Let's Make Robots!

(Howto) Walz a Hard Drive Spindle Motor

an example of a driver for a brushless DC motor without microcontroller
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3phase_pulsegenl293d.sch92.71 KB

This is a continuation of my blog on the same subject. Please continue your commenting here.

 


 

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 circuit with the driver is much simpler:

The EN/able pins apparently do not need pulling down to work. The three diodes D2, D3, D4 only serve to cut a tiny 0.7 V off the voltage. That keeps the current maintainable for the driver chip (rated at max. 1.0 A continues duty). I tried lowering the motor's voltage supply, but the driver would not separate the two supplies very well, when I did. It works OK when V-motor is higher than V-logic. Not the other way around.

The video lasts as long as 10 minutes. Oh, and you'd better take your sea sickness medicine! The video compression kills any details, so here is a closeup of the experiment as demonstrated.

Avenues of improvement

It has been suggested (by oddbot and robologist) that the shape of these square/block wave can be improved upon. Advantages include higher rotational speeds or power efficiency.

Also the control method can be improved a lot. Removing the need for a manual boot up and automatic ramping up of the speed.

Furthermore a decent feedback mechanism could make the driver much more intelligent. Two main alternatives remain to be inestigated: external feedback (e.g. hall effect or optical sensing) telling a processor about the state of the entire system, or internal feedback (e.g. voltage detecting on any of the motor's coils when it is not being fired) which in turn could help the exact firing of the next (round of) pulses. That could even help gradually ramping up (or down) the speed.

Practical issues

Finding the right leads. In this picture, I soldered in the wires shown. I also chose the colour coding to be like the international colour convention of traffic lights. Nothing to do with reggae or rasta.

Just as in a stepper motor, measure the resistance through the coils. In the above diagram any coil from a coloured wire to the "black center" would be a very low resistance: somewhere between 0.5 and 1.5 Ohm. You need a reasonably good multimeter (M-thingey) in order to get an accurate measurement. And some patience.

The resistance through any connection from a colour to a colour would be about twice as much.

The bottom line

You're probably better off using a microcontroller after all!


Watch this space (not the other space) for updates.

8ik

 

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If you follow my video carefully, You understand that this is not the right way to drive a brushless motor. It is a lot of fun trying though!

If you really want to give this a try, learn how to read electrical schematics. Mine are all in the post. With values for all components.

kun je ook gewoon een batterij op de hard drive motor aan sluiten zou je mijn een email terug sturen naar jeffrey_om@hotmail.com of je dat kan doen en hoe aleen met batterijen en die motor

No I will not answer forum questions via e-mail. I even answer e-mail questions via the forum.

You asked if a hard drive motor can be simply powered from a battery. The answer (again) is no. Just a simple battery will not make this kind of motor turn. You need a (complex) electronic circuit between the power source and the motor. Even more complex than the one above, as I learned from trying.

See what just happened here? I answered your question for everyone to read. That will save many people (including me!) a lot of effort and time in the future.

I hope my English is clear enough for you to understand.

hello,

i tried the circuit you have shown here but still i am not abel to get the motor to rotate, can you tell me some connections which i missed? i set the timer in astable mode, gave its o/p to pin 8, connected the switches and gave 3 o/p to the l293d driver and from there to the motor, but my 74164 is getting heated up and motor is locked but not rotating!!! can you help me with some clear circuit connection diagram!!!

First of all, this method of mine is NOT a very good one. If your really NEED a turning hard drive motor, look into other drivers. But if you are in it for the fun, keep on trying. Cause fun it is!

Did you measure the resistance between the leads into your motor? Are they the same as I described? There are different models out there.

Did you feed 5V from a battery directly into each coil of the motor? Did it twitch? It should. Did you repeat the twitching for alternating coils? That should make your spindle twitch around and round. My circuit is basically doing just that: give a short pulse to each one of the leads. One after the other and round again. But so much faster.

Does your pulse generator work? Use a very big capacitor to slow it down, so you can follow the pulse with an LED or a piezo buzzer. I used a bank of different capacitors in parallel. By adding and removing caps, I could adjust the total value of the capacitance.

Hook up LEDs to each output of the 74164. Check if they are indeed pulsing in the expected order.

About the LD293: you don't need that one. Any other way of amplifying the pulses would work. I just happened to have the LD293 and wanted to learn more about it. And I sure did. Pick transistors (BJT or FET) if you know more about those.

Did you try to feed manual pulses (just touch wires to the V+ rail) through your amplifier into the motor? Just to check if the amplification is working.

I needed to start my motor real slow and then ramp it up by decreasing capacitors. Or the motor would stall. I often hand started it like an outboard motor on a boat.

When I get home later, I will try and find that LD293 circuit. I must be able to upload a better readable version of it.

Rik

See the attached files: on e big graphic (gif) plus the same circuit in Eagle.
Ask a question,74 HC164s of 1 input  the low level at any time, how can let 74 HC164s of 3,4 and 5 output the high level?
i was trying to build the above circuit but could'nt build the clock properly.what are the exact values of resisitors & capacitors needed?please reply.

The clock is based on a 555 timer chip. See the post I linked to.

astable_circuit_mono500.png

i built the clock input and connected it to the IC74164 but the three LED's after the 74164 didnt glow.Are there any other connections in the circuit other than the ones in the schematic?(i started building circuits very recently and without the complete design it's hard for me to figure out any connection left out)

so,can you please post the remaining connections (if any),and what is the value of v+ that you recommend.(i set V+ to 5v and did'nt give any potential to Vcc of the IC)