Just wondered which types of junctions people use to take a single power line in and split it for say two tz85's etc.
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Just wondered which types of junctions people use to take a single power line in and split it for say two tz85's etc.
I tend to use 2 wires coming off each side of a connection, simple but effective and hasn't let me down yet
Sorry to sound dim but how do you do that? Solder them together?
Yeah I just solder 2 wires in, twisted together and tinned up first then its all fine :)
I use a Y harnas. Simple enough.
Can you buy y harnesses pre made?
yes,
Example.
http://www.hobbyking.com/hobbyking/s...in_Series.html
Handy if you want to connect two packs in series, but just to make you aware Dave, that one won't be any use for powering two ESCs from a single power connection. The easiest way to do it would be as mentioned and just solder two wires to the one tab on the connector, or if there's not much room, solder one wire on and then splice a second wire onto it just slightly further up. I did this on Drumroll this year to massively simplify the wiring loom. There is a picture of it somewhere that I'll try and find (if I can on this phone)
Actually it was last year I changed it all, but here it is anyway. The link and battery connector are on the left, fuse at the top, three Deans connectors (two for the TZ85s spliced together, one for the weapon ESC) on the right and a mini Deans at the bottom for the LED. That's literally all there is to it.
Attachment 5624
That's really simple, I knew I was making it more complicated than it needed to be :)
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?Quote:
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.Quote:
Originally Posted by Coolspeedbot
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 :p -
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. :) But I would be concerned if it was more like 4.2V and 4.0V.
I've used 2 cell lipos without a balancing charger (but with a lipo-specific non-balance charger, I'm not plugging it into the wall or using a funnel to feed electrons in) for years and years in antweights and never had any issues with them, but the advice holds for anything where batteries cost more than £5 to replace.
I can reccommend the Accucell-6, the manual is a little impenetrable (such is China) but it does a very good job very nicely for me. And it's black and yellow, what more could one want? :)
ohhhhhh I see.
Of course lipo's have sacks in, they make them from the same hessian santa uses for his sacks haha :D
Found these handy videos on the wiring of a combat robot, including a video on making a removable link.
https://www.youtube.com/watch?v=8kxCR5i9f7c
https://www.youtube.com/watch?v=IktcgbzK2Ow
https://www.youtube.com/watch?v=bVjqrTv1KRI
https://www.youtube.com/watch?v=vLIN9FpaE9M
just to get a general idea, when you guys are attending events that run over multiple days, do you guys put your lipos into 'storage' charge after each day? or do you leave some, fully charged, over night?
and besides lipo sacks, do you guys used anything else to store your lipos when they're not in use? because I'm thinking of getting a box to put them in.
in my case I was thinking of storage charge all my spare batteries, and leave one fully charge over night for use in the first fight the following morning (If my bot hasn't been trashed or knocked out).
Storage charge is only required when you're not going to be using them for a long time, a number of weeks for example. At an event this isn't necessary, so just charge them all up the night before, ready for the next day. They need to be in the lipo sack when charging but if leaving them overnight once they're charged, it's fine to store them somewhere such as a box, so long as they're safe. Many choose to leave them in the lipo sacks as a precautionary measure though.
Oh ok, now I just need to worry about some 2mm metal sheets to surround the battery when it's in the bot, then my research and planning phase will be (sort of) finished and I can start the build phase.
If you want a ready made box that will happily store them, look at buying an old ammo storage box like one of these
http://www.ebay.co.uk/itm/Army-Ammo-...UAAOSw4HVWEWTY
Plenty more sources available on ebay and they are perfect for keeping them contained should the worst happen.
oh that's good, thanks GaryQuote:
Originally Posted by typhoon_driver
Just going back to the discussion on fuses, I found fuses for this battery:
http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html
But I was thinking of using this LiPo instead:
http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html
but doing the maths for the rated amp of the battery and its burst discharge, but the only fuses I can find are 100amps and 150amps, seeing as the rules say the fuse has to be rated under the max burst discharge will the 100amp fuse handle the 5cell Lipo?
If you had put the 100A fuse on the first lipo it would have done nothing. The rated current of the lipo in burst is 64A so the fuse would not have melted or protected anything while your lipo struggles.
On the second battery your fuse actually serves a purpose. It is rated up to the nominal discharge and well below the burst (100A and 150A) so if the battery gets that much current draw the fuse will start to do its job.
I see. ThanksQuote:
Originally Posted by leorcc
as for the smaller LiPo, yeah I knew that 100amp fuse would be no good, I had found a 50amp fuse for that but I wasn't sure if the bigger LiPo was too much for the 100amp fuse.
I have a 100A Automotive fuse on my FW's spinner weapon. The ESC is actually rated to 160A and the motor is 120A Burst, 85A Cont. You can put spike currents of roughly double a fuses rated amperage though it, in the same way that LiPo's have C ratings for continuous and burst.
On start up the motor has drawn 200A through a 100A fuse and 160A ESC, but because its only for 1 second its fine.
Rating your Fuse for the expected continuous rating for a system +20% is a rule of thumb I have been using since I started and I have never had one blow (I have no idea if that is a good thing or not but heck, I have been able to keep fighting). This will cover both regular combat currents, spikes from collsions/shoving matches, and major spikes in spinner weapons when they make contact.
Oh ok, I'm only building a ram/wedge bot for my first feather weight so I should be fine thenQuote:
Originally Posted by Eventorizon