[NSRCA-discussion] Futaba R6014FS Receivers
Ed Alt
ed_alt at hotmail.com
Sun Nov 23 11:22:38 AKST 2008
OK, I set up an attenuator on the signal to get results on a handful of servos. Jim O. already did this, but I think it was with just one servo? I don't have his post anymore.
This test was done with a 10K Bournes precision pot, ground to one lead, signal out to servo the wiper, signal in from the receiver to the other end. Aileron channel on the R921 used for signal attenuation tests, rudder used to add a separate DS8611 servo load to induce crosstalk. Added lead length of attenuator network about 1 foot of extension wiring. Signal level measured about midway in the 1 foot of added wiring. This would be rouighly equivilent to what's happening halfway along an aileron extension in a Pattern bird. Also, I tried a couple of old analog Futaba servos I had.
Results:
DS8411A
Loads the test network by about 0.05V drop
Below 1.2V, totally uncontrolled response or no response.
1.2V - Very jumpy, not really controllable, even when the 8611 was silent or disconnected. Significant crosstalk from 8611 when active. The lightest touch on the 8611 to try to move it would set off the 8411 on the test channel. You would crash.
1.3V - Jittery, but controllable. Noticeable, but improved crosstalk from 8611. You might make it in, but your shorts may need laundering.
1.4V - Solid.
DS9411A
Loads the test network by about 0.05V drop
0.1V better than the 8411, otherwise a carbon copy of it's performance, just offset by +0.1V. The small difference is likely explained by component tolerances and less noise injected on the power rails because the 9411 is a lower torque servo.
DS8611
Loads the test network by about 0.05V drop
0.1V worse than the 8411. It's a much higher torque servo and injects about 0.2V of noise on the ground lead every time the motor moves. The 8411 injects a little less noise, something like 0.5V less, but I can't measure that accurately.
DS821
Loads the test network by about 0.2V drop
0.85V - No response
0.9V - wild response (see 8411 notes above about crashing at 1.2V)
0.95 - Just barely controllable, a lot of crosstalk. You would still crash, but it might take a little longer.
1.0V - A little jumpy, some crosstalk.
NES-4131
Loads the test network by about 0.1V drop
1.3V - Very wild response, frequently drives to the stops
1.35V - Slightly jittery, some crosstalk
1.4V - Fairly solid, milder crosstalk
1.5V - Solid, very mild crosstalk
Futaba S3101
Requires 1.5V to work solid
Futaba S9602
Works well at 1.1V
I also tried adding a 2nd DS series servo to the test channel (added a 9411 to an 8411) while the 8411 was set to work at 1.3V (controllable, but jittery). I deliberately did not adjust the signal level to compensate for the additional load and observed that it became very wild for both servos. This is to be expected, since the signal level was already a what I would consider the minimum controllable level. The 9411 added load knocked it down roughly another 0.5V, but also added more noise to the equation.
So to summarize, when you get out at longer lead lengths, the effects of signal degration to to crosstalk, capacitive loading etc becomes worse than in my test. In a pattern plane, not so bad, but in a big IMAC thing, watch out. Double up on servos on an extension, worse again. Add higher torque servos, worse again. These are intended as useful guidelines and not absolutes. I still think the margins are uncomfortably low with only a 2.7V receiver output, but maybe Futaba or JR has a different view.
Ed
----- Original Message -----
From: Ed Alt
To: General pattern discussion
Sent: Saturday, November 22, 2008 9:00 AM
Subject: Re: [NSRCA-discussion] Futaba R6014FS Receivers
I don't know what their limit is, but I did just scope the output of a Spektrum R921 and it's a 3.4V pulse on an unloaded channel. A lot of this can depend on lead length and drive capability of the channel output, so 3.4V from a R921 or 2.7V from a R6014S becomes something less at the servo input. I still have an R955, but I can't measure it since I no longer have a PCM Tx (it's for sale too - cheap!).
Ed
----- Original Message -----
From: John Pavlick
To: General pattern discussion
Sent: Saturday, November 22, 2008 1:36 AM
Subject: Re: [NSRCA-discussion] Futaba R6014FS Receivers
Ed,
What do the typical JR servos that we use in Pattern planes (8411, 9411, etc.) like to see? I want to use them with my Futaba 5114 (PCM - G3, 72 Mhz) receivers. I'll check the signal levels on the receivers this weekend.
John Pavlick
http://www.idseng.com
----- Original Message -----
From: Ed Alt
To: bob at toprudder.com ; General pattern discussion
Sent: Saturday, November 22, 2008 12:00 AM
Subject: Re: [NSRCA-discussion] Futaba R6014FS Receivers
Aside from using a purpose built servo that matches logic families with the receiver, the only real solution is to insert a level translater in between; basically a simple buffer that allows you to take a lower voltage ourput signal from one logic family in the receiver and boost the signal level to work with a servo that requires higher levels for safe operating margins. Personally, I would not fly other servos without doing this, even if they seem to be working fine. Jim Oddino's post used two very instructive words: "ragged edge".
Ed
----- Original Message -----
From: Bob Richards
To: General pattern discussion
Sent: Friday, November 21, 2008 9:42 PM
Subject: Re: [NSRCA-discussion] Futaba R6014FS Receivers
I think I read somewhere that the R608FS receiver uses the same chipset and has the same problem.
So far I have not had any problems with the servos that I use, but I was not able to check the pulse width out of the higher channels with my Hitec programmer. I have to wonder, however, exactly what is the logic level for the various servos? Also, does the logic level of the servo change with a different battery voltage? Does the output level from the rx change with a different battery voltage?
I guess this is a good reason to use some sort of output conditioner (powerbox, etc) if mixing brands of receivers and servos.
Bob R.
--- On Fri, 11/21/08, MKMSG <mkmsg at cox.net> wrote:
From: MKMSG <mkmsg at cox.net>
Subject: [NSRCA-discussion] Futaba R6014FS Receivers
To: "NSRCA Discussion List" <nsrca-discussion at lists.nsrca.org>
Date: Friday, November 21, 2008, 1:15 AM
I was reading the FAQ section of the Futaba website when a particular item caught my eye regarding the R6014FS 2.4 receiver. The FAQ states that the use of non Futaba digital servos with the R6014FS receiver may be problematic due to the 6014's lower output voltage of 2.7 volts. Since I do occasionally mix and match Futaba and JR servos and use the 8 channel 2.4 receiver, I wondered if this issue was common to all Futaba 2.4 receivers. Here's Futaba's answer: "The FAQ refers only to the R6014FS receiver, this is the only one that has the lower voltage." Just thought I'd pass this along in case someone experiences performance anomalies with the 6014 receivers using other than Futaba servos.
Mike
NSRCA 35
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