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July 2013

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RC Car Action - July 2013

Monocoque Suspension

Monocoque Suspension All-new monocoque suspension arms are found on all four corners and feature bolt-on covers that increase strength and stiffness while keeping dirt out. Attached to each corner, the arms are held to the ground by a set of aluminum-bodied, 16mm longtravel shocks that are mated to 5mm aluminum shock towers. A closer look at the inner arm mounts reveals the level of tuning that HB offers both their team drivers and their customers. The D812 includes a full set of blocks that allow you to set both toe and rake however you wish to dial it in. The overall suspension system features aluminum hubs and steel turnbuckles to keep it efficient and lightweight. 6.3 in. (160mm) 12.2 in. (310mm) The chassis on the D812 moves everything as close to the centerline as possible for optimum balance and handling. Out back you’ll notice the replaceable skidplate allows you to freshen up the chassis when things take a beating. VEHICLE SPECS 12.9in. (327mm) 18.9 in. 480mm Item no. : 109428 Scale: 1/8 Price: 0 Weight, as tested: 122 oz., 3,400g All-new monocoque suspension arms are found on all four corners and feature bolt-on covers that increase strength and stiffness while keeping dirt out. Chassis: 3mm aluminum plate SUSPENSION Type: Lower A-arm with adjustable upper camber link Inboard camber link positions (F/R): 4/4 Outboard camber-link positions (F/R): 3/4 Shock positions, towers (F/R): 6/5 Shock positions, arms (F/R): 2/2 Shocks: Threaded 16mm aluminum body shocks with bladders DRIVETRAIN Type/ratio: Shaft drive with 4.4:1 Spur gear/pinion: 48T/16T Slipper clutch: None Differential: Bevel gear, fluid filled Driveshafts: Aluminum constant velocity style Bearings: Metal-shielded WHEELS & TIRES Wheels: White dish style, 17mm hex Tires: Not included Inserts: Not included ENGINE AND ACCESSORIES Engine: HB 21XZ-B Hara Edition Displacement: 3.49cc/.213ci Carburetor: Slide valve Pipe/header: O.S. T-2060SC Fuel Capacity: 125cc Low Rotating Mass Drivetrain Hot Bodies aimed to increase acceleration by lightening the entire drivetrain. Lightweight steel gears were used throughout the buggy and small diameter diff and pinion gears were selected (44/10) to keep the amount of mass down. Mated to the clutch bell, the center diff lines up the drivetrain straight down the middle of the chassis and transmits power to the front and rear through a pair of shafts. On both ends of the buggy, another fluid-filled, 4-gear diff spools the power out to the wheels and to the ground through a set of CV-style aluminum axles with captured boots that keep dirt out. The drive system as a whole is very free and spins easily, even by hand, due to its low rotating mass. Plastic covers are bolted to the monocoque suspension arms to increase their stiffness and keep dirt out. 36 RCCarAction.com

The engine and fuel tank are just to the left of the center of the car. On the opposite side, the onepiece radio tray offsets them to balance the chassis laterally. Lightweight Chassis The D812 features a narrow, lightweight 3mm aluminum chassis that positions all of the buggy’s components as low and close to the centerline of the car as possible for optimal handling. The top of the chassis has been milled out to further reduce its overall weight while the bottom rear section is also milled and fitted with a replaceable steel skidplate to extend chassis life. An overall view of the buggy’s layout shows its most important design in action; the engine, fuel tank, and radio tray hug the centerline of the car and are offset just enough to balance things, such as the main body of the engine, that otherwise could not be directly on center. The Hot Bodies 21XZ-B is the product version of the engine that Atsushi Hara ran in the 2008 and 2010 IFMAR Worlds. Every spec was replicated down to the finest detail to bring you the same engine Hara runs. Team Driver Powerplant The engine, pipe, and fuel are not included with the D812, so for the test, our buggy was fitted with a Hot Bodies 21 XZ-B Hara Edition .21 engine and O.S. T-2060SC pipe. This is the same configuration that Hot Bodies team driver and former World Champion Atsushi Hara used to power his way to an IFMAR Worlds podium finish in Thailand in 2010. The O.S.-based engine is replicated to the exact specs that Atsushi ran at the 2010 Worlds and comes complete with a P3 glow plug. We ran O’Donnell Speed Blend 30% fuel to finish out the buggy in team spec trim. What is a Fluid-Filled Diff? This morning, you may have put syrup on your pancakes and while you didn’t notice, they were teaching you a lesson about your 1/8 buggy. Sometimes, the syrup takes a long time to pour out while other times it’s much thinner and a hefty pour results in syrup that gushes out all over the place, soaking your delicious breakfast. Fluid-filled differentials rely on silicone fluid of various thicknesses to adjust the speed of their operation and much like your syrup, the thinner fluid allows things to move much faster. Inside the diff, gears spin around through the fluid to actuate the diff mechanism. Without the fluid, things would spin very easily and the diff would constantly be changing which side it transfers power to. By using thicker fluid, the diff moves slower and holds power to both wheels until the forces on it overcome the slower movement and send the rotation of the drivetrain out through one side. JULY 2013 37

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