In terms of splicing, a good soldering iron makes life a lot easier. I used to have one that I got from an 'electrician's starter kit' out of Argos (aka a pile of rubbish) and could never get a good joint. I later got a good quality Antex one and it made all the difference, along with a few extra years of practice/experience.
Off to Maplin now to buy a decent one lol
whats the fuse for exactly?Originally Posted by RogueTwoRobots
and do all robots need them?
Not intending to sound harsh, but if you need to ask that question then really you should be looking up both basic electronics and the FRA rules.
Fuses are basic electronic safety devices, to put it in simple terms if you get a runaway of power demand then the fuse breaks the circuit by failing in a fail-safe way below the level where other more critical components would do the same. Fuses hence protect your house, and i believe by law are built into the plug of every standard UK appliance - so should they ever have a short, electrocute someone ect - instead of blowing up they just burn the fuse instead.
Similarly the question of "do all robots need them" is answered in the FRA rules. Read them, because otherwise there may be some other safety information youve missed.
A fuse is an electrical item, rather than an electronic device, but that's just me splitting hairs.
When you run components in your robot (such as motors), they draw an electrical current from your power source; in this case, your batteries. Most of that energy is converted into motion (your motors turning) but some of it is converted to heat. If there is more resistance in your components (say you're driving the robot into a brick wall so the motors are pushing against a solid object), they draw more current from the batteries which, in turn, also generates more heat. Every electrical component, so speed controllers, wires etc, will have a current rating, given in Amps. This is how much current the component can comfortably handle; if you greatly exceed this rating by drawing more current, you will likely destroy the component as it is unable to get rid of the excess heat from the higher current, hence the smoke/fire you get from a speed controller if you exceed its operating spec.
Fuses are designed to protect against this happening to components. They're basically a piece of wire or strip of metal that is designed to melt/break, caused by the heat, when a certain amount of current is drawn through them. They're usually designed to be fast-acting so that they blow quickly before the current has a chance to cause damage to your electronics. It's much cheaper to replace a 10p fuse than a £100 speed controller.
Fuses are recommended on all robots but are only mandatory on robots that run li-po batteries in the featherweight class or higher, though I believe it may be making its way down to the beetleweights.
oh I see, now it makes sense the fuse acts as a fail safe in a way.
part of my confusion and the reason why I asked about the rules relating to them was that Jamie's example of a circuit was the first I had seen that uses a fuse.
and yeah fair point Gareth the FRA rules are there for a reason but my dyslexia often makes me miss stuff, I also find it easier to understand stuff through the wording of other robot builders.
seeing as we're talking about electronics, could someone explain what makes a charger, a balanced charger for lipo batteries?
is it as simple as, one that has the same charging port as the lipos?
I was thinking of using one these:
http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html
I only asked as I can't seem to find anything thats clear on balance chargers in the forums.
A balance charger will have a port for the white block you see with (in this case) 5 wires coming out of it. Generally any charger described as being for lipos should have a port for that somewhere (though may require an adaptor).
Btw only reason im abit hands off with regards to safety in text is because you need to understand it rather than be told. If i know you or was there in person itd be a different matter, however as an extreme example if i told you how to fire a gun but forgot to tell you not to aim it at people then thats kinda on me for not giving a full instruction.
Fuses
A fuse just melts when the running gear of the robot pull too much current for whatever reason. Lipo batteries and speed controllers have a knack of catching fire quick when they get past the rated amps. So, if you stick a fuse in rated at the max amps everything should be running at, it will pop before
a/ the robot catches fire and burns everyone alive
and
b/ ruins all your expensive robot clobber.
You will notice a lot of robots using the fuse AS the removable link. This is because fuses need a circuit connection and to be easily removable from a fuse holder for changing, thus making them by proxy the ideal removable link.
Lipo Chargers
Lipo batteries use a chemical compound that can only produce 3.7 (ish) Volts. To make a 12V battery or whatever, you need multiple sacks in your battery full of the compound. They then get wired together to produce voltages in multiples of 3.7V. A 2S batterry is a "two-sack" in Dave speak, so means 2 x 3.7V = erm...7.4V. When discharging, the sacks will give off energy altogether, but to be charged each sack needs to balanced. This is where you have a Lipo Charger with a power plug and a balance plug. The balance plug is an extra connection from the charger to each individual "sack" in the battery so that they all charge evenly in the same rate. Otherwise, they get hot, blow up, and again, burn everyone alive.
For any more Dave explanations, just ask
Sorry to correctly you David but some of that is wrong-
Each Cell of a LiPo (not Sack), has a nominal voltage of 3.7V (This is the voltage that anything plugged into the LiPo will see when its under load). When fully charged a LiPo has a voltage of ~4.2V per Cell. You never really want a cells voltage to drop under that 3.7V nominal, but its not the end of the world if it does go to say 3.5V or even 3.4V, anything lower and you can start to cause damage. Some ESC's have built in cut offs that you can adjust to your liking, the default is usually 3.2V per cell.
LiPo's must be balanced when you have more than 1 Cell wired together, in series or parallel (Which in the case of fighting robots is 99% of the time unless you are talking about Antweights). Cells at different voltages have different internal resistances and are also trying to move electrons at different speeds, which will cause damage, produce heat, and potentially cause fires.
The balancing process is done automatically by a Balancing Charger, such as the Turnigy Accucel 6. It charges the LiPo but measure all the cell voltages at the same time and can charge/discharge 1 cell individually if it falls behind/goes over the others.
You need not worry if you measure a Pack and find that the highest cell might be 4.21V when charged and the lowest 4.18V. 0.03V won't cause an issue.
Posting Permissions
Reply With Quote
Bookmarks