Hello, everyone! I’m back with my latest NXT project, the RC4W-2T Plethora! Read on to find out more about its plethora of unique mechanical functions!
See a video of the RC4W-2T Plethora here: https://www.youtube.com/watch?v=sZvaIH4WqAo
The heart and soul of the Plethora is the transmission, namely the two speed synchromesh automatic in use here. An EV3 Medium motor is used to drive the car. An NXT motor is the shift motor; it’s programmed to rotate forwards/backwards 0.18 rotations to select gears. First gear’s ratio is 1:1, but second gear is sped up at 1:1.6. The transmission’s output gear is a 24 tooth cog that drives the center differential at a 1:1 ratio. Lastly, the whole transmission can be removed just by pulling out a few pegs at its base.
All Wheel Drive System:
The transmission can put out a lot of power, so the Plethora needs a hearty AWD system to get that power to the ground. There’s a total of three differentials for the best handling results. When you’re turning, each of the four wheels wants to turn at its own speed; having three diffs allows you to do that. The center differential gets the power from the tranny and transmits it to the front and rear diffs; since the center diff has to sit lower to clear the NXT, the drive shafts have Universal and Constant Velocity joints to link them. In the front, there’s two Universal joints to transmit the power while steering. In the rear, there’s four to allow the suspension to operate. In total, there’s two CV joints and eight U joints.
Unless you’re a drag racer, you’re going to need something to point your car in the right direction. Luckily, the Plethora was engineered with an accurate and innovative Rack-and-Pinion steering system! The steering is driven by an NXT motor mounted longitudinally (lengthwise). With the motor mounted this way, the rack must be, also. The picture to the left shows the rack with the casing removed. It’s directly connected to the left wheel and a track rod transmits the steering motion to the right wheel. The wheels turn whenever the rack moves forward/back.
The disadvantage of having three differentials in an AWD system is when you’re driving over uneven ground diagonally (like transitioning from hardwood floor to area rug). A rigid chassis would have one wheel off the ground, and since differentials take the path of least resistance, that one wheel would get all of the power and the car would be stuck. My solution was to install independent rear suspension, which keeps all four wheels on the ground at once. The suspension resembles a dual wishbone setup and each side contains two U joints to transmit the power. you can compress each side independently, hence the name independent. It’s extremely difficult to make a durable setup, and I’m very proud of this one because it’s my first successful system!
The program is written in NXT-G, and a screenshot is displayed to the left. The top fork is a MyBlock created by HiTechnic, which creates a digital tachometer on the NXT screen. The middle fork utilizes a built-in HiTechnic Angle Sensor to determine when to shift up/down. The bottom fork uses a HiTechnic Infrared Receiver to interpret signals from a Lego Power Functions remote and translate it into throttle and steering commands for the NXT. Steering is operated by a HiTechnic Motor PID.
Overall, I am super pleased with the Plethora. I made many personal advancements while building this technological tour-de-force. The Plethora debuted my first suspension system that was resilient to withstand the car’s torque. Also, it lead me to develop the longitudinal rack steering system, which is great for keeping a low front profile. It’ll definitely make a return in my future models. I learned a thing or two about making the body panels modular so they’re super easy to put on/remove. In addition, it’s also my first project that uses the Angle Sensor, which makes shifting ultimately precise. Lastly, I learned that when using a transmission in future cars, to ALWAYS use two drive motors, because the transmission wastes a lot of the car’s torque. I hope you enjoyed the RC4W-2T Plethora. And, as always, thanks for reading!