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Feb 16

eRally (2014)

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Hello! I return with the eRally, an All-Wheel Drive, RC NXT rally car with four wheel independent suspension. This is the final result, my second quickest MOC ever! Continue on to find out what makes the eRally so unique. (I offer LDD close-ups for the first time, in each section.)

See a video of the eRally here: https://www.youtube.com/watch?v=Avm6Y245NQw

Styling

eRally

After receiving much praise for the styling of the Rally Sport AWD, I decided to make it a top priority to make sure its successor, the eRally, looked good as well. It has styling details such as flared rear fenders, a rally car spoiler, a faux rear diffuser with orange “blades” and a “carbon fiber” front spoiler. I believe that all of these details, plus the general body shape, make the eRally one of the coolest looking MOC’s I’ve created.

Suspension and Steering

eRally Front Suspension

The eRally is my first vehicle to feature all wheel independent suspension and AWD. The most challenging part was making independent front suspension that would also allow the u-joints to deliver power to the wheels and allow steering; all with just ordinary parts (no specialty elements). I am happy to report my success. I simply put my most up-to-date steering knuckle design on the end of 5-module wishbones and ran u-joints through. The front suspension is shown in pic 1, with yellow beams taking the place of the shocks. The rear suspension is the same design I’ve been using for almost a year. Both front and rear suspension are very soft for off-road driving. The steering is driven by an NXT motor laying flat. Its power is transmitted 90 degrees to the steering rack, which steers the wheels using track rods. The rod geometry gives each wheel about 2 degrees of toe-in. As a whole, the system works great!

Drivetrain

eRally Drivetrain (Bottom)

The most important part of the eRally, just like any rally car, is its AWD drivetrain. Two NXT motors propel the eRally; they are hard-coupled. Here’s how they transmit power to the wheels: first, they route their power 90 degrees on a 1:3 ratio, which turns a 24 tooth gear. Next, this gear turns the center diff on the 24 tooth side. Then, the power is sent forward and back to the front/rear diffs, which are of the 90 degree variety. There is a total of four u-joints on the rear axle, two on each half-shaft, to allow the suspension to work. Similarly, there are two u-joints and two cv joints on the front axle; one of each on each half-shaft, with the cv joint connecting to the wheel for optimum smoothness. Why use three differentials, rather than two? It allows all four wheels to turn at their own speed, sending more power where its needed, and less where it isn’t. This allows for the tightest, cleanest, most accurate turns possible from an AWD car.

Program

eRally Programd

The program is a basic RC program, based heavily upon HiTechnic’s IR Kart program, but with a twist. This program allows you to control the eRally using an IR remote; signals are received by the HT IR Receiver in port 4. At the beginning of the program, the steering centers itself using a HT Motor PID block. Next, an engine revving sound file is played. Here is the exciting part: now, you can use the Color sensor located in the front bumper to choose between two drive modes: Race or Touring. Both modes give you complete control over throttle and steering. Race is the default mode, which is also selected by scanning in a blue brick. It has a steering factor of 15; the sharpest turns possible with this steering rack. Scanning green activates Touring mode, which changes the steering factor to 8 for slower, more controllable turns. This program is structured so you can change drive modes at any time.

Conclusion

Road CourseIMG_7695

I am very pleased with the finished eRally. It looks as sharp as it drives and I have made a few great personal milestones while building it, such my first AWD car with full independent suspension. When tested on my 74-foot test circuit, the eRally posted a time of 26.57 seconds, bested only by the monstrous Terminal Velocity at 17.02 seconds, which took a thousand tries to finish one lap without crashing. (The ThunderSmart II and III have yet to be tested, but likely won’t be as fast). So, the eRally brings intelligent and easy-to-use speed, something I am happy with. Tell me what you thought of the eRally! And, as always, thanks for reading!

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