I have a question about electroadhesion. SRI International recently came with a way to utilize this with wall climbing robots with the help of some kind of microgrippers.
From the information on the SRIs page I can read that the microgripper "clamps using induced electrostatic charges from on-board battery power".
The question I wanted to ask is, how can you convert the direct current from a battery to static electricity?
Pointers to a book or website that explains this would also be appreciated.
The page (BTW next time give a URL so I d "...electroadhesion is an electrically controllable adhesion technology. It involves inducing electrostatic charges on a wall substrate using a power supply connected to compliant pads situated on the moving robot."
The "compliant pads" are presumably non-conductive, hence the electrodes within set up an electric field which reaches out through the pads and induce opposite charges on whatever surface the pads contact. The attractive force between the charges on the electrodes and the induced charges on the surface allow the robot to walk up walls. The simple fact that the pads are non-conductive means no DC can flow; the field can be redirected by switching the wiring upstream of the pads allowing the attractive force to dissipate as the induced charges relax back to their neutral equilibrium positions, allowing the robot to lift that foot away from the wall.
You are apparently assuming that "static electricity" automatically means the carpet-shuffling type of sparky stuff, but that's not the case. Here it means charges that don't go anywhere but whose fields do work by inducing charges elsewhere.
Frinst pick up any charged battery; an electrostatic field exists between its terminals with a volts/meter value determined, oddly enough, by the voltage to which it is charged divided by the distance between its terminals.
By the way a question about what you wrote above. Is this static electricity (used by SRI's robot) still the same kind of static electricity as what is present in the "carpet-shuffling type of sparky stuff"? Or is this a different feature of electromagnetism?
You can't, at least not directly. The electrons generated by a batter must flow in a loop to complete the circuit which ultimately is a chemical reaction. The chemical reaction requires, for it to be "perpetuating" that what whatever gives up electrons are recieved by the other side to complete the chemical reaction.
You can build a van de graaff generator that is run off a battery and get static electricity that way.
Electrons in copper are not free because they are governed by the EMF generated by the chemical reaction. (you can't just peel off an electron and use it for what you want because then your chemical reactions would not react)
They're the same, or at least indistinguishable to any instruments we've yet invented. ;-)
They're both essentially electrons (or, probably more correctly, charge(s)) that's('re) just sitting there. You can generate a high DC voltage and draw the same spark as shuffling across the carpet.
If the humidity ever gets low enough that you have "dry, fly-away" hair, you can take a kid's toy balloon, rub it on your head, and it will stick. ;-)
Same basic machinery, slightly different way of using it.
The facts that charges exist in complementary pairs in atoms as positively charged nuclei and negatively charged electrons, and that electrons are fairly easy to remove from atoms, is what makes it so easy for us to manipulate electromagnetic forces. To generate fairly large-value electrostatic fields all we have to do is peel some electrons away from some atoms and hold them at some distance.
The carpet-shuffling trick involves mechanically rubbing the electrons off, while batteries use chemistry to separate charges. In both cases, when the charges go back where they came from, that's called "current" and when it goes through air we generally call it a 'spark'. Chemical battery voltages run from large fractions of a volt up to several, maybe a dozen volts while carpet-shuffling can generate thousands of volts with amazing ease. An extension of the concept, the Van de Graaf generator, gets up into the millions of volts.
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Anyway, the robot's feet basically work because the field extending out from them reach into the atoms of whatever surface is nearby and stretch the bonds between the nuclei and the electrons of those atoms. This causes patches of charge opposite to that on the feet to appear on the surface (that's basically 'electrostatic induction') and as you no doubt know, opposite charges attract so the feet are attracted to the surface. Then the voltages connected to the feet are switched off and the induced charges in the external surface relax back to neutrality, so the attractive force disappears.
The only real difference between robofeet and the sparky carpet stuff is that no charges need actually be peeled off any atoms to make the robofeet work; it's all in the fields.
ive come in on the end of this thread as i havnt looked here for a while so i havnt seen the OP, but I thought I'd add my 2pence worth..
basically static electricity is just ordinary electricity that doesnt move as someone already said, however this isnt particularly helpfull. also getting it from a battery implies moving so its not static but this isnt realy helpfull either lol.
usualy static electricity is noticable when it is quite high voltage, and is on the surface of an insulator, particularly such as a old crt screen, or balloon, hence it is quite dificult to actually move it as such, wich is why its tended to be called static in this case.
if the surface has a metal coating or is just a conductive body insulated form earth, then it becoes a plain old capacitor and just plain old (moveable) electricity but the atrarctive effect is little diferent.
humans carrying an electric charge is often refered to as static electricity, but its not realy static, we usualy pick it up from insulators wich have a static charge though.
so wether it static or not is probably a insignificant distinction to you, I expect what you probably need is just plain old ordinary high voltage, but just very low current, this can be got from a battery by a flyback type step up converter.
it sounds like you need quite high voltage, 25kv is doable from a small batery and if you have an old tv you can see how much that much it atracts baloons, and especially dust etc to the front of the screen lol.
not to mention you need a surface with a conductive coating or else theres little way to get the electricity there, ofc like in a tv the conductive surface can be on the back side and this causes a static charge to build up on the front side.
wether 25kv is enough I have no idea, I gues 250kv becomes quite hard from a small battery as losses+leakage mean you need a bit of power, not to mention it requires a good thickness of insulation and the air gap needed is quite large too! once you get to 1Mv it becomes a bit silly.
I dont know if I'm correct in assuming that if you have a high K insulator you might get more atractive force.
theres some realy interesting pages on the internet about whats the highest voltage acehivable in air, and why its hard to go much above many megavolts.
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