Tuesday, October 30, 2007

How-To: Nitro-to-Brushless Conversion: Part 6

Part 5 can be found here.

OK, this post isn't so much a how-to as an update on a previous how-to, but I feel that keeping the title consistent is important.

I've been quite happy with the performance of my brushless-powered Losi 8IGHT, but I couldn't resist tweaking it a bit. Below is a list of some of the changes I've made since my last post, several of which were predicted therein. Most of these changes are clearly visible in the photos that follow the list.
  • I successfully tamed the motor braking. The car still stops quickly, but it's more controllable, and now I don't feel like I'm going to damage the motor every time I slow down. I really would have liked to use the disk brakes that came with the kit, but there just wasn't room for the servo required to operate them.
  • I've replaced the batteries and speed-control's Dean's connectors with 5.5-mm bullet connectors. The bullets will have lower resistance at high currents. This higher conductance is important, since I expect to draw close to 200 amps for short periods.
  • I added a second temperature sensor, this one is thermal-epoxied directly to the motor. Now I can monitor the temps of both the motor controller and the motor. I've found that both temperatures mostly stay below 130 degrees F, which makes me feel confident that I'm damaging neither component.
  • I've replaced the single battery tray with 2 smaller ones, which allows me to hold 2 6300-mAh 2-series LiPo batteries. I've soldered the batts together in series, giving me a 4-series LiPo with 26% more capacity than my single 5000-mAh batt. This change should not only give me longer runtimes, but also higher currents and thus more power. Additionally, the new setup creates an almost perfect left-right weight balance. As a bonus, the new battery configuration also fills previously unused space on the left side of the car, making it look a little more efficiently laid out..
  • I've mounted some Pro-Line Moab tires on orange Kyosho 10-spoke wheels, which are visible in the first pic. The tread on these tires has a good multi-purpose pattern, useful for on- and off-road driving. Additionally, these tires have transverse ribs on the inside, which helps prevent them from ballooning at high wheel speeds. Not only will these ribs keep more tire in contact with the ground, but they will also keep the tires glued to the rims. The wheels, by the way, are probably my favorite 1/8th buggy wheels; they are both well made and attractive.
  • Speaking of tires, I also found some GRP Rally tires, which I mounted on orange Kyosho 5-slot dish wheels. These wheels and tires are visible in the second pic. In addition to being made of a surprisingly sticky compound, these tires have an extremely low profile, which not only keeps them from ballooning, but also reduces side-wall flex during corning. They don't absorb jump-landing impact as well as higher-profile tires, but that seems like a good trade-off, given that they are intended for on-road use. The major downfall of the tires is their outside diameter; they not only look too small on the vehicle, they also necessitate a significant gearing change. I'd really prefer tires with the same profile mounted on wheels about 10 mm larger in diameter. The wheels, meanwhile, aren't as attractive as the 10-spokers, in my opinion, but they do give the car a somewhat futuristic look, which I find pleasing. I think they certainly look better than the stock dish wheels. (These wheels actually look quite a lot like the wheels that come stock on the Honda Civic Hybrid, which, being a hybrid, is meant to look all future-y.)
  • Gearing is, of course, determined by terrain, but I've been running mostly 15/39 on the road and 14/39 or 13/39 off. It's much easier to change the pinion gear (mounted on the motor shaft) than the spur gear (mounted on the center differential and holding the viscous silicone fluid therein at bay).
  • Since my electrified car is heavier than the stock nitro version, especially with the larger batts, I've stiffened the suspension, cranking up the front and rear spring rate by 14% and 19%, respectively. I also increased the damping concomitantly. The suspension is now set to something much closer to the truggy version of my buggy.
  • I've replaced the stock plastic steering knuckles (axle carriers), servo-saver arm, and servo arm, with their hard-anodized aluminum counterparts. This change should rigidify the entire steering system, resulting in better steering in high-speed situations with only a slight weight penalty. Several other hard-ano aluminum parts are available for the 8IGHT, but I'm not convinced that they offer improved performance or that, if they do, said improvement justifies the additional weight and cost. Incidentally, only the servo arm is visible in the first photo.
  • I've also purchased a Pro-Line Crowd Pleazer 2.0 body, which I've painted almost identically to its stock counterpart. I don't think I like the CP2 as well as I do the stock body. I'll put up a pic later and let you be the judge.
  • I haven't had a chance to measure the top speed of the vehicle to see if the larger battery and taller gearing had an effect. Certainly the car seems fast enough, and the acceleration is more than sufficient for my purposes.

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