Can you put 2 receivers in a drone? Possible? - RC Groups
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Sep 03, 2017, 05:55 PM
Registered User
Question

Can you put 2 receivers in a drone? Possible?


Hey RC experts and enthusiasts! I have a few questions about receivers.

1)If installing multiple 2.4ghz receivers in a drone/plane, can you piggyback them? In other words: link them together and get 16 channels instead of 8 for example? Theoretically.

2) Can you run 2 receivers off of one ESC?

3) If you have a 8 channel receiver, and a 4 channel transmitter... will that work? Can you control the receiver with the transmitter? Or do you definitely need a transmitter that matches the channel level of the receiver? I guess Im asking cause I know you have to match things like DSM and DSM2 on transmitter and receiver, but Im not sure what else needs to be matched.

The reason Im asking is cause Im working on a project plane. The receiver/transmitter that comes with it is a 6 channel DSM2 spectrum. I want to add a bunch more servos to the plane so I can do random funky unnecessary cool stuff. So I want to add a second receiver, plug a few servos in the plane, and take apart an old transmitter and turn it into a control board that can sit on my lap or off to the side with a joystick and switches etc. Thats the plan. So if anyone comes up with any advice they want to share with me knowing my project, Im all ears. Thanks everyone!!
Last edited by frogfly; Sep 03, 2017 at 06:03 PM.
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Sep 04, 2017, 07:55 PM
No bounce, No play.
davidmc36's Avatar
Best bet is FrSky. Supports two Rx's and 16 channels right out of the box.
Sep 04, 2017, 08:50 PM
If it flies, I can crash it.
rocketsled666's Avatar
1) Many radio systems support channel expansion, you don't necessarily need a second RX. If your FC has serialRX support you have additional options.

2) Yes. But the BEC that's in the ESC, which is what provides the power, has limits. Depending on what else you attach to those RXs, you might overload the BEC.

3) The transmitter has to have as many channels as you want to use. But you don't have to use them. A 4 channel RX will work with an 8 channel TX and a 8 channel RX will work with a 4 channel TX. In both cases, you will only get 4 channels.

What you're suggesting doing is using two TXs and two RXs in the same plane. There is no problem with doing that. They will coexist just fine. Many people do this. On more complex scale models a second TX with a co-pilot might be used to control the extra functions. More commonly, camera drones use one radio system for piloting and a second for camera/gimbal control. You don't have to worry about anything except #2.

You plan to run servos and servos draw current. You need to add up all the current that the servos can draw (assume worst-case, that they all draw their maximum at the same time) and make sure the ESC's BEC can handle it. Most ESC BECs are 5A max, which is good for about 4-5 servos. If you plan to use more than this, which it seems you do, you should use a second stand-alone BEC to power the second RX and its servos independent of the primary flight RX/servos, which are powered off the ESC's BEC.
Sep 04, 2017, 10:16 PM
Registered User
Quote:
Originally Posted by davidmc36
Best bet is FrSky. Supports two Rx's and 16 channels right out of the box.
Awesome! Thanks david, I'll look into the frsky
Sep 04, 2017, 10:19 PM
Registered User
Quote:
Originally Posted by rocketsled666

2) Yes. But the BEC that's in the ESC, which is what provides the power, has limits. Depending on what else you attach to those RXs, you might overload the BEC.

You plan to run servos and servos draw current. You need to add up all the current that the servos can draw (assume worst-case, that they all draw their maximum at the same time) and make sure the ESC's BEC can handle it. Most ESC BECs are 5A max, which is good for about 4-5 servos. If you plan to use more than this, which it seems you do, you should use a second stand-alone BEC to power the second RX and its servos independent of the primary flight RX/servos, which are powered off the ESC's BEC.
Ok perfect. I have an extra esc and batteries. I dont mind throwing another esc in there, just trying to avoid adding more battery weight (thats why I was hoping to run the main setup + the new rx and servos off the one ESC). All in all, the 2nd receiver will only really run a couple servos, maybe 3-4 max. So glad you filled me in that its ok the run 2 rx in a setup. Heck, actually thanks for answering period haha. I didnt think anyone was going to so I went ahead and bought a few servos and rx already! Just waiting for it to come in the mail.
Last edited by frogfly; Sep 04, 2017 at 10:20 PM. Reason: Better detail
Sep 05, 2017, 12:22 AM
If it flies, I can crash it.
rocketsled666's Avatar
You can use a second ESC just for its BEC and just not connect a motor, sure. But you can get a stand-alone BEC that'll be smaller, for cheap $.

In either case, plug the ESC (or BEC) in to the BATT port of the second RX. You don't need to plug it in to the Throttle channel, and this will let you use channel 1 for one of your servos.
Sep 08, 2017, 10:09 PM
Registered User
Quote:
Originally Posted by rocketsled666
You can use a second ESC just for its BEC and just not connect a motor, sure. But you can get a stand-alone BEC that'll be smaller, for cheap $.

In either case, plug the ESC (or BEC) in to the BATT port of the second RX. You don't need to plug it in to the Throttle channel, and this will let you use channel 1 for one of your servos.
Ok. Ive never used a BEC and dont know much about them, guess this could be a good time to get one! Any recomendation on what type to get? I dont mean brand, I plan to go to banggood for low priority things like this. But Im seeing thing like:

3A 5V 2-5s
5.3v
3A/5A/7A/15A
6A 6V

Not sure what I need really. I have a 3cell 11.1v lipo and plan to add the second RX with maybe 3 or 4 servos. Doesn't seem like a servo would call for much power
Last edited by frogfly; Sep 08, 2017 at 10:14 PM. Reason: detail
Sep 08, 2017, 11:46 PM
If it flies, I can crash it.
rocketsled666's Avatar
You have used a BEC, you just don't realize it. The thing on the ESC that powers the RX is a BEC. It's just built in to the ESC instead of being a separate device. Many ESCs (the ones for multirotors) are BEC-less (they call them "Opto" which isn't what they are, no one knows why they're called this).

The best efficiency will be a BEC that's got about 20% more capacity than you need, and that has an input voltage range that's closest to the battery you'll use. But in practice it doesn't matter a lot. Though it's worth noting that higher-Amp BECs usually have reduced maximum output currents on 6S (like, it'll be rated for 10A on a 3-4S pack but only 5A on a 6S).

How much the servo needs is a function of the size of the servo and the load you're going to put on it. The swash servos on my big FBL heli can draw close to 5 Amps each when they're working hard. Tail servo pulls a lot, too. These servos have metal cases with heat-sink fins machined in to help keep them cool. In contrast, the tiny servos in my UMX 2S A-10 probably max out at a couple of hundred milliamps.

If you're just going to use the servos to do things like point a camera or operate a door or drop-release you don't need big servos so you don't need a big BEC. I'd go for a 5V 5A good for 2-4S input voltage. If the servos have to carry flight loads (control surfaces) then it'll depend on exactly how big the servos are and how much control surface they need to move and how fast you'll be moving when they do it. Not easy to figure out. But the servo's specs will say what it's maximum current draw will be. Jut use that if you're not sure how much load the servo will have to deal with.
Sep 10, 2017, 02:16 AM
Registered User
Quote:
Originally Posted by rocketsled666
You have used a BEC, you just don't realize it. The thing on the ESC that powers the RX is a BEC. It's just built in to the ESC instead of being a separate device. Many ESCs (the ones for multirotors) are BEC-less (they call them "Opto" which isn't what they are, no one knows why they're called this).

The best efficiency will be a BEC that's got about 20% more capacity than you need, and that has an input voltage range that's closest to the battery you'll use. But in practice it doesn't matter a lot. Though it's worth noting that higher-Amp BECs usually have reduced maximum output currents on 6S (like, it'll be rated for 10A on a 3-4S pack but only 5A on a 6S).

How much the servo needs is a function of the size of the servo and the load you're going to put on it. The swash servos on my big FBL heli can draw close to 5 Amps each when they're working hard. Tail servo pulls a lot, too. These servos have metal cases with heat-sink fins machined in to help keep them cool. In contrast, the tiny servos in my UMX 2S A-10 probably max out at a couple of hundred milliamps.

If you're just going to use the servos to do things like point a camera or operate a door or drop-release you don't need big servos so you don't need a big BEC. I'd go for a 5V 5A good for 2-4S input voltage. If the servos have to carry flight loads (control surfaces) then it'll depend on exactly how big the servos are and how much control surface they need to move and how fast you'll be moving when they do it. Not easy to figure out. But the servo's specs will say what it's maximum current draw will be. Jut use that if you're not sure how much load the servo will have to deal with.
Ok lots of good info. Well when the new rx and servos come in the mail, I guess Ill just test them with a multimeter to see how much juce they use, add them up and see what bec I need at that time and add 20% to it to be safe. Thanks rocketsled!
Nov 13, 2017, 03:16 PM
Chasin' that Neon Rainbow
Grantham Kid's Avatar
Did you realize you need a FrSky Transmitter to run the FrSky reciever you ordered?
Your transmitter and reciever must be the same protocol and I don't see any mention from you about a transmitter.


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