Author Topic: How to unfix this fan from the shaft of this DC motor?  (Read 2432 times)

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Offline saalucTopic starter

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How to unfix this fan from the shaft of this DC motor?
« on: December 12, 2024, 02:41:58 pm »
Dear users of EEVblog Forum

The DC motor you can see in the attached pictures, is not working; I connected different voltages (6-24 VDC) to it but it drew no current and did not react at all. I think I have to replace it.

But the problem is that it does not come off by just pulling it out. And there is no direct access to the base of the fan, because of the plastic housing.

My questions are:
1. How these kinds of fans are fixed on the shaft of these kinds of motors? by glue, or by melting, or other methods?
2. How can this fan be unfixed from the shaft?
 

Offline Ian.M

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #1 on: December 12, 2024, 02:56:59 pm »
Probably a machine press or shrink fit.  Extremely difficult to remove non-destructively and even more difficult to reattach successfully as prying it off often wallows out the hole enough it will spin on the shaft during startup acceleration if you simply push it back on and many glues are no good in a tight fitting plastic/steel interface.  Loctite and similar thread and bearing lockers *MUST* *NOT* be used as they degrade many plastics causing microcracking and brittle failure.
 
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Offline elektryk

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #2 on: December 12, 2024, 03:13:11 pm »
Maybe carbon brushes are worn out?

It is a bit tricky to replace them but possibile indeed.
 
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Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #3 on: December 12, 2024, 03:32:21 pm »
Maybe carbon brushes are worn out?

It is a bit tricky to replace them but possibile indeed.

Excellent idea!
Do you mean by "brushes" the things that I have encircled in red in the attached picture?
 

Offline themadhippy

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #4 on: December 12, 2024, 03:38:59 pm »
did you try chucking a meter across the terminals and seeing if the windings are good? I
 
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Offline elektryk

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #5 on: December 12, 2024, 03:39:30 pm »
It is better to buy complete brush mount if you will be able to find it.
 
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Offline Ian.M

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #6 on: December 12, 2024, 03:43:29 pm »
Do you mean by "brushes" the things that I have encircled in red in the attached picture?
Yes, those carbon blocks.  Historically called 'brushes' in English as early DC electric motors used layered woven copper braid brushes for sliding contact with the commutator.  Then it was discovered that the extra resistance of a carbon brush decreased arcing between commutator segments reducing wear.
 
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Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #7 on: December 12, 2024, 03:46:44 pm »
did you try chucking a meter across the terminals and seeing if the windings are good? I

If you mean measuring the resistance across the terminals, yes I measured it and it was "O.L".
 

Offline timeandfrequency

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #8 on: December 12, 2024, 04:15:11 pm »
Hello saaluc ,

2. How can this fan be unfixed from the shaft?
Easy peasy.

You need 0.8 m of very strong cotton thread or woolen yarn. Cotton butcher twine is the best choice.
Tie it to make a big loop.
Roll up the large loop to have 4 small ones (because there are 4 blades).
Attach each small loop to a fan blade as close as possible to the center.
Hire a second person to hold the motor + fan assembly.
Use a vice to hold the latter under the jaws (open those enough to that the fan rotor passes through the open jaws, but the fan case is being hold by the jaws).
Pass a big screwdriver through the 4 small loops, and use it as a lever by resting on the top of the jaws.
Once the fan rotor removed, you'll see 2 small Philips screws that hold the motor.

Usually, it's a RC380 motor with a 3,17 2,27 to 2,3 mm shaft...
A compatible one, from RS.


PS : I would not try to repair the existing motor : it will never run reliably. Just replace it with a new one.
« Last Edit: December 12, 2024, 04:51:43 pm by timeandfrequency »
 
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Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #9 on: December 12, 2024, 04:16:41 pm »
As the first post indicates, the shaft of the DC motor is trapped in the fan; so the whole motor cannot be pulled out.

To check the brushes (and, if needed, replacing them), is it enough to just open the holders of the cap which contains terminals and pull it out?
 

Offline elektryk

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #10 on: December 12, 2024, 04:45:33 pm »
Apply a bit of "dremeling" on every crimps.
 
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Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #11 on: December 12, 2024, 04:57:23 pm »
Hello saaluc ,

2. How can this fan be unfixed from the shaft?
Easy peasy.

You need 0.8 m of very strong cotton thread or woolen yarn. Cotton butcher twine is the best choice.
Tie it to make a big loop.
Roll up the large loop to have 4 small ones (because there are 4 blades).
Attach each small loop to a fan blade as close as possible to the center.
Hire a second person to hold the motor + fan assembly.
Use a vice to hold the latter under the jaws (open those enough to that the fan rotor passes through the open jaws, but the fan case is being hold by the jaws).
Pass a big screwdriver through the 4 small loops, and use it as a lever by resting on the top of the jaws.
Once the fan rotor removed, you'll see 2 small Philips screws that hold the motor.

Usually, it's a RC380 motor with a 3,17 2,27 to 2,3 mm shaft...
A compatible one, from RS.


PS : I would not try to repair the existing motor : it will never run reliably. Just replace it with a new one.

Frankly, I did not understand your method.

May I ask you to upload a video or at least some pictures of your method?
 

Offline langwadt

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #12 on: December 12, 2024, 05:01:24 pm »
Apply a bit of "dremeling" on every crimps.

better to bend them out with pliers so you can bend them back for reassembly
 
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Offline elektryk

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #13 on: December 12, 2024, 05:13:02 pm »
Apply a bit of "dremeling" on every crimps.

better to bend them out with pliers so you can bend them back for reassembly

It may work on this small motor, with larger ones from impact wrenches or cordless drills I prefer dremeling because it is to hard to bend them.
« Last Edit: December 12, 2024, 05:14:50 pm by elektryk »
 

Offline timeandfrequency

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #14 on: December 12, 2024, 05:34:26 pm »
May I ask you to upload a video or at least some pictures of your method?
Yes but not this evening.
 

Offline drhex

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #15 on: December 12, 2024, 05:40:09 pm »
You wrap a piece of strong string around the fan blades so you can pull on them. Then you rest the fan shroud underneath a bench vise so that the shroud sits on the vise which is opened enough for the fan itself to pass through. Next you use a suitably stable lever pushed through the string to lever against the top of the vise to pull the fan of the axle. This may break the shroud, but you wouldn't have gotten it off another way then.
Another idea would be to drill a hole through the center of the fan until you arrive at the axle and use a suitable bearing puller.
 
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Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #16 on: December 13, 2024, 04:37:23 am »
You wrap a piece of strong string around the fan blades so you can pull on them. Then you rest the fan shroud underneath a bench vise so that the shroud sits on the vise which is opened enough for the fan itself to pass through. Next you use a suitably stable lever pushed through the string to lever against the top of the vise to pull the fan of the axle. This may break the shroud, but you wouldn't have gotten it off another way then.
Another idea would be to drill a hole through the center of the fan until you arrive at the axle and use a suitable bearing puller.

Frankly, I was unable to understand your method without a video or some pictures. But it seems that it will break some parts. Except the DC motor, I need all the other parts for repair.
 

Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #17 on: December 13, 2024, 04:45:56 am »
May I ask you to upload a video or at least some pictures of your method?
Yes but not this evening.

Except the DC motor, I need all the other parts for repair.

Might your method break some parts?
 

Offline CatalinaWOW

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #18 on: December 13, 2024, 05:07:45 am »
There are three methods I have seen for mounting fans like this to a motor.

1.  Press fit (or adhesive).  The only way to remove these is to drive the shaft out using a pin punch at the hub or pull it off with something like the string approach mentioned earlier.  A fixture with legs that pass through the shroud blades and catches the edge of the fan would help, and a potentially useful version wouldn't be too hard to design and 3D print.  Another approach to "pulling" it off is to bend a piece of flat steel into an L shape, with the base leg of the L just long enough to slip between the base of the fan hub and the motor body.  This can be used as a prying tool (preferably with one on each side working together).  As stated before it is easy to damage parts with this method.  Particularly if it is attached to the shaft by method 2. 

2.  Threaded onto the shaft.  Possibly with some Loctite or similar.  The base method here is to grab the back of the shaft with a vise or perhaps a drill chuck and then unscrew the fan.  For metal parts heat is applied to loosen any Loctite.  Here there may be some appropriate solvent, but I don't have any recommendations.

3.  A collet.  A tapered slotted cone with a hole down the center is pulled up into an external cone forcing the tapered cone to squeeze the shaft tightly.  I don't see any real evidence of this type of attachment in your pictures, but there might be some clever variant, something that might work by driving the pin visible in the center down into the core.  You can get a better view since you can twist and turn the part to see what might be going on.

If you have a friend who is a dentist you might be able to talk him into using his X-ray machine to get a better idea of how the fan is attached.
« Last Edit: December 13, 2024, 05:10:17 am by CatalinaWOW »
 
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Offline amyk

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #19 on: December 13, 2024, 06:00:05 am »
It's almost certainly not threaded - there would be an obvious way of holding the shaft from rotating if it was, and motors of this size don't commonly use threaded shafts. My bet is on a press fit. The end of the fan has a convenient hole where a suitable puller's shaft can sit. You'll need a puller that grabs the hub and presses on that shaft end.
 
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Offline Simmed

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #20 on: December 13, 2024, 06:59:35 am »
You wrap a piece of strong string around the fan blades so you can pull on them. Then you rest the fan shroud underneath a bench vise so that the shroud sits on the vise which is opened enough for the fan itself to pass through. Next you use a suitably stable lever pushed through the string to lever against the top of the vise to pull the fan of the axle. This may break the shroud, but you wouldn't have gotten it off another way then.
Another idea would be to drill a hole through the center of the fan until you arrive at the axle and use a suitable bearing puller.

Frankly, I was unable to understand your method without a video or some pictures. But it seems that it will break some parts. Except the DC motor, I need all the other parts for repair.


lets call the nose part of of prop = the hub of the prop
the string is like a little noose behind the hub
1 pair tied around = all the force will rest on 2 string
so maybe it will need 10 12 14 + pairs on the hub and then another set for the plastic housing?
so now you play a tug of war
V=I.R  Q=h.A.(dT) q=(dT).p  Q=C.V  F=m.a  F=q.v.B.(sinθ)
 
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Offline Poroit

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #21 on: December 13, 2024, 07:25:37 am »
G'day saaluc,

I suggest it is a press fit on a keyed or splined shaft.

Do you own or have access to a drill press?

1.Get some square pieces of chipboard or similar, slightly larger that the diameter of the fan body.

2.Cut holes with a hole saw through the centre of these pieces of chipboard just slightly larger than the diameter of the motor.

3.Stack your pieces of chipboard on the drill press table, high enough so you can drop the motor and fan into it with clearance beneath the motor.

4.Use a suitable size pin punch or similar, inserted into the chuck of the drill press and gently push down against the shaft.

5.If I am correct, you should feel them start to separate.

I hope this is clear enough.

 
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Offline timeandfrequency

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #22 on: December 13, 2024, 09:12:21 am »
[...]
5.If I am correct, you should feel them start to separate.
Separate : actually not, but it will probably break the whole assembly.
Don't forget that the motor is attached to the plastic frame by two screws, as I mentionned earlier. Watch the motor drawing to locate the screw holes.
Actually, the screws can only be safely unscrewed once the fan rotor has been removed.

If you did not have such an assembly in your hands before, it is pretty difficult to figure out how to disassemble it safely. A few fails (= assembly destroyed) are required before devising a suitable method.


Might your method break some parts?
No, if you follow the method and use the tools I suggested, usually they survive.
Please remember that due to their construction, these fans are made in such a way that they cannot be taken apart.
« Last Edit: December 14, 2024, 12:02:13 am by timeandfrequency »
 
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Offline saalucTopic starter

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #23 on: December 14, 2024, 03:25:56 pm »
Thanks to all you for your insights.

If I manage to unfix this fan from the shaft (for example, by the string method), can the fan be refixed strongly on the new DC motor's shaft? Or I will need a new fan too?
 

Offline Poroit

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Re: How to unfix this fan from the shaft of this DC motor?
« Reply #24 on: December 15, 2024, 05:40:59 am »
Cheers timeandfrequency,

Oops.....I missed those mounting screws.

The tug a war method does not have any finite control on how quickly the parts separate.

Both participants may end up on their backsides with a handful of broken bits........but nothing ventured nothing gained.

G'day saaluc,

Do you have any contacts who might have a bearing pulley you could adapt for the job?

Reuse of your existing fan will depend on the new motor shaft size and type.

Hopefully you can find something similar.
 


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