PC Case Fan Motor

[Aethur]

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

[corrado33]

Short answer... no. 

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

[Soeren]

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.

[corrado33]

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? 

[Aethur]

Thanks for the help everyone!

[rbtying]

[...]
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.

[Soeren]

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!

[joe61]

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

[rbtying]

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.

[bobthefirst1]

pc fan does have 3 wires like a servo

[rbtying]

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.

[Soeren]

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.