Friday, April 27, 2007

How-To: Nitro-to-Brushless Conversion: Part 1

Some of you may know that I spent a big chunk of 2005 working on and modifying a radio-control monster truck, specifically a Traxxas Revo. I learned a lot about 2-stroke glow-fuel1 engines and quite a bit about suspension settings: caster, camber, toe, droop, and so forth. These suspension settings are important in full-scale cars, but there importance is exagerated in smaller-scale vehicles due to the very high power-to-weight ratios and scale speeds. Eventually, I felt like I had learned most of what there was to know on this topic, and I was tried of futzing with and cleaning the temperamental and messy engine.

Well, a couple of months ago, I became re-interested in building RC cars and experimenting with suspension mechanics. This time, however, I wanted to run a clean, quiet, electric vehicle. Traditionally, nitro engines have put out more power than electric motors, so the larger, more complex---and thus more interesting---models have typically been powered by nitro. In particular, the class of vehicle I was most interested in was the "Formula 1 of off-road RC," the 1/8th-scale. These buggies have 4-wheel drive with 6-gear differentials front, rear, and center, front and rear disc brakes, extremely adjustable suspensions, and long-travel shocks that can absorb the landings that follow 30-foot jumps, and are nitro-powered. In recent years, though, brushless motors and lithium-polymer/ion/manganese batteries have advanced to the point that electric power systems can be more than competitive with combustion-based systems. Thus, since I'm in favor of voiding warranties and believe that if you can't open it, you don't own it, I decide to convert a 1/8th nitro buggy to brushless/LiPo power.

Further, I've now decided to chronicle the conversion on this blog, much to the consternation of the readership, I'm sure. I'll wager2 you're asking, "Where's all the sci-fi news and puppy photography I really want to see?" Well, you'll have to wait a bit for that.

My first step was to select a buggy model. I chose the Losi 8IGHT,3 partly because it is generally well regarded, and partly because the unique, extremely offset position of the center differential---designed to allow the engine, and thus the car's center of mass, to sit close to the centerline of the vehicle---seemed helpful for mounting the huge battery pack4 I'm planning to use. I also like that most of the aluminum parts are hard-anodized. The downside to this car is that is uses Imperial hardware; ugh. Anyway, here's a photo the buggy still in the box:

Please note that the dog is not provided with the kit; he is an optional accessory. Said dog will actually slow down your assembly of the vehicle, but he will also put a few smiles on your face during the build. And look how cute he is!

I hope to report the next part of this conversion, the assembly of the mechanical components, soon.

Part 2 can be found here.

1 Model-car engines usually run on a mixture of methanol with 10 to 30% nitromethane and about 15% lubricant.
2 If I wager 4 Quatloos, will that make you feel better?
3 I should point out that RC is one of those industries where no one pays the so-called retail price. For example, I paid significantly less than half the MSRP for the 8IGHT and about half MSRP for my Revo.
4 4 lithium-polymer cells,5 wired in series, each nominally 3.7 volts with a capacity of 8 ampere-hour.
5 Actually, each of these is really 2 cells wired in parallel, but I was trying to keep things simple and clear.6
6 Aren't footnotes great?