Revolving Platform

One drive will be easier to control then many. Hydraulics can be messy to set up and tear down. Due to varying loads and speed it would use one electric motor with speed controller.

Then it will have to be a very strong reduction gear unit. Noise?

Yes that confirm my fears. Hydraulics is out.

Hi. Thanks for the ideas. How does a chain "warp the perimeter" ? I am not entirely sure what that means.

I'm describing a chain that wraps around the skip tooth sprocket at a diameter that is close to the perimeter. If the platform is 8 feet, the skip tooth perimeter sprocket would be just below the platform and about 7 feet diameter.

Or it may be part of a warp drive... I'm givin it all she's got captain!

Hi. Your comment of a chain warping the perimeter made me think of the following. The big sprocket does not have to be perfectly round. It can consist of 24 half small of the shelf sprockets evenly spaced facing outwards around the perimeter. Or would it be better to design and laser cut the big skip tooth perimeter sprocket. This can be in sections and welded together.

Your solution is propubly a brushless servo with flat-belt reduction and fluid bearings. This combination can be as noiseless and controllable as your budget permits. 53 2E 4D 2E

Put rubber tires under the perimeter. Drive one tire with a belt drive (the quiet ones, not the noisy cogged ones. Put lots (I mean, lots) of inertia in the system. There are several such systems (some with different drives) in use in the US. Are you doing gait studies?

Hi. I am a bit concerned with squeakiness when rubber tires are involved. If only one tire is driven there might be a problem when the weight is on the opposite side of the drive. I like the idea of a chain and sprocket or a toothed belt drive. Brushless motors and controllers are expencive and electronics can damage if transported... ?? I think the drive should be around the perimeter rather than around the center. The support wheels of nylon fitted to the platform running in or on a steel track. Some stages floors are not even.... A fixed center is essential. What do you guys think of wheelchair DC motors? I could have one drive wheel and two support wheels. 3 point contact is better than 4 where one wheel could maybe not touch the ground.

I looked around on the web and found this : [http://www.360platform.com/auto1.html]

Build your carousel so that the wheels run on a flat solid base. Just shim the base for the unevenness of the stage. Use caster swivel wheels there are different wheel materials to combat the noise issue. Chains and gears will have some play which could cause some jerking. A large ring gear or tooth sprocket to run the perimeter will be costly. A spring loaded traction tire around the inside perimeter would stop that. If spring loaded it would follow any surface so the perimeter construction will not need to be so exact.

I would think in the line of a rim of a car on wheel bearings. The drive can be a servo driving on the rim like the belt drive in a tumble dryer. (with tension pulley) .

The servo on a A0 plotter should do fine - quite small with a reduction gear and very Little noise.

how many times must it turn in each direction for each viewing? How long is the interval between viewings? How fast must it turn? There could be significant advantages in cost, reduced noise, and smooth operation, if you could 'wind up' (against a coiled spring or counterweight) the platform prior to each viewing. it would be fairly easy to set uup two different springs or two sets of weights and remote control of brake system for each.

Numerous Tires (on felt?), casters or rollers on the perimeter, as earlier suggested is definately the way to go... check out turntable construction for LPs.

Benbenben

The speed must be variable. Sometimes very slow other times bit faster but never very fast. I would guess between 10 and 20 RPM. Mostly in one direction. This platform must be used for different productions. There is a budget to spend a bit, so I will rather go for motors. Winding up is not an option. But thanx for those ideas. Keep them comming

I would consider building this as a solid disk platform with a skirt extending down to say 1/2 inch from the stage, and concealing the drive within the hollow space. At the modest speeds, a cogged belt would probably be quiet. How about a fairly large pulley attached to the platform, with a small-pulley drive motor off to the side, but still below the disk? Control the motor with a reversing VFD. The shaft and bearing may need to be pretty stout to keep the platform from deflecting, but if you can find quiet enough perimeter wheels, you would get good edge support.

Interesting challenge; several good ideas might emerge with a few people batting it around. Good luck! Can you tell us more about the nature of the performance? When you reverse the rotation, does the reversal need to be quite fast, or is it a smooth slowdown followed by a smooth acceleration? This will affect the torque calcs.

What can also work is a stationary skirt that is attached to the stand rather than the rotating disk to cover the works. Then I just have to make half a skirt and you don't have the distraction of a big moving uneven surface. What is a reversing VFD? I will go search on that.... I found some good ideas on the net for the construction. I don't know how to insert images since the page changed and I don't see the tools anymore.How do you link and insert images now? What happened to all the tools? I will try to insert a pic.... Ok, I tried... it does not seem to work. I have a mac by the way. ∇∑⊄!! I can insert special characters.∞⠵ Images: [steel construction.tiff][Users/christoff/Desktop/Revolving platformsteel construction.tiff]

Your idea of making the concealing skirt remain stationary is good; let the platform disk rotate inside. But watch out for the chance of a performer planting a foot partly on the disk and partly on the skirt, and being spun off balance. A reversing VFD may require a pair of contactors to accomplish this. I'm not sure, but I think that some VFDs have this capability, anyway. A half-skirt, as you mention, would allow the motor to be placed farther off to the rear, which might be useful (better wrap of the belt around the small pulley, for instance).

I'm casting a bit afield now, but another way to do this would be some pins around the circumference of the disk, engaged by a thick UHMW sprocket on the drive motor. This idea comes from a former employment, in which a circle of about 4 feet diameter was hand divided into 150 1-inch spaces to engage a standard RC80 sprocket.

A "pancake" motor might work here, if any of the right size are available.

I had the same problem with Safari. Download Firefox it works fine in CR4. Good luck with your design.

Hi,

how much load? axially, radially, tilting, static, dynamic?

How much allowed runout? synchronous, asynchronous - radial, axial, tilt?

How smooth to drive? Range of speed, allowed deviation /as function of frequency?

Continuous constant revolution or any oscillations to command?

How much stiffness? Any direction.

If you know 70% of the above, then you may proceed immediately, else discuss these questions!

There are ready to buy solutions existing -depending on specs.

RHABE

Thanks for all the questions. Just to clarify. I am in South Africa. There is a time constraint of one month to complete the project. I don't want to take the risk and expense to import something "ready to buy" and will have to make plan with what I have available in this country. Because this show is a traveling show an off the shelf product will have to be modified anyway to be easily broken down and packed for about 25 times a year. Weight is also an issue. It can not be too heavy because the people involved are mostly dancers and they are the crew also. To answer some of your questions. No tilt. Load : about 200-250KG static weight including the structure. To turn in one direction speeds from 20-40 rpm smooth.Stop and go can be gradual. No continuous running. Will turn 180 deg and stop when one side is prepared and the other is towards audience. Must not be too complicated. Simplicity and functionality, reliability, low maintenance, and quiet will be the aim.

Hi Oomsarel,

for this purpose I would take:

one of the modern ball-bearing-assembles of modern cars front wheels (preloaded and not to be taken apart).

These have a flange ready to mount to adjacent structures.

And an axle to mount your (wooden I assume) table.

Attach V-belt or toothed-belt to connect to motor.

Motor to choose depending on available voltage, speed and torque.

If AC 220 V or 110V available then use AC motor with variable frequency drive, command by potentiometer.

Care for emergency stop and other safety issues!

RHABE

Here is a concept that might be out of the mainstream thinking but

it is simpler and provides stability and rigidity. If your base platform

has to be made of wood, than a metal flat track can be bolted to it.

The drawback is that it could be hard to find the large diameter pipes.

Anyhow, as you see the gearmotor would be mounted onto

and travel with the platform.

Interesting project. Good luck with it!

Hi. Thanks for the drawing. I am just struggeling to see the text. Can you perhaps make the text a bit larger? I would not however have the motor travel with the platform.(if I understand your description correctly) How are you going to wire it ?

How about making a disc mounted on caster type wheels to support the weight you need carried. Have a remote electrical winch or pully system acting on the circumference of the circle around a central pivot. The drive from the motor may be in the form of an inverted cone which holds a variety off pully diameters, giving a variety of gearing which can be changed quickly off stage, to suit the particular requirements of the production.

Apart from a temporary fixture in the stage floor for the pivot point of the disc and a quadrant which would be taken up with the ropes to the motor, nothing else need be on stage. The motor may be silenced for any degree you want and the control can be effected by wireless or wired controls in the normal way.

Good luck with the project.

Interesting idea. I am just not too sure if they would like a long rope or cable that runs where people walk. It is dark back stage and most stages does not have space behind, so the system would have to run from the wing... not from the back. This could be a bit hazardous. Also what if they run out of rope or cable and the platform is not in the required position...

Hi. I'm a potter. I've done this. Although the 500 lbs. of clay was not dancing on the platform, it did have to remain stable as intermittent loads (pounding/pushing/pulling) were applied at random intervals.

It started with a 4 foot diameter 3/4" plywood base. Face down in the center went a car wheel hub - with the lug bolts sticking thru so we could use the lug nuts to fasten it (This was done outside - the ground was accommodating). The hub contained the wheel bearing and sawed-off axle (with a hole drilled/tapped in the end). The center of the 3/4" plywood (yes, we used one 4x8' sheet to do this) platform was bolted to this. This supported the center. The perimeter was supported by 8 heavy-duty casters. Ours were the 'really hard plastic' kind, and made a little noise. You might want to use a softer/rubber wheeled caster, and while I'm thinking of it, also face the plywood base with a hard/smooth/shiny malamine paneling (the white one used for bathrooms etc. comes to mind.) Now for the drive... we found 3 treadmill motors with worm-gear reduction boxes. (You might get by with two - or want four.) They had dual shafts sticking out at right angles to the motor. We stuck on some lawnmower wheels, attached the motors to the base (as near the perimeter as possible) with a BIG hose clamp around the end of the motor so the gearbox end could 'float' a little (side motion constrained with a couple of bolts alongside the gearbox) and used a compression spring to push up on the gear box to provide compliance - because once the platform was on we couldn't adjust anything :-) Getting to the end here... Each 90V DC motor had it's own 10-Amp bridge rectifier and all were run in parallel from a VARIAC. Because this was outside we could just dig a trench for the AC cord to come up from below. YOUR PROBLEM, after all this is done will be to regulate the speed. The worm gear reduction was pretty smooth, but we COULD load it down and almost stop it. In our application, this was a good thing, as the clay could set the pace. If it was stiff, it went slower, and 'flowed' in a consistent fashion. IF you free-run this, the first person will stepping onto a 'fast' platform. You might have a stage hand 'ramp-up' the power as weight is applied?

I hope this gives you some food for thought. Good luck.

PS. Drive wheels that are as small as possible would help.

0nce i copied from other thread in this forum this adress:http://www.mekanizmalar.com/index.html ,Not only you will find beautiful mechanisms:one of them, i think is what you look for, may be is a "geneva mech.several arms",possible too i didn't understand wrightly.Let me know.-

These are very handy to take a look at. Thanks a lot for this link!!!

There are many such revolving platforms on the market already. I had a patent on one about 30 years ago, and since then, many companies have built them.

Uses are: 1. For wrapping shipping bundles with clear plastic to hold bundles, and

2. uncoiling metal coils to feed into stamping presses, and

3. Numeous other uses.

Most use D C speed control . You may want one with a damper.

P E Bobimm

Hi all. Thanks for all the input. I will end this session by saying what I decided to do and will post a new thread some time with updates on how the project went. Conclusion: DC motor and variable speed controller (wheelchair and golf cart company), sound proof box (plywood box with sponge) , Sprocket and chain drive, Main sprocket off the shelf, big sprocket self designed and laser cut. polymer support wheels fixed x8 off running on steel laser cut track, Fixed center bearing (automotive wheel hub). Light weight steel construction covered with plywood. Stationary skirt cover front 180 deg and open back. Breakable in 4 major parts bolted together not more than 10 bolts and nuts. have a great week!!

Thanks to Oomsarel for for an intriguing discussion. The final approach sounds pretty good. It may be a suitable candidate for plastic chain, which will tend to be quiet. Best of luck! I look forward to the follow-up, and would also enjoy a description of the nature of the performance. Or even a You-Tube video?

Hi. This is the rough plan that I will use to get quotations to fabricate. There is also a screen on the plan that needs to change size but that is a seperate challege. Cheers for now.

This design takes advantage of available components, except for the large sprocket; but that is not difficult to make. You don't have much angular engagement on the small drive sprocket, however. This may not be a problem if the acceleration loads are moderate, but you will probably need to tension this arrangement pretty tightly to keep the chain from skipping. I doubt this is insurmountable, but it would be good to keep it in mind.

If you look closely on the top view i added an adjustable tensioner with a spring. I realized when drawing this that the motor can not move more outward because of the support wheels around the perimeter. The only way to get pass this is to have the motor and big sprocket outside of the support wheels and then I will have to have a very long chain. The motor will already have a reduction gearbox so to keep all simpler this is the way to go. I am sure that the chain will also work better even if the welding causes distortion, where as a pin gear needs everything to be perfectly round. I could even add a guide around the chain at some places to keep it from falling off.

an adjustable tensioner with a spring

I'd add two one either side of the motor sprocket. This will reduce jerkiness, and, force slightly more of the motor sprocket teeth to engage.

Plastic chain.... That sounds much more user friendly and I bet it will be very quiet... Thanks for that idea.

This reminds me an old thread:http://cr4.globalspec.com/thread/28390#comment300364

From: Tim Hawley Master Mech.

What is your budget?

How many times do you want to rotate in one minute?

What type of vehicle will be transporting this equipment?

Who will be setting up the carousal?

Is variable speed and reverse that important? Remember your budget!

Hi. The budget is fair but I don't want to make a Rolls Royce if a Mercedes will do. The rotation will have to be fast enough to not be boring for the audience but slow enough to not make people scared or dizzy that is on the platform. I t is not a continious round about, but it will move and stop a couple of times in one performance. I want to make something relaiable, quiet and medium tech. I already bought an electric weelchair that has two very strong 24v 250watt dc motor and gearbox assemblies. I am re-thinking the chain and sprocket idea to rather use the unit as is with the wheelchair wheel running spring loaded on a rolled steel flat rim. I will frist build a rough setup to test the motor, see what speed I get adjust the rim size if needed and then if I still need to change rotation speed I will add some resistor/s to the output of my 24v DC power supply. This equipment will be transported by a big truck among lots of other equipment. The performers set it up themselves. Variable speed is not that important, but it would be nice. If there is some money left in the budget after the project is working, I could shop around for a nice adjustable power supply. If I need to have it rotate in two directions I will build a simple polarity changing switch. Thanks for the input. Regards OS.

From Tim Hawley Master Mech.

CONTROLS:

It would be nice to know what type of controls the electric wheel chair has. I assume it had forward and reverse and a variable speed joy stick. To fix the controls. Rewire and use a three way switch. Off, forward , reverse. Because it is joy stick controlled. use a Ohm meter and measure the resistance from center position to forward, center position to reverse. Find a potentiometer with the same resistance range to vary the speed. Use a resistor in parallel to potentiometer to reduce speed. Remember you will be putting a load on the circuit and will have to calculate current draw and rate the watts of the resistors used.

CAROUSAL FIXED BASE

On a front wheel drive car the best wheel hub to use is on the rear wheels. They are connected with 4 bolts and you can use the lug bolt pattern to mount the upper support flange for the platform.

Make a center support and mount hub to proper height. Have 8 to 12 strong pipe poles extend from the bottom of the center support using a WELDED spider connection hub. On each end make an additional support to the same height as the center support. Mounting caster wheels is not a good idea. They will swing 180 degrees during reverse rotation and cause a non-stability problem. Use strong fixed rubber wheels mounted in-line to the platform circumference. All pipes can be connected using a clevis pin with safety wire for easy assembly. Make 8 to 12 additional pipes and connect each of the pipes to the outer wheel supports, in-line to the circumference.

Connect pipes into a large tube that is welded to each side of the outer supports. Use clevis pin in these pipes as well.

Know you have each outer support braced with three pipes and the center hub braced with 8 to 12 pipes. and everything is allowed to flex to compensate for ground surface imperfections.

PLATFORM

Platform will rest on top and can be made in 4 to 6 pie shaped pieces that inter lock together with slip fit hinge and safety pins. On the out side you can mount steel C channel matched to the circumference and drive a rubber belt inside the C channel this will avoid slippage and will not allow the belt to come off. An extra belt is a must.

Use your previous writers idea that provided the diagram to connect the motor and tension wheel.

Good Luck

I don't understand what it is for? Whats the purpose?
Chris

The purpose is to have actors and a small scene change on the one half of the platform that has a screen in the middle. Then it revolves bringing the new scene and actors in view of the audience taking the previous actors back stage ready to change with new actors.

Do you have a solution or to you need ideas. I would use 2 end vertical suports as a base and vert. rods with a horz. connection cross top to support a cloth curtain or back ground.

Regards, Tim

Hi Thanks for the reply. We already built it and it is working well. See link to the update in the last post.

Just for completeness link to the update.

From: Tim Hawley Master Mech:

I haven't here from you since 1 22 2010. Have you decided the type of drive platform you are going to use. Do you need any additional information.

Please respond,

We are at your disposal if you require any additional information.

Best Regards,

Tim

Hi. I have been very busy. This is one of many projects I am busy with. I am sorted. I used an old electrical wheelchair motor and it works good. I must just change the drive wheel to dia 150mm and the client wants to pay additional amount to have variable speed. The motor I am using does have a braking system, but I removed it because I struggled to wire it for testing the motor. I will re-fit it and sort that out. If you have any input to give regarding the controlling. I heed a remotely controlled variable speed power controller for this. My remote has 4 buttons. One is already used to control the screen, so 3 are open. I want to make it so that the 3 open buttons is foe 3 speeds. Press one starts, press again stops it. Thank You , regards OS