1/3 scale RC Go-Kart

By all measures this project has surely got to be the definition of ambition. The project is to build, from scratch, an RC third scale go-kart on a shoestring budget. I've already spent about three years on it.

Now I realise that, for “RC people”, 1/3 scale may sound very big but you have to remember that a real kart is quite small anyway so it’s about the size of an eighth or tenth scale car, quite manageable.

Why did I decide to build an RC go-kart? Well I love RC, and I like building things and I used to race ‘real’ karts. So I thought why don’t I combine the three and build a remote control go-kart?

You might be thinking why didn't you just buy an RC go-kart? Well there’s no shortage of RC karts on the market, some of them quite cheaply too, take the Turnigy kart: http://www.hobbyking.com/hobbyking/store/__15284__TURNIGY_1_4_Scale_Brushless_GoKart_ARR_.html or for a slightly more expensive option, how about the Kyosho BIREL R31-SE? http://www.kyosho.com/eng/products/rc/detail.html?product_id=104501 And of course there are several others. Now these are all very well but none of them are really true to scale. In terms of their structure, they have mock frames which are there only for aesthetics, and then they have sub-chassis which are load bearing. They also have features that are very different to a real go-kart like the fuel tank in the wrong place, the break disc on the wrong side and in the Turnigy’s case being electric powered. These are things which, in my mind, shake their very identity as go-karts.  They are also not true to scale in a rather more literal sense, let me explain. The Turnigy claims to be 1/4 scale but the Kyosho, which is exactly the same size to within a few millimetres, claims to be 1/5 scale. But in fact they’re both wrong, and I know because I've checked this, they are both about 1/4.5. So how could I be expected to buy something that doesn’t even know what size it is? Another reason I went with the DIY option is that I had a TRAXXAS T-MAXX and I was getting a little board with it so I thought I’d take the engine and radio and so-on out of it and make something else for them. The engine was, in terms of external dimensions, a perfect 1/3 scale match for the full-size kart I had but there was no one who sold 1/3 scale karts, not even 1/3 scale kart chassis. Most of the karts on the market were smaller than 1/3 scale and frankly, I wanted my go-kart to be bigger than that.    

If there is anyone out there selling 1/3 scale karts or someone who has made one, I would love to hear from you. 

This is what it will eventually look like. This is the ‘real’ kart I used to own and race.

For the frame I used 6mm copper tube which is not ideal as it should be 11mm to be true to scale but that’s all I could find, compromises must be made. My thanks to my grandpa who helped me silver solder the chassis. You may have noticed that the steering arms are bamboo skewers, that’s just because I don’t have some threaded rod for them yet.  

The engine I’m using is a Traxxas TRX2.5 which I ripped out of my old T-MAXX. I made the rear axle and stub axles at school where I had access to a lathe. On a real kart the drive is transferred to the axle via chain and sprockets, which means the engine rotates in the same direction as the axle. The problem with the TRX2.5 is that is rotates in the opposite direction to the axle, and it has a gear, not a sprocket. The solution I chose for this was to have the pinion gear on the motor meshed with the spur gear, from the T-MAXX, on the axle. This solution eliminates the need for a chain and sprocket and also reverses the rotation from the engine so the kart actually goes forwards. Unfortunately this means that the drive system is not true to scale but I think it was the best compromise. Another thing that’s a compromise is the rear wheels, well it’s not really a compromise, as there was no other option for them. They are a few millimetres small in diameter, they’re way too narrow and they have studs on them as opposed to racing slicks. The go-kart tire is such a unique shape that there is simply no 1/3 scale substitute. However the studs will come off with a few donuts so I’m not worried there.       

I’ve started working on the body panels now. They will be made from fibreglass even though the real ones are made of plastic; this is because I wanted to make something out of fibreglass as I haven’t used it before, you won’t tell the difference. I’ve made the body panel moulds out of polystyrene and I’ll cover them with fibreglass, and then dissolve away the foam. After that they’ll need a little bit of cleaning up and then they’ll be ready for painting.  

The original nose cone and the 1/3 scale nose cone mould.

Once I laid out the chassis and the body panels, I suddenly got an idea of just how big this model is actually going to be. The rear track is about 415mm and the front, 325. It’s about 530mm in length which is roughly comparable to a 1/10 scale car or off-road truck.