DIY GRINDER WITH DO-IT-YOURSELF SPEED ADJUSTMENT

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Surely, most people in the bins are idle old hard drives. From it you can make the necessary and useful thing for sharpening knives, scalpels and other items - a miniature grinding machine with a wheel speed control.

Will need

An old hard drive, even if it doesn’t spin, or without a board at all.
Three-phase motor control controller with Ali Express.
Speed controller with Ali Express.
Sandpaper.
A pair of terminals for connecting the power supply.

You will also need wires, cambric for insulation and a few more little things.
Three main components are:
Hard drive in any condition. The engine in it is difficult to burn, so it is 100% suitable. And the board with the control driver will be purchased from us.

The motor in the HDD is three-phase, brushless and very powerful. It will not work just like that from direct current, and to start it you will need a controller or driver for controlling a three-phase motor.

To control the controller you need a speed controller, it looks like this:

Assembling a grinding machine from a hard drive

So, open the hard drive. Here you have a problem - you will need specialized screwdrivers, since the bolts and screws are non-standard there. I advise you not to suffer and buy, or rent, a set with such screwdrivers.

In general, we untwist everything: from above and from below, since nothing but an installed motor is needed.

We remove the board, leaving only the connection contacts to the motor. Now look: motors in hard drives can have either three outputs or four.

All envy on the method of turning on the windings. Somewhere they are turned on according to the "star" scheme, and somewhere according to the "triangle" scheme. Both options are suitable for us.

Except that for a three-pin HDD, everything is clear with the phases - "ABC", and for a four-pin HDD you will have to look for the phases with the help of a tester. We do not need the middle or common wire - it will not be involved.

We connect the wires to the engine from the controller, isolate and fix with a metal jumper (you can cut it from a can).

With the same jumper, we fix the controller itself from the side of the rotating disk.

To cut a circle from sandpaper, remove the disk itself from the HDD motor. Attach it to sandpaper, draw a pencil around the back and cut with ordinary scissors.
It's time to stick the cut circle on a metal disk. It is all glued to double-sided tape. Your circle will not go anywhere, and it will be easy to change it when worn.

Screw the disk.

From the cover we make a protective casing for the controller. We cut out a semicircle with a dremel.

And from a piece of tin we make a protective casing so that wear products do not fly to the controller.
The tin strip is soldered with a soldering iron to the hard drive cover.

We collect everything. We connect the speed controller. Connection is made using a pin connector. These two modules are specially created for each other and are actively used in modeling.

We connect 12 V power. Using the knob, we adjust the speed of the disk. Everything should work without configuration.

Using a PWM controller, the speed is regulated very smoothly and within wide limits.
Now you can sharpen at least metal, at least plastic. Such a useful design is sure to find application in your home.
Thanks for your attention!