whats the difference?

[mattydred]

i have been told i need to change from ppm to pcm. my transmitter can be both so i only need to buy a pcm reciever.

i need to chande because i am using digital servos on the tail & throttle. the rest of the servos are standard futaba 3001.

anyway, after looking for a new pcm reciever i come accross single and duel conversion. which conversion should i be buying for my heli? i dunno - probebly sounds like a stupid question to most of you.

matt

[robgt]

If you're buying a PCM reveiver, buy dual conversion as it is less prone to interference than single conversion.
Make sure you get the appropriate crystal for your receiver too.
Cheers,
Rob

[mattydred]

If you're buying a PCM reveiver, buy dual conversion as it is less prone to interference than single conversion.
Make sure you get the appropriate crystal for your receiver too.
Cheers,
Rob

do i need to get another crystal for my transmitter aswell and will the duel conversion reciever work with my older type ff7?

thanks matt

[3dx]

You only need a a dual conversion xtal for the reciever- normally has an orange band on a white background- the tranny can use a normal 35mhz xtal,,,, yes it will work on the older type futaba tranny- in fact Any futaba 35 tx- Futaba FF6 thru to FF9. The other thing to remember is when you change from PPM TO PCM,switch off the tx then switch back on again- that way it remembers the switchover..

[mattydred]

is anybody using digital servos with a ppm reciever?

[3dx]

Used 3152's on my Raptor V2 when it was on 35mhz( Futaba FF8) single conversion and ppm- no probs then, now converted over to 2.4.... Actually ,the only "problem" was I got less flights out of my reciever battery- only managed 4 flights,then batt monitor would start flashing it's leds- think at the time was using 2400mah- now using with on board glow start 3700mah.....

[Leebert]

I have a Rappy 50 with 3152s and PPM until a while ago. I had a major glitching issue which turned out to be the PPM rx getting upset with a monster digital pitch servo that I had fitted (9350 I think). Went to dual conversion PCM and all was good. Have since gone to 2.4 and all is even better

[phil485]

Yup I have PPM recievers in my knights. I have just bought a pcm as I think I might be getting some glitches on my Pro, This might help, in general though no real issues.

[antsis]

Assuming you have a Futaba setup, most come with a ppm dual conversion rx, so the crystal would work for both receivers. The main benefit with pcm is cleaner commands resulting in less glitching. I doubt you'd notice a major difference in the performance of your digital servos.

The main difference is in the way the control signal is sent to the RX . Both PPM and PCM are transmitted by a FM carrier wave (As with radio stations). The control signal is too weak to be sent to the RX , so it's combined with another, stronger frequency for transmission. The RX then spilts the two to retrieve the control inputs. This is why you can use the same crystal.

PPM or Pulse Position Modulation is the format usually referred to as FM. The transmitter scans the stick position and creates 8 pulses. These pulses vary in width according to the stick position. these are combined with a starting pulse and sent to the RX . However, this method is susceptible to electronic noise.

PCM, Pulse Code Modulation, takes the stick position and converts it to digital format (8-10 bit number). This is combined with a long start pulse consisting of many "1"s and "0"s which cannot be mistaken for data and therefore less susceptible to interference. Because PCM is able to send more info in the same space as a PPM pulse, additional info such as failsafe can be added to the signal. Of course this needs microprocessors to encode and decode the information which costs more.

Dual conversion relates to how the receiver extracts the commands from the carrier signal. It uses two stages (as opposed to one in single conversion) which helps to reduce interference further.

[mattydred]

i have been told that i should change my ppm reciever for a pcm reciever because i am using digital servos. is this correct?

ive got a raptor 50 v2 with scale md530 fuz
futaba ff7 (older type)
futaba 8ch ppm reciever
csm sl560 gyro & jr nes 8700g tail servo
jr nes 517 throttle servo
and the other servos are standard futaba 3001.

i have had the heli for about 4 months and have been flying it lots until the tail servo packed up.

what i want to know is do i need to change from ppm to pcm because i am using the jr8700g?

also is the jr nes517 a digital servo?

matt

[Jamez]

No real issue's with my sceadu, GWS rx ppm, 3152's and a 9254.

[Smoothound]

GWS rx ppm

Now that shows a real sense of bravery, IMHO of course

[Jamez]

I know, works though,

[Smoothound]

So far

[Jamez]

what ever do you mean? had that rx ever scince i started flying, might change it now though, kiss of death'ed it i reakon