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Old 01-19-2003, 10:18 PM
ph2t's Avatar
ph2t ph2t is offline
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Join Date: Jan 2003
Location: Melbourne, Australia
Posts: 269
Proportional Controller EMULATOR

Got a few Bit-G clones for xmas and I gotta say they're nuts!
Took 'em around to a mates place and we raced them all night around a home made track on the living room floor.

During this time all I could hear was this incessant clicking sound from the RC controllers. None of us ever held down the steering buttons for very long since every turn on the race track varied in length / sharpness, etc... So how do you control a Bit-G that doesn't have a proportional control? Click the bloody left-right pads repeatedly depending on the shape/sharpness of the corner, ouch!

This gave me an idea. If I could control the left/right steering as a series of pulses instead of a constant on / off maybe, just maybe I could EMULATE a proportional controller! You could do this for forward/reverse as well, effectively giving you speed control in both directions.

At this point let me say that all I'm trying to achieve is to EMULATE a proportional controller to the best of my ability. There is no way known given the circuitry of the transmitter & receiver to be able to achieve a fully proportional controller since it has been well established that the custom RX/TX IC's use a pulse width encoding scheme that either outputs a 0 (OFF) or 1 (ON) to the motor / steering circuitry on the receiver board.

So, with all of that in mind I came up with a design that sends a pulse to the left/right switch (on the IC side) of the controller. This pulse pretty much emulates the action of clicking on the left/right button instead of the operator of the controller doing this himself. This pulse is controlled by a potentiometer (a variable resistor, found in many computer joysticks) that is used to control left/right functions. This is what you use to steer the Bit-G.

In layman’s terms what does this mean? Well, having the dial in the middle means steering is in its default state, centred with no action. Turning the dial to the left starts a pulse that is very “thin”, this causes the wheels on the Bit-G to turn to the left for a very short amount of time. As the dial is turned to the left even further, this pulse becomes “wider”, therefore the wheels stayed turned for a longer period of time. Turning the dial all the way to the left causes this pulse to stay “on” all the time, therefore keeping the wheels permanently turned to the left. This is the same as when the left button on the controller is pressed.

This is still in heavy testing and development, I’ve been able to get this to work but so far for one direction only. I will need to modify the circuit to add the extra “channel” to be able to turn the car left AND right. The schematic below is for the left. Notice that the circuit requires 6V. I use a 3.3V Zener diode to bring the voltage down the 3V for the controller circuit. I haven’t tried this part yet since charging the Bit-G “might” blow the diode due to excessive currents.

For you tech’s out there the circuit is a basic PWM (Pulse-Width- Modulator).
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