Instructables
Picture of A Centrifuge built from VCR parts

A centrifuge is a very useful piece of equipment for isolating aquatic organisms. Centrifuging a sample of water containing micro organisms will drive them to the bottom of the container, where they become more concentrated and easier to manipulate. A high speed laboratory model costing several hundreds of dollars isn't necessary for the purpose, something much simpler will do the job quite adequately. At the most basic, you can just tie a piece of cord SECURELY to the container and whirl it around your head. You can easily generate a centrifugal force of 10 G with this method ( but do it outside in an open area, where nothing will get damaged if it comes loose ! )

A safer and more convenient solution is a motor driven apparatus, such as the one I built using parts from an old video recorder. It cost me only a couple of dollars for the plastic bowl housing the rotor head and some PVC pipe fittings, all the other parts were obtained from my “junk collection” of defunct VCRs and other “dead” electronic gadgets. If you don't have a dead VCR lying around, just ask a few friends and you are bound to find someone who will give you one. The parts required are the video recorder spinning head mechanism, plus the video cassette loading motor with its drive pulleys. Some newer VCR models may not have belt drives, a good alternative source for these components is an old inkjet printer, but these usually have stepper motors which require a special driver circuit to power them. If you can find an ordinary DC motor which will fit the pulleys it is much simpler than trying to get the stepper motor working. You will also need a 12 Volt DC plug pack. It should be capable of supplying at least 400 milliamps, otherwise it will probably burn out before long. If you need to, you can buy a new one for about $ 5, but these are very common items found in garage sales for only one or two dollars.

 
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elabz1 year ago
I couldn't quite grasp if the original BLDC motor is used in the 'fuge. Are you reusing the BLDC controller from the PCB? I did see a step to remove it, I didn't see a step to add it back (probably just missed it) and BLDC will not turn without the controller that's on that board. Any tips on hooking that up to a DC source?
kymyst (author)  elabz1 year ago
The motor which drives the video head rotor is just the 12 V DC cassette tape drive motor. It is driven directly from a 12 V DC plug pack. The video head rotor is driven by this through a belt drive and doesn't require any electrical connection.
mhempen1 year ago
You could also just use an old corded drill.
Nicely done. I was trying to come up with a centrifuge for forcing liquid plastic into rubber molds for making miniature figures for a train set. The mixed liquid plastic is too light for gravity to do the work, unlike the old lead figure method. Now to figure out how to deliver the liquid plastic while the device is spinning. Probably a simple funnel through the protective cover as well as some serious clamps for holding the molds. One of my local junk stores has a suit of armor that I might invest in first. :-) Thanks for the excellent ible.
kymyst (author)  Gartholameau1 year ago
How long does your plastic stay liquid ? And how big are the moulds ? If they are small enough that you could have a reservoir of plastic in the upper part of the centrifuge tube connected with the mould underneath, it might work. Otherwise, what about a connection in the bottom of the mould to a small vacuum pump, which would suck the plastic into the mould ? You can buy these on ebay for under $ 20.
I have about a minute before the plastic starts to harden, so maybe the vacuum pump would be a better idea. The items I want to mold are N scale so maybe 1.5cm in height.
A centrifuge like this could be a life saver in under developed parts of the world. I've spoken with medics who've done care in low-tech regions and they've been reduced to the whirling sock on a rope method for blood separation.

But based on my own, uhmmm, experiences with lab centrifuges, I would recommend a couple of enhancements.

1) Make the base wider and able to take a clamp to the worksurface. The principle cause of catastrophic centrifuge imbalance is a breaking test tube while the unit is spinning. That will happen a lot more often than you think.

The angular momentum of the remaining single test tube is shockingly high even in a low speed rig like this.  If one tube fails under speed, a lightweight design like this just won't vibrate, it will take on a life of its own and go on merry adventures about the lab. The combination of oscillating vibration and gyroscopic precession make the unit move jerk and even fly in random directions that make it look more like the target of a poltergeist than a physical phenomena.

That's the main reason that commercial units are so heavy. It's not just internal armor  it's to keep the damn thing on the bench.

Ah, don't ask me how I know this. Long story.

-) If possible, rig a kill switch sensitive to vibration. Not sure how to do that low tech but it will keep the unit from self-destructing  when the tube breaks.
I was thinking the same thing! Well, actually for research purposes in remote places. I'm adding this to my "Jungle Lab" collection!
kymyst (author)  shannonlove1 year ago
I understand your concerns about the unit vibrating and running amok, and I am well aware of the tendency for centrifuges to walk about on the bench if not perfectly balanced. But perhaps you have missed my warning in step 5 : "It will need to be clamped to the work bench so that it doesn't run around and develop uncontrollable vibrations. " Also because it is only running at about 250 rpm, it doesn't have the same inertia as a heavy device running at much higher speeds. It wasn't designed for use in medical laboratories, but it could possibly be used for some simple blood testing etc, in a pinch. Thanks for your input.
Nyxius1 year ago
Nice, simple and cheap.
rwill531 year ago
I am wondering if this can be modified to make a spin art device?
kymyst (author)  rwill531 year ago
I am totally unfamiliar with spin art. Does it involve spinning a flat board and dribbling paint on to it ? It would be possible to do this by attaching the board to the rotor with a couple of screws, You would probably also need to slow down the motor using a LED dimmer control.
zherman1 year ago
Don't sell it to the Iranians... :-}
kymyst (author)  zherman1 year ago
They won't live long enough to concentrate a few kilos of U-238 with this apparatus, it would take centuries.
foobear1 year ago
this is great!
carlos66ba1 year ago
Well done! And you have a decent protection for the user.
kymyst (author)  carlos66ba1 year ago
Thanks for your comments. Although this is not a high speed device, it could still cause a nasty injury if you put your fingers inside. I would not recommending using any kind of centrifuge device which does not have a protective shield.
And I was thinking also of parts breaking off (will happen eventually), so the protective shield around and above is well thought.