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Solved FC not recognising PPM signal.

HariUp

New member
#1
On Cleanflight, when I jiggle the joysticks of my transmitter, nothing shows up on the screen when I go to the Receiver menu.

I am using an SP Racing F3 Evo Brushed Motor FC with Cleanflight, and a FlySky FS-T4B Transmitter with a FS-R6B Receiver. The PWM signals from the receiver are converted to PPM via a PPM Encoder.

As per the manual https://hyperion-world.com/download_files/manuals/HP-FCF3EVOB2-MAN.pdf, I have connected the Rx/PPM Encoder to UART2. I then set up Cleanflight, but even though the receiver and the PPM Encoder recognizes the transmitter's signal (the lower the throttle, the faster the Encoder flashes), it's just not being picked up by the drone. The drone will not fly. I don't know if it's a connection issue (my soldering is messy but it looks connected), or perhaps I have damaged my FC in the process of soldering. I've set up UART2 in Cleanflight, but nothing is happening. What am I/could I be doing wrong?
 

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FDS

Well-known member
#2
You are going to struggle flying any quad on 4 channels. Usually you need a minimum of 6 to get the 4 flying channels and 2 Aux channels for arming switch and mode selection.
 

HariUp

New member
#4
Try disabling MSP on UART2. MSP is a serial protocol used to talk to OSD's etc.
I've done so, but with no effect. I feel that this is an issue with the PPM Encoder. It was intended to be used with autopilot drones such as the Pixhawk. I am trying to do some research as to what kind of PPM signal the Pixhawk requires, and see if I can somehow change the PPM signal to that which normal drones use (if there is any difference in the type of PPM signal). The encoder can be reprogrammed if needed.

You are going to struggle flying any quad on 4 channels. Usually you need a minimum of 6 to get the 4 flying channels and 2 Aux channels for arming switch and mode selection.
All 6 receiver channels have been plugged in.
 

FDS

Well-known member
#5
Your transmitter is only 4 channels if it’s a FS-T4b.
The receiver shouldn’t need to be converted to PPM , the flight controller should work with its usual output. Most Flysky receivers have iBus and ppm out directly.
 

HariUp

New member
#6
I see. I am reluctant to buy a new transmitter - perhaps as a last resort. I'll try and look for a solution or a modification, but if I run into another dead end, I may just have to splash some more cash. Thanks for your help!
 

FDS

Well-known member
#7
If you can’t safely arm and disarm the quad after plugging in power, you cannot safely fly or prevent a fly away. You have to ask yourself what price a serious injury from a prop strike is worth to you or the cost of a total loss of your quad vs buying a safe transmitter. Flysky are not a good make for quad receivers IMO but they are cheap.
Have you tried honking the receiver up directly via the ppm out without using the converter? Read your receiver manual it should tell you which port it is.
 

FDS

Well-known member
#9
Well it’s not going to be much use for running a quad. It would be ideal for a plane or a wing however.
I think you are making a lot of work for yourself with this build. You are using an old FC and a not suitable radio. I am all for saving money but although it’s possible to get what you have to fly a quad it would be much safer and more rewarding to use a more reliable set up.
What you have would work great in a fixed wing, there’s several FT designs for wings, or a stable 4ch conventional plane would work, either with FPV or just to fly line of sight.
I don’t know what you are looking for in a quad but safety and reliability should be considered first. You absolutely need to be able to disarm the quad from the remote, so even if you can get the flying channels working you have no spare capacity for a disarm channel, or any way of controlling which flight mode you are using.
Have a think about what you want, how much you have to spend and what parts you already have then maybe people here will have some good advice on what sort of set up you could get working for minimal outlay.
The radio gear you have would be fine in a plane.
 

FDS

Well-known member
#11
I would spend about $20 or so more and look at an OpenTX radio if possible. Theres also second hand, both my transmitters were got that way and cost me about half what they would have new.
 

HariUp

New member
#12
Before I start, thank you guys for all your help and advice. It's my first ever time making a drone, so I'm pretty keen on seeing the final product.

Firstly, I understand that a 6CH is more suitable than a 4CH regarding drones. I have been researching, and if I were to buy a new radio set, the FS-i6 with an FS-iA6B would be it, as the RX supports PPM and SBUS.

But you asked me what I was looking for in a drone. To be honest, I just want to be able to reach an end result which may not be best, but which works. But I also want to do this with the tools currently available to me - I feel that building a solution that barely works would give me more satisfaction than just buying a solution which would work flawlessly. Stick arming may not be as safe as switch arming, but if that's the case I'm prepared to stand well away from the drone and take any other safety precautions possible. I'm happy to keep the drone in self-level mode rather than acro, hence no need for the second switch. Even so, I am trying to research ways to possibly add more switch channels to a TX - after all, switches can only be either on or off. If I feel that I've no other choice, then I will just buy a new set, but I want to exhaust all other possibilities first. I'm all for creative/educational solutions, so long as they aren't overly complex. Many DIY Tx/Rx projects mention an Arduino Mini, I could get one if I really needed it.

Another problem I'd need to sort out is why Cleanflight isn't recognising my PPM signal at all. I've done as said on https://www.rcgroups.com/forums/sho...n-SP-Racing-F3-Not-registering-on-CleanFLight (the board mentioned is different but the issue is with Cleanflight) and changed failsafe settings and channel mappings but to no use. I should try remapping channels again. My hunch is that the Encoder is fine because it responds to my throttle movement, but I'll try as many wiring combinations as needed.

Again, thanks for all your help. I will try to keep safety in mind. I don't want to suddenly switch to making a plane now, because I'm quite close to completing a working version.
 

FDS

Well-known member
#13
The problem with stick arming and not having spare channels is not when you start it up but when it’s flying.
I have had tuning problems where I was flying a test hover and the quad would take off then hover fine, but when a pulse of throttle was applied it would keep accelerating. With an arming switch I just flicked it off and it landed safely. You can’t do that with stick arming. Similarly if you lose video you need to be able to quickly disable the quad or if you clip a prop and it spins out of control. There’s a reason nobody uses just stick arming.
I wouldn’t fly a quad on a 4 channel set up, in my opinion it is NOT SAFE to do so. I would also never advise someone else to do so. Safety is your first consideration. A 5” quad is potentially able to inflict damage to persons and property, we have enough bad press as a hobby without more easily preventable flyaways.
I understand budget is a consideration, it took me 5 months to save for and build my first 5”, I had to buy components in stages and take my time to ensure what I ended up with was safe and reliable.
My advice is still to slow down and build a better, safer quad. It’s up to you wether you take it. I won’t say anything more in this thread, good luck with whatever you decide.
 

HariUp

New member
#14
I see. Stick arming is now definitely out of the question. I'll see if I can mod the 4CH into a 6CH, but if that doesn't work, then a new radio kit is the way to go. Again, thanks a lot for your advice.
 

FDS

Well-known member
#15
Thank you for thinking of the safety of others and what’s best for the wider hobby’s image first.
6 channels is an absolute minimum for quads, even bunching some AUX functions together most builds end up with 8-10 channels required.
A better build will be much more fun to fly as well as safer. Don’t rush transmitter choice, there’s been a lot of changes this year in the market for radios. I wouldn’t recommend Flysky for quads as a whole, despite their low price, there is a good thread here about transmitters but some of it is more fixed wing focussed. Generally for quads an OpenTX supported radio is best as there’s lots of good support on setting those up for multi rotors.
https://forum.flitetest.com/index.php?threads/which-transmitter-you-should-buy.37966/