Wierd Radio Problem - Help!

[Si Goodchild]

Guys,

I've been having a nightmare with by Mini Pred and need your sage advice.

The other day I went out for a flight and all was well until I made the minipred fly away from me about 30 or 40 feet. She made some awful erratic movements and it was all I could do to get her back on the ground with just a few bumps and scrapes: she momentarily went full negative pitch and all controls were very erratic. I swapped out the rx (I'm using the standard 35MHz radio) and flew again in the back garden and all seemed okay for a while, then she did it again - another minor prang!

So, I got her on the bench, without blades, for some power-on diagnostic testing and found to my horror that at about half power all the servos were twitching at full scale deflection in certain conditions! I isolated the gyro and all of the servos in turn and the fault was still there. I've even changed the rx for a 3rd item and the fault is still there. I haven't got any other xtals. The motor is brand new so I don't suspect that and I don't have a spare ESC but the cables seem soundly soldered and don't respond to any prodding when the motor is running.

I do have my suspicions about the stock Art-Tech tx though. I get the erratic servo problem with the aerial fully collapsed and the tx about 5 feet away from the model. Raise the aerial and the problem seems to go away. I'm thinking that when I flew the model 30-40 ft away from me I was getting the same problem but with the aerial fully extended: which clearly isn't good enough. When I turn the tx off the heli goes to fail-safe. So, the problem is repeatable when I touch the tx aerial which I reckon either means that the tx is outputting very little power or there is sufficient noise being developed in the heli to partially mask the transmission: perhaps in the ESC.

Now I do have a Spektrum DX7 and AR7000 rx sat here awaiting transplant in to my new-to-me Raptor 50 and I'm wondering if I can use the AR7000 temporarily. The problem is that the 35MHz rxs I've been using so far do not require a discreet power supply (it comes off the ESC control line): will the AR7000 be able to take its own power in the same way or will I need to provide power from another battery (which I don't have)?

The second problem is that the Art-Tech / Century servos I have do not feature a chamfered "shoulder" on the plug (to make sure they go in the right way round) and therefore won't fit in the AR7000 as they are. Can I carefully cut a "shoulder" on these plugs with a craft knife and get them to work?

Sorry for the long post but I really need your expertise before I do something potentially stupid and break my new radio gear. If it does work then I'll just get another 6-channel Spectrum rx for the minipred and re-position the AR7000 in the Raptor later!

Your help is much appreciated.

[Guest]

Test the radio with separate battery pack and ESC disconnected

[Oli]

Hi, i know very little with regards to spectrum kit, but i don't see why you would need to run a separate battery for the receiver, surely the AR7000 will run off the ESC's BEC?? With regard to the servo plugs I cant see a problem with shaving a chamfer on them (make sure you get the correct side) its much the same as needing to cut the tags off futaba servo plugs to fit JR gear.

Oli

[chugga-bug]

If you do plug the servos in the wrong way round it won't do any harm. They just won't work.
35mhz is a nightmare in small electric models. So many reasons for interference. Buy a 6100 speky RX and you'll never look back.
No problem running any rx off the ESC.

[xygax]

Just a silly thaught... Have you got a ferrite ring on the power lead from the ESC to the RX....?

I set a belt up did exact same thing until i fitted a ferrite ring..

[Si Goodchild]

Great stuff, thanks gents. I'll give it a go tomorrow and let you know how it turned out. Spektrum 6100 is the rx of choice if it goes well!

...and as for the ferrite ring - no I haven't. Can you offer any more advice on why that should be?

Si

[xygax]

The ferrite ring provides a shunt for high frequency 'noise' that is made by the ESC. The switching is effectively a three phase square wave.... and a square wave is composed of a sine wave and all the odd harmonics.... one of these is the one that gets into the wrong bit of the reciver and disturbs the incoming radio signal.

There are two types of modulation and two types of reciver (broadly speaking) and they all have various noise tolerances
1. PPM single conversion about the most suseptable
2. PPM double conversion better at rejecting noise as the rf section is more advanced
3. PCM single conversion better than PPM as the singal enryption is more robust more tolerant then PPM
4. PCM double conversion Best at 35mhz
5. 2.4G Airbourne router..... dont buy a belkin one...! so far up the frequency spectrum the noise from the ESC just cant effect it. there is also substantial error correction as the technology is borrowed from wireless routers and the have to transport programs that are bit perfect or they wont run (i know windoze would use this as an excuse)

[Si Goodchild]

Struggling to recall A-level physics, but it does all make sense. Will the 2.4GHz system be less sensitive to this noise or would a ferrite ring be a wise investment anyway?

Si

[xygax]

Just do both... the ferrite ring is pennies and it made a massive improvement to the response of a belt cp i set up....

[cjcj1949]

Guys,

I've been having a nightmare with by Mini Pred and need your sage advice.

The other day I went out for a flight and all was well until I made the minipred fly away from me about 30 or 40 feet. She made some awful erratic movements and it was all I could do to get her back on the ground with just a few bumps and scrapes: she momentarily went full negative pitch and all controls were very erratic. I swapped out the rx (I'm using the standard 35MHz radio) and flew again in the back garden and all seemed okay for a while, then she did it again - another minor prang!

So, I got her on the bench, without blades, for some power-on diagnostic testing and found to my horror that at about half power all the servos were twitching at full scale deflection in certain conditions! I isolated the gyro and all of the servos in turn and the fault was still there. I've even changed the rx for a 3rd item and the fault is still there. I haven't got any other xtals. The motor is brand new so I don't suspect that and I don't have a spare ESC but the cables seem soundly soldered and don't respond to any prodding when the motor is running.

I do have my suspicions about the stock Art-Tech tx though. I get the erratic servo problem with the aerial fully collapsed and the tx about 5 feet away from the model. Raise the aerial and the problem seems to go away. I'm thinking that when I flew the model 30-40 ft away from me I was getting the same problem but with the aerial fully extended: which clearly isn't good enough. When I turn the tx off the heli goes to fail-safe. So, the problem is repeatable when I touch the tx aerial which I reckon either means that the tx is outputting very little power or there is sufficient noise being developed in the heli to partially mask the transmission: perhaps in the ESC.

Now I do have a Spektrum DX7 and AR7000 rx sat here awaiting transplant in to my new-to-me Raptor 50 and I'm wondering if I can use the AR7000 temporarily. The problem is that the 35MHz rxs I've been using so far do not require a discreet power supply (it comes off the ESC control line): will the AR7000 be able to take its own power in the same way or will I need to provide power from another battery (which I don't have)?

The second problem is that the Art-Tech / Century servos I have do not feature a chamfered "shoulder" on the plug (to make sure they go in the right way round) and therefore won't fit in the AR7000 as they are. Can I carefully cut a "shoulder" on these plugs with a craft knife and get them to work?

Sorry for the long post but I really need your expertise before I do something potentially stupid and break my new radio gear. If it does work then I'll just get another 6-channel Spectrum rx for the minipred and re-position the AR7000 in the Raptor later!

Your help is much appreciated.

I like these problems but it can be very difficult to track down the problem. I've made a list of possibilities. Sounds more like range than interference. I assume you have a brushless motor. Do you get low range with motor off. Might be an idea to invest in a switching bec, useful with digital servos.

With the aerial down you should get 30 yds range. Five feet is not good enough. A quick range check would have found the problem. You'll have to eliminate things one by one. Are you pcm? If not how do you get failsafe?

Aerial
TX
Tx battery
Tx Xtal

Rx
Rx Xtal

Esc
Motor ( A new motor, always suspect some thing new. )
Any servo

By the way the 6100 is a park flyer Rx.

What are you trying to remember about A level physics?

I'd try and get a working (decent range) system. Then test each component one at a time.

[Si Goodchild]

Many thanks for the gen. Haven't had a chance to fire up the DX& + AR 7000 yet as I need to get read-in to the binding and setup process. Did another range check without the motor on and had erratic servos at 4 feet with the aerial down - went away once the aerial was raised a bit. The motor even started up and shut down on its own - quite scary!. TX voltage is okay and the stock minipred motor is a brushless item and although new, come to think of it, I have had a few sharp tail wags in the past (different motor) which thankfully went away. I must have changed every component since then, including ESC, so I'm definitely thinking it's the tx.

I note your point on the 6100 being a park flyer but don't really understand the scale of the difference: just how much shorter is the range than, say, the 6200? £50 seems a bit steep for an rx on this model, but if needs must!

Si

[cjcj1949]

Don't know how far is ok for a park flyer, it's one thing I keep meaning to check. I've got a 6200 and a 6100. How old is your tx? You could have crystals out of spec or dirty pins or a loose connection in the tx to the aerial. 2.4Ghz DSM2 is so much better than 35Mhz that it's academic. My club in Bracknell has had problems with interference on 35Mhz. Don't forget to do a range check on the Dx7, I must do one on my Dx6i before I fly my heli at a distance. I hope I do but I would if I had a problem.

[Mojogoes]

If its dirty pins try some dioelectric grease or spray from mapplins.....we use it on mass air sensors/meters on the electric connectors it works a treat it keep water out too.......i guess for people who sometimes fly electric i light rain it would be a good idea to smier the grease formular over the electric connections such as tx esc connections etc.

[Ade_Law]

If you do plug the servos in the wrong way round it won't do any harm. They just won't work.
35mhz is a nightmare in small electric models. So many reasons for interference. Buy a 6100 speky RX and you'll never look back.
No problem running any rx off the ESC.

mute point in this case but...

35 is ok on electrics as long as your electrics installation is good and use the right rx. my g5 i have kept the high and low voltage stuff as far away from eachother as possible and use a schulze reciever.

Ade

[Smoothound]

Like Ade says keeping high and low voltage stuff as far apart as possible is the main thing and then using a good DSP Rx is the other