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Member postings for Peter Christy

Here is a list of all the postings Peter Christy has made in our forums. Click on a thread name to jump to the thread.

Thread: 2.4 interference from FPV?
29/05/2017 15:30:22

"Legal" FPV gear on 2.4 GHz is restricted in its power output to 10mW - way below the 100mW allowed for model control. On 5.8 GHz, 25mW is allowed. Any decent R/C system shouldn't have a problem with this. The trouble is that some are using illegally high powers - I've seen kit advertised as having 1 watt output! Against those kinds of output, a standard R/C system has no chance, no matter what kind of magic smoke and mirrors is used in the modulation system!

5.8 GHz tends to have less range than 2.4 GHz for video transmission, which is why some are adopting very high power outputs on 2.4, and then using some other frequency for control, typically 459 or 433 MHz, but 35 MHz is also very viable.

Fortunately, all the UHF frequencies won't travel beyond the horizon, and will be effectively screened by any large hills in the way. But if someone is using a high power video transmitter on 2.4 GHz just down the road, you could well be in trouble.

Remember, 2.4 GHz is a shared band, and there are other legal users with just as much right to use it as us. Fortunately, most of those other users tend to be in urban areas, not out in the sticks like us! Its illegal users who are the problem, just like in the bad old days of CB and 27MHz! Luckily, there aren't too many people around running illegally high powers.

If you want an exclusive frequency, stick to 35 MHz!

--

Pete

29/05/2017 14:21:37

Frank,

Video on these systems is normally transmitted as an analogue signal rather than digital, and would typically have a bandwidth of some 4-5 MHz for standard definition (if digital it might be a fair bit higher!). That whole chunk would be completely and continuously occupied during operation of the video transmission. If they had two up at once, you can double that. This would fill up the available spectrum pretty quickly. LBT should be able to contain itself within the available frequencies left, ignoring those already occupied.

Of course, the reduced spectrum availability would certainly have an impact - this usually takes the form of increasing latency in the control response, but it *might* have allowed sufficient control to be retained to land.

As for FrSky's EU firmware being inferior to the rest of the world, that's a little off topic here, so I'll confine myself to saying there is little or no evidence for that. Note that I'm not promoting FrSky's system here, I did say "such as"! As far as I'm aware, all the manufacturers have had to introduce LBT in order to meet the media utilisation requirements. Its just that FrSKy's is perhaps the best known. If you don't use LBT, you are restricted to 10% media utilisation, IIRC.

MaL: Yes! I should have remembered that project! Seems to me that it would make an excellent construction article for RCM&E! (Is the editor reading this?) wink

--

Pete

Thread: SBach umx RX re-progammed Itself ???
29/05/2017 09:17:36

Denis: Remember that these models have gyro stabilisation built in. Whilst checking as you say is a good idea, it is not sufficient just to reverse the function at the transmitter, as the gyro function will still be reversed!

In my case, tilting the nose up caused the gyro to add more up elevator instead of correcting with down, resulting in an uncontrolled loop into the ground on take-off!

I thought my instance was a one-off, but it looks as if there is a weakness in the servo design that can cause it to reverse direction. I have no idea how this is possible!

Pete: Mine occurred during the last months of the UK operation, and I sent it back there. I guess now you have no option but to send it back to Germany. During their shut-down period it became almost impossible to get a response from HH UK, the only option was to send it "blind" and hope! Reports vary on how good the German operation is at communication, but in view of the expense of sending it back there, it might be worth an email or phone call first!

Best of luck, and let us know how you get on!

--

Pete

Thread: Classic Aerobatic Model Photo Thread
28/05/2017 19:15:55

At the Pontefract Retro meet last week, Ali Machinchy Snr turned up with some stunning models:

I believe the Veron Concord was the actual model flown for the Shah, when RCS and Veron laid on a display in Iran back in the 60s! There was also an immaculate Orion in there - one of my favourite models - but somehow I neglected to photo it!

In my dreams...... <sigh!>

--

Pete

Thread: SBach umx RX re-progammed Itself ???
28/05/2017 19:03:50

I had a similar problem with a UMX Pitts Special, where the elevator decided to reverse itself between flights! That would have been bad enough, but the gyro function was also reversed!!! This implies that the servo itself had reversed direction without warning!

After attempting - and failing - to contact HH service dept, I sent it back, and a replacement arrived a few days later. No explanation, but so far that has behaved itself.

Advice to anyone else flying a UMX Bind'n'Fly: Don't just wiggle the controls before take off - check for correct direction as well!

--

Pete

Thread: 2.4 interference from FPV?
28/05/2017 15:19:29

I don't think there's a cheap option available. I've got one of these:

**LINK**

Its a pocket spectrum analyzer that covers all the bands we use including 27, 35, 40, 459 MHz, 2.4 GHz and 5 GHz (for video). There are cheaper models that cover only specific bands, but none of them are particularly cheap. I think the 2.4 GHz only version is around £100

Another option - but it requires a laptop - is WiSpy:

**LINK**

Still not cheap, only covers 2.4 GHz (plus 5 GHz on some models) and needs a laptop. I think the BMFA actually have one of these, which can be lent out to clubs who suspect interference problems. Check with BMFA Head Office.

There used to be on called the Ubiquity Airwave - a bit like WiSpy, only cheaper, but it appears to be no longer available.

If anyone knows of a cheap but effective 2.4 GHz monitor, I'd love to hear about it! Nice little hole in the market for someone like HobbyKing?

--

Pete

28/05/2017 12:17:28

Its possible that they were using 459 or 433MHz for control and 2.4 GHz for video, as this set up can offer better range (though 433MHz is not legal in the UK). Your comments about them using "serious kit" and ground station aerials indicates that they might have been running illegally high power levels.

If so, then a 2.4 GHz video signal is likely to wipe out a large chunk of the entire band, and it is unlikely that any system would have survived. That's why we have rules and regulations, and when they are ignored, chaos ensues!

Having said that, DSM-2 is generally pretty good in that it won't activate unless it can find free channels to use. However, if they switched on *after* you, and were using boosted 2.4 GHz for video, you stood no chance.

Some sort of LBT system, such as FrSky's, might have stood a better chance, but its performance would still be seriously degraded in the circumstances described above.

--

Pete

Thread: Landing a Dynam Spitfire
26/05/2017 16:06:28

Jon is right! You might get away with it in very long grass, with full flap deployed and holding it off as long as possible, but that prop is very prone to snapping.

Don't deploy the flaps over short or medium grass unless you have the wheels down!

I've broken two props so far, just from nosing over - something they are prone to, as the wheels are small and close to the CofG!

--

Pete

Thread: stuck to one Manufactures 2.4Ghz protocol no more
25/05/2017 09:49:37

A lesson I learned many years ago was to never put new radio gear in a new model! I always keep an old "hack" around for checking out new gear before it gets transferred to anything valuable!

There are only a handful of factories world-wide making these chipsets, so the actual components almost certainly come from the same source as those used by the "big names". Similarly, for components this small, hand assembly is no longer practical, and nearly all radio gear these days is assembled and soldered on automated machines. These also come from a very restricted range of manufacturers, so there is no reason to believe that the quality of the electronics will be any better or worse than the big names.

Where differences usually show up is in mechanical parts - sticks, servos, transmitters, etc - which still have to be hand assembled. Since this module requires no hand assembly, I see no reason why it should be any better or worse than any other manufacturer.

In any case, things digital work on a 0 and 1 basis - it either works, or it doesn't! Fly it a few times in a "hack", and as long as it behaves, transfer it to anything you like!

I am certainly tempted......!

--

Pete

Thread: Forum members' new models: Let's see them.
18/05/2017 16:33:48

Maidened this morning:

Its a Saturn Skydancer, dating from the early 70's - built from a NOS kit, which needed a fair bit of remedial work! Power is provided by an OS Max 40, which I bought to power my original Skydancer, back in 1974! Radio is provided by this:

Its a 1969 Royal Classic transmitter, which I've Gigerized with a FrSKy "hack" module and one of Phil Green's excellent Arduino encoders! Proper retro!

I've been rushing to get it finished for the Pontefract Retro meet this week-end, and its been touch and go whether it would be ready! The engine proved very reluctant to throttle properly until I remembered the magic cure from all those years ago: A long reach, idle-bar plug!

It flew straight off the board! Its a bit touchy on the ailerons, though the roll rate seems fine. Maybe just me getting used to proper sticks again! The first landing was dead-stick due to poor throttling, before I remembered the magic cure for this engine!

Its a bit under-propped on a 10x6 - revs more appropriate to a pylon racer, in fact, so I'll be fitting an 11x6 before the week-end! It also has a period "quiet" silencer (P&R) - ie: not very quiet by modern standards! But hey-ho! Its all proper vintage!

wink

--

Pete

Thread: EASA NPA 2017-05
17/05/2017 10:29:20

"Invisible drone-proof fence"?!?!?

Good Grief! What have they done? Nicked Captain Kirk's force field?

laugh

--

Pete

17/05/2017 09:13:11

will-0: The only transmitter that gave me any problems back in the day was a prototype from a British manufacturer! Every time it got between me and my model, mine went into fail-safe! That never happened with any of the kitted or home-brew ones back then......

And if it wasn't for the home-brew ones, we wouldn't have the systems we now enjoy!

--

Pete

Thread: FrSky, DJT/X8R Binding problem
15/05/2017 18:15:44

X series receivers can be bound to D series transmitters by jumping a couple of pins during the bind process. I believe this is legal, as the ERP of the downlink from the receiver plus the low media utilisation of the telemetry downlink brings the system under the ETSI medial utilisation requirements, but I stand to be corrected!

However, to get the full X series telemetry on the Taranis requires the receiver to be bound in D16 mode, rather than the D8 mode used by D series transmitters.

This also means that both the transmitter and receiver must be using the same firmware standard - be it EU or Rest Of The World.

Whilst there is a module that does D16, you will only get the full features by using the internal module on the Taranis - unless you also bolt on one of FrSky's dahsboards, at which point the whole thing starts to become a bit unwieldy. It is also rather pointless given that the internal module does all that is required.

Hope this helps!

--

Pete

Thread: EASA NPA 2017-05
15/05/2017 09:03:05

Rich2: A very good point! We've already pretty much killed the home electronics side of the hobby!

I got into RC when I was 14 or 15, and much of my early equipment had to be home made - couldn't afford the commercial stuff! Magazines were full of circuits for receivers and even transmitters. I learned how to make printed circuit boards, solder and fault find at an early age. These were abilities that stood me in good stead later in life, and I've enjoyed a good career in electronics largely from building on those early skills.

"Regulations" now mean that it is almost impossible for anyone to provide kitted RC gear, or publish circuits for youngsters to experiment on. I can see the same thing happening with the model building side of the hobby due to excessive regulation.

Yet another self-education door slowly being closed by ignorant authorities and vested interests......

--

Pete

Thread: Tell us about your most embarrassing stories from the field...
14/05/2017 23:40:21

Like Geoff, I've also managed to switch off a Taranis whilst fumbling for the elevator trim - much to the detriment of the model - and really, I should have known better as I accidentally switched off a transmitter at an inopportune moment many years ago.....

I had just finished test flying my new - and first "modern" - helicopter. I offered to let the club expert (Hi, Dave!) have a go on it, and in unhooking the neck-strap, I must have inadvertently caught the power switch! Now this was an FM PPM set, and in the absence of any meaningful signal, the servos would twitch erratically. The throttle twitched wide open, and the model leapt off the ground and headed straight for me! I started running, but the thing locked on to me like a heat seeking missile, and followed me around the field! Realising that it was gaining on me, I threw myself forward, and it hit me right where I keep my brains!

Now luckily, it was mid winter, I was wearing ski trousers on top of my jeans, and a thick poachers jacket on top of that! The blades were only wood, but the thwack to my posterior was certainly painful!

Luckily, at this point, the motor stalled (Did I mention that it had quite a pokey 61 installed?). Damage to the heli was limited to broken blades and a bent flybar. Damage to my self-esteem was considerably greater, and it was only when I got home and started to change that I discovered that the blades had gone right through the poachers jacket, ski trouser and jeans, and inflicted a long cut to my rear end! Of course, by that time the blood had dried, making removal of these garments more than a little painful! I got very little sympathy from my beloved, who could barely assist me for laughing!

I developed a very large bruise that made sitting uncomfortable for several days, just to rub my stupidity in!

After that, I fitted another lock to the slide switch on that transmitter, so that not only could I not switch it ON accidentally, but also I could not easily switch it OFF!

I have an old American transmitter on which the trims are crossed - ie: the elevator and aileron trims are on the LEFT stick (assuming mode 2), and the throttle and rudder trims on the right. This avoids having to reach across over the power switch when attempting to trim whilst holding the stick in the desired position. On my own home-built transmitters with mechanical trims, I always used to install them with the trims on the OUTSIDE of the sticks, nearest the edge of the case, for the same reason! I never understood why the bulk of manufacturers insisted on putting the elevator and throttle trims in the middle! Its just plain WRONG!

I think you can program the Taranis to have crossed trims, but it has to be done on a model-by-model basis, and is not available as a default setting. But at least you can do it!

And of course, computerised transmitters take quite a while to reboot when you restore the power, and will often only come back up when the throttle is shut and all the switches are in the right position! Not easy to remember in the ensuing panic when you've managed to switch one off in flight! So if anyone wants a very bent WOT-4 Foam-E fuselage, I have one in my garage.....!

angry

--

Pete

Thread: Hammerite
09/05/2017 19:51:34

I used smooth Hammerite on an old AcroWot undercarriage to replace the (much too solid!) original one on my SpaceWalker. The two are visually identical, but the AcroWot one is a lot more suitable for our field! The Hammerite red is an almost exact match for the red on the SpaceWalker! laugh

The engine is mounted at an angle, so that the exhaust exits between the u/c legs. So far, it has proven remarkably resilient to hot glow fuel!

The only proviso I would add is that the engine is a Super-Tigre, so straight fuel, no nitro.

--

Pete

Thread: firmware frsky
03/05/2017 09:37:38

According to Ofcom (ir_2030-june2014), frequencies in the band between 863 MHz and 869.4 MHz are for short range, non specific devices and limited to 25mW power. If the device does not use some form of interference mitigation (ie: LBT) it is restricted to a 1% duty cycle.

There is a small part of the band (869.4 - 869.65 MHz) where you are allowed 500mW, but with the same interference mitigation requirements.

Neither of these requirements sounds very promising for our purposes, and certainly not for "long range" systems.

There may have been an update to these requirements, but that is the most recent I've been able to find at present....

Remember, the UK does not always follow EU band plans precisely. That is why we have 459MHz whilst Europe uses 434MHz in a similar manner.

--

Pete

02/05/2017 08:36:31

Yes, I'd heard the "land-grab" theory as well, though when I heard it, it was German car manufacturers trying to set up live diagnostics for their cars, by placing 2.4 GHz monitoring points at regular intervals along the autobahns!

Still, whatever the reason, we are stuck with it!

One other point, though: Those cut-off dates do have a loophole in them. If the equipment was already "in the supply chain" prior to the cut-off date, it is still legal to sell it! So if someone had a warehouse-full of (for instance) DSM-2 stuff prior to the cut-off date, it would still be legal to sell it!

Frankly, the whole regulation is "not fit for purpose" to use the well-worn phrase, and whilst I don't condone breaking rules and regulations, it seems to me to be completely unenforceable. And unenforceable rules are the worst kind, as they simply bring the whole regulatory system into disrepute.

I'll get off my soap-box, now! devil

--

Pete

01/05/2017 22:38:36

Gary,

Take note of what MattyB says! He is dead right! My preferred method these days is to flash the RF firmware from within OpenTx, but that will only work with versions 2.1.X AND the corresponding bootloader, I believe. This removes the need for a PC, other than as a means of getting the firmware on the SD card in the first place.

Don't tick the "EU" box when downloading OpenTx! All it does is remove the option to select D8 and similar non-EU modes from the OpenTx menu. It doesn't actually remove any EU firmware, only the switch needed to select it!

Regarding "limited": There are two ways of complying with the EU rules. One is LBT, or "Listen Before Transmit" to ensure a channel is empty before transmitting on it. The other is to transmit blindly, regardless of channel occupancy, but in this case you are restricted to 10% media utilisation. Think of it as only being allowed to transmit for 10% of the available time, and you will get the general idea.

In practice, the whole point of spread spectrum is to transmit in a way that is essentially undetectable to any system not using the same spreading code, so adding these restrictions seems utterly pointless. No doubt it keeps bureaucrats somewhere in a job....... angry

--

Pete

01/05/2017 19:30:43

Hi Gary,

That's why I kept my original answer simple, though it would have helped to know the date of your equipment! In your case the answer is a double yes. Yes, it can be done, and yes, it is legal.

To be honest, the EU-LBT firmware is just as robust as the international version, and is legal everywhere, as far as I am aware, so I'm not sure what advantages you are expecting to gain. But its your choice, and there's nothing to stop you.

--

Pete

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