Home made centrifuge build?

I was wondering about the feasibility of building a homemade centrifuge for use with microtubes, test tubes, etc.

While I have the general idea down in my head, I'm stuck as to the logistics of it (i.e. r/min considerations, g accelerations, layout of the device), so if anyone could help steer the project it would be kindly appreciated. A few questions I have to start off:

1. What RPM range does a typical centrifuge operate at (right off the motor, what is the motor RPM)?

2. How effective would using gear ratios be to modify the motor RPM input to rotor output, and what gear ratio would be a good compromise between high RPM output and overshooting on torque?

3. How easy would it be to come across and purchase a motor capable of the above? (I'm a last-year high school / first year college student, cheaper is better )

4. I have utterly no electrical wiring expertise whatsoever. Mechanics, some. Electrical, none. How easy would it be (diagrams / walkthroughs appreciated) to wire the device to a simple 3 step switch mechanism (I'll explain below) which could feed off of standard 120V wall power?

What I mean by 3 step switch mechanism is:

1 switch to power the device on
1 switch also on that main circuit to 'lock out' or safety key the device (preferably keyed, i.e. car ignition keyed)
1 switch on the lid of the device to act as a breaker or 'fail safe' device - switch is nominally down, when the lid is lifted the power to the rotor is cut for safety purposes.

Thanks, it'll be an undertaking.

 

I'm fairly familiar with the systems of locks & failsafes on a lot of the tabletop ones I've used.

I've used centrifuges in the past two years of advanced level bio and chem courses (in such realms as biotech, determination of unknown solutions, etc.), so at least procedurally I'm up to spec and at least aware of safe handling.

That is why I'm also asking about the safety keys and lid switches - even though this would be for personal use and I know how to use one safely, you never know. A lot of the higher power ones fail catastrophically if a slight error is made. I plan on fabbing a shell of wood to contain the entire assembly and then waterproofing it (in case of a liquid spill),as well as having the failsafed lid switch.

The centrifuges and microfuges I've used in my chem and biotech labs so far have had lids that are primed to a switch. If it's midcycle and you lift it, it'll short the motor. Not to say we didn't strategically do that sometimes (against procedure/lab safety).

As far as construction & safety concerns, I know how to construct the enclosure. It's the electronic, logistic & mechanism concerns that I need help on.

Put it this way; I want simpler and less complex, but as long as that does not shortcut the design. From all my lab courses, building common sense, etc. I've learned that shortcutting only leads to disaster. I want a simple, safe one, not an uber-easy, questionable one.

 

Would a starter motor for a car provide the necessary acceleration factor and torque?

What sort of motor would be adequate for the build?

 

Alright, a few questions about the motor:

- Where could I get one, and for how much?
- Under how much load to they typically run (the application would probably be 2lbs max)
- How much voltage do they use?

And please elaborate on the enclosure concept - it sounds like an interesting idea.

 

Addt'l info

That's actually an interesting idea, I'll have to see about the feasibility of it though. Worst comes to worst, I'll make an enclosure out of wood for it.

I'm also considering using a starter motor for a car. They run 3.6-4 krpm, but that's at at least 100lbs of inertial load (remember, they're designed to turn over all the moving parts of a car's engine). So they're a very high torque design. I'll look into motor and stuff as I move further with the design.

Here's my idea behind the centrifuge rotor design:

- Hot-swappable. Bore different rotors for different size tubes, unscrew & interchange.
- Particular one: 16 x 10mm wells to accommodate microtubes, 7.5cm external diameter.

 

Hmmm....maybe Physics 1 this semester'll come in handy

As far as bearings, I was planning on using a tapered thrust roller bearing cassette. From a bit of research, they handle radial loads a lot better than many ball-bearing designs, which would at least at a glance make it sound a bit better for handling vibration & slight imbalances in forces (balancing a centrifuge, so I've learned in 2 years of advanced chem & bio classes, is an art, doing so PERFECTLY is hit or miss often times).

What are engineering notebooks? My strong suit is chem, not design (sorry)

 

Oh God, the good old lab notebook. Yes, now I know perfectly what you mean.

The improvisation factor. For example, I figure I'll reuse some roller thrust bearings, because I have them laying around (less to purchase), as they're better suited to radial loads. When I was younger I used to be into the higher power hobby RC cars, and I've seen what shaking can eventually do to an unprotected motor.

I figure it's a good compromise between protection via design and then simplicity - the bearings will allow the motor to withstand slight vibrations because of small imbalances - to defeat the bearings would require more force, meaning more of an imbalance, meaning I didn't have the skill to load it right and thus shouldn't be building a centrifuge

And yes, I will have fun!