looking for a "center-bore" motor

[sidius]

What I mean by this is a motor with a large hole in the middle, instead of a shaft.
Some motors I found allow to easily remove the shaft, but the bore/shaft diameter I need (at least 4 cm) and RPM (700-900) are not even close.
Where can I find such a motor?

(the motor has to be small. Why it is needed: http://i.imgur.com/eoL79BU.jpg )

 

[CDRIVE]

A "small' motor with a 4cm hollow spindle? Seems like an oxymoron.

There are some wood turning lathes that employ this type of motor (hollow spindle) but not with a 4cm bore. Those motors aren't small either. The motor is the headstock itself with an MT2 or MT3 taper on the inboard end. Neither of which equates to anything near 4cm.

Did you Google it?

Chris

 

[duke37]

You may be better off to separate the motor from the hollow shaft. Then you could use a small high speed motor and drive the shaft with a belt.

 

[KJ6EAD]

Where can I find such a motor?

The closest thing that comes to mind is a ceiling fan motor.

 

[sidius]

I just need something which will allow me to rotate a disc shaped object around its center while having a large hole in the center. It doesn't have to be a 'hollow shaft' motor only. The search results for these have been extremely confusing so far.
There were few articles about this device mentioning terms like ''ring motor'', ''center bore motor'' and '''hollow shaft motor'' so I assumed there would be something like that easily sourceable.

1) A belt setup could work. But what's the maintenance for belts? Would it need to be changed every month or so if ran regularly?

I'm only familiar with XML and GT2 belts as I've used them in my 3d printer. They both seem to have some backlash but only when starting or switching directions. That's as far as my knowledge of belts goes.

Would something to hold the bearing and also the belt need to be custom machined? Or are there readily available thing for this (rotating a bearing with a belt) I'm unaware of?

2) I don't like the idea of a gear setup because of wear and noise.
There seems to be something ready which uses gears I just found, "hollow rotary actuator": https://www.google.com/search?q=hol...ved=0CAYQ_AUoAWoVChMIwdC_vb6ZxwIVxRUsCh2RlQJt
Anyone heard of these?
But again, not a fan of using gears for this. Maybe you'll convince me otherwise.

 

[CDRIVE]

The closest thing that comes to mind is a ceiling fan motor.

Ah, I forgot about them. Too bad the bore is much smaller than he needs. After all they're quiet and efficient.

Chris

 

[Martaine2005]

Can the hole be plugged like a cd player?
Or do you need the hole to look through?

Martin

 

[sidius]

Can the hole be plugged like a cd player?
Or do you need the hole to look through?

what?

 

[Martaine2005]

Well excuse me for trying to get more info from you!

what?

You said "all I want to do is spin a disc with a hole in it"

I just need something which will allow me to rotate a disc shaped object around its center while having a large hole in the center. It doesn't have to be a 'hollow shaft' motor only.

So, do you need that hole while it is rotating, or can it be plugged?
Like a record has a hole for the centre spindle or a cd player has a centre plug to keep the cd aligned!!

Can it be plugged or does the hole have to be left open?
I thought that my reply was quite clear first time round.

Martin

 

[sidius]

I thought my explanation was clear as well, not close to what you put in quotation marks.
There has to be a hole in the middle of the object which is rotated (along itself, its middle point). The hole is needed for laser/video projection to pass through it, like in the illustration in my first post.

Follow the link for "hollow rotary actuator" I posted, there are photos, you'll get the idea.

 

[Martaine2005]

Your post was not very clear at all. That is why other members were trying to help with hollow motors!
As for my post in quotes, I simply made your comment smaller with the same result. Spinning a disc with a hole!
But this forum is to help others like yourself and me too
If you want the hole for laser/video, you probably want something like a lens ring motor for focus.
Or the hollow actuators you linked to.
This sounds like a home made project and all projects like this are trial and error.

Martin

 

[sidius]

Sorry but you don't really get what I need. Other members are trying to help with hollow shaft motors because that's what I've asked help for, and is one way (fastest) to achieve my goal. I've already explained what I need and people don't seem to have problems understanding what I ask for, I'm not here to argue, but clearly I'm not "not being clear at all" and suggesting to find the solution by trial and error shows you just don't understand the question.

 

[CDRIVE]

I just need something which will allow me to rotate a disc shaped object around its center while having a large hole in the center.
1) A belt setup could work. But what's the maintenance for belts? Would it need to be changed every month or so if ran regularly?

First off please understand that no one here gets paid. Help is dispensed free of charge. So please take it in the spirit it is given.

The belt longevity issue can't be answered without knowing the load and RPM of same. Even with that it will be based on the manufacturer's specs.

Chris

 

[Martaine2005]

It doesn't have to be a 'hollow shaft' motor only

It clearly does. Or you don't know what you are asking for.
I am not here to argue with you either.
Best of luck in your search.

Martin

 

[sidius]

It clearly does. Or you don't know what you are asking for.
I am not here to argue with you either.

How many posts has there been by now talking about using gears/belts and driving a separate hollow shaft (bearing) with a regular motor?
You don't seem to have even clicked the link I mentioned twice by now, which leads to images like this:

http://fastech.co.kr/bbs/data/cheditor4/1207/MllraJ5HHMLWAebcVB5O.jpg
Which shows how it ''clearly doesn't'' have to.
You're blaming me that I'm not being clear at all when the said link was posted already and others didn't have an issue understanding my posts so far and saying I don't know what I'm asking for. I appreciate everyone's help, but in your posts so far you have shown that you didn't really read the previous posts and just want to argue how that's not the case and I'm being confusing and not knowing my needs instead. Nobody wants to read all this.

To post something on topic, these kind of "hollow actuators" seem to be used for up to 200 RPM (need 900) and are crazy expensive ($1000+) for this kind of project.

 

[CDRIVE]

It would seem apparent that an off shelf solution is not in the cards. Since this is not a commercial endeavor with deep pockets; that leaves only your ability to execute home shop fabrication. Sounds exciting! Get to it.

Chris

 

[sidius]

I would spend about $300-400 for an off the shelf solution, if there is any. The only ones I found use gears and are meant to run no more than 200 RPM. Please let me know if you find what I need somewhere else.

Otherwise there seem to be 3 homemade solutions:

1) building my own motor with wide hollow shaft
2) ordinary motor+gear+bearing setup (like in above image)
3) ordinary motor + belt + bearing

1 will be difficult for me and maybe not good enough, 2 I feel will make too much noise and the teeth will wear off faster.
Solution 3 sounds promising, but I'd like to know what off the shelf parts there are and which I will need to get milled myself.
For example I've found both v-groove pulleys for a motor and v-groove bearings.
http://ebay.to/1DHK7W3
http://ebay.to/1ITH3Cf

http://ebay.to/1L05OQO

As for attaching something to the top and bottom of the bearing to make objects attachable to such bearings, I can't find anything. Maybe nothing exists, or maybe I don't know what to search for.

 

[duke37]

I would go for the belt solution.
You will need to decide the size of the tube and the torque required.
If you decide on a tube of 25mm OD then the bearings will be quite large to hold it. Two bearings in plummer blocks spaced 100mm will give stability.
If the torque is low, a flat belt will do and could run directly on the tube. It may be able to run directly on the motor shaft, giving a large speed reduction so allowing a small high speed motor. I use a wooden pulley on my coil winder motor which seems to work OK.
For more torque, a toothed belt could be used with a toothed pulley on the motor.
A V belt will be well over the top and will need considerable power to bend the belt and to make it slide in and out of the pulleys.

 

[sidius]

Thanks for this. A ''square flange bearing'' seems like a pretty close out of the box solution: http://www.ebay.com/sch/i.html?_sacat=0&_nkw=square+flange+bearing&_frs=1

The 4 holes would make it easy to attach the top disc which holds the diffuser and mirror on it. An inset could be machined in the area highlighted in this image, where the belt will go and not slip and rotate the whole thing,

As for attaching the whole thing to the base of the device, I see two set screws, maybe adding two more and/or gluing to a thick pipe would be fine.

I'm not sure how much torque I'll need. The disc, with the diffuser and mirror will be around 1 kg I believe, and the whole thing will be enclosed in an acrylic dome.
Illustration of the device without the acrylic dome:

Red part is what rotates. It might seem like much, but the whole middle part is thin reflective mylar.

 

[duke37]

These bearings are probably deep groove ball bearings so they can take some axial load as well as radial load. They will probably have a enough clearance to make them floppy. Thus to get a shaft without wobble you need two bearings. Cars and washing machines use preloaded bearings to take out this clearance.

I would use two fixed bearings and a rotating tube which can be driven directly by a belt.