Quick question about electronic matters; Mercury

37637598 on 28/9/2007 at 19:07

I am designing a gravity sensor based on the logic of a human's balancing system. I have come to a pause as the liquid I would like to use is mercury.

Is mercury conductive with little resistance? (Close to that of a solid conductor such as copper...)
Is mercury close to the weight of water?
Will mercury have any shift in behavior when applied heat or cold, in such a way that it would alter the way gravity affects it? (Such as making it lighter or heavier...)
Does mercury react to magnets in a similar way as metal?

What I have created is a hollow sphere with 24 contacts lining the walls of the inside of the sphere. I need something to be inside of the sphere that will close the circuits of the contacts. Essentially when the contacts are touched together by either mercury, metal shavings, or whatever my best option is, signals will be sent to a computer telling it precisely at what angle compared to the earth (up/down/left/right) the sphere is at. The idea is to re-create a balancing system similar to the human body that can be used to determine which way is up. Also it will allow for an easy route for creating a memory system that can be used in self-propelled robots. I'm sure it's probably been created before me, but I still want to try it because I came up with it and think it can work well in time.

Thanks in advance!

TBE on 28/9/2007 at 19:27

(http://www.societyofrobots.com/sensors_mercury_switch.shtml) Robotic use of Mercury switches.
(http://en.wikipedia.org/wiki/Mercury_(element)) Mercury (the element) on Wikipedia.
Yes, Mercury does conduct electricity, and as it rolls around a tube or globe, the electrical contacts would let electricity flow when certain contacts are in circuit.
There is a high resistance to electrical flow in mercury. There is also low conductivity as compared to other metals. But other metals aren't liquid at room temperature either, you know? Mercury would be ideal for a hollow globe with sensors around it to show gravity and the leaning of a robot/whatever device in its relation to being horizontal.
(http://hyperphysics.phy-astr.gsu.edu/hbase/tables/elecon.html) Here is a chart that shows electrical resistance and conductivity. Notice copper (CU) and Gold (AU) have much better properties in conducting electricity. Mercury (HG) isn't ideal for electricity, but it does work.

SomeGuyNamedAl on 28/9/2007 at 19:55

While this would accomplish what you are aiming for, have you thought about using similar to a solid-state gyro? They're much easier to work with, cheaper, and unlikely to be extremely poisonous. It would be able to tell your angular position in 3 axis. You can add an accelerometer to this which would help have a similar effect, and would be sensitive to lateral movement.

You can find a variety of these systems on (http://www.sparkfun.com/commerce/categories.php?cPath=23_85) Sparkfun

CyberFish on 28/9/2007 at 21:25

Ok, to answer your questions and to add a few more points of which you may be unaware:

Is mercury conductive with little resistance? (Close to that of a solid conductor such as copper...) As stated above, mercury has a relatively high resistivity compared to copper and gold. However, it does conduct electricity much better than most other room-temperature liquids.
Is mercury close to the weight of water? Good lord no. Mercury is VASTLY denser than water. You can float rocks on it.
Will mercury have any shift in behavior when applied heat or cold, in such a way that it would alter the way gravity affects it? (Such as making it lighter or heavier...) Temperature can affect density, but not mass. Cooling mercury down will make it fractionally denser, heating it up will make it slightly less dense. It boils at about 350 C and freezes solid at about -40, but you're unlikely to ever reach those temperatures.
Does mercury react to magnets in a similar way as metal? Mercury isn't ferromagnetic and won't be attracted to magnets.

Three crucial points that you REALLY need to know about:
1) Mercury is very, very toxic.
2) Use of it is probably legally restricted wherever you are.
3) Mercury will dissolve or corrode some metals. In particular, it eats through aluminium very rapidly.

theBlackman on 28/9/2007 at 22:26

It also dissolves GOLD, which is what most high quality contacts are made of or coated with.

It seems that GYRO control might be a better way to go.

Turtle on 28/9/2007 at 23:32

It's good to drink.

Trust me.

37637598 on 28/9/2007 at 23:44

Quote Posted by Taffer_Boy_Elvis

What he said

Thank you very much for the information, it will come to good use! :D Resistance is a big issue for me as the finished product will run off of battery power. I need the contact conductivity to be as clean as possible so I'm not wasting energy or creating any un needed heat. This helps me a TON, Thanks!

Quote Posted by SomeGuyNamedAl

What he said

A Gyro is a perfect idea for the application, I've never even heard of these things though they look very handy! When I am ready to make the finished product, I will most definitely look further into these. Right now I'm experimenting with everything to try and figure out my best possible options. Thank you VERY much! :)

Quote Posted by CyberFish

What fish said

This is very good information, thank you for answering my questions. As I realize temperature will not alter the mass within the glob of mercury, I thought someone told me once that heat makes mercury turn into a gas which will build up pressure, or simply begin to dissipate. The fact that it is very toxic does make me weary to use it, but I've found no better replacement. It seems downright idiotic to use though now that I know about the gyro things... The fact that it can dissolve other materials, enough said.

I forgot about Wikipedia and HowStuffWorks, I suppose I could've looked there first, though I really do appreciate all of your help. For those of you wondering, my winter project is to build a robotic copter that will travel long distances and remember its course. If I can get it functioning correctly, I plan to turn it into a shopping robot so when I need something for my work, I can press a button and the robot will use its memory and sensors to fly itself to a store and from that point I can control it with a remote control and video camera, and 2-way communication. It may seem to most out of my league, but believe me. It's just my next step.

I've already created the door opener for doors that are not automatic. Power is my main issue at the moment but I hope to create a miniature alternator and cap pack that will store energy from solar panels on the bot, and generated energy from the alternator. I also plan to experiment with static cells and perhaps create a static generator/ alternator. It's all pen and paper right now and I'm still in the early stages but I think I'll be able to finish it within a little over a year, If I don't drop it within the first week... Feel free to discuss it, or ask questions.

I'm sure I'll be posting more soon. I've designed a wheel system that will allow the robot to drive on land up stairs and still maintain balance (when I get the gyro devices figured out...)

Thanks again for all of your help!

dvrabel on 28/9/2007 at 23:57

12345678's lack of knowledge on even the most basic physics makes me cry, but then I laugh at the idea of him even remotely getting close to implementing any of his ideas.

37637598 on 29/9/2007 at 00:05

Quote Posted by dvrabel

12345678's lack of knowledge on even the most basic physics makes me cry, but then I laugh at the idea of him even remotely getting close to implementing any of his ideas.

I'd like for you to quote my lack of knowledge on even the most basic physics. I'm no expert, but i've learned enough to do what I do. I've built remote control planes and a helo in the past so I know enough to get by in this project (I hope). But if not, I can always use all of you!:D

Peanuckle on 1/10/2007 at 00:51

What surprises me is that your apparently capable of building a sensor to model the balancing system of the human being, but you don't know the basic properties of a widely used element. Didn't your chemistry teacher hand out those little periodic tables that folded out with all the informations?