RX confusion

[lesbaldry]

Ok chaps work this one out "I cant"

I swapped(transposed) RX's from one car to another,one was a Spectums own,the other a KO spread srectrum unit.
For some strange reason the car that received the spectrum unit had decreased steering throws and the other car that the KO spread RX was fitted too the steering throws had to be reduced buy 20%.
To my simple mind a signal is a signal why the hell did my steering throws alter just because I changed RX,and just to confuse things both ESC seemed to still have max throttle and brake in the right places ?

Correction,Ive just double checked and Max throtle/brake end points had altered too.

[lesbaldry]

Oh come on you lot,there must be some bofin that can answer this...please.

Ive just swaped RX back again into another car and exactly the same thing has happened (changed TX module and RX over to spred spectrum from std spectrum ) and both steering and throttle end points have changed even though the trany settings have not been altered,HONEST!! I'm not dreaming nor have i been on the "wacky" nor is this a wind up

[Reuben]

Only thing i can think of is the resolution of the two receivers?

eg, if you resolution is 1 degree, and you have 100 points of movement on your transmitter, your total movement is 100 degrees, if you resolution is more accurate, eg 0.6 degrees and you still have your 100 points movement, you max movement becomes 60 degrees.

if that makes sense?

[Reality Racer]

That makes sense Rueben. I now remember having a similar problem a few years ago.

[lesbaldry]

Thanks chaps I was beginning to think I was going mad .....Ive always thought a signal is a signal regardless of freq but it seems not to be with versions of 2.4.....its worth remembering should anyone borrow a different system for their tranys.

[Dave Chamberlain]

Argee with Rueben,

Actual operating frequency (2.4Ghz) would not directly effect the amount of available servo "throw" but the different RX's output as full or minimum "throw" could be different between manufactures.. A more sensitive RX (higher resolution output) would not throw the servo as much and a less sensitive (lower res output)RX if all other TX settings (End point etc) remained the same.. I guess this could be checked by hooking up the two RX's two a scope and looking at the O/P volts signal??

[Reuben]

not bad for a complete guess then

[wessex88]

Could be that the 2 systems use a different pulse width for 100% setting.

[mattsedgley]

Nov 9, 2010 15:27:18 GMT wessex88 said:

Could be that the 2 systems use a different pulse width for 100% setting.

i expect so, and i think i've got a little box that'll prove it also!

[Dave Chamberlain]

Are we saying the RX's O/P is PW modulated? and thats how the servo is controlled??

[mattsedgley]

yeh they normally are

I'll bring my box down tomorrow to show you!

[Dave Chamberlain]

OK found this which pretty much explains everything..

Serve control signal is PWM shorter width moves servo in one direction and longer moves it in the other.. Simples!

Les your issue could either be the PWM on one RX is not reaching the same min /max widths as the other one or the actual gap between pulses is different and the servo can't cope with the variation.

All interesting stuff :-)

Attachments:

[mattsedgley]

i expect if you go into more detail it might be the speed the receivers are working at causing issues

[Dave Chamberlain]

Could be, more reading required.. I'd assumed the TX speed was not the issue as Les said it was steering end points were less from one RX to the other not the reaction time from Tx command to servo action.... I'm not convinced the signal from the TX to RX is the same PWM signal, but I could be wrong..

More Google required..

[lesbaldry]

Blimey chaps thanks for your input. im not going mad after all!! In all my years of RC(40 and 35 meg and the old 27) I've never experienced this befor so it must be something just in the 2.4 alternatives?(spread and normal spectrum)