Transmitter on FIRST!

The reason is to have a viable signal going to the receiver when it it switched on, keeping the rx from picking up spurious signals which could cause the servos to run amuck and overunning their limits, causing damage.

Consequences are evident...

Cheers,

Ben:

With FM PPM,...The result can be potentially serious servo / linkage damage. In the absence of a Tx signal, the Rx will try to make sense of almost any EMF. It will behave once the Tx signal is there. So Tx first,...then Rx.

For the record. I use PPM mostly and sometimes get this wrong. I've never damaged anything that way myself, but I have witnessed the dance. Its' normally a bit of chatter and some strong movement, but can be very strong and damaging movement. ;-)

With PCM,....nothing. Doesn't have the same problem.

Cheers,

Ah ok.. thanx..

Another thing that could cause problems is with electric power planes, when an ESC first comes alive it is looking for a signal to set throttle. If it doesn't see a signal it could set the end points of the throttle curve incorrectly. I have seen this with my Zagi, where if I accidently turn it on without the TX on first, and then turn on my TX, it thinks that the zero throttle position is at about 50%.

The tx has a serious tendency towards jealousy and has been known to throw a hissy fit if the rx takes butts.

Actually, this is true only for AM or FM (PPM). One turns on the transmitter first so that a valid signal will be present when the receiver is powered on. This prevents noise from triggering large moves or jitter in the servos.

With PCM systems, the reverse is sometimes better. Hitech's Prism PCM transmitters send the fail-safe information first, so if the receiver isn't on, you don't have fail-safe. The time delay before fail-safe is fully activated on Futaba gear is also better if the receiver is on when first transmitting. PCM receivers won't jitter the servos due to noise, so there is no reason to power them on after the transmitter.

Jim - AMA 501383

Ben wrote:

that could get NASTY!

In the early days of proportional control, say 35 years ago, if you turned on the receiver and not the transmitter the servos would go to the end of the travel and keep "trying" to go farther. They could tear themselves up. Now, if you turn your receiver on without the transmitter, the servos will jiggle a little and that's it. No harm. I don't know the technical aspects of how this was solved, but it was solved.

| > > > Everyone knows the radiotransmitter must be on while the receiver is | > > > switched on. | > > >

| > > > But why is this? | > > > And what are the consequences of sloppyness in this matter? ... | > In the early days of proportional control, say 35 years ago, if you | > turned on the receiver and not the transmitter the servos would go to | > the end of the travel and keep "trying" to go farther. They could tear | > themselves up. Now, if you turn your receiver on without the | > transmitter, the servos will jiggle a little and that's it. No harm. I | > don't know the technical aspects of how this was solved, but it was | > solved.

That's very radio and installation dependant, even today.

Some radios won't jiggle at all -- PCM receivers, and the FM receivers that have PCM-like error correction.

Without one of those radios, your servos may jiggle a little this time

-- but next time they might jiggle like crazy, and some servos may go to the end of their travel, which may damage your plane depending on how it's set up.

If you have an electric plane, that jiggling will happen on the throttle channel too, and while many ESCs do try to reduce this danger by being clever, there is still the danger of the prop suddenly going to full throttle -- and that can really hurt, even on a small speed

You may be able to get away with it most of the time, but it really is a good idea to always turn the transmitter on first and turn it off last, every time. Certain planes may not really need it (because they use PCM, or because they're glow and all controls can safely move the full servo range) but the habit will go with you to other planes that are not so forgiving. The plane and flesh you save may be your own!

As I said in a previous post, this may not be a good idea when using a PCM system. Some Hitec transmitters send the failsafe data only once. Even when using other failsafe schemes which update periodically, there will be a delay. Not having failsafe during the takeoff roll might be even more dangerous than loosing control during flight. When using PCM, I turn on my receiver first. I will continue to do so. It's safer.

Jim - AMA 501383

The danger of turning the receiver on first, is that it may respond to any stray interference and or over drive the servos. Or indeed, in teh case of SOME OLDER electric motor speed controls, have a burst of throttle at an inappropiate time.

The dangert of turning the receiver on first, is the wally who opens the throttle as he trips over your tranny as you are tuning the engine.

Actually, it occurs to me that a simple switch in the throttle servo, that is only switched on when you finally get ready to leave the pit area, might be useful.

Lets face it, you will soon know if its off when you try to taxi :-)

There is no danger of having the receiver respond to stray interference with a PCM system. What you are saying is true only for AM or FM (PPM) systems. PCM systems employ check codes which prevent action unless the message frame can be validated by use of a complex poynomial check. The computer used within the receiver won't position any servo unless it has previously received a message specifying a failsafe position for that servo.

The problem with turning on the transmitter before the receiver is that any failsafe data transmitted before the receiver is turned on will be lost. This can result in a total loss of such information in some systems or a fairly long delay in others. Be careful!

Jim - AMA 501383

True.