Hi everyone!

Just installed 3 Futaba 9252, GY401/9253 in my raptor .30. And they are all buzzing like hell! They seem to struggle to keep the center position maybe. It does not seem to be much resistance in the controls (e.g. mechanical pushrods). However the heli is pretty much new, and the ball-linkages might be a little tight???

They must certanly (right spelled??) use a lot more current in this condition as without the buzzing...?

Any suggestions are more than welcome!

Maybe I must purchase the JR resizing tool?

That is normal, dig servo's buzz because they are always trying to find and hold center.

If you are running a PPM(FM) system they will buzz more than a PCM system. PCM operates at a higher frame rate and send centering information more frequently.

To get the best performance from digital servo you should PCM.

and 1024 verse 512 also.

The resolution on PPM is whatever the deadband on the servo. And how does PCM have a higher refresh rate? It's the same as PPM. If it's any faster it's repeated data.

Buzzing is normal? I have found that while most of the digital servos buzz, that if I tune the subtrims well, I can eliminate the buzz... I always figured that if the servo is buzzing, especially while there is no control inputs, that the servo was still somehow receiving input to move.... I could be wrong here, but it makes sense to me that any unwanted movement should be eliminated....

LYNX: I like cats too! ---For breakfast that is!!!

I'm using a JR X-8301 with a N-649 reciever (PCM), so that's not the problem.

Subtrims? I'll give that a go and see if it helps.

Any opinions on tight ball-links?

Thanx so much for the replies so far!!

uhhhh

Lynx,
The baud rate is much higher with PCM. This has been beat to death. If you buy a GY-601 the instructions tell you to use PCM to take advantage of the higher frame rate. In addition, JR even encourages the use of PCM when running digitals. Their is faster alot more data being sent from the receiver and with digitals it can process it fast enough and produce greater holding power.

Guys don't use subtrim to get your servos to stop buzzing. They buzz because their is always some resistance in the pushrods and links and it is difficult for the servo to find a perfect enough center to stop the buzzing. You can usually move it with you finger and get it to stop. With PPM though it's tuff.

What's the exact baud rate it transfers at and what's the frame information? I've had a hard time finding this information anywhere. I'm more than curious to find out exactly how much faster than PPM PCM is supposedly. I won't believe it till I see hard numbers. I understand a PCM receiver may very well regenerate the servo signal more times than a PPM receiver, but is it getting actual new data faster? If it's not it doesn't matter with a digital servo. You could send 500 extra servo pulses a second with PCM and it wouldn't matter if they were all the same. TX to RX update rate is what actually influences performance.

Sorry Lynx, but he's right...
Even my Futaba Gyro came with info in its manual telling about the higher frame rates with PCM.

Well I for one certainly learned something!

I understand that the frame rate to the servo might be higher, they're digital the signal can be regenerated on demand at any conceivable rate the processor can put out that won't cause the servo to tweak out, this would be an obvious marketing point. What is the rate the data is sent from the Xmitter to the receiver though cause that's the only important number. Anyone know where to get this information? Or more information on the PCM packet format in general? I need this info eventually and I'm dreading decoding the packet myself. Also all you people out there that can actually notice the speed up of PCM on their craft over PPM, how many channels are you using?

Orignially developed for the military, anyone remember when 1024 PCM was considered missle code? That's what it was! This explanation is intended for voice communication, but the theory is the same, just a different media to convert, and please remember that PCM is a digital way of transmitting code instead of a nice signwave or analog PPM.
TDM/PCM Interface: The TDM/PCM interface carries the fixed bandwidth media signal. It consists of 32 data streams (128 timeslots/stream = 8Mbps/stream), an 8KHz Frame Sync Pulse, and an 8.192MHz clock. The data streams are segregated into sequential groups of four: Send In (SI), Receive Out (RO), Receive In (RI), and Send Out (SO). Each logical channel uses a timeslot from each of the four streams (SI, RI, RO, SO). Thus, the 4,096 timeslots on the TDM/PCM interface allow a maximum of 1,024 logical channels.
Then Futaba has a short blurb on its PCM without getting into details. http://www.futaba-rc.com/faq/faq-pcm1024.html

Hope this mush helps.. Got to go detox now!

Orignially developed for the military, anyone remember when 1024 PCM was considered missle code? That's what it was! This explanation is intended for voice communication, but the theory is the same, just a different media to convert, and please remember that PCM is a digital way of transmitting code instead of a nice signwave or analog PPM.
TDM/PCM Interface: The TDM/PCM interface carries the fixed bandwidth media signal. It consists of 32 data streams (128 timeslots/stream = 8Mbps/stream), an 8KHz Frame Sync Pulse, and an 8.192MHz clock. The data streams are segregated into sequential groups of four: Send In (SI), Receive Out (RO), Receive In (RI), and Send Out (SO). Each logical channel uses a timeslot from each of the four streams (SI, RI, RO, SO). Thus, the 4,096 timeslots on the TDM/PCM interface allow a maximum of 1,024 logical channels.
Hope you can see from the above that the time slots are many, convert that into individual position requests to be decoded to command the servos. Then Futaba has a short blurb on its PCM without getting into details. http://www.futaba-rc.com/faq/faq-pcm1024.html

Hope this mush helps.. Got to go detox now!

Another good place to go for an explanation.
http://www.vantec.com/pcmadv.htm

skydog

I've read the Futaba FAQ, that's a bunch of useless information. I need to know the format of the data packet and the various timings for the bit's and frame pulses. There's a sequence of bits sent with a fixed packet format, what is it? BTW, you can't fit 8mbits worth of data at the 72MHz spectrum, we don't have the bandwidth, so the baud rate has to be SIGNIFICANTLY lower. Given that the highest end PCM xmitters are 9 channel, 9000-9600 baud seems about right for the spectrum space, and that's about right for modern TNC modems, I imagine it uses an encoding method similar. Anyone have information? REAL information?

I beg to differ, also being involved with HAM radio, am very familiar with TNC's and data packets. If you need this level of information, your sure not going to find it here on this forum. I would recommend that you seek a higher level, like asking Futaba. It serves it's purpose well for most on this forum, and I for one have no need or desire to pick at the nuts and bolts of something that does it's job. Digital servos do buzz, they do work faster, they do consume more energy, and they do the job.
Sorry we couldn't help more.

Go up on RunRyder and ask Angelos. He is the most knowledgeable person I have seen on the Futaba PCM system. He has worked out their encoding scheme, and sells a menu enabler for the 9Z. I know he monitors the Radio, Gyro, Servo forum on RunRyder.

Excuse me.
The output signal of PCM receiver of Futaba is being repeated at the time of about 14mS.
That signal is repeated in 2mS on a general digital-servo , and it is working.
This isn't thought that there are a frame rate of the transmitter and relations.
Thanks
kobayan