thomasnc41

My Feedback: (45)

I have a curious question about servos.

If I turn on my rx WITHOUT the transmitter turned on, some servos don't move, some move a little and some move a lot. Obviously they have power going to them but no signal. So, if there is power but no signal, what causes the servo to move and will it alway move to the same position.

Thanks for any help or explanation..................................

BarracudaHockey

My Feedback: (11)

Depends on the RF environment, its just picking up noise. PCM will stay put till the reciever gets a good signal.

Campgems

I was warned when I first started that you "ALWAYS" turned the transmitter on first and turned it off last. They beat me with this until it has almost become a subconsious sequence.

Now, I've never had one of my planes show any servo movement when the receiver was on first, That is until I picked up a couple small electrics from one of the guys at the field. I plugged everything together and the plane went absolutely nuts, in cluding the motor starting and stopping. This was on my bench where I set up all my planes, so there was nothing in the "air" around the bench causing it. That receiver and servos just have to have the TX on first. It's one of the small 4 channel single conversion receivers, so that may be a clue. All my others are dual conversion and some are PCM. It was a shock, and I'm really glad there wasn't a prop on the engine when it went spastic.

Don

Mastertech

My Feedback: (31)

This is one way to find out if anyone is on your freq. Turn the rcvr on first.

TFF

With no signal the gain goes up in the reciever as it is looking for a hint of what it is to do. Back in the 80's I did a bench test, I rapped the reciever antenna around an electric drill. with tx on it would stay in control; no tx they shook and jittered and moved. Range under these circumstances would have not been good but just a kid doing an experiment. With everything so reliable today, we forget that the TV on upstairs, besides recieving signals, is also generating them as anything electric; if the resonance is right anything can be the cause.

A.T.

Not recommended:
1. An extraneous signal may try to drive servos beyond physical stops and lead to early burnout, especially digitals servos. Can also cause loss of programming in some ESC and unwanted start up of EP Motors.
2. Many recent receivers employ auto gain circuitry, IDP or PLL systems and may lock to a close signal and be out of kilter with your TX when it is turned on. If you must use RX to check frequency, turn off again and then turn TX on, allowing any computer TX to finish initialisiation, before turning RX on again.
Further information on my web page under "Glitches & Jitter in RX & Servo - causes and cures"
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links

thomasnc41

My Feedback: (45)

" An extraneous signal may try to drive servos beyond physical stops" is what got me asking the original question. I have 4 servos. When power is applied but no signal 1 doesn't move at all, 2 move some and the 4th one seems to rotate almost 90 degrees. The obvious solution is to turn the tx on first but I still wonder why so much variation.

Thanks for all your comments..................................

A.T.

[/quote] " An extraneous signal may try to drive servos beyond physical stops" is what got me asking the original question. I have 4 servos. When power is applied but no signal 1 doesn't move at all, 2 move some and the 4th one seems to rotate almost 90 degrees. The obvious solution is to turn the tx on first but I still wonder why so much variation. Thanks for all your comments.................................. [/quote]
That extraneous signal, or auto gain type RX trying to lock onto a signal, may act on any one or multiples of channels at the same time. (Similar to your input via TX to individual or multiple servos.)
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links