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I advise using NiMH batteries for a beginner. They are easier to charge, simpler, safer and cheaper than LiPo. They don't have the density of LiPo, but are so much safer. You don't want to end up like Chompalot, do you? Hobbyking have a good range of well priced NiMH batteries, two 7.2v packs would work nicely. The Botbitz 30A would work with featherweight motors, I think, and ranglebox sells the brushed version of it for a reasonable price, or get a FeatherTwo from Rory, though I think he's quite busy since robot wars came back.
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Thanks Runsler, I hadn't even considered going for rear wheel drive but that makes a lot of sense.
My my logic regarding cheap or expensive is right now I need to buy everything, so it's less of a strain if I try and stay low cost right now and then I can upgrade to better parts one at a time at a more steady pace, effectively spreading the cost out over several months instead of one big payout right now.
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If you want safe, go for LiFePo4 cells.
NiMH is not up the task, unless you want an absolute low power machine or have a kilo of batteries in there.
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I'm happy enough using lipos, as long as I follow the safety precautions and don't do anything stupid I should be safe enough. I have a balance charger and I'll be ordering a lipo sack with the batteries.
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I've got a small wiring question, I've decided to go for a removable link and an LED power light, so that should I get the opportunity, the robot will be legal.
I know what I'm doing for the removable link, but I need some advice for the LED. I thought I probably wouldn't be able just wire the LED straight into the 5s battery, but seeing as I had two LEDs i decided to test that hypothesis. brief flash of light, funny smell, theory confirmed. So my question is, how do i power the LED from with the 18.5v current I have? Do I need a resistor? If so what type?
Many thanks.
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Your ESCs should have a battery eliminator circuit built in. The red wire in your connectors (those three-pin cables with orange, red and brown) should be at about 5V. If you connect your LEDs to this, or one LED and a resistor, and the other side to the ground/negative rail, you should be fine. If you want, you can pop the red wire out of the connector to secure it to your LED.
As for what resistor, you just need to make sure your LEDs aren't getting more of a voltage drop across them than they're rated for. LEDs' voltage rating goes up roughly along with the energy of the wavelength they emit, so red LEDs only need around 1.8V, while blues usually need around 2.2-2.4V. So either put LEDs in series until their ratings add up to roughly 5V, or put a resistor in (330 Ohms is usually fine for supplies 9V and under) with fewer LEDs. If your LEDs seem dim, just try lowering the value of the resistor a little. But if your blue/green LEDs start to glow red, that's when you know you're giving it too much juice.
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Thanks for the reply. I think i understand but I have a couple of follow up questions. I understand that I need to cut the BEC wire on one of my ESCs so as not to fry the receiver, should this be the BEC i use for the LED? Secondly what do you mean by the ground/negative rail? and where would i find it?
If it helps at all I will be using Botbitz 30A ESCs, just waiting for Ranglebox to get some more in stock.
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Yes, ideally you need to use one of the BEC wires you've removed as the positive for your LEDs. By ground, I mean any negative wire. It might be easiest to just connect it to one of the spare ground pins on your receiver (that's the one that normally takes a brown wire). You can do this if you have a jumper wire with a female connection at one end - you can just plug it straight in.
