Small Rotating Platform 4

[tft2001]

I am currently in the initial stages of design for a small (~8 ft dia.) rotating light platform that will be protected from direct contact with weather elements, however, this system must be very reliable with very minimal need for servicing/maintenance due to very restricted access conditions.

Any suggestions regarding best rotating platform bearings, gears, motors or any possible "pitfalls" to avoid would be greatly appreciated - including design references.

Thanks!

 

[MintJulep]

Typically initial design includes identifying and defining the requirements for the system. But you have given us nothing.

Loads?

Speed?

Constant rotation in the same direction, or reversing?

Speed and positional accuracy required?

Definition of "very reliable" in terms of something quantifiable like hours before failure, or hours before maintenance required?

Cost constraints?

 

[Walterke]

Perhaps a small sketch of what you want to build could help.

NX 7.5
Teamcenter 8

 

[tft2001]

Understood. Again as this is just starting off, we do not have all of the items ironed out yet. However, the following list might give some further understanding of the system:

Loads - N.T.E. 500 pounds

Speed - 2 to possibly 4 rpm

Constant rotation in same direction - no reversing - only dusk to dawn operation

Speed constant and positional accuracy can have some "play"; however, should try to maintain a level condition.

Maintenance - should try to achieve a maintenance schedule of at least 3 years.

Cost constraints are really not an issue - especially if reliability can be achieved.

 

[MikeHalloran]

Latitude?
Ambient temperature range?
How do you propose to get the power to the lights?

Does "..protected from direct contact with weather.." mean
- sheltered from falling rain?
- sheltered from blowing rain?
- sheltered from blowing dust?
- sheltered from blowing snow?
- protected from condensed moisture?


Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

Plenty of options.

Google "crane bearing", "slewing bearing" or "turn table bearing".

or

A shaft at the center with a tapered roller pillow-block to take the thrust and a ball pillow-block a suitable distance down to handle the tipping loads.

or

Small flanged steel wheels (three of them) riding on a track.

or

You could probably find a reduction gear drive with a suitable slewing output bearing already included from SEW-Eurodrive, Camco-Ferguson or the like.

 

[tft2001]

approximately 42 degrees latitude

ambient temperature range -20 degrees F to 110 degrees F

Power to lights is not a problem and has been under development.

Sheltered from all items listed; however, condensed moisture might come into play.

 

[tft2001]

Thanks for the options MintJulep!

 

[sreid]

A starting point would be rolling bearings, a gearbox and an induction motor running off the line. For reliability, the KISS principle applies.

 

[kingnero]

@ Mike, why would you ask for latitude? I understand that is the geographical position?
Does that do anything towards the mechanical design?

Apart from the implications of an artic surrounding, ofcourse, however if extreme conditions are expected to be met, those should be mentioned in the opening post.

I appreciate your input...

 

[MikeHalloran]

I heard of a wind turbine that used mercury wetted slip rings to get power out of the rotating assembly. It was designed and successfully tested in Bethpage, NY (<42N) and later installed in Potsdam, NY (>44N), where it failed because the mercury froze.





Mike Halloran
Pembroke Pines, FL, USA

 

[kingnero]

So, that must be the advantage of living in a small country like Belgium, which has a smaller area of, I'd say NYC (I hope no-one goes through the effort of actually looking this up, but you get the idea!).

 

[asimpson]

If you have the vertical room a cental pillar with tapered bearings would probably be easiest. Lower maintenance plane bearings from IGUS or Pacific bearings are an alternative.

 

[gadkinsj]

THK makes some curving rails. The drive has so many options I won't bother.

 

[imagitec]

I don't remember how I was fortunate enough to stumble upon neubauplan.com, an Indian design firm with entertaining and elightening articles by the founder, Harshwardhan Gupta. The articles were written for an Indian audience, poking fun at the local approaches, but they're a worthwhile read for any mechanical engineer. A group of civil engineers trying to scope a project like you describe would definitely benefit.

I'd start with Avoiding Overdesign:

http://neubauplan.com/Design Tips 14 Avoiding Overdesign.pdf

An excerpt:

I’ll give you a real-life example: I once saw a "robust” 6-station visual inspection table of 1 meter dia designed to carry 4 Kg connecting rods, with a pick-and-place mechanism to load and unload, rotating (not indexing) at 1 rpm! It was made from 30mm thick (for rigidity no?) MS plate covered with a 10mm rubber sheet. The table was supported on a thrust bearing of 150mm bore, not the light 51130, but the heaviest 51430. It was directly driven from below via a 1 hp motor driving a worm box of 1.5 hp rating, which drove another worm box rated at 1.5 times the rated output torque of the first box since a single reduction could not reduce the speed by 1400:1. This gearbox had an upward pointing 100mm dia output shaft that drove the turntable through a massive coupling! The whole contraption weighed around a ton! Moreover, the table was so high the inspectors hadto sit on high, uncomfortable stools with no legroom.

Sounds like a good analog for your problem.



Rob Campbell, PE
Imagitec: Imagination - Expertise - Execution
imagitec.net