2 futaba 7008sb rx's vs 3 decoders?
11-10-2015, 05:50 AM
#1
2 futaba 7008sb rx's vs 3 decoders?
Setting up my Bobcat, & have never used 2 rx in a jet, anyone using this setup? Also any idea if there are any benefits to either 2 rx's or 3 decoders? with decoders being $57 a piece, the price is approx the same.
Thanks, Jay
Thanks, Jay
11-10-2015, 06:01 AM
#2
Are you planning an sbus set up using non sbus servos? Any bus servos at all?If using all non-sbus I think I would but a decoder in each boom, wire the rudder, flap, aileron on each one, and run the elevator straight from the rx, then one decoder for retracts /brakes/throttle if needed. I think you would only need two though???
11-10-2015, 06:23 AM
#3
Thanks for the reply. It has all JR servos. I purchased it RTF with a 14ch rx and a 12FG radio. I am retro fitting a 7008sb and reprogramming the Bobcat to my 18MZ to use it's telemetry capabilities. With only 7 ports (8th for batt), I think I'd need 3 decoders since every port on the 14ch rx was utilized.
Jay
Jay
11-10-2015, 07:39 AM
#4
Nope, two decoders will do it, even one would do it, but be harder to wire. run a hub for the two decoders to middle of plane, have the decoders in each boom.
1 throttle
2 gear
3 brakes
4 elevator
5 open
6 open
7 open
8 battery
1st decoder
10 rudder
11 flap
12 ail
2nd decoder
13 rudder
14 flap
15 ail
Love the 18mz and sbus!!!
1 throttle
2 gear
3 brakes
4 elevator
5 open
6 open
7 open
8 battery
1st decoder
10 rudder
11 flap
12 ail
2nd decoder
13 rudder
14 flap
15 ail
Love the 18mz and sbus!!!
11-10-2015, 08:50 AM
#6
They are JR servos. I an going to attach a drawing of how I think I have to utilize the decoders & see I am misunderstanding something. It has a Cortex gyro also, not sure if that matters, but I love playing with this stuff. It's going to be a fun install. Thanks guys, I'll draw something up later
11-10-2015, 10:26 AM
#7
If you are using a gyro anyway, both the cortex and the i-gyro (the original one, not the new 3e) can take s-bus in and put out all the primary gyro-controlled flight surfaces as standard PWM outputs. So you get a "free decoder" function from them.
With some of my planes the gyro outputs plus the "native" ports on the RX have been enough channels (you get 5 from the gyro (on the cortex you can actually get a 6th), and 7 from the RX this way (since you are using channel 8 for Sbus) .. for a total of 12 or 13).
This benefit from the gyro assumes you had wired all 5 primary flight surfaces as one channel each.. if you had used matchboxes or Y-connectors, you'd only get 3 channels from it... or 4 from the Cortex. So you'd probably need an SBD-1 or two, or an SBD-2.
CB electronics has an Sbus decoder with a separate power feed. They make nice stuff but I have not tried their decoder (http://www.cb-elektronics.de/NH-5%20...ta%20sheet.pdf). Dreamworks is now carrying some of the CB stuff, but I have not seen this decoder yet .. but their speed sensor works well.
Futaba also has an 8-channel decoder (SBD-2) that Tower has for $89.00 if the SBD-1 3-output decoder is not sufficient. This should cover most cases. I don't see the point of two RXs to gain channels. To really benefit from two RXs, you would want RX redundancy - you can get that with the i-gyro (not the cortex), or a Powerbox or a Robbe/Emcotec DPSI unit...
Dave
With some of my planes the gyro outputs plus the "native" ports on the RX have been enough channels (you get 5 from the gyro (on the cortex you can actually get a 6th), and 7 from the RX this way (since you are using channel 8 for Sbus) .. for a total of 12 or 13).
This benefit from the gyro assumes you had wired all 5 primary flight surfaces as one channel each.. if you had used matchboxes or Y-connectors, you'd only get 3 channels from it... or 4 from the Cortex. So you'd probably need an SBD-1 or two, or an SBD-2.
CB electronics has an Sbus decoder with a separate power feed. They make nice stuff but I have not tried their decoder (http://www.cb-elektronics.de/NH-5%20...ta%20sheet.pdf). Dreamworks is now carrying some of the CB stuff, but I have not seen this decoder yet .. but their speed sensor works well.
Futaba also has an 8-channel decoder (SBD-2) that Tower has for $89.00 if the SBD-1 3-output decoder is not sufficient. This should cover most cases. I don't see the point of two RXs to gain channels. To really benefit from two RXs, you would want RX redundancy - you can get that with the i-gyro (not the cortex), or a Powerbox or a Robbe/Emcotec DPSI unit...
Dave
Last edited by ww2birds; 11-10-2015 at 10:53 AM.
11-10-2015, 10:34 AM
#8
Dave, the cortex can take the s.bus info from one wire? Or, do you have to have an encoder in-between the two? I have the gyro and cortex, never tried to make them play with sbus. You are going to have to use matchboxes or Y-leads and mechanically adjust on this plane, that would blow. I'd rather do without the gyro.
Hello Futaba…. Can we please have an s.bus rx with a built in 3-axis gyro and full assignability of channels with the tx???? I can do it with the power box royal SRS, but that is way overkill for most planes.
Hello Futaba…. Can we please have an s.bus rx with a built in 3-axis gyro and full assignability of channels with the tx???? I can do it with the power box royal SRS, but that is way overkill for most planes.
11-10-2015, 11:59 AM
#9
Yes, the Cortex can take one Sbus wire as input. The Sbus has all the channels in a serial format. No decoder needed in this case, it's internal to the Cortex. But you do need the PC software to configure it this way. The the Cortex will read a total of 6 channels from the Sbus stream (L ail, R ail, L elev, R elev, Rud and a "spare" they refer to as throttle but can be anything). The Cortex PC software is again used to configure the channel number for each of these 6 inputs.
The iGyro can do all this, and can also take two input RXs (one wire each for Sbus) and select the one with a better signal. The iGyro can also do dual digital outputs for Sbus servos if you want to set it up this way. In this case, it selects the RX with the stronger signal, applies the gyro corrections and creates a new Sbus stream with the Gyro functions mixed in. Very nice.
Dave
The iGyro can do all this, and can also take two input RXs (one wire each for Sbus) and select the one with a better signal. The iGyro can also do dual digital outputs for Sbus servos if you want to set it up this way. In this case, it selects the RX with the stronger signal, applies the gyro corrections and creates a new Sbus stream with the Gyro functions mixed in. Very nice.
Dave
11-10-2015, 12:01 PM
#10
Join Date: Nov 2006
Location: yorba linda,
CA
Posts: 595
Likes: 0
Received 0 Likes
on
0 Posts
Also Futaba now has the SBD-2 (As stated above)
http://www3.towerhobbies.com/cgi-bin...FQQPaQodZM4Aqg
It's a little more economical approach that the SBD-1's and it would be a good place to pl,ub in your second battery to help share the servo load.
There is also the New Rx the R7018SB
http://www3.towerhobbies.com/cgi-bin...&I=LXFFFR&P=SM
It eliminates the need for Smart switches and such and gives you 16 standard PWM outputs. It looks Nice I have one but haven't yet installed it on anything. If you eliminate the Smart switch and an SBD-2 or a couple of SBD-2's i think you are ahead of the game vs the R7008SB on cost.
I don't think I would be a fan of dual 7008's. You don't really gain redundancy unless you can split up your servos in a way where you could fly on only one Rx if the other one quit. You already have a fair amount of redundancy built into the diversity antenna's on the 7008.
There is a little known log function on the 18mz that is quite handy. I have it set up on my throttle trim switch. The log starts with trim up(turbine start) and continues until trim down (turbine off). This will then record all of your telemetry items onto the SD card including Signal quality (RSSI).
This is real handy on a new install to make sure the antenna placement is optimum. 3=Great Signal 2=Nice Signal 1=One of the Diversity channels fell out but still able to control with no issues and 0=Both channels blocked and going into failsafe.
http://www3.towerhobbies.com/cgi-bin...FQQPaQodZM4Aqg
It's a little more economical approach that the SBD-1's and it would be a good place to pl,ub in your second battery to help share the servo load.
There is also the New Rx the R7018SB
http://www3.towerhobbies.com/cgi-bin...&I=LXFFFR&P=SM
It eliminates the need for Smart switches and such and gives you 16 standard PWM outputs. It looks Nice I have one but haven't yet installed it on anything. If you eliminate the Smart switch and an SBD-2 or a couple of SBD-2's i think you are ahead of the game vs the R7008SB on cost.
I don't think I would be a fan of dual 7008's. You don't really gain redundancy unless you can split up your servos in a way where you could fly on only one Rx if the other one quit. You already have a fair amount of redundancy built into the diversity antenna's on the 7008.
There is a little known log function on the 18mz that is quite handy. I have it set up on my throttle trim switch. The log starts with trim up(turbine start) and continues until trim down (turbine off). This will then record all of your telemetry items onto the SD card including Signal quality (RSSI).
This is real handy on a new install to make sure the antenna placement is optimum. 3=Great Signal 2=Nice Signal 1=One of the Diversity channels fell out but still able to control with no issues and 0=Both channels blocked and going into failsafe.
11-10-2015, 01:17 PM
#13
Join Date: Nov 2006
Location: yorba linda,
CA
Posts: 595
Likes: 0
Received 0 Likes
on
0 Posts
I saw that with super high torque servos, on the bench, with very rapid movements they were able to get the Rx to glitch for a second.
The addition of something like this capacitor on the servo side completely eliminated the problem:
http://www.rcplanet.com/Spektrum_Vol...opping+Feed%29
I think the theory was that the ultra heavy duty servos (540 oz/in) going through very rapid stick movements with no load were acting like little generators. At the endpoints of their strokes they were producing rather than drawing current. It was likely freaking out the Smart switch circuitry. IMHO I don't think a jet could produce the same type of movements on the servos without aerodynamically destroying the jet. But the addition of the capacitor completely eliminated the problem.
I also would not be surprised that under the same tests, other brands of "Smart Switch" dual battery electronic switches might also experience some unexpected behavior.
I think I would feel safe flying with the R7018SB in a normal jet setup but the capacitor is light and inexpensive. I think it would be cheap insurance. Just my 2 cents
11-10-2015, 01:25 PM
#14
Steve is right .. using two 7008s to get more channels is not a great setup. However using two 7008s where the "downstream" device monitors both and picks the one with a stronger signal makes sense to me. I've done this with the iGyro, and with the Emcotec DPSI/Robbe PSS2018.
Since the PSS logs data I have scanned the log files from my UB flights and it's interesting .. the signal is listed in the PSS log as 0-100, and it flips around in the high 90s and occasionally swaps from one RX to the other as one might be 98 when the other is 96. So at least for that install, the dual RX is overkill. But cheap insurance for a plane...
Of course you can't use any of the RX's own "native" PWM outputs in a setup where you use two RXs to gain redundancy.. you have to rely on either an all-Sbus setup, or use some decoders. The PSS2018 has many PWM outputs built in that turn out to be convenient for the "utility" functions usually found on the main board in the fuse where you might be using simpler or older servos or non-servo devices that only take PWM (e.g. brakes, retracts, smoke systems).
Nice tip on connecting the telemetry logging to the throttle trim. I use the left slider as an analog throttle trim, and sometimes also use it to turn the master lighting switch on and off...
Dave
Since the PSS logs data I have scanned the log files from my UB flights and it's interesting .. the signal is listed in the PSS log as 0-100, and it flips around in the high 90s and occasionally swaps from one RX to the other as one might be 98 when the other is 96. So at least for that install, the dual RX is overkill. But cheap insurance for a plane...
Of course you can't use any of the RX's own "native" PWM outputs in a setup where you use two RXs to gain redundancy.. you have to rely on either an all-Sbus setup, or use some decoders. The PSS2018 has many PWM outputs built in that turn out to be convenient for the "utility" functions usually found on the main board in the fuse where you might be using simpler or older servos or non-servo devices that only take PWM (e.g. brakes, retracts, smoke systems).
Nice tip on connecting the telemetry logging to the throttle trim. I use the left slider as an analog throttle trim, and sometimes also use it to turn the master lighting switch on and off...
Dave
11-10-2015, 07:00 PM
#16
Yes! ... just one small swizzle:
When the 7008 outputs an Sbus signal, it uses the Channel 8 pin for Sbus out .. so you only get 7 PWM channels in the Sbus modes B and D .. but in your picture you are only using 5 channels on the SBD-2 so Gyro can go on the SBD.
So, specifically, set the 7008SB to mode "B" (channels 1-7, Sbus out on channel 8); set the SBD-2 DIP switch to position 3 (channels 8-15) and you are good to go! Plus you are using 13 channels and this setup gives you 15 (the battery port on the SBD-2 is in addition to the 8 outputs!) .. so two to spare .. woo hoo :-)
Dave
When the 7008 outputs an Sbus signal, it uses the Channel 8 pin for Sbus out .. so you only get 7 PWM channels in the Sbus modes B and D .. but in your picture you are only using 5 channels on the SBD-2 so Gyro can go on the SBD.
So, specifically, set the 7008SB to mode "B" (channels 1-7, Sbus out on channel 8); set the SBD-2 DIP switch to position 3 (channels 8-15) and you are good to go! Plus you are using 13 channels and this setup gives you 15 (the battery port on the SBD-2 is in addition to the 8 outputs!) .. so two to spare .. woo hoo :-)
Dave
11-10-2015, 07:09 PM
#17
Yes! ... just one small swizzle:
When the 7008 outputs an Sbus signal, it uses the Channel 8 pin for Sbus out .. so you only get 7 PWM channels in the Sbus modes B and D .. but in your picture you are only using 5 channels on the SBD-2 so Gyro can go on the SBD.
So, specifically, set the 7008SB to mode "B" (channels 1-7, Sbus out on channel 8); set the SBD-2 DIP switch to position 3 (channels 8-15) and you are good to go! Plus you are using 13 channels and this setup gives you 15 (the battery port on the SBD-2 is in addition to the 8 outputs!) .. so two to spare .. woo hoo :-)
Dave
When the 7008 outputs an Sbus signal, it uses the Channel 8 pin for Sbus out .. so you only get 7 PWM channels in the Sbus modes B and D .. but in your picture you are only using 5 channels on the SBD-2 so Gyro can go on the SBD.
So, specifically, set the 7008SB to mode "B" (channels 1-7, Sbus out on channel 8); set the SBD-2 DIP switch to position 3 (channels 8-15) and you are good to go! Plus you are using 13 channels and this setup gives you 15 (the battery port on the SBD-2 is in addition to the 8 outputs!) .. so two to spare .. woo hoo :-)
Dave
Jay
11-10-2015, 07:11 PM
#18
Assign all the stuff in the front end to the channels that can reach directly to the Exact 1-8. Just because the tx assigns functions by default, doesn't mean you have to keep it that way.
flex your 18mz muscles!
11-10-2015, 08:00 PM
#19
one of the primary benefits of sbus is shortening the amount of wires. The way you have it laid out, you might as well use a regular 14 channel rx. Put the decoder in the back by the tanks, and assign all those channels higher numbers.
Assign all the stuff in the front end to the channels that can reach directly to the Exact 1-8. Just because the tx assigns functions by default, doesn't mean you have to keep it that way.
flex your 18mz muscles!
Assign all the stuff in the front end to the channels that can reach directly to the Exact 1-8. Just because the tx assigns functions by default, doesn't mean you have to keep it that way.
flex your 18mz muscles!
Thanks Dr Scoles,
Jay
Last edited by BlueBus320; 11-10-2015 at 08:02 PM.
11-11-2015, 06:24 AM
#20
Jay, Your thread has taught me a few things because others chimed in. This is the beauty of these forums, people exchanging information and helping each other.
Here is one of my sbus set-ups for a big P-51. Having the ability to assign channels and name them makes things so much easier for programming a plane IMO. I set up a buddy's plane with a JR 12X. I wanted to shoot myself. I see where JR is going, they want to make the process as simple as possible, so they don't let you do certain things. With the 18MZ, it is more complicated, no doubt. But if you wanted to you could assign 18 channels to one slider and name every channel differently and have them all firing at different intervals! This radio is very flexible, you get a default template, I just clear it out and start over.
Just touch the name of the function in the FUNCTION screen and it will allow you to change it to anything you want. If what you want isn't available, I will assign an aux channel, then go to FUNCTION NAME and rename it. Makes things a ton easier when you are troubleshooting or just adjusting throws...
Here is one of my sbus set-ups for a big P-51. Having the ability to assign channels and name them makes things so much easier for programming a plane IMO. I set up a buddy's plane with a JR 12X. I wanted to shoot myself. I see where JR is going, they want to make the process as simple as possible, so they don't let you do certain things. With the 18MZ, it is more complicated, no doubt. But if you wanted to you could assign 18 channels to one slider and name every channel differently and have them all firing at different intervals! This radio is very flexible, you get a default template, I just clear it out and start over.
Just touch the name of the function in the FUNCTION screen and it will allow you to change it to anything you want. If what you want isn't available, I will assign an aux channel, then go to FUNCTION NAME and rename it. Makes things a ton easier when you are troubleshooting or just adjusting throws...
11-11-2015, 05:13 PM
#21
Jay, Your thread has taught me a few things because others chimed in. This is the beauty of these forums, people exchanging information and helping each other.
Here is one of my sbus set-ups for a big P-51. Having the ability to assign channels and name them makes things so much easier for programming a plane IMO. I set up a buddy's plane with a JR 12X. I wanted to shoot myself. I see where JR is going, they want to make the process as simple as possible, so they don't let you do certain things. With the 18MZ, it is more complicated, no doubt. But if you wanted to you could assign 18 channels to one slider and name every channel differently and have them all firing at different intervals! This radio is very flexible, you get a default template, I just clear it out and start over.
Just touch the name of the function in the FUNCTION screen and it will allow you to change it to anything you want. If what you want isn't available, I will assign an aux channel, then go to FUNCTION NAME and rename it. Makes things a ton easier when you are troubleshooting or just adjusting throws...
Here is one of my sbus set-ups for a big P-51. Having the ability to assign channels and name them makes things so much easier for programming a plane IMO. I set up a buddy's plane with a JR 12X. I wanted to shoot myself. I see where JR is going, they want to make the process as simple as possible, so they don't let you do certain things. With the 18MZ, it is more complicated, no doubt. But if you wanted to you could assign 18 channels to one slider and name every channel differently and have them all firing at different intervals! This radio is very flexible, you get a default template, I just clear it out and start over.
Just touch the name of the function in the FUNCTION screen and it will allow you to change it to anything you want. If what you want isn't available, I will assign an aux channel, then go to FUNCTION NAME and rename it. Makes things a ton easier when you are troubleshooting or just adjusting throws...
11-14-2015, 09:21 AM
#23
That was the original intent. Put power downstream and you have a redundant system. I am the first to admit that electrical stuff is like a foreign language to me. I do know that if you wanted To do that with the second battery lead and have it isolated from the other rx power, you. Just have a signal wire go to the hub, then power that. Th initial videos from futaba made it sound like you could plug in second. Power source anywhere in the system and it would equally power... Love for someone with better understanding to explain how that works.
Please se forgive typos. On iPad and too lazy to go back and. Fix..��
Please se forgive typos. On iPad and too lazy to go back and. Fix..��
11-14-2015, 09:31 AM
#24
My Feedback: (38)
I just experimented this am. It will not back feed. If you have power only to Sbd2 you have none in receiver. Also, I have a combo of sbus and non susbus servos. If you are using a sbus outlet in the 7009 receiver, the Sbd2 will not work. I tried hooking the sbus servo to the sbus inlet and the Sbd2 to the sbus inlet aND the Sbd2 did not work. I also reversed it and then the servos would not work unless I am doing some the wrong. The 7008 is set for 1 to 7 and Sbd2 to 8 plus.