d385 The Actual GT1

Quite some time ago now I posted a GT1 Test Painting saying that I might talk about the GT1 more in the future. Well, now it’s the future, it just took more time to get here than I’d thought.

Probably close to a year ago now, J proposed a project that was like “build a car” or something to that extent. It might have been more specific than that, but it wasn’t specific enough such that we didn’t take drastically different approaches to building these cars. J decided to make something more akin to a traditional Technic set, while I decided to make a RC car. At the beginning I think I was under the impression that we were both going to make RC cars, but I guess that didn’t happen…

First I designed the car. For once, I didn’t consider any sort of Lego limitations and just designed something I liked, which turned out to be a 20s or 30s style cross between a GG1 and a T1 (hence the name). I reasoned that there were trains that took design cues from cars, but I’d never seen it done the other way… so why not? Other than that, I could rant for an entire post about car designs, so let’s just get on with the project.

J must have rubbed off on me as I originally thought I’d be making the car very small. I also wanted suspension. It quickly became apparent that the car would be way to small to hold all the bulky electronics even without suspension, so I started to scale up. At that time I was still planning to use the 71427 or 43362 geared Technic motors and I became worried that the increasing size would hurt the performance a little too much, as the motors are only good for a little less than a watt of power (for a random comparison a 2010 MBA 11 idles at about 4W). Thus, at some point, I decided to dig out and install my 5292 “Race Buggy Motor”, and the first fully functional prototype was basically a small, bare chassis with all the electrics rubber-banded in place.

5292 is good for about 6W (six times as much as the old geared motors!), but I didn’t realize how awesome that was until I drove the test car. Then I realized I could make the car plenty big, and work on the real thing began. The next prototype already had all of the mechanical features of the final car at the right scale. It was really fast, and with all of the electronics still just strapped on, I could flip it at less than quarter throttle. Then it was just tons and tons of refining to make everything fit, lower the CG, and make it look like more than just a bare chassis. Still, when everything was said and done it only somewhat resembled the drawings…

Driving the thing was pretty amazing though. I timed the top speed at about 3m/s with an acceleration of about 1.7m/s^2. This translates to a scale top speed of about 87mph, which is not quite as good as the 500mph+ of the Titanic, but it felt plenty fast driving around. On plain old hardwood floor, there was enough power to do burnouts and donuts, though the performance really deteriorated throughout the lifetime of the car. Any way, it was certainly better than anything I had expected when I started the project.

So the final car is set up with the front and back axles on single swing arms (ie not one arm for each wheel, but one for each axe), and the front axle is also pendular. It’s not quite independent suspension, but you can like raise one wheel and keep all the others on the ground, which is good enough for me. The engine is geared 1:1 with the rear wheels, but the suspension and differential necessitate a drive train through a bunch of old 16 tooth gears, and the torque was enough such that I destroyed two during the lifetime of the car. I mentioned that the performance deteriorated as well, and that was probably because the vegetable oil I used to lubricate everything started to collect debris and rot. That may have also contributed to the destruction of the gears.

The car’s already been dismantled now, but here’s some video that we shot on the last day as we drove it fast and as it tore itself apart:

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