plus 200 to minus 200?

[kokopeli]

I am using er9x.
It seems the max output to the servo is plus 125 to minus 125.
For a sailboat it would be a big improvement if I could get plus 200 to minus 200.
That would allow the use of much cheaper sail control servos. It would bring the price down for my sail servo from $80 to about $25 if I could provide a pulse width of 0.5 ms to 2.5 ms to the servo.
125% just doesn't get your there
I need 180 degree swing instead of the usual 90 from an inexpensive servo. Yes I can remove the physical stops to allow that much swing if needed but I know of a cheap one that will not need the modification.
I am also able to install resistors on both ends of the potentiometer to get the extra swing with only the usual signal, but would rather have the 9x provide the extra swing without modifications to the servo.
Is there some way to do this with er9x? or open9x? or other firmware.
Maybe there is a way to suggest to the programmer people to add that feature if it doesn't now exist?

Thanks,
Walt

[Kilrah]

The problem is that even if it was implemented on the firmware, most RF modules won't accept to send such a signal. There are devices to do the conversion onboard the model after the receiver, but the cheapest method is of course the resistors.

[kokopeli]

Thanks, I was not aware that there was also a limitation in the Tx RF module.
I guess there must be a minimum pulse width for the signal - is that the problem?
I am working on a pulse stretcher using a Atmel mega8 controller between the Rx and the servo.
But it occurred to me that it would be a cleaner solution if the stretching was done in the Tx - Oh well, back to the drawing board {or the micro dev. sys.}
I guess I will just have to provide a stretcher for all of my friends instead of just telling them to get a 9x and install firmware - LOL
Thanks,

Walt

[Kilrah]

The problem is that nobody expects a radio to output pulses beyond about 800-2200us. So some manufacturers will use that fact to adapt their coding, or not - what happens beyond the spec will be different for every RF module manufacturer.
Back in the MHz days the PPM signal was sent as is, so no problem... but now the signal is digitized and sent as numeric data packets, and how the pulses are measured and encoded to use as little bandwidth as possible might prevent from sending out of spec pulses. Or they might simply be rejected as invalid.

I only tested frsky modules, those are happy with short pulses even down to 150us or so, however anything above 2250us or so will get truncated.

[kokopeli]

Really interesting!
I was not aware that the data was transmitted as digital packets.
Us old retired folk need to keep up with the advancement, eh?
Yeah, 2250us will not quite cut it.
Humm... actually, the sail servo doesn't really care about the center setting - conceptually, I could use the span from 200us to 2200 us to get what I want.
BUT, it certainly isn't practical to put a mod into the firmware for so small an faction as we sailors are.
So, back to making the pulse stretcher.
Thanks so much for the good info.

Walt Bankes

[Kilrah]

If you can compile the firmware yourself, I recall it's not terribly complicated to modify it to allow for higher values. I had increased it to 600% or such for testing... then you could see if your module handles it or not.

Another reason not to allow higher values in the standard firmware is that if they can, some people will just use 300% without thinking of the consequences on PPM timings and control linearity... 125% on *9x is already more than what common radios will allow.