Rotary Encoder vs Hard Drive Motor - Using a Hard Drive as a Rotary Encoder

As I understand it… a rotary encoder is pretty much an on/off switch per side with an offset… So something like an Arduino can see its direction and increments when you turn it. I generally see them used on the digital inputs…

I always thought a hard drive motor was basically a brushless DC motor or maybe a stepper motor?

I came across a few YouTube videos were people used a hard drive motor as a rotary encoder… for example as a jog wheel. Here are a couple videos as an example of what I am talking about.

Can someone help me understand a little more about using a hard drive motor as a rotary encoder? Are they connected in the same fashion? How do they work in comparison?

I don’t have a specific application, but I am just looking to understand more about them. I would love to salvage these motors from hard drives as I come across dead drives all the time.

That's a terribly clever idea!

A hard drive motor - or floppy drive motor, or various other types of "brushless" motors - contains two components in association with its multi-sector permanent magnet rotor. There are the coils - generally about three - that generate torque, and Hall effect sensors to determine the relative position of the rotor in order to control the drive to the coils.

This does presume that the design actually uses Hall sensors, rather than just sensing current in the coils themselves, so it entirely depends on the design of the particular motor. The Hall effect sensors give you your rotary encoder, as the motor really is a rotary encoder used to control the drive coils.

Salvaging the actual motor as such may be a more difficult task as it may be integrated into the drive casting.

Salvaging the actual motor as such may be a more difficult task as it may be integrated into the drive casting.

Being in IT I had a stack of dead hard drives or just old drives which are no longer in use... Originally I dissembled them for their magnets but removed the motors as well. Almost all were easily removed from the drive casing. The sad part is, I had an e-waste run before I knew how useful they were going to be so I tossed about 7 of these motors. I have a few more drives but I still have to take them apart.

I did notice that some had different wire counts... like 4 wire, 5 wire, or 6 wire... I dont remember but I did see some differences.

What you said about the hall effect sensor makes perfect sense!

I remember taking my multimeter and measuring the coils resistance to identify which was the common/ground...

I'm curious if there are other ways to use this aside from needing a hall effect sensor. There are quite a few projects on YouTube with the use of HDD motor as a rotary encoder.

After looking at the first video I posted... I was wondering why the HDD platters were fanned or cut out like that... Maybe he is using an optical encoder with the platters and the the hard drive motor isn't doing anything?

Either way, I see plenty of examples where the motor alone is used as a rotary encoder.

Anyone else have any experience or ideas with this concept?

Here is another good example.

So did you try Googling it to find a schematic ?

Google search for stepper motor rotary encoder

Google search for stepper motor encoder schematic