is it a solid or a fluid?
 

i remember a while ago watching this thing on tv that was showing new shocks in a car, i dont remember what kinda car, but the stuff in the shocks was a substance that either reacted to electrical current or magnetic fields, i am unsure about which one it was, but when it reacted it would harden up

i was reading a post buy FIRST_jersey kid in the educational robotics about a brake system then they were going to try next year, and if you wanted to make brakes with that stuff would it be legal in terms of FIRST's rules and regs?

for the system you could maybe do multiple pieces in a cylinder that were cut out of some thickness of metal that would be low drag and have that cylinder full of that substance so that when you apply either current or a magnet field(i dont remember what one) it would harden up and not beable to rotate

Re: is it a solid or a fluid?
 

or you could even maybe do use it for a transmission so that you have certain parts in a cylinder but then when you harden it up the whole cylinder would ratate inside a bearing it is in

like a planetry transmission with no clamps or movement, it would in theory be a good shift-on-the-fly transmission

Re: is it a solid or a fluid?
 

I saw the exact same show you are thinking of. The stuff is called ferrofluid (google it). It is basically fluid with lots of very very fine iron filings/dust in it (at least that's my understanding of it). Not sure if it would be allowed in FRC. Cool stuff though.

Re: is it a solid or a fluid?
 

The technical term is actually a magnetorheological fluid (MRF). Ferrofluids just attracted to magnetic fields, they don't change viscosity or anything. I'm unsure about using it as a brake, however. While it solidifies under a magnetic field, that's only while the pressure applied to it doesn't break the chains of nanoparticles that are solidifying it. Think of it as really quick setting jello as opposed to ice. So as a brake, it'd be somewhat less that useful. Viscous braking isn't typically useful anyways, as viscous resistance is dependent on velocity, so you wouldn't have much luck sitting in place not moving.

Re: is it a solid or a fluid?
 

There has been some experimentation using these multistate fluids in CVT transmissions. By varying the excitation you get variable coupling with very little loss. This is an outgrowth of the study of snail locomotion. Snails produce a mucous that is fluid but turns solid enough to push against under pressure. Works OK for the snail but they spend a lot of time producing the mucous.

Re: is it a solid or a fluid?
 

Wow!!! No there's a thought. "Mucus drive".
I think any competition using this would get very boring very fast. Not only slow, but messy!

Re: is it a solid or a fluid?
 

I've been intending to play with MR fluids for several years. As soon as I find the time.

A good source of information is the Lord Corporation MR Fluid Home . There are several technical papers there and a list of outside references.

There is a recipe for a DIY MR Fluid using readily available materials. The commercial products are a bit pricey for playing around.

Greg

Re: is it a solid or a fluid?
 

The C5 corvette had an option for variable damping shock absorbers that used a magnetorheological fluid. I'm not sure if this option is still available on the C6.

-Kevin

Re: is it a solid or a fluid?
 

It's not a magnetorheological fluid, but a mixture of cornstarch and water in the proper ratio has the neat property that it will flow like a fluid if poured from a container, but act like a solid if impacted or moved quickly. This is an example of a class of materials called non-Newtonian fluids. Here's a google link where more information can be found.

-Kevin

Re: is it a solid or a fluid?
 

Is the link not working? It should take you to a page titled "Dr. Dave's Do-It-Yourself Magnetorheological Fluid". It uses iron filings, low viscosity oil, and lithium grease.

I haven't tried the recipe (that time thing), but the page says it will work for demo purposes.

Greg

Re: is it a solid or a fluid?
 

That stuff is so cool, and so easy to make.. it's just a matter of getting the proportions correct. The cool thing to do is to make some in a small bowl and let your finger/hand just slowly sink in it. Then when you go to pull it out quick, you can't.. You have to work it out slowly again.

Fun stuff to mess with in a kitchen laboratory.

Re: is it a solid or a fluid?
 

Interesting it sounds like this liquid reacts kind of like piezoelectric polymers (despite a completely different composition). I wonder whether its being put to applications besides shocks?