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smaerd
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DIY Centrifuge?
So I just got done working out the kinks on a DIY stir-plate for my heating mantle and I've got to say I'm actually impressed with the performance. It
got me to thinking, I've been considering somehow acquiring a centrifuge. I looked up some prices and they are not in my range($500+, $100 for tube
holders?), and I don't need anything serious, just something to help pop out precipitates from solutions.
I don't need anything micro or super-speed.
I've seen some designs on-line but none of them impressed me and many of them do not look safe. For example...
http://hackteria.org/wiki/index.php/DIY_handheld_centrifuge
so I started to do some basic research. Here is a nice pdf explaining the bare-bones of these devices - PDF
| Quote: |
"relative centrifugal force" (RCF)
where
g is earth's gravitational acceleration,
r is the rotational radius,
N is the rotational speed, measured in revolutions per unit of time.
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(taken from the Centrifuge wiki)
My original idea was to chop up a bicycle but then I realize just how ridiculous it would be to be hand turning a centrifuge, stability/balance
issues, etc. So I started to think, let's go even simpler.
I know some computer fans can hit 2,000 RPMs. This surprised me because a $500 centrifuge only hit's 3,000 rpms.
http://www.grahamfield.com/Medical_Product/Laboratory_Centri...
So why not scale it up to a 2foot(~0.6m) by 2 foot(~0.6m) house-fan? Remove the fan blades(sand nice and smooth), build a guard cover and a nice
safety window, maybe drill some wholes in a plastic dinner plate, and epoxy some PVC tubing(and end caps) to hold the test-tubes, and give it a
whirl. Sure it won't be as stable or quiet as a real centrifuge but as long as it's not wobbling I see no reason why it would really interfere with
anything? If it's under the specs of a commercial one, than it would still work right? Just take a couple minutes extra?
I guess my ultimate fear here, is that I've totally underestimated the function of a centrifuge(some of them look really high-tech). If I have, please
feel free to pull apart this idea entirely, I never said I was smart, just trying to think of idea's for more DIY equipment.
[Edited on 12-9-2010 by smaerd]
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Magpie
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Quote: Originally posted by smaerd  |
My original idea was to chop up a bicycle but then I realize just how ridiculous it would be to be hand turning a centrifuge, stability/balance
issues, etc.
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There's nothing ridiculous about a hand centrifuge. See:
http://www.carolina.com/product/equipment+and+supplies/biote...
The single most important condition for a successful synthesis is good mixing - Nicodem
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smaerd
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Pardon my arrogance  . I just read about how that was the way it was done back in
the day. That's actually a pretty cost effective solution, but if my plan works I could get an electric powered one for maybe 30 bucks and some elbow
grease.
Depending of course on the fan specs and assuming there's no error(with me there always is though).
Uh-oh chem test tomorrow, I need to get off sci-mad for now and get back into the books. 
I'll report back as the idea or project develops.
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bbartlog
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| Quote: | | I know some computer fans can hit 2,000 RPMs |
DVD player motors can hit 30K RPM! But rpm isn't everything and such a small motor would require very small components (including the volume you could
centrifuge), making it pretty useless unless all you did was microscale work. I expect a computer fan motor would not be much better.
In general I think the range of commonly available motors (even via salvage or improvisation) is such that a reasonable design approach is to decide
on the desired mass (vessel and solution) you want to centrifuge, and then work backwards from there.
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aonomus
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Another alternative is to use a hobby RC brushless motor and ESC (electronic speed controller), they already have the bearings and everything made,
you just need to interface to the shaft coming off the motor. They are relatively cheap, have loads of torque (for their size), and come in many
sizes.
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psychokinetic
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My current hand operated centrifuge IS my hand.
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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Contrabasso
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It's easy to get the speed you need, it's not so easy to get the balance stability that you need -or the machine shakes itself to bits!
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smaerd
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@BBartlog - I wasn't planning on using a computer fan, I was just mentioning the surprising specifications on the little computer fans.
| Quote: Originally posted by aonomus | | Another alternative is to use a hobby RC brushless motor and ESC (electronic speed controller), they already have the bearings and everything made,
you just need to interface to the shaft coming off the motor. They are relatively cheap, have loads of torque (for their size), and come in many
sizes. |
That's a really good idea. I'll have to look into that .
@contrabasso - do you think a house fan would spin too uneven?
The flaw I'm seeing with cheap house fan's is they mostly run at 1,000 rpms, but with the blade's removed I'd imagine it would spin a lot fast but I
have no idea how to calculate that. It's gotta have something to do with drag.
edit - I think I could get a $15 box fan to about 200 or so RCF assuming it rotates cleanly around its axis... hmmm...
[Edited on 13-9-2010 by smaerd]
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ScienceSquirrel
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High speed centrifuges are really deadly if they fail at speed.
If you are going much over a few thousand rpm you have to start thinking about containment.
I reckon 30,000rpm would need heavy machined parts and an armoured drum to run in.
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smaerd
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Yea that's the first order of business like I said in my OP was build a nice guard cover and safety window. House fan's only go at about 1,000rpms,
but by expanding the radius it increases the RCF. I'm thinking 2,000rpm's would be far more ideal however... hmm I need to figure out how much RCF I
need to generate to suit my basic needs.
http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=bas...
This link has some really good information in it, thanks again cole-parmer!
[Edited on 13-9-2010 by smaerd]
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ScienceSquirrel
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That looks more like a weapon than a piece of scientific equipment. Imagine turning up at your local hospital with a piece of PVC tube embedded in
your chest.
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smaerd
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Yea I know! So crazy and hes holding it over his head like some kind of dark-ages mace or malice or something.
Actually a 200-500 g-force centrifuge from a house fan should be sufficient. Like I said before this isn't for bio-chemical analysis or anything, just
to get precipitates out of solution faster(in this case with a gravitational force 200-500 times greater). Which should greatly decrease the time of
waiting for some operations. And a wall fan shouldn't juice too much electricity especially if it's only being run for like a an hour or so at a time.
Sure a dremel or a high-powered brushless motor would be better, and have use for things in biochem, etc, but for my home-lab I don't need anything
too crazy. I'm not like separating dna or organelles or anything.
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aonomus
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I guess I'm more used to the concept of a centrifuge for minipreps or biochem. If you are more interested in larger volumes at lower speeds, have you
considered using something like a variac with a larger rotor and a HVAC fan induction motor? They have multiple windings for speed selection, have
built in bearings and some level of vibration dampening.
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smaerd
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Wow an hvac fan is far more ideal and still affordable. Nice bearings do seem essential. The rotor is going to be troublesome, but once it's all
written down on paper then I'm sure the idea will come together better.
Not planning on doing anything on a large scale maybe 50mL's and 6 slots(so 300mL's total). I'm a poor bastard so my experiments are always small.
I really appreciate the advice in this thread by the way.
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denatured
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I'm also interested in this so if you have any results, do post them.
I've been thinking of using an air blower like this. just remove the fan cover then punch holes on each blade and attach tubes or tube holders. you can cover it while using it with a strong
plastic barrel (PVC,PP).
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DougTheMapper
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Balancing is not really a big problem. Simply make two identical holders on either end of the centrifuge. Each holder should be able to support up to
maybe a 500mL standard-form griffin, but attachments can be dropped into the cups to hold other things like small flasks and test tubes.
(Maybe even a sep. funnel - that could be really useful) Since both sides are identical, simply weigh the entire item to be centrifuged and put an
identical weight into the other cup to balance it out.
Speaking of centrifugal force destroying things, check out this hilarious video: http://www.youtube.com/watch?v=364dzVsBs2o&has_verified=...
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smaerd
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@denatured - Woah that's probably the best alternative out there. Cheap, and effective!
@DoughTheMapper - Those guys were standing way to close to that, way, way to close... Interesting none-the less. I never thought of spinning a sep
funnel but honestly that's also a really good idea as long as it's rigged adequately as you stated.
Awesome ideas!
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Rogeryermaw
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cheap diy centrifuge from salad spinner
Two girls entered a contest and won with this design: http://shine.yahoo.com/channel/health/salad-spinner-centrifu... its based on a salad spinner and requires no power.
a video of the project: http://www.youtube.com/watch?v=COOIjVGPCt4
[Edited on 21-9-2010 by Rogeryermaw]
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MagicJigPipe
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Destroying a perfectly good washing machine? Not funny.
If I blew up a stack of $100 bills in a similar fashion would that be funny too?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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aga
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I thought a centrifuge would be useful for precipitation too, so i made one from a bit of steel, a nut & bolt, and a couple of reagent bottles.
Works pretty good.
 
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Texium
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Nice! I use my bike. Don't even have to chop it up or anything, just turn it upside down, so it's a multi-purpose machine. I talk about it in this thread. There is also discussion of other centrifuge related ideas there.
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smaerd
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Very nice Aga, That is a really good design concept, because it's simple and modular(multi-purpose). Forgot that I even made this thread (4 years ago
wow, before I even took a physics course). Maybe I'll revisit this idea over the summer as it never came to fruition. All depending of course on
whether or not I am working and going to school, and finally finish up the DIY polarimeter...
Looks like the bike actually worked out well zts very nice.
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mayko
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Paperfuge: An ultra-low cost, hand-powered centrifuge inspired by the mechanics of a whirligig toy
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Sample preparation, including separation of plasma from whole blood or isolation of parasites, is an unmet challenge in many point of care (POC)
diagnostics and requires centrifugation as the first key step. From the context of global health applications, commercial centrifuges are expensive,
bulky and electricity-powered, leading to a critical bottle-neck in the development of decentralized, electricity-free POC diagnostic devices. By
uncovering the fundamental mechanics of an ancient whirligig toy (3300 B.C.E), we design an ultra-low cost (20 cents), light-weight (2 g),
human-powered centrifuge that is made out of paper ("paperfuge"). To push the operating limits of this unconventional centrifuge, we present an
experimentally-validated theoretical model that describes the paperfuge as a non-linear, non-conservative oscillator system. We use this model to
inform our design process, achieving speeds of 125,000 rpm and equivalent centrifugal forces of 30,000 g, with theoretical limits predicting one
million rpm. We harness these speeds to separate pure plasma in less than 1.5 minutes and isolate malaria parasites in 15 minutes from whole human
blood. By expanding the materials used, we implement centrifugal microfluidics using PDMS, plastic and 3D-printed devices, ultimately opening up new
opportunities for electricity-free POC diagnostics, especially in resource-poor settings.
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http://biorxiv.org/content/early/2016/08/30/072207
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Dr.Bob
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Pretty spiffy. Another hand cranked item that might work would be a honey centrifuge, designed to spin honey from combs, mostly they are hand
cranked, but big enough to handle tubes or vials in a rack. I still have a spare (old, used, but working as best as I can tell) vacuum centrifuge,
designed for evaporating solvents under vacuum, but I use one like it at work sometimes to simply centrifuge vials. No pump or trap for it, but I
could use getting rid of it, if someone wants to buy it or make an offer. I sold another one for several $100, but am getting more motivated to sell
this one, due to a shortage of storage space.
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phlogiston
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You should also consider whether you would prefer a fixed angle or a swing-out design.
What kind of volumes are you planning to use it for?
At high speeds, air friction becomes an important factor in choosing the motor that you need. The speed of a motor in another application is not very
relevant. You should look at total power and transfer that power efficiently to your rotor at the speeds you are interested in. Most commercial modern
centrifuges I have seen use direct drive by a brushless motor, which is also used for controlled braking BTW, an added advantage, because another
thing to note is that you will want to be able to gradually accelerate and decelerate. Sudden changes can resuspend a precipitate.
Also be warned that a non-aerodynamic rotor is also going to be -extremely- noisy at high speeds.
And it has been said already, but please consider containment. Some of the motors you are looking at are quite high powered, and at these kinds of
speeds, all it takes is a very small imbalance for your device to catastrophically disassembly itself.
I have witnessed a large centrifuge running at 40,000 rpm jump from its spot and through a wall. The thing was too heavy to lift with two people. No
joke. Even small table top centrifuges typically have 5 mm thick steel shielding surrounding the rotor and an imbalance detector that will prevent it
from going above a few hundred rpm if it is not sufficiently well balanced.
Proper enclosement will also prevent people from getting caught with long hair in the spinning rotor.
[Edited on 15-9-2016 by phlogiston]
[Edited on 15-9-2016 by phlogiston]
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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