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RC Differential Drive
I had not yet received my first
8475 RC Race Buggy
and I was already thinking whether the RC unit was suitable to control
differential drive vehicles (the kind of vehicles driven by two independent
motors respectively linked to left and right treads or wheel groups).
The easiest solution would be ignoring the steering control, using the drive control for one side of the vehicle and the third channel for the other side. However, this solution is less than satisfactory. The main problem is that while the drive channel allows for controlling speed, the third channel doesn't.
I then came to setting up the mechanism you see in the pictures, which allow for driving a differential drive vehicle in the same way you would drive a steering vehicle: one control is for steering, the other one for speed. The third channel remains free.
The electric connections are not shown in the pictures, however they are pretty
simple: connect one side of both the swithces to the speed control socket of
the unit (the red one), and the other side of the switches one to the left side
motor and the other to the right side motor.
As you see in the photo, the steering output of the receiver is attached to a long axle. Until the steer control is straight, both the switches are closed and both the motors at the sides of the vehicle receive power, thus making it go straight (provided that you have connected the motors with the right polarity!). When the user operates the steer control, the axle turns, pushing one of the levers attached to the polarity switches. Doing so, the involved switch opens, thus the motor connected to that side stops, and resulting in a turn of the vehicle. If the user applies more steer, the switch reverses the polarity, and the motor connect to it goes backward, thus making the vehicle turn in place.
In this side view you can clearly see the rubber bands that keep the switches
in their "normal" position when the steering control is centered.
Each switch is attached to the receiver with two Technic triangles. Notice that
there's a plate below the switches, and 1x5 half beams between the triangles
and the body of the receiver.