I’m attempting to create a hexapod chassis using a combination between styrofoam and metal to reach a very rigid result. However, when i worked with the styrofoam i noticed it gave away static electricity.
So I’m wondering how this may effect the electronics, that will be housed inside the body of styrofoam, maybe not directly on to it, but with a small standoff between.
For instance, how robust is the SSC-32? Over at the societyofrobots community, I’ve been told that the hobby parts we often use are made less delicate and thus more robust. Is the SSC-32 sensitive? Has anybody experienced failure of it, perhaps from something less strong than the static electricity of styrofoam. Im sure the ATmega 8 on the board will hold, as i once got a ATmega 168 shipped in a package of styrofoam. But what about the other IC:s on the board?
I do not recollect any specific ESD protection devices in the SSC-32 schematic like TVS arrays. Some of the requirements for its operation make adding r-c type protection not possible. However the SSC-32 benefits from using 5V circuits and simpler ICs so as an assembly it is not likely as delicate as say a modern video card for your PC might be. If you assemble using normal ESD control methods like grounded wrist straps and table mat it should not be “sensitive” but it is certainly not abuse proof either.
There is something else you may need to consider.
Having worked with paper handling equipment, where for example product is spooled off of a roll, it has been my experience that even if you are not discharging static electricity to a circuit you can disrupt its normal functioning with very high static electric fields. I am talking 50KV or more which is quite possible to obtain with tribo-electric effects and a well insulated or non-conductive surface. without specific mechanical solutions to bleed off accumulated charge you could find yourself thinking something is damaged electrically when in fact it is just being, for lack of a better description, over-ridden by a high level of electric charge. My recollection is the smaller PIC microcontrollers were quite susceptible to this and while they were not damaged per-se they would reach a point where they just sort of stopped working, especially in battery operated products with no real earth ground connection. Problems have been solved using corona wires and selectively carbon loaded plastics to bleed off and distribute the charge. A direct Faraday cage enclosure is also an option but is usually cost prohibitive for consumer type products.
Where this situation comes into play with your concept is even if you do not have a direct discharge situation you could have surface contact with the styrofoam by your environment that accumulates large static electric fields. If you do not provide a means to allow that charge to bleed to some common ground point then you could get eratic behavior that seemingly disappears when you pick up the robot.
I would recommend looking for styrofoam such as used in packaging of electronic equipment… not equipment wrapped in a anti-stag like most commercial stuff… but actual pink styrofoam that has anti-stat coating applied to it. You may be able to buy a can of such a coating from someone that supplies ESD control equipment to manufacturers. Failing that you may be able to glue fine wire mesh or even just an array of bare tinned wires to the inside of your styrofoam and connect it all to a common point. IF you are going to be tethered to a PC using a normal DB-9 cable the shield of that DB-9 is usually tied to chassis ground of the PC. If you are planning on being fully battery operated then you will need to be careful in how you manage the common ground point and when it can come in close enough proximity to a grounded surface that a spark may occur.
Good luck and if you have the opportunity please post some pictures of what you wind up with for a design.
Thanks, i just love fast and long and informative posts!
SN96 - No, actually not. It was the same white kind of styrofoam that you see in most consumer packaging.
Ok, so the anti-static styrofoam is always pink and non anti-static is never pink, is it? Nothing to take wrong there, right?
Btw, I read from somewhere that spraying Fabric softener on the styrofoam removes the static ability. I dunno, it feels highly unlikely to me. It maybe just prevent it temporarily…
Color is not a guaranteed indication of foam properties. I can spend a whole lot of money on a small slab of pink anti-static foam, or I can go to the hardware store and spend a couple of dollars on a 4-by-8-foot sheet of pink house insulation foam that has the same look and feel, but none of the anti-static properties. The same goes for white and blue foam sheets.
A lot of suppliers take the cheap and easy way out with shipping ICs and DIP modules, in that they stick them in regular white styrofoam that has a layer of foil glued to the top of it. The foil provides some small amount of protection, but I never trust it beyond the time that it takes to remove the chips from it and place them in real, conductive, black foam.
I’ve never heard of that one before. If you’re looking to keep static away from your electronics, the best method would probably be to avoid styrofoam in the first place. Beyond that, you may wish to protect your electronics by fully enclosing them in shielded and grounded enclosures, making sure that all faces of the boxes are electrically connected to each other and to ground potential. Of course, by the time you’ve achieved this, you’ve probably added enough weight that it would have been better to have built using something other than styrofoam in the first place.
Sorry for the pink color mis-direction. Color does not define the anti-static properties. Frequently the foam used to package circuit card assemblies that is anti-static coated is also tinted pink to make it easier to differentiate from standard foam. The same applies to plastic anti-static coated bags, pink is typically anti-static but I know we can get clear anti-static bags now too. I have no idea if this is a standard somewhere or not, it is just a convention we have used where I work for many years, but I have seen products packaged elsewhere using the same convention so… just be careful that what you choose is actually labeled anti-static and don’t rely so much on the specific color.
Fabric softener is frequently some kind of ionic thing that does usually help with static. I say usually because there are many many different products out there and I am generalizing based on my experience alone. The biggest problems are knowing how much to apply, what it’s dry characteristics will be, and how long does it last before it evaporates enough that it isn’t useful any more.
There are conductive coatings typically used for EMI control that could be spray applied. This is literally a paint with carbon or metal in it that forms a conductive layer as the solvent evaporates. I have no idea where to buy this in quantities for a hobbyist level, and usually they are quite expensive per gallon (or liter, whatever.) Also many of them have a real high VOC (typically the solvent) so they are not especially environmentally friendly unless applied with special care and tools, and they might also eat the foam. Heh. Still you may be able to research this and find a semi-local vendor that can apply it to your styrofoam if you want/need a professional solution for some reason.
PS: Isolex WB-120 is an example of a low VOC conductive coating. As to whether it eats foam or is available to you… you are on your own.
I used to use this to protect industrial drive boards after repair, back in the day… It puts a thin layer of plastic on the board. You have to mask off all terminals and connectors. I don’t remember names or sources though.
I’ll mount the SSC-32 on the plastic layer on the top of the disc (Ugh, perhaps hard to see, apologizing for my poor camera). I will cut a hole for the wires to go through (from underneath the disc).
So, any suggestions on how i could work it through with just anti-static bags? How is servo wires and servos affected by the static electricity?
Fredrik, I think we are probably over-worrying here. I was envisioning something much bigger with a LOT more styrofoam. If you are really worried you could glue some heavy duty aluminum foil sheet, like the kind you use to cook with, to the top of the styrofoam and be done with it. I really doubt you are going to get any significant charge build up on what you have shown in the picture, especially if the bottom hex part is already metal. Many of the Lynx hexapods are plastic based chassis and I don’t think people have lots of static issues with them.
Sorry about the color confusion. At my current job, and other jobs I had in the electronics industry, pink is the most common color for anti-static. True the color can’t garuntee the electrical properties. There were also black rubbery/plastic bags than came from venders that Compaq used which were cool.
At my current job we use static-shielding bags that go inside anti-static bags which are bubble bags for component protection. Anti-static material will not protect circuits boards from high static charges from penetrating, which is why static shelding is used in combination with anti-static materials.
Anti-static only means it will not generate static charges (or very little) when moved around on a surface or against other objects. Static shielding acks like a protective shield which is why in many cases both types are used.
Although there will be a lot more styrofoam. I’ll redirect you to my other thread so you can see the CAD scetch and how I’ll build everything enclosed in the styrofoam…
What is it that charges the styrofoam by the way? Is it when the styrofoam is rubbed against another material? It will probably not, as It’s screwed pretty hard together and therefore very rigid.
A favourite tip of Practical Wireless (UK electronics magazine popular in the 70s/80s) was to varnish the whole board. You can buy a small tin of clear varnish and brush on two or three light coats leaving a few hours between each coat. Larger hardware stores will also carry spray-on clear varnish or clearcoat in clacky cans. I’ve used this method hundreds of times for high voltage traces or waterproofing whole boards.
Oh, I seem to have gotten this completely wrong then. So, instead of anti-static bag, I meant a static shielding bag. Would that work? Once again, how is wires and servos affected by the static electricity? For instance, if I put the boards in static shielding bags with small holes for wires and mounting screws, would that work?
