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Author Topic: PC Case Fan Motor  (Read 1611 times)

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Offline AethurTopic starter

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PC Case Fan Motor
« on: August 04, 2011, 10:21:02 AM »
Just got everything I needed for my $50 robot build, except the servos..
I have a bunch of PC case fans sitting around, any way I could swap these into the build without much fuss?
Any help would be appreciated :)

Offline corrado33

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Re: PC Case Fan Motor
« Reply #1 on: August 04, 2011, 02:56:19 PM »
Short answer... no. 

Long answer:  They spin way too fast and they'd need an h-bridge to control it.  (AKA a pain)

Offline Soeren

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Re: PC Case Fan Motor
« Reply #2 on: August 05, 2011, 11:15:32 PM »
Hi,

Just got everything I needed for my $50 robot build, except the servos..
I have a bunch of PC case fans sitting around, any way I could swap these into the build without much fuss?
Not really, unless you want to use one for a LASER scanner mirror motor.
PC fans are brushless "DC" motors of around 1W to 1.5W and next to none torque at all. They're built to spin fast with very little resistance and to live long doing it.


corrado33 <- Brushless control won't do with an H-bridge. If you reverse the power to the in-built controller you probably blow it.
If you remove the controller, you have (at least) 3 coils in star or delta formation that needs their power 120° apart - i.e. a rotating field. Some have more coils.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline corrado33

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Re: PC Case Fan Motor
« Reply #3 on: August 06, 2011, 09:27:26 AM »

corrado33 <- Brushless control won't do with an H-bridge. If you reverse the power to the in-built controller you probably blow it.
If you remove the controller, you have (at least) 3 coils in star or delta formation that needs their power 120° apart - i.e. a rotating field. Some have more coils.


Ah, I stand corrected.  I just assumed it was a little DC motor.  I was wrong.   :)  So a brushless motor is similar to a stepper motor?  I'm talking how both have multiple coils and power needs to be applied to them in a rotating field? 

Offline AethurTopic starter

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Re: PC Case Fan Motor
« Reply #4 on: August 07, 2011, 09:44:52 AM »
Thanks for the help everyone!

Offline rbtying

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Re: PC Case Fan Motor
« Reply #5 on: August 07, 2011, 09:51:10 AM »
[...]
corrado33 <- Brushless control won't do with an H-bridge. If you reverse the power to the in-built controller you probably blow it.
If you remove the controller, you have (at least) 3 coils in star or delta formation that needs their power 120° apart - i.e. a rotating field. Some have more coils.

You could get away with having n half bridges, where n is the number of coils - a number of commercial RC brushless controllers use a triple-half-H-bridge for controlling the motor.

Offline Soeren

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Re: PC Case Fan Motor
« Reply #6 on: August 07, 2011, 08:51:49 PM »
Hi,

[...]
corrado33 <- Brushless control won't do with an H-bridge. If you reverse the power to the in-built controller you probably blow it.
If you remove the controller, you have (at least) 3 coils in star or delta formation that needs their power 120° apart - i.e. a rotating field. Some have more coils.

You could get away with having n half bridges, where n is the number of coils - a number of commercial RC brushless controllers use a triple-half-H-bridge for controlling the motor.
"Half an H-bridge" is correctly named "a half bridge", not "a half H-bridge". The name "H-bridge" is only used about an... H-bridge and it's due to the imaginary "H" the setup is usually drawn like of course.

You wouldn't call a motorcycle a "half-car" either, would you?  ;)


Either way you name it, you still cannot drive a brushless motor with an H-bridge!
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline joe61

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Re: PC Case Fan Motor
« Reply #7 on: August 08, 2011, 06:19:00 AM »
You could get away with having n half bridges, where n is the number of coils - a number of commercial RC brushless controllers use a triple-half-H-bridge for controlling the motor.


I was looking for a data sheet and ran across these a while back, show the 3 half bridge setup, and give some other good information about it.

http://www.atmel.com/dyn/resources/prod_documents/doc2596.pdf
http://www.atmel.com/dyn/resources/prod_documents/doc2596.pdf

Joe

Offline rbtying

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Re: PC Case Fan Motor
« Reply #8 on: August 08, 2011, 07:42:01 AM »
Hi,

[...]
corrado33 <- Brushless control won't do with an H-bridge. If you reverse the power to the in-built controller you probably blow it.
If you remove the controller, you have (at least) 3 coils in star or delta formation that needs their power 120° apart - i.e. a rotating field. Some have more coils.

You could get away with having n half bridges, where n is the number of coils - a number of commercial RC brushless controllers use a triple-half-H-bridge for controlling the motor.
"Half an H-bridge" is correctly named "a half bridge", not "a half H-bridge". The name "H-bridge" is only used about an... H-bridge and it's due to the imaginary "H" the setup is usually drawn like of course.
[...]

I get what you're saying here... but: many dual H-bridge ICs are marketed as quad-half-H-drivers or some such (see L293, TI SN754410, etc) so it seems to be reasonably common to say half an H-bridge, technically correct or not (xD)

Not really trying to make an argument about the brushless motor here... this is getting off-topic.

Offline bobthefirst1

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Re: PC Case Fan Motor
« Reply #9 on: September 05, 2011, 04:53:53 PM »
pc fan does have 3 wires like a servo

Offline rbtying

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Re: PC Case Fan Motor
« Reply #10 on: September 05, 2011, 05:14:22 PM »
It has three wires, but they're not a like a servo - they are power, ground, and a tachometer line, instead of power, ground, and a servo control line.  Don't mix them up.

Offline Soeren

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Re: PC Case Fan Motor
« Reply #11 on: September 05, 2011, 06:16:49 PM »
Hi,

pc fan does have 3 wires like a servo
So does most transistors (eg. b, c and e, or g, s and d) and a lot of mains equipment (L, N and E), but there's a wee bit more to electronics than wire count.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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