Changing motor in Mirrorball rotator to be variable speed?

[Karel Bata]

I have this rotator. The motor has internal gearing making it turn the shaft at 1 rpm, which means the rectangles reflected off the mirrorball go around the room at 2rpm.

 

I'd like that to ba a lot slower. At least half that.

 

Anyone here able to point me to suitable motor and potentiometer? Or suppliers? I'd be very happy for this run at 12V and put a transfomer powered from mains into what is a very spacious box.. The 50cm ball weighs 50g..

 

Now to images. Hm...

 

 

 

Sorry they've come out so huge!

[pmiller056]

The motor will be a fixed speed synchronous motor. It is not economically practical to control the speed of this type of motor by electronic means. If you only need fixed speed operation, change the motor pulley for a smaller diameter (1/2 diameter = 1/2 speed). If you do this you will need to either change the drive belt for a shorter one or use some of the unused holes by the motor shown in your photo to move the motor further away from the driven shaft.

 

If variable speed operation is required, the simplest and cheapest way will be to change the motor for a DC motor+gearbox, but you will then need to add a speed controller and appropriate power supply. Plenty of online sources (UK and overseas) for the relevant parts. With this solution, significant metalwork modification will be required to make it all fit together.

 

The empty holes and taped up wiring shown in the photos strongly suggest that this system has had previous significant modifications.

Edited December 28, 2019 by pmiller056

[Jivemaster]

Have you actually timed (or read the label on) the installed motor? It's probably not the original! RS offer a range of geared synchronous motors that would likely fit your box and functional needs among others 1/12 and 1/2rpm are available in the UK, may fit the existing holes and pulley.

 

Making your motor rotate slower would need a variable frequency drive but halving the speed would mean finding and supplying 25Hz at which the motor may not be happy.

[Karel Bata]

 

I think I've found a solution now - a high-torque reversible 12v geared motor nominally running at 1rpm (£6 from China!) and this https://www.ebay.co.uk/itm/1pc-12V-24V-48V-40A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-2000W-MAX-9-50V-/401868754256?hash=item5d913e8d50

[david.elsbury]

Your posts really worry me. I’m glad I won’t be attending any of your installations or exhibitions! ;)

I hope you are confident with the mods you are making, and hanging this over peoples heads. Feel free to engage the services of a professional engineer to ensure that someone who is competent gives it an “ok”. :-)

Edited December 30, 2019 by david.elsbury

[Karel Bata]

Good grief. How rude.

 

I've been doing this kind of stuff for a very long time. For instance, I created Europe's first projection-mapping rig back in 1981 - before you were born sonny. No accidents yet.

 

It's always bugged me that there have been a surfeit of upstart AV technicians with rule books tucked under their arms ready to tell lanyone they're somehow breaking the rules. You see them all over the world. "Oh you can't do that." Good for the ego is it? Grow up.

Edited December 31, 2019 by Karel Bata

[timsabre]

Please don't take offence but I agree with David, your questions do often come across as if you don't have much experience and some of the things you ask about have potential for disaster if done wrong. So it is slightly worrying.

 

It's very difficult to tell on a forum like this whether someone is very experienced and just needs advice on a particular thing, or if they have no idea what they are doing and might go off and do something dangerous.

 

So it is good to know you are experienced but you must accept we need to be cautious about people's competency when we make suggestions.

[Karel Bata]

OK. Thanks Tim.

 

I use forums like this to bounce ideas around, particularly for really out-there experimantal stuff. In the end though I often go the well-trodden route (I'm really an absolute stickler for safety and will be the first to say no) but even an unfruitful investigation yielding only wild ideas is all grist to the mill and later on can maybe be put to use. Fact is, it's fun to throw stuff around and see what turns up. The first person I saw doing that prifesionally was David Hershey on Cats. A lot of interesting ideas never made it into the show. And I wouldn't have done a fraction of the stuff I'm proud of if I'd just stuck to the rule book.

 

Happy to be told I'm wrong, but that lecture crossed the line.

 

Cheers!

 

[timsabre]

If I may suggest, I think if you gave more background in your question as to what you are actually trying to achieve it would help. Your questions are often very vague.

 

E.g. your LED question you posted earlier would have been much easier to answer if you had included the information about beam size, colour, brightness and application in the original question rather than someone having to probe your intentions to find out. Also tell us what you have already tried so we don't suggest the same things again. It all helps to get a useful discussion.

 

 

The worry with your mirrorball question was when you suggested modifying the rotator - without a good understanding of what is keeping the mirrorball in the air it is all too easy to make something which has a danger of falling (I have seen people hang directly from the motor shaft) and there was no indication in your post that you were aware of that risk.

[Karel Bata]

Thanks for the pointers. Will do.

Yes, the info on the LEDs was a bit minimal.

 

As to the mirrorball - the way it is constructed the mechanism that supports the ball inside the box is independent of the drive and is connected by a rubber belt. I thought that was clear from the pic. So changing the motor won't affect the safety aspects of the ball. If it doesn't work, or even buns out(!), the ball will just stay up there. It's why I bought this particular rotator. I gave the weight of the ball (50g) as an indication the starting torque required (though that doesn't take account of the mechansim's friction or the initial oomph to get it all going).

Edited December 31, 2019 by Karel Bata

[Jivemaster]

One real challenge of this forum is recognising a 12 year old with enthusiasm and a full (school) CNC enabled workshop from a mature skilled person with fewer toys but a lot more skill.