Novice-Need Help with Motorized Rotating Disk for Display Case

[newbie1234]

Hello!

I have no experience with electronics of any kind. I would like to buy or build 3, low profile, motorized rotating display disks for a display case. You can see the mockup for the display case here:

https://tinypic.host/i/W6xie

Ideally, I would have the rotating display disks rotate at a slow pace, controlled by a switch built into the display case. If it doesn’t sacrifice the profile, I would like to have the speed be variable and adjustable by a knob on the switch, with a high bound cap on the speed. The disks will be supporting a series of statues. The largest of which is Width: 20.5” Height: 22.5” Depth: 17” Weight: 30 lbs. Note that I would just buy a rotating display disk, however they are all to high. I can drill into the ¾ inch wood platform the disks sits on to reduce the height if need be.


My primary questions are:


• Ideally, the rotating disk and motor would be less than an inch high, if that isn’t possible, I am wondering what the lowest form factor as possible would be? I am not sure if anyone has any ideas of small form factor motors?

• What are all the parts I would need to buy in order to make this? Do you have any recommendations?

• What is the best way to wire everything together?


I am of course open to any and all suggestions, or better ways to build the project. Thank you so much in advance for your time and help, it is much appreciated.

 

[KlausST]

Hi,

size of motor surely depends on power- Mechanical power.
Mechanical power depends on torque and RPM.

You have to determine. Both.
RPM should be rather easy.
But torque depends a lot on the bearing (system you use).
For low torque I recommend ball bearings.
There are ready to buy turntable bearings. Maybe something like this is suitable. (seen on ebay)
Several sizes from 5 to 40 inches in diameter.

Klaus

 

[newbie1234]

Hi,

size of motor surely depends on power- Mechanical power.
Mechanical power depends on torque and RPM.

You have to determine. Both.
RPM should be rather easy.
But torque depends a lot on the bearing (system you use).
For low torque I recommend ball bearings.
There are ready to buy turntable bearings. Maybe something like this is suitable. (seen on ebay)
Several sizes from 5 to 40 inches in diameter.
View attachment 177318
Klaus

Fantastic thank you Klaus, I’d be happy to use ball bearings. I’m wondering what kind of motor you would recommend and how to hook it up? I would need the disk to support a 30 lb statue, at rough one full rotation every 45 seconds- or thereabouts, it doesn’t have to be exactly 45 seconds- just roughly a slow turn for display purposes. Do you have any recommendations for a setup that could achieve that? Thanks again for your help!!

 

[KlausST]

Hi,

Still you need to determine torque. ...

if the rotation speed does not need to be very accurate, then a DC motor is more simple to control.
But also a stepper is not difficult.

Now it depends. Doyou want the moto to be in the center of the disc with diriect drive? (motor RPM = disc RPM)
Or do you want the motor to be placed off center and connect both with a belt for example. Which gives a natural gear rate.

Klaus

 

[newbie1234]

Ah thank you Klaus, I am not sure which would be better in terms of belt vs centered motor- but I am assuming the latter is better, as it will be easier and less noticeable to have wires running under the wood platform vs a belt. So if we have a centered motor, I am not sure how much torque I would need. Do you have any idea you would recommend?

 

[BradtheRad]

For a small, slow motor powered from house voltage, consider an old-style clock motor. The gear turns at 1 rpm.

If you're lucky you can get one with a steel gear-train robust enough to spin a large turntable.

 

[newbie1234]

For a small, slow motor powered from house voltage, consider an old-style clock motor. The gear turns at 1 rpm.

If you're lucky you can get one with a steel gear-train robust enough to spin a large turntable.

View attachment 177319

Wow thank you Brad that helps a lot. When you say “old style” do you mean these types of motors aren’t made anymore? If they are made today, do you happen to know a brand or a place to find one? Thank you again in advance.

 

[betwixt]

If there is space, also consider driving the rim with or without a belt. Driving the rim has the advantage of providing a very high gearing ratio (motor pulley diameter : table diameter). Consider that electric motors themselves are very difficult to control at low speeds so unless you choose a stepper motor solution, a high gear ratio is essential. A high gear ratio also gives more torque at the table.

For background information - a conventional motor continuously rotates as long as the power supplied to it can overcome the friction and load placed upon it. Their good point is being cheap but the speed can be difficult to stabilize, especially if the loading changes. A stepper motor does as its name suggests, rather than continuously turn, it moves in steps. The upside is the speed can go from zero to maximum and is decided by how quickly you switch power to the different coils inside the motor, the downside is needing the electronics to do that (not particularly complicated) and they tend to be a little noisier as each step creates a small vibration.

Brian.

 

[KlausST]

Hi,

While the synchronous motor gives about the RPM you need. .. I wonder if they provide enough (starting) torque to move the 30 lbs mass. Controlling the RPM is rather difficult, since you need a mini VFD.

The stepper motor needs the frequency to be ramped up. No problem even for a tiny microcotroller.

Klaus

 

[BradtheRad]

Ebay is a good place to find old clock motors. Some may be used, some new. Plug-in electric clocks were the norm before there were battery powered quartz crystal movements.

Try an internet search on 'motorized rotating display stand.'

In these modern days we have low-rpm motors turning disco/mirror balls. Some feature variable speed.

 

[dick_freebird]

I see a lot of gear-reduced motors and occasionally some turntable-like ones w/disk at electronic / electrical surplus places.

"The surplus center" (out of Iowa or Nebraska I think) and "surplus center of Nevada" are a couple I've bought project motors / fans / blowers from, if you Google you'll find likely sources with good selection. And a whole lot of junk you shouldn't buy but can't resist....

 

[newbie1234]

Ebay is a good place to find old clock motors. Some may be used, some new. Plug-in electric clocks were the norm before there were battery powered quartz crystal movements.

Try an internet search on 'motorized rotating display stand.'

In these modern days we have low-rpm motors turning disco/mirror balls. Some feature variable speed.

Thanks Brad I have actually gone to great lengths to find a motorized display stand, I find that none of them are low profile enough. I am wondering if I build one, if I will be able to make one at a lower profile- or sink it into the platform a bit to reduce the profile there. I have considered taking apart a stand and repurposing it for the display platform, but not sure if that is advisable or if it is better to make one from disparate parts. Anyway thanks again for your help, I welcome any other thoughts or advice.

 

[newbie1234]

If there is space, also consider driving the rim with or without a belt. Driving the rim has the advantage of providing a very high gearing ratio (motor pulley diameter : table diameter). Consider that electric motors themselves are very difficult to control at low speeds so unless you choose a stepper motor solution, a high gear ratio is essential. A high gear ratio also gives more torque at the table.

For background information - a conventional motor continuously rotates as long as the power supplied to it can overcome the friction and load placed upon it. Their good point is being cheap but the speed can be difficult to stabilize, especially if the loading changes. A stepper motor does as its name suggests, rather than continuously turn, it moves in steps. The upside is the speed can go from zero to maximum and is decided by how quickly you switch power to the different coils inside the motor, the downside is needing the electronics to do that (not particularly complicated) and they tend to be a little noisier as each step creates a small vibration.

Brian.

Thank you for that breakdown Brian- I had no idea about conventional vs stepped. I am leaning conventional and am a bit adverse to a belt system as I it will be less concealable. Do you have any motors you recommend for this type of thing? and if so, what are the best places to find them? Ebay has been mentioned, but not sure if there is an electronic store that sells motors of this nature. Thank you again for your help Brian.

 

[betwixt]

Unfortunately motors tend to be designed for specific applications so finding one 'off the shelf' that meets your requirement might be difficult. Most of the readily available small motors run at several hundred RPM so you would need significant gearing to reduce the speed. Like the motors themselves, finding a suitable gear system would be quite hard. This is why it was suggested you look for 'surplus' supplies but finding several identical geared motors might be a problem.

Personally, I think I would opt for turntable bearings like those in post #2 and a small stepper motor. For the relatively small expense of the motor and electronics you get greater torque, absolute speed control and can even reverse the rotation it if you like. Thing of direction, look at the turntable in a microwave oven, normally these are geared AC motors but you might have noticed one of the problems with them. Try starting and stopping a microwave oven a few times and you will see the turntable direction is random, perhaps this is undesirable for your display.

Brian.

 

[BradtheRad]

I used a ball-bearing turntable to support 25 pounds and 16 inches across (the rotating base for my telescope). Worked well. Turned easily with the slightest push.

The platform can be 1/4 inch plywood. Cover it with a round mirror, or a disk of shiny chrome sheet metal, etc.

It could be convenient to mount the motor under the shelf, unseen, and drill a small hole for the shaft to protrude up through the shelf.

 

[newbie1234]

Thank you to all who have replied thus far! It has been insightful to say the least. Due to all of your great input, I have what I believe to be a more sound design (attached). My main concern is still the size of the motor. I am thinking a small DC motor, that has 1 RPM. It is for a display so the thing is great if it's slow. As stated, it has to turn a 30lb statue, with a height of less than .75 inches. I looked into microwave motors, which would work well- many are just .4 inches tall, but they cant turn 30lbs. If anyone has any links to motors they think will work it would be much appreciated.

 

[betwixt]

Your proposed design is good but doesn't take into account that small DC motors generally run at several hundred RPM and their torque if you drop the voltage to slow them would be woefully inadequate. A gearbox would allow faster motor speed and greater torque but also increase the size considerably.

Another possibility to consider if you wish to use a DC motor is a worm drive gearing. The motor shaft would have a spiral worm gear and the turntable a conventional cog wheel. You can get substantial gear ratio that way and because the motor would be on it's side, less height would be needed.

example: https://www.rapidonline.com/rapid-gear-starter-pack-18-37-0230
or

worm | Rapid Electronics

www.rapidonline.com

( I'm a customer but have no other interest in that company)

Brian

 

[newbie1234]

Your proposed design is good but doesn't take into account that small DC motors generally run at several hundred RPM and their torque if you drop the voltage to slow them would be woefully inadequate. A gearbox would allow faster motor speed and greater torque but also increase the size considerably.

Another possibility to consider if you wish to use a DC motor is a worm drive gearing. The motor shaft would have a spiral worm gear and the turntable a conventional cog wheel. You can get substantial gear ratio that way and because the motor would be on it's side, less height would be needed.

example: https://www.rapidonline.com/rapid-gear-starter-pack-18-37-0230
or

worm | Rapid Electronics

www.rapidonline.com

( I'm a customer but have no other interest in that company)

Brian

Wow thank you so much Brian- I had never heard of worm gears before- do you feel like this is the best / only option for my project? or is there another way to use a centered linear motor that has a low profile? I might be able to give it some more room if I use a 1 inch platform vs a 3/4 inch... not sure if that would provide enough room. Either way do you feel like the worm motor is my only choice here? Thanks again in advance.

 

[FvM]

Acceptable noise level hasn't been yet addressed. I'd suspect many drive solutions discussed in this thread (e.g. geared DC motor) to produce rather loud noise when running.

 

[newbie1234]

Acceptable noise level hasn't been yet addressed. I'd suspect many drive solutions discussed in this thread (e.g. geared DC motor) to produce rather loud noise when running.

Thanks FVM- do you think the worm motor would run quietly? If not, do you have a motor you would recommend that would have a quiet operation?