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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: Are we being ripped off
23/09/2017 19:35:40

Its not just the model trade!

I recently needed some heavy duty velcro, and the only place that I know stocks it is Halfrauds. Whilst I was there I thought to buy a tube of contact adhesive. They wanted £8 for a small tube of EvoStick!!! Alongside was a similar tube of Bostik for £3!

Guess which I bought!

What on earth was in that tube of EvoStick? Liquid Gold???

--

Pete

Thread: Classic Aerobatic Model Photo Thread
21/09/2017 09:05:19

Tony Bennett: That looks like a "Phoenix", a design that appeared in the American RCM magazine in the mid 60's. I think the published plan was something like the Mk 6 version of the design, as it took the designer a while to overcome the traditional problems with swept and tapered wings - particularly tip stalling!

IIRC, he overcame that by making the tips thicker relative to the chord than the roots, and claimed it cured the problem completely.

Never saw one in the flesh, but I always thought it looked right, and if the old adage is to be believed, it should fly right!

Just watch out for any tip stalling issues when you test fly it! Try a few stalls at altitude first, as per full size!

--

Pete

Thread: FrSky Taranis - user chat
18/09/2017 09:19:09

Martyn, I had a strange one on my Taranis a while back, whilst programming a vintage helicopter. It might well be related. I quote from my post on the OpenTx forum and the replies I got:

"The helicopter in question is quite an old design, and doesn't need any of the special helicopter functions for swashplate mixing, so all these are ignored. However, like most helicopters, it does need a throttle curve to simplify starting, take-off and landing.

A typical "Normal" throttle curve will have five points. On a helicopter, it is important to get the rotor-head up to speed quite quickly, so the throttle curve rises quite quickly initially, then flattens off across the middle of the range, before rising quite steeply at the end again (the "get me out of here!" portion of the curve). For example, in my case, because I was using a modern engine in an older design and needed to reduce the power in the hover as well, I started off at 0, 35, 40, 50 and 100 as my five points. 0 represents a fully shut throttle that will kill the engine, but with the trim advanced from the bottom, this should give a reasonable tickover. I found that I needed to advance the trim up to about 75% to get a decent tickover.

The first test flight indicated that I had set the throttle curve a bit low across the middle, so I landed, shutdown, and then advanced the pitch curve to 0, 40, 45, 55 and 100.

When I restarted the engine, I had the fright of my life, as the throttle was now way too far open, the engine was revving very high and the clutch engaged!!!

Luckily, I had a firm grip on the rotor head, but there followed a frantic few seconds while I dis-engaged the starter (the wand flew off across the pits!) and pulled the fuel line off!

Moving the throttle curve had affected the idle setting, despite the trim being set to "idle-only" in the model setup page!

This is NOT expected behaviour, and completely different from every other helicopter radio out there. It is also potentially dangerous. A "hot start" is not a pleasant experience on a helicopter!

The issue appears to be that when a curve is applied, the trim acts to move the lower point of the throttle stick position - moving the "cursor" along the X axis of the curve. As a result, any alteration to the curve affects the idle."

The problem was caused by my application of the curves. One of the OpenTx devs pointed out to me that here is a difference in behavior whether you apply your curve in the Inputs or the mixer. If you do so in the Inputs then the trim is independent from the curve. If you do it at the mixer stage, then it "goes through" the curve.

So in my case, I was getting an unexpected response because I'd applied a curve where years of computer experience told me it *should* be applied, but it gave me a completely unexpected result!

I wonder if your problem is similarly related? In effect, the idle trim is "mixed" in to the main function in a similar manner to your throttle to elevator mix. Maybe what you need to do is set up a spare "dummy" channel to track the throttle *stick* rather than the throttle *channel* and use that as the source for your throttle-elevator mix?

Sorry about the length of the explanation, but it is quite complicated to get your head around unless explained in detail!

--

Pete


Thread: Webra spares
18/09/2017 09:00:21

Mecoa in America (Model Engine Corporation of America) have a lot of stock of out-of-production engine parts, and are re-manufacturing an awful lot of them!

**LINK**

Perhaps not the cheapest or most convenient, but if you are stuck......

I can't see a listing for a Dynamix, but I've only had a quick glance. They do have lots of Kavan carbs in, which were a good substitute for most carbs. If your engine is one of the German made cross-flow engines (Blackhead, etc), then a lot of parts were common with the HB 61 and Veco 61 of the same era. The later Schnuerle ported engines (Austro-Webras) were made in the same factory as the HP (Hirtenberger) engines and probably share common parts.

You'll find Kavan carbs under "Accessories" on their site, and Webra parts under - er - Webra!

Best of luck!

--

Pete

Thread: V8R4-II 4 Channel receiver firmware
13/09/2017 18:37:43

Thanks, PatMc! I wasn't sure as I only have a single V8 series 1, left over from my early days with FrSky! I did suggest that he re-check the instructions.

I have to say that I find the way that FrSky try to achieve backward compatibility - where regulations allow - a refreshing change when compared to older and more established brands. It can lead to some confusion over the differing standards, though....!

--

Pete

13/09/2017 11:57:32

Geoff, The version 1 V8 receivers would only bind to a V8 transmitter. The Taranis doesn't support V8, unless you install an external module in the back. The version 11 V8 receivers will bind to D8 (an option on all but the latest Taranis' ), but you won't get telemetry.

As I thought, if you jumper two pins during binding, it will make the receiver recognise a D8 signal, but since the receiver doesn't have a transmitter for telemetry built in, you won't get any!

Make sense?

P.S. I think you'll find those instructions are referring to the *receivers* F/S button, not the Tx. You will still need to put your Taranis into bind mode via the menu. I think you will also have to hold the receiver F/S button down, as well as jumpering the pins in order to bind, but re-check the instructions. Once bound, power down the Rx, remove the jumper and take the Taranis out of bind mode. All should then work!

--

Pete

 

Edited By Peter Christy on 13/09/2017 11:57:58

Edited By Peter Christy on 13/09/2017 12:02:12

12/09/2017 18:27:44

Geoff,

From memory, the V8 receivers are non-telemetry receivers anyway, but they will bind to a transmitter set to D8 (the earlier FrSky protocol). Since D8 is non EU anyway, as long as you can select it on the Tx, you should be able to bind a series 11 V8 receiver to it anyway. You might need to jumper some of the pins whilst binding, to tell it to accept a D8 signal, rather than the original V8.

Unless my memory is playing tricks on me, you shouldn't need to upgrade or downgrade the receiver firmware.

--

Pete

Thread: Strange goings on with an FP40
07/09/2017 15:58:14

You may find its more a question of long reach plug vs short reach plug. Most modern 2-stroke engines are designed for a short reach plug, whereas older engines - particularly European ones - are designed for long reach.

The old OS max 40 I referred to in my earlier post is designed for a long reach plug. Whilst it will run quite happily on a short reach (OS 8, Enya 5, etc) when upright, it doesn't like it when inverted! Because the plug doesn't reach the bottom of the threaded plug hole, when inverted, it tends to trap liquid fuel and extinguish the plug. This is less likely to happen with a long reach plug, and an idle-bar will also help to stop liquid fuel "pooling" in the plug.

Its a long time since I looked at an OS 4-st plug, but I have a nagging feeling it may be long reach. It is also a much hotter plug, so not so easy to extinguish!

--

Pete

 

Edited By Peter Christy on 07/09/2017 15:59:33

Thread: 2 Volt plugs
07/09/2017 09:09:52

Actually, most people over-drive plugs. They should only glow cherry red rather than bright orange! I've always found a C or D size NiMh or NiCad perfect for the job, and much more reliable than power panels.

Ignition in the engine is performed by a catalytic reaction between platinum in the plug and the methanol fuel. Modern plugs use platinum coated wire, rather than pure platinum, for cost reasons as much as anything else. Overheating a plug will eventually cause the coating to flake off, leaving the plug wire looking a dull grey colour. At that point, you will start having engine problems no matter how bright it glows!

If you use a single NiMh or NiCad of sufficient capacity, as described above, your plugs will last for years!

I do put an ammeter (up to 5 amp, from an old car battery charger) in series with my batteries, as it is very easy to tell if an engine is dry or flooded from the meter readings.

--

Pete

Thread: Strange goings on with an FP40
06/09/2017 08:29:03

Doug, the earlier post by carperfect might hold a clue. I have a model with an old OS MAX 40 in it, and like yours, it is mounted inverted. I had no end of trouble getting a reliable tickover until I fitted an idle-bar plug. Now it will run all day at tickover.....!

--

Pete

Thread: fuel for OS 55AX
06/09/2017 08:25:14

Phil, your engine will be fine on 15% oil. I think that recommendation is a hang over from the castor oil days.

Some years ago, I was involved in trying out a new fuel formulation that used 15% synthetic, and never had any issues with it in a variety of engines, old and new. Eventually the manufacturer upped the oil content to 18% as a result of the OS recommendation, and the only effect was to make more mess on the model.........

--

Pete

Thread: New switch required
03/09/2017 23:09:20

Cymaz, I don't like the look of those crush marks on the wires, where the back of the case has obviously been trapping the wires. Proceed with caution!

--

Pete

Thread: Identifying Vintage Diesel
03/09/2017 23:05:32

Cliff,

I have a book that belonged to the late, great John Haytree that should be able to identify it. You should have my contact details in the club records. Give me a shout.....

--

Pete

Thread: New switch required
03/09/2017 16:41:22

I was warned about using those switches with built in charge sockets many years ago, and now I know why! The switches themselves are fine. The weak spot is the PCB and the way the wires can easily be damaged by the back of the case. The switches with the separate charge lead do not have a PCB in them. The wires are soldered straight onto the back of the switch, with the poles paralleled up for extra security. The case the acts solely as a strain relief.

Never had one of those fail - yet! wink

--

Pete

03/09/2017 12:35:46

I've always used the JR heavy duty switch harnesses (JRPA001) in everything above tiny models. Its the one with a separate charge lead, not the one with a socket built into the switch. Unfortunately, they appear to be no longer available.

I've still got a few Noble 4-pole change over switches left. These were always reckoned to be the "best of the best", and the poles could be paralleled up for even greater security. Sadly again, these are no longer made, but if you want one, I have one. You will have to solder it up yourself, though....

--

Pete

Thread: Charging low dischrge NiMh batterries.
03/09/2017 12:21:40
Posted by Allan Bennett on 03/09/2017 08:38:14:But one of the advantages of 1/10C charging is supposed to be that it keeps the pack balanced because 14 hours or so is plenty of time for all cells to have reached their peak, and the slow rate of charge won't harm any cells that reached their peak before that time.

The first part of that statement is quite true. 1/10C charging will help balance the cells, if they are out of balance. However, with modern NiMhs, an out of balance condition is far rarer than it was in days of yore. This is especially true when using manufacturers pre-assembled packs, where all the cells should be of a similar age and condition initially.

In my experience, the problem with continually charging at 1/10C overnight is that some or all of the cells end up being continually over-charged. Whilst this is OK occasionally - and modern cells are much more tolerant - it is not a good idea to do this continually. The cells will end up giving off gas after they peak (that's why they are vented!), which comes from the stuff inside them starting to break down. Just as overcharging a lead-acid car battery will eventually dry up all the acid inside, continually overcharging a NiMh will eventually damage the internal electrolyte.

IMHO, NiMhs are best charged with a peak detect charger at between 0.5 and 1C. NiMhs do not have such a well defined "peak" as NiCads, and at low currents the peak will be difficult to detect. 0.5 to 1C should give the charger a nice positive peak to detect. Ordinary 2000mAH Eneloops will charge just fine at 1A, without getting too hot, and can certainly be charged safely at 1C, though they will get warmer at that rate. All NiMhs will get warm as they reach their peak voltage, though the higher the current, the warmer they get.

To summarise: The best way to charge NiMhs is at between 0.5 and 1C using a peak detect charger. Occasionally (once or twice a year) it *might* be worth trickle charging to re-balance any wayward cells, but this should only really be necessary in well used and abused packs.

--

Pete

Thread: metal to metal interference
31/08/2017 09:42:51

There appear to be two different issues being discussed in this thread. 1) Internal metal linkages in the model, and 2) external metal structures.

Lets deal with (2) first, as its the simplest. When a radio wave hits a metal structure - typically a fence, in our case - it will get reflected, just as sunlight gets reflected off a damp road. However, unlike sunlight, which contains many different frequencies, 27 / 35 MHz systems use one very specific frequency. Because of the different path lengths taken by the direct and reflected signals, at certain points, these will arrive at the model exactly out of phase with each other and cancel out! This will cause a momentary loss of signal - or "glitch" as we used to call it!

Glitches were less common with PCM gear, not because the signal was not being interfered with, but because the PCM system disguised it. The glitch was still there, but the PCM system papered over the cracks!

At 2.4 GHz, the wavelengths are MUCH smaller, and so ,correspondingly, are the dead spots. Further, frequency hopping ensures that the dead spots are in a different place with each hop, and finally, the method of modulation used , like PCM, disguises momentary losses of signal.

Moving on to the internal metal to metal noise problem, the reasons behind this are less clear. However, scraping two long pieces of piano wire together near a VHF radio will often produce a crackle of interference. As our models invariably operate in close proximity to the transmitter (in radio terms), it is highly likely that the transmitted signal will induce small electrical currents in a wire pushrod. If this pushrod is in intermittent electrical connection with another piece of metal - say a z-bend into a metal throttle arm - then the radio resonant length of the pushrod will change, and produce a slight frequency modulation onto the signal reflected from it. Since it is very close to a sensitive receiver, it is not really surprising that the receiver might get upset by this! And before anyone says "but we had it in the AM days as well", remember that an AM receiver will pick up FM signals, if slightly off-tuned!

In addition, an AM receiver requires a constant level of signal at the detector stage, a feat achieved by an Automatic Gain Control or AGC circuit, which attempts to "iron out" fluctuating signal levels. However, it can only do this for variations that occur more slowly than the actual modulation, so any fast fluctuations will get through, and cause a glitch.

Peter Jenkins is right in that most ignition type interference tails off over 300 MHz, but it is a gradual fall off, rather than an instant disappearance. The same is probably true of metal-to-metal noise, though I have no idea if this has ever been investigated. And again, the shorter wavelength of a 2.4 GHz signal, combined with a robust modulation system, should make 2.4 GHz pretty much immune to such things.

Hope this helps!

--

Pete

Thread: Receiver losing bind with servo use
29/08/2017 08:05:28

Cliff,

Might also be worth checking the battery under load - you may have either a cell going down or a switch harness going high resistance. I agree with Mr.B's analysis though - it does sound like a volts drop issue, whatever is causing it!

--

Pete

Thread: converting frequency
23/08/2017 21:49:30

In principle, yes, no problem, but converted to what? 35 MHz or 2.4 GHz?

2.4 GHz using a FrSky hack module is probably the simplest route and has been carried out successfully by many with limited electronic experience.

If you don't feel competent to carry this mod out yourself, then in the first instance, I would suggest contacting Mike Ridley:

**LINK**

Details on a FrSky "Hack" module here:

**LINK**

Cheers,

--

Pete

(another single stick flyer!)

Thread: Spektrum AR600 Aerial Lengths
21/08/2017 22:47:33

Cliff, its the bare bit at the end which is important, and needs to be the correct length. The plastic "sheathed" bit is just a feeder - much like the co-ax that feeds your TV - and within certain limits, the length of the feeder doesn't matter.

--

Pete

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