Ok, so far we’ve looked at the chassis, motor and speed control side of things. The next two big choices to make when building your own car are batteries & charger and radio gear.

Batteries

It’s exciting times at the moment in terms of r/c batteries. When I had my first car over ten years ago, the only choice was NiCad packs. They took ages to charge and didn’t last long. Now, though, we have better chargers, and a choice of NiMH or LiPo batteries. Which do you choose? Well, as you’ve probably guessed, they both have their pros and cons.

NiMH batteries are cheaper than LiPo, and because they’ve been around longer there is a wider choice. You can also build your own packs quite easily, to fit a specific space, for example (a stick pack for a touring car, or a two-part “saddle” pack for a rock crawler). There’s also a large range of chargers available. Drawbacks are that NiMH packs are quite heavy, and compared to LiPo can give you shorter run times (but if you’re racing that’s less of an issue as you only need about five minutes anyway).

LiPo batteries are more expensive – £70 would not be an unusual price for a pack which would be maybe £40 as NiMH. However, LiPo will probably last longer and give a more consistent power delivery, compared to a car running NiMHs which will slow down before a LiPo would (and the LiPo car would be faster). Plus, if you’re going to go brushless, you’re only going to get the full benfits with LiPo. Drawbacks, apart from the cost, are a smaller choice of batteries and chargers, and a slightly confusing terminology which is used to describe the make up of each pack. The biggest drawback to some people, though, is that LiPo batteries can explode if damaged or handled incorrectly. The same can be said of all batteries, of course, but with LiPo it’s a bit easier to mishandle them. Even discharging them too much can be dangerous, and that’s why you need to either have a LiPo-compatible ESC, or a special LiPo cutoff circuit, to warn you when they’re getting too low. This does put some people off, but if you treat them carefully and sensibly you should be fine. LiPo batteries also need special chargers – so if you’ve got an old charger it probably won’t be LiPo compatible, so you’ll have to allow for the cost of a new charger too. LiPos also benefit from being “balanced”, which is yet another thing to think about…!

So – NiMHs are cheaper and easier to handle and charge, but LiPos last longer and are more powerful (for want of a better word).

Personally, I’ve chosen to use the two NiMH packs I already have from my rock crawler, and I’ve bought an additional LiPo pack to try out. If I get the YTraxxas E-revo I’ve got my eye on, then I’ll also get LiPos for that, and with suitable connectors I can use them on my touring car as well.

Charger

If you’ve got batteries, you’re going to need to charge them. The first thing to bear in mind when thinking about a charger is that if you’re going to go racing, then you’re going to need a charger that can run off a 12v supply. This is because, when you’re in the middle of a field, a mains power supply can be hard to come by! Instead, you can use a 12v leisure battery to power your battery charger and any other electrical equipment you might want to use, such as tyre warmers or a soldering iron etc. I specifically mention a leisure battery, and not a car battery, because leisure batteries are designed to be used as power supplies – car batteries (although they look similar) are only designed to start engines. In a pinch you could probably recharge one or maybe two batteries off your car’s battery, but more than that and you probably won’t be able to start your engine.

So, you need a battery charger that can run off a 12v supply, and since you’ll also need a leisure battery (at least 75Ah) and a leisure battery charger, you don’t really have to worry about getting a charger with mains input as well – they tend to cost more, and be larger (unless you get an external power supply “brick” which turns 240v AC into 12v DC).

Ok, so now you know about leisure batteries for running your charger – what else do you need to think about? Well, the main thing is what batteries will you be charging. If you’re never going to use LiPos, then it doesn’t really matter what charger you get. However, I reckon that sooner or later, everyone will end up using LiPos as the performance benefit is too big to ignore. So, if you’re buying everything fromscratch, you might as well spend the extra and get a LiPo-capable charger right now. The Core UDC-20 is a popular choice, and it’s what I’ve gone for. It charges (and balances) LiPo as well s NiCad, and I’ve also bought the optional 12v mains power supply so I can use it at home. The only thing it doesn’t do is charge LiPos for storage, although the more I read about this, the less it seems to matter, and I’m not going to go into it because I don’t think it’s relevant.

Radio gear

So, that last major component of your car is the radio gear- transmiter and receiver. Up until a few years ago, all radio transmitters and receivers operated a couple of megahertz bands – 27Mhz and 40Mhz. You would have different sets of crystals to control which exact radio frequency you were using, but if someone else was using the same frequency – and this was often the case – then you would interfere with each other’s vehicles. This woulkd be a big problem at race meetings, as you could easily ruin a race if you accidentally switched on your transmitter and it had the same frequency as someone racing! Now, though, there is some more of this new-fangled technology, and it’s making things simpler. We now have the option of 2.4Ghz digital transmitters and receivers, which are paired (so only your receiver will listen to your transmitter) and can check to make sure they’re using a clear frequency. This way you don’t have to buy and carry multiple sets of crystals – your transmitter and receiver switch channels until they find an empty one, and anyway, only your transmitter will operate your car so there are no worries at all.

There aren’t as wide a choice of 2.4Ghz systems around as yet, but this will chage. I’ve chosen a Spektrum DX3S system, which has a few neat extras such as telemetry and a second receiver included. It’s one of the wheel-type transmitters, which might take some getting used to – my rock crawler currently has the older stick-type transmitter, but I’m sure I’ll get the hang of it.

Ok, so that’s all the major bits out of the way – next up, I’ll go over actually building the car!