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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: 4.8 v or 6 v receiver battery
11/02/2018 17:05:28

Hmm! That's a tricky one! The problem is with that phrase "everything else being equal"!

In my experience, lower capacity generally indicates lower internal resistance. Its been the race for more and more capacity in a given cell size (primarily for non-RC applications) that has resulted in the increased internal resistance.

However, battery technology marches ever onwards, and lower capacity cells may well be a) older and b) as a consequence of "a", of an earlier technology.

Eneloops (and the equivalent Vapextech) cells seem generally to have lower internal resistance than similar cells from other manufacturers, but I suspect that if you could get AA eneloops of 1500 mAH capacity (say), they would have a lower internal resistance than 2000s. My personal belief is that it is a mistake to go for the cells with the greatest capacity. I use sub-C cells in many applications not because I need the capacity, but because they offer lower internal resistance.

The cells are made by winding "plates" of material into a spiral to fit them into a cylindrical container. The capacity is a function of the surface area of the plates. If you can make the distance between the plates thinner, you can get more "winds" in, and hence greater capacity. But making them thinner makes them more susceptible to shorts, if physically damaged, and also appears to increase the internal resistance.

In principle, the answer to your question is "yes"! But life is never that simple, and everything else is rarely equal!

wink

--

Pete

11/02/2018 15:03:23

Hi, Martin - I'll bet you find that if you replace the eneloops with sub-Cs, all the performance will come back. My model was an old (very!) Hirobo Bell 47, with a 20cc "Echo" engine. The original Hirobo ignition used a magnet on the flywheel, and a pick-up coil on a moving arm that was driven by the throttle servo. It also had a separate HT coil in the cooling shroud. I never did think much of that mechanical advance mechanism, and one day, the LT wire to the coil (hidden from sight, so not checkable) fractured. This resulted in the engine stopping instantly and a fairly heavy landing!

I think the original system was just "transistor assisted" contacts - similar to an old-fashioned car or motor bike, but with the contact breaker replaced with a transistor. Whatever, it provided adequate power on four eneloops, but with the RxCel, I couldn't even get it off the ground! As you say, it sounded OK, and I spent hours fiddling with the timing trying to fix it. It was Steve Roberts from MacGregors who suggested a bigger battery pack, and sure enough, that provided an instant cure!

I think RxCel have now modified their ignitions to accept higher voltages (2S LiPos or LiFes) but mine is an early one and strictly 4-cell NiXX only!

If you don't have room for sub-Cs, try and find an old (but good!) 4-cell NiCad pack. NiCads have a lower internal resistance, and should hold up better.

And yes, a 'scope is the only way to accurately analyze the problem!

I'll be interested to know how you get on!

--

Pete

11/02/2018 09:55:18

You need to be a bit careful when measuring voltages on Rx and ignition packs, as there can be transient "spikes" of current draw that may pull the voltage down momentarily - too quickly to measure on a voltmeter.

To illustrate: a couple of years back, I replaced the ignition system on an old gasser helicopter of mine with an RxCel systems. The original system relied on a mechanical ignition advance and had not proved to be very reliable. Once the new ignition system was in place, I no longer had enough power to lift off! Same battery pack as before, only the ignition system had changed.

It took a lot of head scratching before I discovered the cause - the internal resistance of the NiMh battery pack!

Although the average current draw of the new system was quite low, it was drawing very short "peaks", which the battery couldn't cope with. I think the RxCel may be a capacitor discharge type, and the internal resistance of the battery was not allowing the capacitor to fully charge between firings. Substituting a sub-C pack for the original AAs provided a complete cure.

Lesson learned: Small NiMhs DO have a higher internal resistance, which may cause voltage drops on high current "spikes". It is not enough to consider the capacity of the battery in mAH to determine its suitability. You need to be sure it can deliver its rated voltage under load.

As I said in an earlier post, if the voltage of a 4-cell pack is dropping below 3.5 volts, it ain't suitable for the job! And that means transients, not just steady current!

Someone mentioned Vapextech cells. These appear to be similar to Eneloops, and have a very low self-discharge property. However, all these small AA or AAA cells are really only suitable for relatively constant current applications. They are fine in transmitters, and models using analogue or small digital servos. However, if you are using a lot of high power digital servos (think helicopters or complex scale models), then use sub-Cs.

It is not simply a matter of battery capacity!

--

Pete

10/02/2018 12:27:53
Posted by FlyinBrian on 10/02/2018 11:45:57:
Posted by Martin McIntosh on 10/02/2018 09:53:19:

The whole idea of using five cells is, as I said above, to insure against a cell failure as you have one in reserve.

This assumes the cell fails short circuit, if it fails open circuit or goes high resistance then the extra cell offers no advantage. In fact you have more chance of a cell failure in a 6v pack as there are more cells in the pack.

Exactly! Keep it simple - less to go wrong! wink

--

Pete

10/02/2018 09:41:33

There is a lot of rubbish talked about receiver voltage requirements. I've used Spektrum receivers since they first became available. I must have 7 or 8 of them now, ranging from the tiny 4-channel ones up to the top of the range JR 9 channel ones. I've always used 4-cell NiCads or NiMhs, and never once suffered a brown-out.

Every case of brown outs I've investigated have been caused either by poor (old) switches, poor (old) connectors or poor (old) battery packs. In fact I've seen far more issues cause by voltage regulators and battery backers than I have by 4-cell pack use.

Not all servos can tolerate operation at 6 volt (JR have already been mentioned).

The only proviso I would make is that AA or AAA cells should ONLY be used in small, light models. For anything greater than about 1 meter in span, or fast and heavy, I would strongly advise the use of Sub-C cells.

Frankly, if you your packs are dropping to 3.5 volt under load, you shouldn't be using them!

To the OP I would say that if your gear has worked OK in the past on 4-cells, then keep calm and carry on!

--

Pete

Thread: Re: Death of IC
04/02/2018 12:24:04

Like many others of my era, my introduction to powered model flying came via control-line. Back then, RC was hideously expensive and not terribly reliable! My early CL fleet was an approximately 50/50 split between diesels and glow motors. Glows were lighter and higher revving, diesels required less "field equipment" to be carried - quite important when you were cycling to a flying site!

Whilst fresh diesel fuel smells wonderful, the exhaust residue does not, and seems to permeate all your clothes! It also soaks into the model more then glow residue, and diesel models tend to end up looking grubby quicker!

Fast forward a few decades, and I now have a small number of LiPo powered models - mostly foamies of one kind or another. The foamies - especially the scale ones - look good and fly well. But they tend not to handle wind or turbulence as well as a balsa model. Also, although they are quite robust, the surface finish can deteriorate very quickly - especially when flying from rough sites! "Hangar rash" is definitely an issue with them. In addition, the radio compartments tend to be very small compared to their balsa equivalents, due to the thickness of foam necessary for structural integrity.

On the other hand, electrics are mostly very quiet - mine are almost inaudible - which means that flying sites that would otherwise be impossible are suddenly opened up.

Electric advantages are convenience, cleanliness and quietness. IC advantages are robustness of the models (out of necessity, because of the vibration and fuel soak issues) and the ability to spread the fuel costs better. I would also add longevity to IC pros, because I have engines that are 50 years old, still hauling large aerobatic models around the sky. Whilst brushless motors may last well, my experience with LiPos is that their usable lifespan is fairly short - and they are NOT cheap!

Electric can be flown closer to civilisation due to the absence of noise, but is often more fragile when flown from rough, remote strips. (The exception, of course, is IC models converted to electric - perhaps the best of both worlds?)

Basically, its horses for courses. Both IC and electric have their pros and cons, and whilst electric will no doubt account for a lot of models going forward, I don't see IC dying out just yet.

Just my 2p worth! wink

--

Pete

Thread: Single Channel Radio Control - RH Warring
04/02/2018 09:50:51
Posted by Percy Verance on 04/02/2018 08:41:06:

"wee MacGregor wasn't always in control......."

Ah Yes! Who else remembers those glorious days of "Radio Control Sometimes" (RCS!) and similar? Even the early proportional sets weren't immune. There was the "Digimite Dance" and "F&M Shuffle" (pilots running down the runway waving their transmitters in the air to cries of "I haven't got it!!!" ).

Happy days!

wink

Actually, most of those early problems were down to poor tuning of the mass-produced equipment. Our local expert, back in the late 60s, was often getting equipment brought to him as "useless", when all it needed was tuning properly. He picked up an almost new Bonner Digimite-4 for peanuts, because the owner said it was "useless". On inspection, he discovered the transmitter hadn't been aligned properly, and the output was minimal. Five minutes with a tuning wand and field strength meter had it working beautifully. He used it for a couple of years, and then passed it on to another club member. Between the two of them, they had years of reliable service from it.

The biggest problem I found with single-channel equipment was the escapements. The radio itself was generally pretty good, it was usually mechanical issues that resulted in unreliability. On Elmic escapements, it was always a good idea to strip them down and carefully remove any "flash" from the plastic mouldings before committing to flight! And the "Compact" also benefited from shorting out the current-saving circuit and soldering up the riveted connection tags, which always gave problems after a few months hard use.

We learned the hard way, back then!

--

Pete

 

Edited By Peter Christy on 04/02/2018 09:51:45

03/02/2018 17:23:22

Shaun: Retro Nats? Where's that one come from? More info needed!

laugh

--

Pete

03/02/2018 15:05:47

I've still got a copy of that book somewhere! It was my bible when I was first starting in RC. My first receiver was a MacGregor Terrytone, built from a kit, and I borrowed a REPtone transmitter off a friend's father. He'd bought it for a boat, and never had any success with it. I had no more luck with it than he did, but eventually saved up enough money for a MacGregor transmitter and matching MiniMac receiver (still have the MiniMac, and it still works!).

I started with an Elmic Conquest sequential escapement, but never got on with it. After writing off my third model due to it skipping, I bought an Elmic Compact compound escapement, and never looked back!

About 25 years ago, I built myself a single channel 35 MHz FM set, and have been flying it on and off ever since. In 2015, I built a copy of my first successful model - a Veron MiniRobot - and went back to the site of my first successful flight for a 50th anniversary recreation:

I've replaced the engine since that video was made, and have enjoyed quite a lot of flying with it.
And you know what? I get as big a kick out of flying that, as I do any of my more conventional models!
laugh
--
Pete
Thread: Horus X12S
31/01/2018 18:48:47

Sorry, PatMc - missed your reply! Should've gone to specsavers....! blush

--

Pete

31/01/2018 16:53:21
Posted by Don Fry on 31/01/2018 15:19:55:

So the restriction is there to reduce the chance of interfering with another user. Is there a reason why this is a bad idea?

The EU restrictions are a political decision rather than a technical one. The whole point of spread spectrum is that systems employing it don't interfere with each other. However, when it was introduced in Europe, the original specification was so badly drafted that every country interpreted them differently! The head honcho of the EU equivalent of Ofcom held a summit meeting at which he read the riot act to those who had drafted the rules, and told them to go away and do better, but without disadvantaging equipment already on the market.

Quite what happened next is the subject of some speculation!

On point of view is that the rule-makers were so incensed at being given such a public dressing down that they deliberately redrafted the rules in such a way as to make them much more restrictive going forward!

Another is that several big companies wanted to use the band for their own ends and didn't want things like model control or wifi getting in the way of their pet projects!

Whatever, we ended up with a totally pointless alteration to the specification, which restricts our compatibility with the rest of the world. It is clearly pointless, because existing equipment was granted "grandfather" rights and can still be used. If there was a problem with the original equipment, this wouldn't have been permitted. And if its good enough for the USA, Japan, etc, etc, what's the problem?

So to answer your question, the rules were changed to "fix" a problem that didn't exist, and more likely, to avenge some severely bruised egos..........! You are no more likely to suffer interference from D8 than you are from DSM-2, or indeed any current system.

--

Pete

Thread: Fuelproofing painted surfaces
31/01/2018 12:23:59

I painted my "KingPin" with Solarlac about 2 /12 years ago now. Whilst it hasn't seen a lot of action - mostly due to the weather - it has held up quite well without requiring any additional fuel-proofing.

Two caveats: I use straight fuel in it - no nitro - and I always wipe the worst excess off after each flight, and clean it thoroughly at the end of each session.

It is advertised as "fuel-resistant" rather than "fuel-proof" - but so is everything else these days! The only really fuel-proof paint of which I'm aware is the two pack stuff - and that requires really careful use as the fumes are deadly!

--

Pete

Thread: Super tigre
28/01/2018 19:17:25

Wilco: That's good news! I know Mick would make them for customers on request, and I still have a couple of engines using those carbs!

Niall: Don't worry! Mick passed away a while ago! The only way he'll be able to send you one is via a ouija board! And if he does, refer him to me!

wink

--

Pete

 

Edited By Peter Christy on 28/01/2018 19:17:58

28/01/2018 17:28:14

Sadly, most spares have become unavailable since production moved to China. I'm not even sure any engines or parts are produced anymore. Any that are made seem to go straight to the USA.

What a sad end for a great marque.

--

Pete

28/01/2018 15:42:07

Just to get back to the OPs engines for a moment: Niall, I notice your engine(s) have the older "wire" type needle valve. These are very scarce, so be careful not to break them!

--

Pete

28/01/2018 12:22:26

I got to know Mick very well during my years working in London. Underneath that gruff exterior was a heart of gold, and a more loyal friend it would have been difficult to ask for. His knowledge of model engines was second to none.

However, having heard him talking to customers, I can well understand why many of them didn't get on with him! I often used to help him out when Sandown was approaching, and always tried to get to the 'phone first, when it rang! The conversations often went like this:

Customer: "That's not Mick!"

"No, its Pete!"

"Thank the Good Lord!", followed by a long question about engines!

Me: " I'll happily answer questions about radio gear, but if its engines, you really need to speak to Mick!"

Customer: "NOOOO! Can you ask him for me?"

And so it went on....

Poor Mick could never understand why people got so upset with him! The trick appeared to be to be just as rude back to him! All those who tried that approach got on very well with him.

He was a character and a half, and I miss him greatly.

--

Pete

28/01/2018 10:10:24
Posted by Niall Reynolds on 27/01/2018 17:50:21:
Thanks guys for all the info. I assume I can adjust the carb to allow the inlet to be in the position you mention Pete??
I ran em today on nitro and they seemed fine.

I see John P has already advised on how to adjust the spray-bar. You may find that the previous owner has fitted shims under the head to allow them to run on nitro. In any event, you shouldn't have a problem with low amounts of nitro (5%) as others have indicated. But its not necessary, straight fuel is cheaper, and nitro can turn to nitric acid if left in an engine for any length of time. This doesn't do the bearings any good!

If you want to run nitro, make sure the engine (any engine, not just STs!) is run dry at the end of your flying session. The best way to do this is set a fast tickover and pull the fuel line off. Once the engine has stopped, flick start it until there is no sign of it firing. Finally, put a few drops of oil down the intake, and flick it over a few more times to let it circulate. Treated this way engines last for ever!

--

Pete

27/01/2018 17:34:06

Super-Tigres are excellent engines. I've still got quite a few hauling models around. They run best on straight fuel (NO nitro), though they can be made to run on nitro if you put some shims under the head, to reduce the compression.

Looking at the images of yours, someone has been fiddling with the carburettors! The fuel inlet pipe should point towards the front mounting bolt hole for best transition. Rotating the spray bar affects the mid range mixture, and hence the transition between idle and full chat.

They use long reach plugs, and although OS8 and Enya 5 will fit, they will be recessed into the head, and may not give the best results. Dave Wilshere at Motors and Rotors is your man to advise on what is currently available for them. (I'm still using up my dwindling stock of Super-Tigre plugs...!)

I've got an S40 that's been in a Morley Bell 47 helicopter for over 30 years now, and never needed removing...!

--

Pete

Thread: Telly tonight - slope soaring at Ivinghoe.
25/01/2018 18:17:58

Have set the video up! Jim used to be the Chairman of the South Midland BMFA Area when I was the rep. Excellent chap! And I met Sean a few times many years ago, as he used to use Mick Wilshere's World Engines radio gear, back in the day when I was helping Mick out. Haven't seen either of them in a good few years now, so I'll be watching with interest!

laugh

--

Pete

Thread: Electric Cars.
25/01/2018 18:06:42

Putting politicians down for a moment (Oh! If only! wink ), and getting back to the original subject matter, my biggest worry with the current electric cars is the fire risk. Anyone who has been an active modeller in recent years will have seen or heard of LiPos going up in flames. Now ours are relatively small, compared to those packed into an electric car, and I certainly wouldn't want to be around if one of those went up!

**LINK**

And that was a factory demonstrator!

I accept that this is a rare case, and that most LiPo fires are caused by external damage. But I wonder how these electric vehicles would fare in a motorway pile-up? And that's aside from the danger of electrocution from damaged wiring in a major shunt! Have you seen how careful the Formula One mechanics have to be, working on their hybrid cars?

I know petrol / diesel cars can burn as well, though usually not as much as Hollywood would suggest. But remember that in a conventional car, only half the fuel is in the tank! The rest is in the air around us. In an electric vehicle, ALL the energy is stored in the battery - usually under and around the passenger compartment.

Not a very comforting thought!

I agree that electric will take over rapidly on the roads, just as it has in our hobby. I just hope that the manufacturers will come up with a much safer battery technology than that currently on offer......!

--

Pete

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