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AndrewM

Tue Feb 21 2006, 11:13PM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

I couldn't resist the opportunity to brag/share. I've just crated and shipped my 160 pounds of ferrofluid zero gravity test rig, and will be flying to JSC in ONE WEEK! to fly with it on NASA's Vomit Comet. (They insist on calling it the "Weightless Wonder" now, but I refuse).

If you don't know, the Vomit Comet is a research aircraft that can simulate zero, or reduce gravity with parabolic flights. Basically you get 30 seconds of zero gravity followed by 30 seconds of 2g's.

So, heres my experiment. Its exploring the consituent relationships of various nondimensional coefficients (Bond numbers) on a rotating ferrofluid droplet. In short, I spin a droplet of ferrofluid on a platform inside some Helmholtz coils until it breaks. The breakup speed, along with field strength, and contact geometry (how does it sit on the platform, wetting, non wetting, contact angle, etc) are used to compare the contributions of the magnetic, gravitational, and rotational bond numbers on the droplet stability.

I achieve this with a syringe pump, metering a precise amount of ferrofluid onto the platform at the start of each parabola. The fluid is introduced into a fluid tight containment area, and though a special seal that allows the platform to rotate while preventing leaks. The disk is then spun by a 3500 RPM brushless motor.

I'm also going to run a secondary experiment, which is simply a pool of ferrofluid spiking up over a magnet. Theres a camera trained on it to watch how the spikes react to 0 and 2g's.

I should add that I led a team of 4 students to this end. Personally, I machined the helmholtz coils, and made all of the electrical components. The helmholtz coils are driven linearly, with a beefy 60W potentiometer. The motor is driven by an off-the-shelf brushless motor controller, which is in turn controlled by a 16F84A which I use to set adjustable ramp rates, and automatic ramp start/stop modes 30 seconds long. The data logging is accomplished with a digital video camera aimed through the coils at the droplet. In view of the camera is a 4 segment LED display, which displays the motor speed by reading a signal directly from the motor's hall effect sensor output. This is processed by a 16F628A and displayed.

Pics:

HV Enthusiast

Wed Feb 22 2006, 12:11AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Very cool. Nice work. Keep us posted to the results.

Carbon_Rod

Wed Feb 22 2006, 12:37AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Thats pretty cool, =o)

btw: Just curious:
1.) Do you look at the electrostatic droplet suspension experiment data to make sure to account for these type of variables in combination with a magnetic field?

2.) Do you monitor rotational velocity changes due to usually negligible internal friction (do you do a dry control run at top speed?)

Cheers,

AndrewM

Wed Feb 22 2006, 01:51AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

Carbon_Rod wrote ...

Thats pretty cool, =o)

btw: Just curious:
1.) Do you look at the electrostatic droplet suspension experiment data to make sure to account for these type of variables in combination with a magnetic field?

No. I believe any errors present will be largely due to magnetic field nonuniformities, or transients. We've taken great pains to exclude ferrous metals and rotating metals from near the test region. Despite our trouble, the motor is still only about 8" away. Most troubling, perhaps, is after testing I've noticed that our ferrous fasteners 12" or more away now hold onto paper clips readily.....

wrote ...
2.) Do you monitor rotational velocity changes due to usually negligible internal friction (do you do a dry control run at top speed?)

I'm not sure what you mean by this. The rotation of the motor is measured from hall effect sensors that trigger when the rotor passes by; not by the drive signal. Thus the frequency displayed is a true shaft rotation.

Hazmatt_(The Underdog)

Wed Feb 22 2006, 02:04AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

You might be able to swap out the steel for stainless hardware. Even Home Depot has some stainless, the troble is that its all randomized in the dwars and you don't know how much they have in stock.

craigsarea

Wed Feb 22 2006, 11:29AM

Registered Member #130 Joined: Fri Feb 10 2006, 08:12PM
Location:
Posts: 15

That's an exciting project to be working on. What sort of background do you have to be working on that type of project? Is it part of a physics degree or something?

AndrewM

Wed Feb 22 2006, 01:49PM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

hit the nail on the head; I'm about 2 months from finishing physics and aeronautical engineering degrees.

AndrewM

Tue Mar 07 2006, 03:02AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

HAHAHA! Tomorrow is the day!!! 42 parabolas of zero gravity!

I posted some pictures of the trip to the neutral bouyancy lab (giant pool) and the hangar and plane that we're flying on here:

You might save yourself some time and just watch the video I put here of me loading the experiment on the vomit comet:

i look angry, probably annoyed at that girl next to me

[Edit: Fixed double post. To add a picture you post it on the Attachments forum and include it in the post with a suitable [img] tag.]

Desmogod

Tue Mar 07 2006, 03:34AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

wrote ...
i look angry, probably annoyed at that girl next to me

Rejection stings hey....

That's an interesting project, and the chance to go on the Vomit Comet is awesome.
I think every Geek has fantasised about a trip on it at least once.

Carbon_Rod

Tue Mar 07 2006, 04:09AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Don't forget to mention and thank everyone if you publish or are involved in some public affairs. It costs you nothing, but failure to do so may create some political friction with all sorts of people.

Even the useless individuals tend to carry a grudge. Often ending up as management later one may even meet them (or their wife) on the board of directors one day -- shiver.

â€œYou do the work â€“ Or get the credit!â€ (?)

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