Low cost DIY Frsky 8ch receiver

by JUSS10 | August 31, 2018 | (7) Posted in How To

I've recently been making the switch to running all my planes on the Frsky protocol since buying a Taranis QX7. To date, I've been flying cheaper DSMX receivers in my foam planes with a module on my radio. A friend of mine gave me some low cost receivers that he purchased from Banggood.com to try out. One was a 4ch which I have been running in my Goblin with great success. That said, I prefer at least 6ch radios so I have a few spare channels to add lights, separate channels for ailerons and most importantly, a lost model beeper (I fly over a corn field at my club). In comes the other receiver he gave me. Its an 8ch receiver that is just the board, no pins. I think a lot of people use them for quads as it has sbus and PPM outputs. That said, it also has a string of 8 PWM outputs on one side. I decided to make a break out board that used the standard servo header pins as well as some smaller header pins to solder the receiver boards to. Below is the info needed to build one of these receivers. 

Items needed

receiver board purchased from banggood: https://www.banggood.com/2_4G-8CH-D8-Mini-FrSky-Compatibel-Receiver-With-PWM-PPM-SBUS-Output-p-1140478.html?rmmds=myorder

PCB breakout board: https://oshpark.com/shared_projects/Q3kRt6W7

right angle header for servo leads: https://www.ebay.com/itm/1pc-90-Degree-2-54mm-3x40P-Male-Pins-Three-Row-Right-Angle-Pin-Header-Connector/252492439694?epid=597449186&hash=item3ac9b8e08e:g:Y3gAAOSw-itXqDbW

2mm header pins: https://www.ebay.com/itm/10pcs-1-x-40pin-2mm-Single-Row-Breakaway-Male-Pin-header-for-Arduino-DIY-New/223028045295?hash=item33ed81e5ef:g:8-8AAOSwrzxbLNpS

Soldering iron and solder

*a note here. I linked the two headers needed from ebay. They are both coming from china so it could take a while but the receivers are coming from china as well. The thought was since you have to wait for the receivers, might as well wait for the headers and save a few dollars as well. That said, both headers can easily be sourced from the US and could be delivered in a few days if you are ok paying a little more. 

Assembly

This is pretty straight forward. Lots of soldering but its not overly complicated. A few notes though. First thing, take a close look at the break out board and make sure the VCC and GND on the receiver board match up properly. The receiver board can be mounted with either side up but just make sure that the VCC on the receiver board is attached to the center pins of the servo header and the GND on the receiver board is attached to the front row of pins on the break out board. If you look at the board under a light, you can see the traces clearly. It is also marked on the PCB. 

Both headers will have to be cut to length as they come in long pieces. two 3 position lengths and one 8 position length is needed for the 2mm header and an 8 position length is needed for the servo header. I soldered the 2mm headers in place first and then the servo headers and finally soldered the receiver to the board. There is a lot of tedious soldering on this board. There are over 50 solder joints so take your time. 

One final note on the soldering. The header spacing on the RC board does exactly line up with the header spacing on the break out board. I used 2mm headers on the break out board. the RX board uses some strange header spacing. Something like 1.8 or 1.9 and finding headers in those sizes are very difficult. That said, the 2mm is close enough that I didn't have an issue making the connections. I've made of a few of these now and some seem to fit better than others but I was able to make them all work.

Binding

For my QX7 binding was pretty simple. Turn on the transmitter and in the model setup screen, choose D8 mode. Next power on the receiver while holding down the bind button. The light will go solid. Now select "BIND" on the transmitter and once the receiver is bound, it will shut off. power down the receiver and take the transmitter out of bind. Now power the receiver back and it should be working. Check all the channels with a servo. Thats it! 

Final Thoughts

The break out boards need to be ordered in sets of 3 and the headers should leave you with enough parts to build 3 receivers for under $30. I know there are Frsky brand receivers that are 6-7 channel for around $20 so its not a CRAZY cost save. That said, I like to tinker and DIY. If I can save a few bucks in this hobby, I will. Another note, these are cheap receiver boards so I wouldn't recommend putting it in anything other than a cheap foam plane until you are certain its operating properly. 

COMMENTS

MikeDon on September 29, 2018
Keep the ideas coming. Just ordered 6 sets. These are going in my FT builds.
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MikeDon on December 8, 2018
My order took awhile, but as of tonight, two built and working great. Have yet to fly with them, but will be doing so soon.
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Fred2510 on November 4, 2018
Thought I would advise on Banggood. Ordered a couple of Rx's on Sept 8th !
Today is November 4th Still Not received (vancouver Canada)
Emails to Banggood resulted in "wait 3 more weeks" advise.. TWICE now.
No Refunds .. No reshipments.
I will never buy Banggood again.

Wee circuit boards were quick and easy though
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JUSS10 on November 4, 2018
Hmm not sure on how well shipping to canada goes from BG. That said, last GB order I made took 5-6 weeks. Their shipping time does seem to be getting longer. Thats why I usually only spend small amounts at a time. I've never had something not get to me eventually but sometimes it did take a month or two. Sorry to hear about that.
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zachaum on September 4, 2018
This is how I explain it to people.. Not sure it is a direct comparison. Frisky uses software called OpenTX. This software is a community based language that allows great programming. All other transmitters use a Closed Operating system. So it is comparing Microsoft during the old Dos days to Apples IOS. Or better Linex operating system to Apple. What does this mean? If you like to develop our own mixes and operation then Frsky is your radio. This is why after market suppliers have developed modules that attach to the Frsky radio to take to there receiver of your choice. OpenTX is a little more complex to use (but lots of YouTube videos to help you) than the others. I just like to do basic mixes and fly so I fly with Spektrum. Also Spektrum was what most of our club flys on so I have help at the field when I get stumped on how to do something. So it a personal choice based on each individual. Hope this helps.. I looked at Frsky when I went from FlySky to Spektrum but thought it to complex for me.
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Fred2510 on September 20, 2018
Ordered Rx and Board bits.. now the wait begins. Am now wondering IF the break out board is needed.. Presumably I can solder pigtail wires directly to the RX pads ?
Given the size/weight of the Rx .. Fitting servos with Teeny Connectors via pigtails seems appropriate.
as Futaba / JR ones are likely bigger / heavier than the RX and breakout board combined :-)
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JUSS10 on September 21, 2018
True, its not needed, but it makes for a much cleaner execution. I just wanted something that was "standard" that i could easily toss in any plane that uses the standard PWM servo connections that most receivers use. For most uses, I don't think the weight would really be an issue unless you are looking at micro planes. Most FT planes that need a 5ch plus receiver, this would work great and be as light as any off the shelf receiver. Regardless, give it a shot if you want to just solder wires to it, that would certainly work!
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Fred2510 on December 21, 2018
Happy day.. Yesterday, I received my Banggood Rx order ONLY 3 !! full months since ordering.
This to Vancouver, Canada. Didn't think it that obscure a destination.
Shipping label shows it was sent to Laos... then shipped... Musta been 1 rimbi cheaper.
One can't make this level of idiocy up.
Unlikely to buy at banggood ...ever again.
That said I can now assemble my Rxs .
Thank you for the article.

PS: I have a couple of micro planes and despite my having the break out boards I will try ..one.. with 1.9 gm servos soldered to the rx.. no plugs, no addon pcb.
Should be V lightweight
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JUSS10 on December 21, 2018
great to hear! and yes the receivers are great if you want to make a super small model with PPM and do direct soldering. Would be great for a small winter indoor flyer!
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Bayboos on September 5, 2018
Not a "crazy" cost save? You cut the cost exactly by half! It doesn't matter it's "just" $10 per unit, it's still more than most of the FliteTest airframes (DIY version)!

Great idea and terrific execution! Thanks for sharing!
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Scottmclam1 on September 19, 2018
Finally received the last of components I will need to make these receivers. Will longer antennas help with range? And also any plans for 3D printed cases would be awesome? I will let you know how things go.
Thanks. For your article!!!
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JUSS10 on September 21, 2018
Not sure on a longer antenna. I use these in my cheap foam planes for line of sight. I require at least 5ch for nearly all my planes, thats why i built this vs buying the mini 4ch receivers that BG sells. As for a printed case, thats a great idea. I can probably draw something up quick and give it a shot. I try to keep things light so I don't usually worry about a case but if I get time, I'll see what I can do!
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Thorondor95 on September 4, 2018
What exactly is the big whoop about Frsky? Is it just an alternative to Spektrum, Futaba, etc., or does it have advantages or superiorities?
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JUSS10 on September 4, 2018
Frsky is really just another protocol. That said, its leans more towards the DIY crowd. The transmitters run an open source software that allows for endless customization. However, its more complicated than Spektrum or Futaba. Also, in my opinion (key phrase there), its a more cost effective radio than most others in its quality range. A $100 frsky radio can do most anything a $200-300 Spektrum radio can do. Also receivers are more affordable and there are a ton of telemetry options at lower costs than most. Spektrum has had low cost receivers thanks to lemonRX for a while now but there hasn't been a low cost alternative for Frsky except for these types of modules coming out of china. My thought with this build was to make a lemonRX quality receiver for the Frsky protocol giving users a low cost receiver alternative for their park flyer foam planes.
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Nigel L on September 5, 2018
FrSky is amazingly cheap. I worked at Aloft Hobbies for a bit and instantly switched over to Frsky. Their 16 channel radio, the QX7, comes in at around $100, with the option to use a module to make it 32 channels over Sbus. The cost of receivers is much less, and the software is fairly easily upgradable to OPenTx, which people love because you can pre-load specific models on your transmitter pre-tuned for a specific plane. Also, everything about the radio is customizable and replaceable, from gimbals, switches, RX modules (I use a R9M for my old Spektrum receivers), and the appearance. If you have a lot of money to spend, go Spektrum, but if you're on a budget or would rather spend the money saved on others planes like I do, I would highly recommend FrSky and Aloft Hobbies.
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AkimboGlueGuns on September 4, 2018
Heck of a lot less brownouts, and receivers are generally cheaper.
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Fred2510 on September 8, 2018
Fascinated by this. Have fitted a Fut Tx with a DHT module . It works Perfectly.
Keep seeing wee Rxs' offered but all seemingly have S bus and frankly have no idea how to connect my 'regular' servos. to one.
Your article explains some of it .. but not all, at least for me. Your build article seems a reasonable path.
It's final ~ weight is ? Also any range concerns Although my uses would be for small light models
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JUSS10 on September 13, 2018
If it just has Sbus, yo u would need another board that can convert to PWM. Thats the joy of this little RX board. it has SBUS, PPM, and PWM. PWM is what you need for direct connection to servos. This is the only RX I have seen that has the PWM pinouts. There is a 6ch version that Frsky makes but I don't know if it would fit on the board I designed here.

As for range, I haven't had any issues yet. In range mode on my taranis radio, I went out to 100ft and it was still working. It had a slight delay but no issues. From what i have read, range mode is 1/30th the power of regular operation so if that is indeed the case, its good out to 3000ft. I was flying my baby blender the other night and looks like I was out 600ft with no issues at all. As stated, I still don't think I would trust these in any of my really nice models, but FT planes, these should work great.
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Low cost DIY Frsky 8ch receiver