Hi all! I looked around at the various forums and hope that I've chosen the right one to ask this question. I should also preface this by stating whole-heartedly how much I don’t know about motors - literally nothing at all other than I need one to make something spin - please excuse my ignorance on the subject.

I need a motor for an art project. It needs to support a ~3-5lb 15” diameter circular object that I would like to spin 1 or 2 times per minute – I’m not picky about the exact speed, as long as it’s slow, but it would be extra cool if I could easily make adjustments to the speed. The circle would be held vertically (like a prize wheel), in case that matters. It needs to spin continuously for a few hours, through the entire length of an art show. While shopping for motors I have come across a few with several options for different no-load speeds and choices between voltages. (I can't post the link, but one of the motors I have been looking at on amazon is called "uxcell 12V DC 5RPM Gear Motor High Torque Electric Micro Speed Reduction Geared Motor Centric Output Shaft").

My question is, what type of motor (if any) would work best for the job described above and what other specific items would I need to purchase along with it to make it work the way I want it to? If possible, I'd love to see some examples or links to a website that sells a specific product. I have seen a few people mention getting a PWM to control the speed, but I am having trouble understanding exactly what product(s) I could buy and how they should be assembled (with the knowledge that I have zero parts already – no wires or soldering iron or anything at all!).

The fewer parts the better for financial reasons, but I do want my project to work well, so I don’t want to be maximum cheap about it, just mid-level cheap. Is it possible that, since the motor would be holding up 3-5lb, a 5 rpm/min motor would spin 1rpm anyway?

Hopefully that is enough of the right kind of information. Thank you so much to anyone who can offer any advise at all! I appreciate anyone reading all the way to this point!

 

Hello, welcome to AAC.

There are several things that you will need to determine before you can choose a motor, and you may find that some actual testing will be required before you can determine which motor works the way you want.

First of all, you have to decide how you will power this. Can you plug it in for the show, or will the exhibit be required to run on batteries?

Second, I am sure your ideal motor is silent, but in practice motors make noise, and depending on the material of the rotating part, that noise may be significant if it is coupled into it.

Third, a motor may have enough power to turn your object but not enough strength to hold it up. A motor with bearings strong enough to handle the load may be considerably more expensive. Additionally, coupling directly to the shaft of a motor will increase the potential for noise.

Though you mentioned your budget, you didn’t use any numbers, and that matters. What is your budget, in dollars?

As things stand, with no other information, you have two choices: a (probably) costly gear motor with heavy bearings directly driving the object, or an idler driven arrangement where the object is driven by a wheel on its rim (probably not visually acceptable), or by contact with the inside of a ring mounted on the rear of the object. In these cases you will also need a central bearing to support the object, but that will be cheaper than the gear motor.

This rim drive arrangement also means speed control would be easier because the motor could be a smallish DC motor something like this: https://www.allelectronics.com/item/dcm-351/24-vdc-gear-motor-w/turntable/1.html

There is more fabrication involved, but I suspect it would work better for you.

In any case, you do need to consider how you will mount the object to any motor that you choose.

 

It may be worth while looking at a geared motor for slow speed. My choice would be a stepper driven by an Arduino so you have good control of the speed.

This would be a good starting project into the Arduino world.

https://circuitdigest.com/microcontroller-projects/arduino-stepper-motor-control-tutorial

 

Using a geared motor with 5 RPM the way to reduce speed for this project would be using mechanical reduction. 5:1 for 1RPM. This would involved couple pulleys and belt. It would give you more mechanical advantage. It may require some testing to make sure you have the torque to get this going using small motors.

Did you mention if it’s spinning like a wheel or spinnng like it’s on a turntable?

 

All Electronics ref. in post # 2 has a variety of gear motors like DCM-469 same as turn table motor with out the turn table, DCM-9120 , a little fast but has double ball bearing 5/16" output shaft. Also a shaft on opposite end ,good place for code disc Rated at 24 V but might be in range
with 1.5 to 3 V C or D cells? What is disc mounted to ? Is it reasonaly balanced ?
Are you in USA ?

 

@Yaakov ‘s suggestion of using separate bearings for the object and a ring attached to the back has consuderable merit. But there is a bit of math to determine the equivalent gearing ratio.

What I mean is if the motor has a 1” circumference drive wheel and the inner circumference of the ring is 10” (just making up numbers for this example), what is the equivalent gear ratio? Answering my own question, it would be 10:1. So to get a speed of 1 RPM, your motor would require a speed of 10 RPM. You can use similar calculations to calculate many combinations.

There are three variables (diameter/circumference of the drive wheel, inner circumference of the drive ring and motor speed). Pick one to be constant and you can create a table of the possible values of the other two.

I do have an additional question. What is the geometry of the object you wish to rotate. A circle is easy. An irregularly shaped object (s lightning bolt?) is more difficult. I have done something like this before. One can calculate the torque required as a function of the degree of rotation. Or, you can do as I have done, estimate where the greatest torque will occur, pick a powerful motor that can still move the load in this case.

I did the same thing (as you’re attemptin) in a haunted house room. I used Yaakov’s suggestion. A couple of objects were circular, rotating spirals. But there were also ghosts whose weight distribution was different at every point in its rotation. And I did exactly what I suggested above.

If you have any more questions regarding how I created the effect, just ask!

I hope this helped.

 

I neglected to mention belt drive using a rear mounted pulley is also possible.

 

Just thought of this after the post.

I used Hankscraft slow speed motors. I don’t know if they’re still available. They have a lot of torque, but there bearings are basic and aren’t great for direct drive for anything other than objects made of cardboard.

You see, they’re the motors often used to animate large advertising displays in a retail environment. Perfect for my spirals. And with a direct drive via a hidden ring, could animate a 3’x2’ ghosts!

 

In old school museum exhibits we used Bodine gear motors. They are tanks, and they cost like it.

 

They are still available.

http://bfy.tw/NCeC

 

I have a pair of bodine gear motors. Very nice but very pricey...

 

The motor will have it's shaft horizontal, that was mentioned. What was not mentioned was the power source. Mains power or batteries are the choices. There are motor packages made for exactly that application as attention getting things in stores. Such a one would be perfect for the application because of being idiot proof, which may be important if the general public is able to touch it.
Friction drive with a small rubber tire on the back side of he disc could work well and provide a mechanical adjust function. Not a real tire, but something like a slot-car wheel/tire combination from long ago, and with a surplus small gear motor and your drive is complete .