Let's Make Robots!

Walzing Hard Drive Motors

Update: This page is just an archive. The real work is continued as a walk through. Please direct all your comments to that page.

I am the proud owner of a stack of scavenged hard drives. I hoped to find really fast, torqueless motors inside. But instead I found myself a project for my new found 555 knowledge.


The logic chip 74164 is a "Serial In Parallel Out bit shift register" (datasheet). S1 acts as a reset button. S2 is the little white wire in the video that "boots" the sequence. Once one serial pulse makes it into the 74164, the system will maintain the sequence. When the pulse reaches the third output (red), diode D1 feeds it back to the first (green).

The motor driver is the well known L293D.

The video lasts as long as 10 minutes. Oh, and you'd better take your sea sickness medicine!


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I will dive into these issues as soon as I erected the howto page for it.

I have GOT to see the tripod-camera-mount-desk-lamp-camera-holder-thingie!!!! Brilliant!!


No, seriously... I love things done without a "brain" just simple logic chips... Good stuff!


Do you recognise its intended purpose>

Very interesting video. I never knew that the spindle motor on a hard drive is an induction motor. I guess that makes sense -- they want it to be as quiet and long-lasting as possible, so it seems like the obvious choice.

I've been looking at lots of electric cars and power tools that use brushless induction motors, and I knew that they were driven by alternating current (single phase or three phase) rather than DC. I know that on the big motors, they usually use an inverter to generate the alternating pulses from a DC power source, which seemed like too much complexity for something smaller like a robot. It's interesting to know that you can generate the pulse train from much simpler hardware.

I guess since your three outputs go from 0v to full voltage, what you're generating is three square waves, whereas regular AC would be a sine wave. So I imagine the motor might not run quite as smooth with your driving method? Maybe the difference isn't really noticeable.I wonder how the HD's onboard controller drives the motor -- with an on/off approach like yours, or by generating something closer to a smooth sine wave? Anyway, thanks for the info.


Would a simple component not even out the square, make it more sine, I wonder?

(We HAVE to get some of them oscillo-thingeys!)

You're talking Capacitors. I believe those are also used to "round off" the sharp corners on a CDROM audio signal. It's the size that I cannot fine tune in my current setup. I need a scope for that indeed.

Also, I was hoping the inductance of the motor might help out. The fact that current through the motor drops with higher RPM seems at least hopefull.


Should this be a walk through or tip?


Most definetly! Chage title to "how to.." and go!

Looking forward to dive more into this :) And thanks for making it.

If you re-enter, PM me or something, or BOA or Dan, to delete the blog entry. If you want to keep a record in your blog, you can aso re-enter this as a tip, and just change the blog entry to a "today I made this: (Link) 


Cool, always wanted to use these motors..