Using a VEX Receiver with Non-Vex Equipment

[gblake]

Originally Posted by Devo1098

hey, just get a standard hobby receiver, and plug in the vex crystal and it works, the hobby receiver already has the chips in it to output PWM for servos
super simple
Devo

Devo - Sorry to need to disappoint you, but I'm pretty sure that there is no such thing as a "standard" hobby receiver.

Originally Posted by boyntonstu

Devo,
Does the 'standard hobby receiver' have to be PCM or just FM?
Does it have to be a 6 channel?
Have you tried any other brands besides Futuba?
Does the VEX transmitter have the same range as a Futuba?
Thanks,
BoyntonStu

Like I mentioned in my other reply (in the other thread), part of what you are asking is easily found on the VexLabs Parts and Accessories web pages. Here are a few things that might not be there. The Vex transmitter emits pulses of two different frequencies. When one frequency is on, the other is off. In this way a train of pulses is modulated into/onto the frequency of the transmitted signal (i.e. it uses FM)

The width of these pulses (from which you can derive their position (in time) in the periodic emissions of the transmitter), is used to encode the state of the operator controls that are part of the transmitter. While some folks like to call this Pulse Position Modulation (PPM), I think that they are confused and that it is more properly called Pulse Width Modulation (PWM).

The current Vex Transmitter/Receiver (Tx/Rx) do not use PCM.

There are a few other Tx/Rx characteristics (like the polarity of the transmitted PWM signals and each channel's location in the pulse train) that need to match before you can say that a non-Vex receiver will work with a Vex Transmitter. Sorry, but I forget if the idle state (what is output between pulse trains) of the Vex transmitter is its high freq (crystal freq plus ___ Hz) or its low (crystal freq minus ___ Hz) freq.

About the range question. You might have more luck asking "How long is a piece of string?" Without knowing anything about which of the many Futaba transmitters you have in mind, and without knowing (because I haven't found anywhere where they tell us) the output power of the Vex transmitter, and without knowing if the receiver you have in mind is truly well suited for use with the Vex transmitter; there is no way to answer your question.

Even if "we" knew all these things, without extensive or sophisticated investigation the answer would still be a guess.

One thing that might interest you is that all RC transmitters operating in the band Vex uses are limited (by the FCC) to supplying a maximum of 0.75W to their antenna. This will tend to give similar Tx/Rx parts a similar maximum range, if the transmitter is designed to emit the max wattage. For this reason I think that many people will gues "Yes" if they answer your question about ranges without having actually tested a Vex and at Futaba transmitter side-by-side in the field, or having opened them up to see if their circuitry is identical/similar.

Blake