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Faast and JR servos compatibility - 5/12/2008 6:23:08 AM   
JetsRC



Posts: 957
Joined: 7/28/2004
From: Santiago-, CHILE
Status: online 		Hi guys, I have some jets with Futaba recievers and JR servos, best mix for me... I want to change to FAAST but I have read a lot of incompatibilities between the new faast recievers and some non futaba servos becasue of a 2.7 volt output.

I do have a powerbox in my jets but a powerbox only has 7 channel output and I am building an F-18 that will use probally the 14 channels. Also all my other jets use all 9 channels minimun.

Well any help or experiences are welcome... I would really like to stick with Futaba but I am thinking that maybe I should return the Faast module and get a Spectrum module...

Thanks in advance for the help.

Michel

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JetsRC / Skymaster Jets / Jet Artes / Jet Central
www.jetsrc.com
       Post #: 1

RE: Faast and JR servos compatibility - 5/12/2008 6:22:05 PM   
Tomas Ahl


 

Posts: 5
Joined: 3/6/2004
From: Linköping, SWEDEN
Status: offline 		Hi Michel,

I saw your question in the Futaba specific sub-forum about FASST receivers' compatibility with JR servos. And you got the usual canned nonsense response from Bax about them knowing nothing about JR equipment and the compatibility issue being a burden of JR's. I think you should instead ask if Futaba is still honoring the industry standard for signaling between receiver and servo that they have previously been honoring for years, even decades, on end. Because that is how these things are controlled, no manufacturer can test all the equipment of all other manufacturers so instead everybody adheres to a common standard.

I don't know if the standard is formally agreed on between manufacturers or if it is informal (i.e. it came to be and now "everybody" does things the same way, until now...). But this is of less importance because obviously Futaba has been compliant earlier and now we see reports of some of their receivers breaking this compliance for whatever reason.

At least six things should be governed by this standard:
- the voltage levels on the servo connectors,
- the signaling frequency from receiver to servo (how often the servo is updated with position data),
- the signaling timing from receiver to servo (the "shape" of each signaling pulse),
- the polarity of the signaling pulses (if the signal is "high" or "low" when active),
- the servo connector (which cable does what - plus, minus, signal),
- how much power may be drawn from a servo connector by the servo.

(in reply to JetsRC)
       Post #: 2

RE: Faast and JR servos compatibility - 5/12/2008 7:58:18 PM   
tkilwein



Posts: 379
Joined: 3/20/2002
From: denver, CO, USA
Status: offline 		I have a number of the affected servos hs5955tg and the problem I see, is the servo requires the RX to sink excessive current.
The servo vendor will rework the servos to reduce the current requirments.
I did the rework myself and they work now. Still have some left to rework.

Some servo models within the vendor require different current sink requirements, this varies with the HW revision of the servo I found out.
Older verses newer. My servos with revision 1.03 and 1.04 all needed to be reworked, the newer ones I have bought recently work.

The servo should not require the RX to sink current from the servo.
The servo should monitor the signal, not influence it.

I also have JR 8711's and they work fine.

< Message edited by tkilwein -- 5/13/2008 3:36:10 AM >

(in reply to Tomas Ahl)
       Post #: 3

RE: Faast and JR servos compatibility - 5/12/2008 10:57:35 PM   
quist



Posts: 1504
Joined: 1/8/2002
From: Glendale, AZ, USA
Status: online 		In my Flash I had JR 8611A's on ailerons and Rudder, 8411SA on Elevators, and Futaba 9151 on flaps. I was running the Futaba 12Z with the 6014 receiver. This setup works perfect with no problems with mixing JR and Futaba 2.4.

(in reply to tkilwein)
       Post #: 4

RE: Faast and JR servos compatibility - 5/12/2008 10:58:51 PM   
Gulliver


 

Posts: 222
Joined: 8/4/2004
From: Boulder, CO, USA
Status: offline 		What do you mean by "sink current from the servo" ?

(in reply to tkilwein)
       Post #: 5

RE: Faast and JR servos compatibility - 5/13/2008 3:35:45 AM   
tkilwein



Posts: 379
Joined: 3/20/2002
From: denver, CO, USA
Status: offline
quote:

ORIGINAL: Gulliver

What do you mean by "sink current from the servo" ?



Certain servos are biasing the input lead due to how the front end logic section is done, the Rx has to sink
current to pull this line down to a logic low level.
The servo should only monitor the input signal, not influence it, IMO.



(in reply to Gulliver)
       Post #: 6

RE: Faast and JR servos compatibility - 5/13/2008 4:11:01 AM   
Flyfalcons



Posts: 6081
Joined: 7/27/2002
From: Bonney Lake, WA, USA
Status: offline 		Michel, keep your FASST module. I flew my 2.4 FASST system for the first time last weekend using a 9C with TM-8 module and 607 receiver with JR 8411 digitals on all surfaces except throttle, and there were no issues at all.

_____________________________

Ryan Winslow

Cub flying - the new EXTREME SPORT!!! (evarrr)

(in reply to tkilwein)
       Post #: 7

RE: Faast and JR servos compatibility - 5/13/2008 7:28:31 AM   
DrV



Posts: 156
Joined: 4/12/2002
From: Los Angeles, CA,
Status: offline 		Michael

In general this problem has always been there even with the PCM Futaba Rx and JR servos. On the regular Futaba receivers (non FASST) signal is regulated to 3.3 volts, so if using 6 volts input, servo voltage can (used as the reference within the servo) get so high that the 3.3 v signal starts to look like a logic low. This causes a glitch. If using a regulator (for input voltage only) or a power management device like a powerbox the signal voltage is regulated and buffered to about 4.8-5 volts, depending what brand product used. Some have used no regulators or powerboxes with 6 volt input without problems. The FASST 6014 Rx signal is regulated down to 2.7 volts in some of the channels and this cause a logic low condition at the servo end. I have always used a regulator/power management systems regulated to about 5.2v without any problems. Having said all this, I haven’t heard anyone having problems with the JR servos with the 6014 Rx. All problems were with the Hitec digitals such as the hs5955.

You should stick with FASST and continue using power management systems. If you need more channels Smart-Fly makes an excellent product such as the PowerExpander 14MZ. Check it out

http://www.smart-fly.com/Products/Expander/expander.htm

Mike


< Message edited by DrV -- 5/13/2008 7:40:23 AM >

(in reply to JetsRC)
       Post #: 8

RE: Faast and JR servos compatibility - 5/13/2008 12:42:13 PM   
Rudy F


 

Posts: 52
Joined: 8/30/2006
From: Vienna, AUSTRIA
Status: online 		Hi everybody,

try this method. The pic is selfexplaining despite of German: http://members.aon.at/flug.fiala/messverfahren.html#VTeiler

Greetings from Vienna/Austria,

Rudy

< Message edited by Rudy F -- 5/13/2008 12:43:10 PM >

(in reply to DrV)
       Post #: 9

RE: Faast and JR servos compatibility - 5/19/2008 6:12:49 AM   
JetsRC



Posts: 957
Joined: 7/28/2004
From: Santiago-, CHILE
Status: online 		Thanks for all the info guys, I just got a whole bunch of JR servos, I am waiting on my new Royales to arrive and I will do some tests. I will post if I find something weird...

Thanks again...

_____________________________

JetsRC / Skymaster Jets / Jet Artes / Jet Central
www.jetsrc.com

(in reply to Rudy F)
       Post #: 10

RE: Faast and JR servos compatibility - 5/19/2008 1:52:23 PM   
wingburner



Posts: 521
Joined: 1/18/2003
From: Beaverlodge, AB, CANADA
Status: offline 		I installed my new FASST 6014 this spring in my 42% Dalton..I have 10 8611a-2-8711 and 1-8321 in it..Smoother than ever

(in reply to JetsRC)
       Post #: 11

RE: Faast and JR servos compatibility - 5/20/2008 6:22:58 AM   
JetsRC



Posts: 957
Joined: 7/28/2004
From: Santiago-, CHILE
Status: online 		Excellent...

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JetsRC / Skymaster Jets / Jet Artes / Jet Central
www.jetsrc.com

(in reply to wingburner)
       Post #: 12

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