Proportional controller for microRC's (major mod)

[b007a]

Here is a project for someone out there with more time than myself ... build a controller that will give the microRC's proportional control. Here's my idea ... (I just give these things away ... I'm not sure if anyone would pay for them though):

1) remove the switches from the Tx PCB for left and right,

2) using two 555 timers build a PWM (pulse width modulated) waveform circuit for each,

3) here's the part I'm not sure of ... the steering on other larger RC's. If it is a pot, use the right resistance to change the pulse width ... more deflection in the directions of the turn will increase the pulse width. The frequency of the square wave will stay constant, but the amount of time the pulse stays high will increase with more steering deflection.

4) the output of the 555 (use the open collector transistor provided to gound (previous) switch input to the TX2 IC.

This scheme is base on the fourier analysis of a square wave. There is a DC component, a fundamental freq componenet, then all the add multiple harmonics of the fundamental. For those un-familar with Fourier Analysis: Fourier (some old dude a long time ago) said that any waveform can be broken down into individual frequencies of differing amplitude and phase. When they are all summed up the result is the original waveform. The DC component is proportional to the duty cycle of the square wave. So, if a PWM signal is low-pass filtered before the fundamental freq, then the result will be a DC value that is proportional to the duty cycle of the PWM square wave ... kind of a poor man's D-to-A converter. The corner frequency of the filter must be sufficiently low compared to the fundamental or the DC value will have a ripple that has the frequency of the fundamental. In our case, the Tx and Rx pair should act as the low-pass filter ... the rub is how to control the PWM signal. I was going to by a el-cheapo RC with a gun type controller, gut it and see how the steering wheel works. If the steering is jerky then the fundamental frequency must be increased. Normally I would control the low-pass filter to reduce the ripple below annoyance, however, we cannot control it in this case (it's should be related to the rate that data is sent to the car).

As for the frequency ... looks as though (re: datasheet for Rx2/Tx2 control IC pair) the repeat rate is approx 14 Hz (based on needing 4 W2's, and 64 W1's). So, make the period 100 times less or 0.14Hz. Why 100 times ... think logrhytmically ... 100 times would give a ripple that is 40dB below the DC value. Some trial and error would be benefical here, it is unknown at this point the order of the filtering action of the system.

For now I am only worried about the electrical side of this project. The packaging will come later ... this may be another challenage, because the capacitors will be huge (or a lot of little ones in parallel.)

If no-one bites ... I will design the PWM's if someone else will build the circuit, but you must build two (one for me) as my design time is not cheap.

Regards.