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Feb 16

Terminal Velocity (2013)

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Hello! I present my latest robot, the NXT Terminal Velocity. It’s my fastest RC car yet, with an extremely innovative drivetrain that rockets it to insane speeds!

See a video of Terminal Velocity here: https://www.youtube.com/watch?v=wq4SpTq36TY

Hybrid Drivetrain

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This is the most exciting part of the Terminal Velocity prototype, because it debuts my first ever hybrid drivetrain. (YAY!) There are three drive motors in total. Two NXT motors supply the main power for the car. A third, non-electric pull back motor is wedged in between the two; when you drive in reverse, it winds the motor up, and when you drive forward again, the power is returned in the form of torque assist. The torque assist makes a noticeable difference an lasts much longer than I expected. When it runs out, the assist motor freewheels, and the NXT motors continue to drive the car. All you need to do is drive in reverse again to rewind the assist motor. The output gear ratio to the rear differential is 1:5. It’s very geared up, but the torque assist makes accelerating to insane speeds very quick. As far as I know, no one else has tried this unique setup!

Steering

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Like all of my other racecars, the Terminal Velocity uses rack-and-pinion steering. An EV3 Medium Servo motor turns a 12-tooth pinion gear, which moves the big 13 module rack gear back and forth. The front wheels only rotate a few degrees in either direction for two reasons. First, the EV3 motor rejects the NXT-G program and refuses to rotate all the way. Second, I kept it that way because it improves the high-speed stability and that’s all you need to turn at V-Max.

Program

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The program is displayed below, and it’s written in NXT-G. It’s a simple RC program that uses a Lego Power Functions remote and a HiTechnic Infrared Receiver to control the car. The Motor PID controls the steering, but as I said before, doesn’t work 100% correct because of the EV3 motor, yet it’s better this way because it’s more controllable at top speed. Both drive motors synchronize when they receive a throttle command.

Conclusion

This was really just a mad scientist experiment with the hybrid drivetrain. I didn’t do too much with it, but with something this fast, I couldn’t resist sharing it with you. This could very possibly be one of the fastest NXT cars ever, with a top speed of 4.55 MPH (7.32 KPH). Decide for yourself; check out the video. Thanks for reading, and see you next time!

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