How can I safely use HDD stepper motors for different applications?

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Discussion Overview

The discussion revolves around the use of stepper motors extracted from hard drives for various applications, including potential uses in remote vehicles and camera mounts. Participants explore technical specifications, operational limits, and practical implementations of these motors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Participants inquire about the maximum safe operating speed of the stepper motors, noting that they were extracted from 7200 RPM hard drives.
  • There is uncertainty regarding the appropriate voltage for the coils, as the original specifications were not available.
  • Some participants suggest that the motors likely have two coils based on the four leads, indicating they may be two-phase hybrid stepper motors.
  • Questions are raised about the torque output of the motors and their suitability for driving small vehicles or camera mounts.
  • One participant suggests that the head actuator in a disk drive is a stepper motor, while the main spindle drive is typically a servo-controlled DC motor.
  • Discussions about the electrical characteristics of the motors reveal low resistance values between leads, leading to speculation about their configuration as three-phase brushless DC motors.
  • Some participants propose using RC motor controllers to drive the motors, while others suggest using modified hobby-servo motors as an alternative.

Areas of Agreement / Disagreement

Participants express differing views on the type of motors extracted from hard drives, with some asserting they are stepper motors while others suggest they may be brushless DC motors. There is no consensus on the maximum speed, torque output, or best practices for driving these motors.

Contextual Notes

Participants note the absence of specific voltage and torque specifications for the motors, which may affect their usability in various applications. The discussion also highlights the potential need for gearboxes to enhance torque output.

Who May Find This Useful

Individuals interested in robotics, DIY electronics projects, or repurposing old hardware for new applications may find this discussion relevant.

Lancelot59
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I recently pulled apart two old hard drives, and extracted the stepper motors. I already know they would have to be fairly accurate to be used in hard drives.

So here are my questions:

1. These were 7200 RPM hard drives. I'm guessing the motors are probably capable of going much faster than that. How fast can I safely run these motors? I can't find any specs for them.

2. I neglected to measure the voltage the hard drive used to run the motors, and as of yet I haven't found anything. About voltage should be going to the coils?

3. Am I correct in saying that they have three coils because the motors have 4 leads?

4. How much torque can I get from one of these things? Would it be enough to run a small remote vehicle? Or would it be more suited to something like a camera mount?
 
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Lancelot59 said:
I recently pulled apart two old hard drives, and extracted the stepper motors. I already know they would have to be fairly accurate to be used in hard drives.

So here are my questions:

1. These were 7200 RPM hard drives. I'm guessing the motors are probably capable of going much faster than that. How fast can I safely run these motors? I can't find any specs for them.

2. I neglected to measure the voltage the hard drive used to run the motors, and as of yet I haven't found anything. About voltage should be going to the coils?

3. Am I correct in saying that they have three coils because the motors have 4 leads?

4. How much torque can I get from one of these things? Would it be enough to run a small remote vehicle? Or would it be more suited to something like a camera mount?


Hello there,

There are 4 lead wires, so your stepper motor have two coils which is two phase hybrid stepper motor most of the time. The driver's speed correspond to its resolution. Full, half, quarter, tenth, 16th, etc. If you want to run a stepper motor too fast, you will lose torque. I don't exactly know it can run your remote vehicle or not because I don't know your motor's holding torque at all. You can try it out.

UIROBOT
 
I thought only the head actuator in a disk drive was a stepper, the main spindle drive is just a servo controlled DC motor ?
 
robotdigg said:
Hello there,

There are 4 lead wires, so your stepper motor have two coils which is two phase hybrid stepper motor most of the time. The driver's speed correspond to its resolution. Full, half, quarter, tenth, 16th, etc. If you want to run a stepper motor too fast, you will lose torque. I don't exactly know it can run your remote vehicle or not because I don't know your motor's holding torque at all. You can try it out.

UIROBOT

Sounds simple enough. It should be a simple matter to code a PIC to run it. I'm curious though, aren't there some motors that have a common ground for all the coils, and then have individual inputs?
 
It's likely a brushless DC motor. How do the leads ohm out?
 
There are 4 leads. 1-4 left to right:
Motor 1:
1-2 = 1.8\Omega
1-3 = 1.9\Omega
1-4 = 1.7\Omega

2-3 = 3.6\Omega
2-4 = 2.4\Omega

3-4 = 3.3\Omega
This seems like a bad thing...everything connects to everything else. Motor 2 is the same.
 
Lancelot59 said:
There are 4 leads. 1-4 left to right:
Motor 1:
1-2 = 1.8\Omega
1-3 = 1.9\Omega
1-4 = 1.7\Omega

2-3 = 3.6\Omega
2-4 = 2.4\Omega

3-4 = 3.3\Omega
This seems like a bad thing...everything connects to everything else. Motor 2 is the same.
That would be a three phase brushless dc motor wound in star with a neutral wire. The simplest way to drive it would be a speed controller for rc planes and cars, you don't need the neutral with these, so just leave it disconnected. Oh BTW, wire 1 would be your neutral.
 
famousken said:
That would be a three phase brushless dc motor wound in star with a neutral wire. The simplest way to drive it would be a speed controller for rc planes and cars, you don't need the neutral with these, so just leave it disconnected. Oh BTW, wire 1 would be your neutral.

Sounds good. I'm planning to get a PIC and program that to drive it. I'm planning to build an RC vehicle so I might as well start there.
 
Now, if you could use the head actuator for steering...
 
  • #10
I have another motor better suited for that. It's also a stepper, but it was fairly simple to figure out. One common power and 4 grounds for each of the coils. I'm not sure how strong it is because I've never fired it up, but if it can handle the load it should be very accurate. It has detents every degree, and I should be able to make it do half steps.

Just so I can get the basic control interface going, I stripped down a lego truck I had and motorized the steering and drive wheels with some lego motors...nice and simple. It's a pity Lego went away from making that stuff. It was incredibly fun. Anyhow I guess I'll start by making it run, and after I get a reliable stepper controller working it should go.

Somehow I don't think the HDD steppers would be able to move a vehicle, but I'll see once I get a controller going.
 
  • #11
Lancelot59 said:
Somehow I don't think the HDD steppers would be able to move a vehicle, but I'll see once I get a controller going.

Think low torque, and include a gear box.
 
  • #12
Phrak said:
Think low torque, and include a gear box.

The only gears I have are lego...the parts probably wouldn't hold up too well. I guess I could make some sturdier gears. I wouldn't need a mix of ratios, so that simplifies the design.
 
  • #13
famousken: How would one use an RC motor controller to run a BLDC motor? Doesn't this motor need a 3-phase sequenced drive, similar to a stepper minus one phase?

Lancelot59: save yourself some trouble and go directly to a modified hobby-servo (gear) motor. e.g.: the motors used in this: http://www.junun.org/MarkIII/Store.jsp with instructions for modification here: http://www.junun.org/MarkIII/Manual/kevin/servohack.html and even further mods on my site: http://www.etantdonnes.com/ROBOCAR/encoder/
 
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