque available to climb whatever infinitesimal hills exist in the turntable, the mechanism stalls.

For a zero- power device like you're trying to build, you need bearings that are way better than 'high quality'. You need AFBMA class 'dead nuts'.

You can't even give up the torque required to drive a seal, or even a little bit of grease. To lubricate the mechanism, use a drop of turbine oil in ~ a liter of volatile solvent. Apply a very small drop of that mixture to each bearing, and let the solvent evaporate.

-Mike-

David, My apologies, I will follow in line. Just to clarify, there was/is just the single weight on the chain. No counterweight. I would like to thank you and the others for your time and suggestions. You have been a great help. With some elbow grease and a little luck this piece of sculpture will be realized yet.

-Mac

Dear Mac:

I don't mean to be restrictive...

OK. My memory sometimes fails me.

Let us know where it can be seen, and when. When.

David A. Smith

Hi Mac, One question, Does the zoetrope spin easily when all is connected? (such as trying to wind up the weight?)

when you had said it will break a chain before it spins.. It actually sounds like you have a gear locking up (incorrect mating of the gear teeth maybe?) (or not enough clearance for easy motion?) Just a thought.

} > cross-posting to sci.engr.mech (there are some cookies over there too) } >

} > I'd look at the bearings, bearing "race", and bearing plate (the } > turntable). Take a look at a lazy-susan for details. Is the plate } > "housing" the bearings (at the same level as the centerline) free to } rotate } > as the bearings roll? Are the upper an lower plates metal, so that the } > bearings don't "embed"? } >

} > If you remove the turntable, does the clockwork mechanism operate to allow } > the weight to fall? } >

} > I would concern myself with the bearings that end up supporting the } > weights. The first driven shaft will be under tremendous strain. } >

} > Thats my first pass. Hopefully others will have other good ideas. } >

} > David A. Smith } >

} >

} }

Spaceman, As the gearbox (clock movement) runs quite nicely without the turntable in place, I assume there is no binding. Thanks for the reply

-Mac

That is why you need to have the turntable in place and make sure that "all" parts can freely spin.

The bevel gears make good, solid, no-bind contact. When I spin the turntable by hand (manipulating fom the turntable end of the gear train), all works rotate quite freely. Thanks