Revolving display stand - lateral thinking required !

[Adrian]

Hi All

I'm seeking inspiration from the lateral thinkers in the 'group...

On my market stand, I have a revolving display using one of those little battery-motor-driven turntables with a chrome 'mug-tree' fixed to the top. Sounds awful - but does the job quite well (small stained glass items are hung from the mug-tree, and are suitably eye-catching as the whole thing revolves). Technically it's a couple of 1.5V batteries with a little motor driving a reduction geartrain.

Now the whole approach with the items on offer on my market stall is 'please touch' - in fact I have little notices that say this. Makes people laugh, breaks the ice etc.

However - seems some people (and we're talking mostly 'grown-ups' here!) can't resist interfering with the rotating display - either grabbing an item as it goes slowly past, and not letting it go, or cranking the whole thing round by hand to see someting that's currently 'at the back', but will be in full view in ten seconds or so...

Just spent a happy time yesterday repairing the turntable, as 'fiddlers' had managed to snap off one of the plastic axles that are part of the reduction gear-train - don't want to have to do this on a regular basis...

So - I'm after diy solution to this problem.

One approach is to bellow (in best RSM-fashion) 'takeyourandsoffthesoddingdisplayyouorriblelittlecustomer' - but, as that's often the first verbal contact with a prospective customer then it might not go down too well and could have a negative effect on sales .

Besides, the product (stained glass) needs to be picked up & moved in the sunlight to help sell it - hence the 'please touch' idea.

Other (more fun) options include some kind of remote switching of the motor, so the tuntable could be stopped if it's in danger of stalling

- or even ('Candid camera' opportunities here) an extra wire & dpco switch so the thing could be stopped & reversed 'magically'....

..or maybe even a proximity or 'overload' detector to 'stop' the thing safely when it's been stalled....

As I say - people are funny creatures, and the obvious 'Please don't touch that' approach isn't really the way I want to go

So - lateral thinkers - over to you....

Thanks Adrian

[Graeme]

In message , Adrian writes

Perhaps you could change the drive mechanism to a rubber belt, which will be tight enough to provide drive, but slack enough to slip, without stalling the motor, if manually interfered with.

[Adrian]

Yes - that's a thought. At the moment, the drive is via a series (3 or 4) of nylon gearwheels, with a large outer gear and smaller inner gear, meshed to give the speed reduction. I guess it 'might' be possible to replace one of these gears by a belt drive, but there's not a lot of room in there for experimentation

I'll give it some thought, as I sit at the Market this morning watching it go round.....

Thanks Adrian

[Andrew Gabriel]

A few thoughts...

Add a resistor in series with the motor (and if necessary, increase the battery voltage to compensate if you don't want any drop in speed). The resistor will reduce the motor torque when under load, allowing the motor to stall. One issue with gearing down of the type you have here is that the torque at the turntable output is vastly higher than the motor torque, in theory by the inverse of the reduction gearing ratio. The classic example here is a mains driven mechanical timeswitch or clock. It has a poxey little synchronous motor running it, but by the time you get to the end of the gear train with one rev per day, the torque available is astronomic. It's so large, that you can never stop the motor by stopping the clock going round -- the torque is way in excess of what will strip the teeth off the coggs. So whilst the resistor is worth a try, you may find you still have too much torque to stall the motor, which will result in some part of the gear train breaking. This also won't cope with someone forcing the display round.

Second idea -- have the mug stand loosly coupled to the rotating table so one will spin relative to the other, such as a single loose screw fixing in the centre. In the absence of external forces, friction will drag the mug stand round with the rotating table, but if anyone stops it or forces it, it will move freely leaving the table rotating.

Third idea -- use a mirror ball motor with the display hanging on a string from it. (Depends on type of items displayed, obviously.)

[Graeme]

In message , Adrian writes

Adrian, what you need is a Meccano set to play with :-)

Nice, solid Meccano motor with a small drive wheel and rubber belt to a larger wheel on the turntable shaft. Two potential problems - the Meccano motor probably needs more than a couple of AAs to drive it, and the space required. Railway modellers have been using Meccano to drive (loco) turntables for generations, but they have almost unlimited space to play with.

More seriously, I can see a tiny motor connected to the shaft, with suitable reduction gearing, powered by a drive band. The fun part will be calculating the reduction required to reduce the high speed motor drive to your requirements, which are probably a couple of revolutions per minute.

[OG]

How about putting a Lazy-Susan on the turntable and the mug tree on the Lazy Susan?

In effect you'll decouple the tree from the turntable.

[OG]

Ooops, Didn't see Andrew Gabriel's answer above.

[Dave Liquorice]

That one I like as it allows the fiddlers to fiddle without stalling motors or trying to force the drive backwards against the motor. Similar to the slipping band but probably easier to arrange and less critical on band tension. If the truntable is fixed to the output shaft ib a blind socket simply loosen the securing screw. Hopefully it's not a splined shaft...

So the string takes up the rotation of the motor when a fiddler grabs something? Wonder what happens when they let go and the string can freely unwind? With only a few RPM that might not be an issue. Does the stall have somewhere, in the right place, that it could be hung from?

[meow2222]

thats what id try, or maybe have it underneath the electric turntable, whichever works best.

NT

[Tony Williams]

[snip]

I've seen a commercial solution to this problem. The turntable was not one solid plate, it was two plates with a low friction bearing surface between them.

[The Medway Handyman]

Try the following sign;

"Poken Verboten Achtung alles lookenpeepers. Das machine is nicht fur gefingerpoken und mitten grabben, Das easy schappen der springenwerk, blowen fusen und poppen corken mit spitzen sparken. Is nicht fur gewerken by das dumkopfen. Das rubbernecken sightseeren keep hands in das pockets, relaxen und watch das blinken-lights. Danke"

[Owain]

Move the turntable to the back of the stall where people can't reach it.

A mirror, or even better two mirrors at angles ie

V o

behind the turntable will reflect the moving glass items at the rear and increase its eyecatchingness. A small halogen spot will provide specular reflections.

Owain

[The Natural Philosopher]

How about a belt drive turntable EX hifi, which will simply slip. Of course you will need more gearing, but the geared motor could then drive the final belt drive.

[The Natural Philosopher]

If you can;t find something in here..

Thanks

[mike]

"The Medway Handyman" wrote in news:f4gfgp$vto$ [e-mail]:

Gawd, I last saw that in about '67 on a newfangled Ampex videotape.

What goes around comes around.

Perhaps _that_ might be a thought for a notice!

mike

[John Rumm]

You need something between stand and turntable that includes a "lazy suzan" type of bearing. The stiction in the bearing should be enough to ensure rotation, however it would also allow the movement of the stand to be stalled or for that matter manually rotated.

[Dave Liquorice]

Last time I saw it was on the 16mm Keller film dubbing transport in BBC Bristol's dubbing theatre in the late 70's. It really did mean it as well, lot's of powerful motors, tooth belt drives and electro-mechanical clutches underneath.

[Adrian]

Don't we all - preferably the nice 'stockbrokers' son' version that came in its own wooden cabinet ! (there - that dates me !)

Yes - longevity of batteries is important. The thing needs to run for

5 hours at a time - at least twice a week. The current unit is on the same set of batteries for the last year....

Yes - I think that the drive band approach is perhaps the way to go. Either that - or fit a rubber band to the outer edge of the turntable and some kind of rubber sleeve to the motor spinde - and keep them in 'gentle' contact with a little spring..?

Seems my original 'fix' wasn't as effective as I'd hoped - my glass was revolving intermitttently today - so I do need to think of a MK II version before next weekend...

Thanks for the thoughts

Adrian

[Adrian]

Hopefully I'll have something in my 'squirrel box' that'll suffice - but site bookmarked 'just in case'

Thanks Adrian

[Adrian]

Yes - that's the kind of thing I was thinking but since the cog drive seems bu**ered anyway.... maybe it's time to adopt a different plan !

Nice idea - sort of a slipping clutch.... Current system is fairly compact though.....

Possibility.... but lack of convenient 'skyhooks' might be a problem. Also, I can see the possibility for 'stalling' the rotation just in order to see how fast it goes as the supporting string unwinds.....

Some thoughts to ponder over Thanks Adrian