'We offer a step by step description of how to make a battery powered 9-24 volt DC motor driven centrifuge for separation of cell in fluid suspension for under 20 dollars. This centrifuge may be used in the field (when no other technology is available), and is set in a cookie tin or coffee can to prevent accidental release of content.

Bullet shells act as the "buckets" for the centrifuge.

Paperclips are bent to hold the shell casings, which spin out when the motor begins to turn.

A DC motor speed controller allows control over acceleration and deceleration.

A motor spinning at 2000-2500 RPM with a radius of 2 inches will develop the
600 g of centrifugal force required to separate cells in fluid suspension.

We used 1 milliliter pipettes which fit into the bullet casings to spin-down a "cell pellet"
in a pleural fluid sample however a "virtual tube" of cellophane will also work .

This project was supported in part by the Center for Parabiotics Research.
Project team members: R Siderits, J Jaworski, W Lecorchick, O Ouattara

Step 1: Finished Prototype

Here is an image of the completed centrifuge. We chose to place the motor, arms, and buckets on the outside of this cookie tin for demonstration purposes. You may choose a larger coffee tin or better yet, a 12" diameter, 2-3 inch deep cookie tin to place it inside.

Use the lid of the cookie tin to completely cover the centrifuge for safety.

The knob on the front of this image is the DC motor control. We used a two part plastic and a bottle cap as a mold for both the rotor head (center) and the speed controller knob.

Step 2: Parts

Here is a list of the parts that we used.
Start with a DC 12-24 Volt flat mount motor
Find a DC motor speed controller (or circuit)
Get a large coffee-can or cookie-tin (12" diameter)
Two 9 Volt batteries
Two paper clips
Two or more bullet casings to serve as "buckets"
Hammer, wood, nail, pointed "needle nose" pliers
Total project time is about 30 minutes

This will run on one 9 volt battery; however, two batteries in series or a 12 volt DC supply will really spin things up to full speed. The paper clips need to be sturdy. The bends and relative looseness help to absorb and distribute imbalances and thereby serve to dampen vibration or precession.

We have included sources for these parts as well as a circuit diagram for the DC motor controller.

Step 3: A Look Inside

These two images look into the cookie tin. The lower half holds the motor speed controller. We drilled a hole in the side of the cookie tin to let the shaft of the controller through and then put the nut on the outside to hold it in place.

The knob is formed from two part plastic (or epoxy, or JB weld) in a bottle cap.

The under surface of the lid shows the wires from the controller going up to the motor.

The motor is set in a hole in a piece of wood and has four small screws holding it to the lid.

Step 4: Computer Model of Prototype

This computer model was done in trueSpace 6.6 by Caligari corporation.

This model with the "Physics" simulation helped us develop the curves at the end of the paperclips and the placement of the hole in the bullet casing.

Step 5: The Rotor Head

These images show a close-up of the rotor head and the paper clips. A line drawn on a piece of paper that corresponds to the shape of the bends in the paper clips will assure that both are identical. We used needle-nosed pliers to bend the paper clips into this shape. The paper clips are set into the holes in the rotor head, not glued. As a matter of fact, there is no glue in this project.

The motor is pressure fit into the hole in the piece of wood. If it's a little loose, then a layer of tape around the motor will snug it up.

The hole in the rotor head is also a pressure fit.

Notice the bend in the "bucket end" of the paper clips. This bend allows the bullet casing buckets to swing out with centripetal force.

The green mark on the top of the rotor head marks the site where reflective tape was placed to measure revolutions per minute (RPM) by using a tachometer.

Step 6: Making the Bucket

These images show how we made the holes in the sides of the bullet casings for the paper clip rotor arms. We made a small wooden jig to hole the base of the casing while we put a small nail into the open end and tapped it with a hammer.

This will put a small hole in the end without distorting the casing. Notice in the first image what happens if you put the hole too close to the rim; it splits the casing.

Step 7: Pipette in Bucket on Rotor Arm Ready to Spin-out

Here is the paperclip rotor arm with the bullet casing "bucket" holding a bulb-down, 1 ml pipette.

When the rotor spins up, the bucket spins out and the fluid in the pipette is subjected to the centrifugal force.

Step 8: Take a Look at These Cell Pellets!

These two pipettes were spun for 5 minutes at about 2500 RPM with a rotor radius (paperclip) of 80 millimeter. This gives a Relative Centrifugal Force (g) of about 500. Not bad for one half dead 9 volt battery. This particular motor would spin up to 5000 RPM and give more than 800 g with a 2 inch radius. This is more than enough force to separate many types of cells in suspension.

The whitish cell pellet at the bottom represents the cells that have been separated from the fluid.

In this case we used a pleural fluid sample that was to be discarded. The separation was surprising.

Step 9: Figuring Out Centrifugal Force

Use of this "nomogram" allows you to determine the relative centrifugal force (RCF) in g's, by aligning the radius of rotation in mm (in this case, paper clip length for the rotor arm measured from the center of the motor spindle to the base of the bucket).

The Revolutions Per Minute (RPM) can be verified with a hand-held tachometer. We used an infra- red tachometer from Harbor Freight.

Step 10: Tips and Learning Points

Use plug in DC power supply instead of battery

Use solar panel (Harbor Freight) to recharge battery

Place a weight on top cover to dampen vibration

Use two part plastic or epoxy resin to make rotor head

Make a virtual tube using cellophane in the bucket

Consider using a tachometer to get a speed check

Make your own speed controller (see references)

Always use all appropriate safety gear!

Step 11: Long Arm Paperclip (14 Cm) With Tachometer

This image shows the "long" paperclip rotor arm (see "arch" to left, beyond lid of tin) which measured up to 14 cm from the center spindle of the DC motor. You can see the tachometer at the top of the image. With two 9 volt batteries in series or a 12-24 volt DC power supply this will "Tach" up to 2000 RPM for about 600 g's. Spinning it up that fast requires that you at least Duct Tape the unit down to a surface (and wear Goggles).

Step 12: This Small Solar Panel Can Recharge the 9 Volt Batteries.

This small solar panel can be used to recharge a rechargeable 9 volt battery. We purchased this type of charger from the Harbor Freight store for 11 dollars.

Step 14: Disclaimer

Follow ALL reasonable safety guidelines and actually wear safety equipment, including
but not limited to:
1)  Full body armor.
2) Using a centrifuge that spins really fast. 
3) Powertools that you never read the instructions for.
4) All tools that you never learned to use properly.
5) Anything that heats up, pinches, cuts, squeezes, flies      off, carries electric current or causes other     traumatic, caustic, or thermal injury.  
We are sharing our experience, not telling you to do it.  
If you choose to try this then - it is at your own risk!
  • No really, we're not kidding about this.

Step 15: What Can This Project Be Used For?

Aside from a hobby or "field" solution for separation of cells in fluid suspension, this
prototype device could be used (in the absence of any other technological solution) for
initial sample preparation of cytology specimens.
There may be a demonstrable need for this capability in supporting evolving health care infrastructures in countries with restricted economy.

For example, in "developed" nations the PAP smear for cervical-vaginal cytology has decreased the incidence of cervical carcinoma by approximately 70%. However, in a country with
restricted economy this is not the case. A woman may need to transport a cervical
cytology specimen herself, sometimes hundreds of miles, and then wait months for the
sample to be prepared and interpreted.

Providing a basic functional centrifuge for cytology slide preparation may help facilitate
aspects of this difficult process.

Step 16: Watch It Spin!

This video segment shows the movement of the buckets as the motor speed is gradually increased.

Step 17: Good Luck!

We hope that you've enjoyed this How-To and that it may be useful to you.

The potential for this prototype to be used in remote areas in countries with restricted economy for use in supporting cervical vaginal cytology field preparation of sample may help to provide critically needed services for these populations.

Good luck and be safe (remember to build yours INSIDE of a cookie tine, not on top).

This centrifuge, with certain modifications, can be used for clarifying home made wines. <br>arun kelkar
As a medical professional who uses centrifuges extensively daily, I found this project clever and interesting, BUT using this for biological material other than plants is incredibly dangerous. Full body armor is not sufficient to protect you from the diseases at large in the general population to which this centrifuge guarantees you will be exposed. Biological aerosols are nothing to fool around with.
I would agree that using this in a medical diagnostic lab or equivalent would be unwise, but saying that using it for anything &quot;other than plants is extremely dangerous&quot; seems extremely cautious. There are any number of non-hazardous uses for a small centrifuge in biological and non-biological lab settings. The majority of clinical centrifuges are used in a non-clinical settings, on both prokaryotic and eukaryotic cells, and it's routine, not extremely dangerous. &quot;Biological aerosols&quot; are indeed nothing to fool around with; that's why I'm much more concerned about the guy sneezing in the elevator than the SF-9 or Top-10 cells I'm centrifuging in the lab ;^)
Your point is well taken and I agree. Here are some thoughts that I had in offering this project Bottom line, we are talking about balancing moral and ethical justification for exploring low cost alternative healthcare technologies in an effort to reduce human suffering in countries with restricted economy, against the risk/benefit of actually utilizing them. As with many projects on this site that spin many times faster, use combustibles or high voltages, this project has inherent risk (even for "botanical" specimen processing). However, we may also consider the reality that for impoverished societies with rural populations new cytology methods that only require centrifuge processing for on-site cytology screening could make a huge difference in the ability to provide any aspect of woman's health care (try for example using an egg beater centrifuge). It is also important to consider that lower speeds, protective encasement, alcohol suspension, sealed pipette tips and longer spin times can be used to increase safety. By the way, having used a series of "coffee-can" prototypes, I was amazed how well these things actually work, especially with the upside down pipettes ( heat sealed at the tip with a hand held 1" hot-wire bag sealer or para-film). Finally, I would be grateful for your opinion, as someone who is familiar with this technology, would you be able to suggest any design modifications (for non-medical use)? We were considering an interlock for the arms or a rigid rotor head with a pin to hold the casings. The design parameters are <10$ and does not require "machining" of parts. Best regards and thanks for the comment.
How about mounting the spinning centrifuge head in something like a tupperware cake container. Sealable to contain those potentially deadly aerosols. Easily cleaned of those inevitable leakages. You will be profoundly appreciative to have added this feature once you see what a huge mess a leak makes and realize what might have happened if you breathed in a lung full. And once you see how often this type of incident occurs. It probably will be resilient enough to contain a failure of the centrifuge head itself.
Excellent idea. One leak is all it takes. We also think that the spent primers should come out if they contain any residual chemicals. We were intending it to go inside the cookie tin and only put it on top for the DEMO, but your idea fits better with clean-up and safety. Thanks!
i drill holes in the blades of a fan then put test tubes in and turn the fan on itx=s back]]great ible 5 stars<br/>
That's brilliant!
Very elegant design and looks very sturdy. &nbsp;I have created another centrifuge using computer cooling fan and foam plate/bowl. The six place computer fan/foam centrifuge can run up to 920 rpm when two 3.5 mL tubes loaded. &nbsp;It will allow total 21 mL of samples to be processed at a time but the speed will drop down to 250rpm. &nbsp;That should be good enough for low speed applications, such as pond life observation.<br> <br> Just to share my design with you: <a href="http://microscopetalk.wordpress.com/projects/homemade-microscope-centrifuge/" rel="nofollow">http://microscopetalk.wordpress.com/projects/homemade-microscope-centrifuge/</a>
Wow, nicely done! Thanks for sharing your design.
This is a great idea for junior high school age science projects on up to adult microscopy hobbiests who with to collect protozoa, check sedimentation of ponds or lakes and about 25000 other uses!!
Thanks, just make sure that the take home point is that when you make one, it goes inside of a cookie tin that is on top of the smaller battery-controller tin. Its safer that way.
Just wondering, aside from remote-location cell culturing, what other applications would there be for a battery-operated centrifuge? Just looking for ideas here...
Mostly for layering or separation of cells in suspension or separating liquids that don't mix well. It can be used to wash cells or "sediment out" things that you don't want.
What a great idea! I would consider building this to separate yeast out of active brewing projects for storage and later re-use. Beer is the second best (after modern medicine) application of microbiology after all...
Wow, never thought of that. I wonder if it would "layer" on top of an oil or underneath. The speed controller would let you go slower for more time. By the way, a hand crank flashlight (hacked) will produce enough energy to run a smaller motor, if batteries are unavailable or cannot be recharged from the solar panel.
I really appreciate you posting this instructable. It will be great to build for my school science department.
really good, looks like it works really well too! another safety note i'd just like to mention: inspect your centrifuge components for wear (particiularly the swing buckets and paper clip rotor assembly) after each and every operation. If anything looks slightly worn in the interests of your own safety it is best to replace it. this is a standard safety practice for commercial centrifuges too. If people don't do it, and a rotor shears, it can literally go through a few concrete walls before it will stop (and in fact the only safe place to be if this happens is directly above or below the centrifuge, as these are unlikely trajectories for projectiles). if you run it in a thick wood/steel box it should be pretty good for the small mass swing buckets. (google centrifuge rotor break for examples of what can happen) 5*'s :)
I'd have to second the box thing. I really hope you're not running this otherwise. When I was in medical research, we lost capillary tubes every now and then, and that was with a real microcentrifuge. Let's just say the shattering glass and biohazardous material combo does not make for a happy day -- even when contained. How much worse still if this device flings the contamination across the room!
You are absolutely right! We put it on top of the cookie tin for Demonstration purposes only. Its meant to go inside a 12" diameter by 3" deep cookie tin. The first prototype, by the way was inside of a one pound coffee can. Interestingly the pipettes did not leak at all because of their shape and the fact that they are inverted in the bullet casings. Did you see the Disclaimer? This prototype is also meant to be a field solution for use in a country with restricted economy for onsite preparation of cervical-vaginal cytology. There was also a coffee cup version with a small 3500 RPM AA motor.
Do you need to know the exact acceleration? If not, a printed table would be quicker to read in the field than a nomogram. You could also use a pocket calculator. Since all you need to do is square the RPM and multiply by a precalculated constant, even the cheapest one will do. I can think of a way to use a microcontroller to get a direct acceleration readout or automatic speed control, but your design is just too elegant to fiddle with.
Good point. You really only need the nomogram once, when you decide on the radius of the rotor (paperclip) arm. Just to make sure that the speed is enough to separate out cells in fluid suspension. After that point, the pellet at the bottom of the upside-down pipette is proof of adequate g force. We also used "Virtual Tubes" made by pushing cellophane over a pencil eraser and then down into the bullet bucket! You can even seal the cellophane with a small battery operated thermal sealer from a dollar store.
it might be interesting to make a similar centrifuge using a dremel or other rotary tool for power. they're relatively inexpensive, have a good amount of torque and have built in speed control between 1,000 and 35,000 rpm. it would probably not be safe to spin that fast but you could dial the speed down whatever level is needed. serious protection would likely be needed to prevent anyone getting hurt when the speed is increased however.
Great project, it has a lot of potential in places with inadequate lab equiptment. It is a good point to build it inside a cookie tin, especially when spinning down blood and body fluids to prevent spillage.
i got 2 of them exact same solor panels from Maplin UK :) usefull
This is awesome, I was actually thinking about building a centrifuge but seeing if I could get an old drill off of craigslist and convert that.
This is an extraordinary project. I'm really impressed that it functions as smoothly as it does, and your directions are (but see below) quite clear. I realize that your "blackboard" slides look really cute, but they can be a substantial impediment to actual users. Because they are graphics, none of the information provided can be searched. They cannot be read or understood by anyone who is blind or visually impaired (they can't be voiced or Brailled). They will be very hard to deal with for users on low-bandwidth connections (the impoverished, or those in impoverished regions). They cannot be translated automatically into other languages than English. Please consider either replacing those images with text, or at the very least, putting the actual text into the content of the Steps.
Excellent observations, I didn't think of that. I'll get the text replaced ASAP. Thanks!
Looks great! Thank you so much for considering my suggestions :-) (rated 4.5 for completeness, detail, and concept).

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