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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: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
03/06/2020 18:58:10

NiMhs don't suffer from "memory" effects like NiCads used to, but can still lose capacity if abused.

Do the initial charge as a trickle charge, ie: charge at 70 mA for 12 hours. After that, just charge with a peak detect charger at 1C (700mA). Set the maximum charge time to 1 hour, but it should trip off well before then.

Once every couple of months give it a 12 hour trickle charge to balance the cells (depending on usage). If not used much, you don't need to trickle charge so often.

Charging at 1C should provide a nice voltage drop for he peak detect charger to see. Trickle charging will wipe out any imbalance in the cells, but should not be done too often. It will result in over-charging, causing the cells to emit gas and dry out the electrolyte. Only do it occasionally.

Its amazing how the old problem of "black wire corrosion" has gone away since the advent of peak detect chargers....!



Thread: Most power i can get from a 6" prop
03/06/2020 12:48:14

I remember racing karts with highly tuned Villiers 9E engines back in the day!

We reckoned if it wouldn't do a ton down the straight at Dunkeswell, you weren't competitive! We were VERY competitive, so I'm sure it producing a lot more than 8HP!




02/06/2020 18:00:10
Posted by brokenenglish on 02/06/2020 17:00:01:

The technical links given are all no doubt valid, but I seriously doubt that a 6" prop will lift 4kg under any conditions.

Imagine a 4kg model maintaining a vertical climb on a 6" prop... and I doubt that any "duct" effect will increase the thrust of a 6" prop to 4kg !!!

But it doesn't have to lift it! It just has to maintain a cushion of air under the vehicle at greater than atmospheric pressure.

The lift motors on the cross-channel hovercrafts couldn't have "lifted" a fully laden ferry, but they didn't need to. They just needed to make positive pressure underneath, and maintain it when it "leaked".

Having said that, I tend to agree that a 6" fan of any kind would have difficulty maintaining the required pressure for a 4KG load. But maybe two, back to back, like a contra-rotating prop? That would also solve the torque issue.



Thread: Cleaning fuel off models.
02/06/2020 17:53:36

Muc-off to remove the excess residue, followed by thinners, iso-propyl alcohol or lighter fuel (be careful!) to remove any soaked into the wood. Might be worth a dab of Clearcoat (if you can find any) over the top, to seal the wood.



Thread: Most power i can get from a 6" prop
02/06/2020 15:10:16

Many, many years ago, I had one of these:


A Jetex Mobo hovercraft! It was powered by an AM .049 glow motor (un-silenced!) fitted with a 3-blade 5x4 prop. (may have been 5x3 - it was a long time ago!) Under the prop were a number of fixed vanes - around 6 IIRC - angled so as to counter the torque of the engine.

I'm guessing that motor ran somewhere in the region of 12,000 rpm. It produced enough lift to make the hovercraft fly a little on the high side, so the air cushion became unstable! Sellotaping an old penny to each side of the body, in line with the engine, loaded it up enough to maintain stability!

It was VERY noisy! Peak power was reportedly .052BHP at 14,000rpm **LINK**

.052 BHP translates to roughly 39 watts.

Bear in mind that the Jetex Mobo was "free-flight", very light, and went wherever it felt like! Enormous fun for an 11 or 12 year old at that time, but not popular with the neighbours! wink

Anyway, those figures may be of interest. Or maybe not! laugh



Thread: Taurus retro aerobatic build
31/05/2020 17:39:05

Excellent! Congratulations on a successful maiden flight!

My KingPin (very similar design) was also maidened in blustery conditions, but handled it extremely well.

I'm sure you'll get a lot of enjoyment from this model!



Thread: Why sudden dramatic voltage drop in 700mAh 4.8v NiMh pack?
31/05/2020 13:24:45

Also bear in mind that that 0.5 amp would only be if the servo was stalled or starting! Once the motor starts to rotate, the back emf reduces the current draw even further!

There is something to be said for slow, low geared servos for a lot of models! As I said earlier, I doubt if 95% of us would notice the difference!



31/05/2020 09:15:57
Posted by Steve J on 31/05/2020 08:45:54:
Posted by Frank Skilbeck on 31/05/2020 08:03:30:

Remember for years the standard battery for all models was a 600 mah Nicd and we used to happily fly for hours on one of those.

I always take such claims with a pinch of salt.

Not really. My Bonner Digimite (the first mass produced digital proportional - c.1966) came with a 600mAH NiCad pack, and would last a days flying.

Bear in mind that back then, we didn't have what are now referred to as "digital" servos. Current consumption was substantially less than with modern, high torque, high speed servos.

The Digimite servos may have had several pounds of thrust, but they were very slow compared to modern servos, not that we noticed at the time! They were used for quite some time by all the major American RC manufacturers, except Orbit. (Kraft were fairly late to the party!). Despite their slow speed, they were used at all major aerobatic events, National, Continental and World Championships and no-one complained about their performance!

Even in the 70s and 80s, most of the popular radios came with 500 or 600 mAH packs which were quite adequate for most flyers, including contest types!

It is only the relatively recently developed servos, that are not only very powerful, but also very fast, that have forced us to increase battery capacity dramatically. And while such servos may be a requirement for jets or 3D helicopters, I do wonder how many people would notice the difference if someone magically replaced their modern servos with ones from 40 odd years ago overnight!

Of course, the other down-side of such powerful servos is that the peak current draw of four or five of them can be a few amps, pushing the standard 3-pin connectors used for the battery packs, as well as the servos, well in excess of their design limits!



Thread: FrSky Horus X10S Express LBT to OpenTX
29/05/2020 23:08:38

Just done this for a fellow club member! I have an X10S and he has an X10S Express!

In Companion / settings / radio profile, make sure you select X10S Express as the radio. It is different from plain X10S!

Otherwise, everything seems much the same.

Also do make sure to back up FrSkyOS as described, as this is your "Get out of jail free" card!





Edited By Peter Christy on 29/05/2020 23:10:13

Thread: Where are the Watts?
29/05/2020 23:03:10
Posted by PatMc on 29/05/2020 19:35:09:

Pete, you're also highlighting why measured static thrust is pretty well useless as a measure of how a prop driven fixed wing aircraft will perform in any other respect but vertically.

Well, sort of! Actually, helicopters use less power once in forward flight! Its hovering that requires the most power (I'm excluding aerobatics here, talking about scale and sport flying!).

At model sizes, helis are more efficient because they are swinging a big "prop", slowly! In the hover, the blades are running in their own turbulence, which decreases efficiency somewhat, but is still better than a fixed wing prop size can manage. Once in forward flight, the rotors are running in relatively undisturbed air, with a resulting improvement in efficiency. In forward flight, you can throttle back quite a long way and still maintain height.

There probably is an equivalent "watts per pound" formula for helis, but the "fudge factor" will be quite a bit different, and no, I can't be bothered to work it out!

But having a wattage figure for the motor makes it easier to work out in your head what will be suitable for a given heli! (I hate mental arithmetic!)




29/05/2020 16:33:04

The popular "Watts per pound" formula only works for fixed wing, not helicopters!

Model helicopters are much more efficient at converting power into lift than their fixed wing equivalents. The early Schluters and Kavans struggled to get under the (then!) 11lbs weight limit, but flew perfectly happily on cross-flow 61s - in the case of the Schluters, at just above half throttle! Try getting a fixed-wing of similar weight to fly on that amount of power!

I've already converted a Schluter HueyCobra and Micro-Mold Lark to electric, and have a Schluter DS-22 awaiting test flights. The Cobra will fly for 10 mins - with a safety margin - on a 6S 5AH. I reckon that's around 675 watts, which ties in fairly well with the 61s they used to fly on back in the day.



Thread: Is there a list of frequencies we can use in the UK?
28/05/2020 14:04:55

Does the UKRCC still exist? I used to be on it, but haven't heard from them in years!

Back when I attended meetings, Ofcom always had a representative there. A very helpful and knowledgeable chap he was, too!



Thread: F3A competition in the 1970's and 80's
21/05/2020 16:23:43

Posted by Martin McIntosh on 21/05/2020 15:22:45:

None of us were exactly rich and as stated above, the SMAE paid the entry fees but everything else was down to the competitors.

I hope that things have changed somewhat now.

Dream on!

If the BMFA have any surplus in the kitty, they will occasionally make a small donation to the competitors, but with so many international contests and so little in the kitty, it is never going to be much.

And with the decline of the model trade in recent years, it is becoming increasingly difficult to raise money through sponsorship - or even raffle prizes!

Its a miracle we do as well as we do!



21/05/2020 11:59:34

I can back up what Martin said! Whilst not a competitor myself, I have been a Team Manager, and traveled to quite a few World and European Championships (F3C - helicopters).

Traveling in western Europe isn't too bad, or even Poland, but when you get to places like Romania, or further afield like Latin America or Turkey, it can be a nightmare. The World Champs that I was Team Manager for was in Turkey, and you wouldn't believe the hassle we went through there. We did quite well overall, better than expected, but even getting something simple like fuel (the days before electric!) was a major issue.

Add to that that the flying site was nearly 3000ft above sea level, and VERY hot and arid, and you begin to appreciate the issues. One team member got dehydrated and quite ill - luckily, being young, he recovered quickly and it didn't affect his performance too much. Everyone was having issues with the thin air and heat affecting the performance of models and engines.

And on top of all this, the team members had to pay for it all themselves, somehow! The BMFA pay the contest entry fees, but travel and accommodation are down to the team members! We had a very good fund raising effort, but all the team members still ended up out of pocket.

So don't imagine for one moment that traveling to World - or even European - Champs is a jolly! Its expensive, and hard work!

On a lighter note, I've recently transferred some 8mm home movies of Nationals from the mid to late 60s to video. Once I've tidied them up a bit and captioned them, I'll put them on youtube. All from RAF Hullavington, in the days before it became Dyson's test track! wink



Thread: Horus and Taranis X9D Express differences?
20/05/2020 19:27:37

One of my flying mates had just bought a Jeti system. And I could have bought THREE X10S systems for the same money, and have change left for some spare receivers! The build quality is certainly no better than FrSkys - indeed he had to touch up the paint trim on it out of the box because it was chipped! It also took him an awfully long time to work out how to set up crow braking on his glider, so not very user friendly either.

And didn't I read somewhere that it took Jeti several attempts to get through the FCC certification in the USA?


Think I'll stick with FrSky!



20/05/2020 17:58:32
Posted by Allan Bennett on 20/05/2020 17:11:21:

One more question:

As I said earlier, I'm familiar with LiPo and A123 packs and their storage requirements. What about these "Li-Ion" transmitter packs? Can they be stored safely in the transmitter at full charge, like A123s?


Actually, most of these cells can be stored safely at full charge, though some will eventually lose capacity, if abused.

The problems usually arise when charging, or, in the case of LiPos, if over-discharged.

In terms of overall safety, Li-Ion cells sit somewhere in the middle, better than LiPo, but perhaps not as good as LiFe.

LiPos offer the highest current capacity for their size and weight, which is why you don't usually see Li-Ions being used to power the motors in models, but for transmitters - and even less powerful models - they are fine.



20/05/2020 11:28:00
Posted by Richard Clark 2 on 20/05/2020 07:49:24:
It was installed in the Taranis for one reason only. It was free, so the Taranis manufacturer did not have to pay any development costs of his own.

And that was reflected in the price, which was substantially lower than any comparable competitors!



Thread: Personal Injuries.
19/05/2020 22:28:57

John, may I add my wishes for your son's speedy recovery.

In addition to the above suggestions about obtaining legal aid, you may find that if he has car insurance, that may also offer legal aid. These days it seems as if every kind of insurance policy offers some kind of legal assistance, so once he is well enough to talk to you, check out every insurance policy he holds.

Personally, I am loath to venture on the highways without being surrounded by substantial quantities of sheet steel! There are far too many idiots out there on the roads!



Thread: Horus and Taranis X9D Express differences?
19/05/2020 22:18:17

Li-Ion (Lithium Ion), LiPo (Lithium Polymer) and LiFe (Lithium Iron - confusingly!) are all different battery chemistries, and must be charged using the correct settings on an external charger. Getting this wrong can be dangerous, so be careful!

Just use the supplied internal charger, and don't worry!



17/05/2020 09:27:03

I've got both an X9D (Taranis) and anX10S. I bought the Taranis shortly after they first became available, and it has proven to be a solid and very capable transmitter. I bought the X10S about a year ago as a present to myself, and the possible requirement for something more sophistacated.

Having previously been a JR man, the Taranis felt instantly comfortable and familiar. The X10S is bigger and heavier, but not excessively so. I feel more comfortable with the Taranis, but that's primarily because I've had it a lot longer, and its similarity to my JR transmitters. On the other hand, the X10S offers a much bigger display and can carry much more information on it. This can be very useful.

For example, I'm currently converting a (very) old and large helicopter to electric. It is almost impossible to read a wattmeter connected to one of these things whilst its thrashing around on or near the ground. With the X10S, and a suitable ESC, I can display volts, amps, temperature and RPM on the screen. OK, I may not be able to watch them while flying, but an observer next to me can. This will quickly tell me if I've made the right choice of motor - something I could have done with a couple of years ago, when I carried out the first such conversion!

In terms of the two antennae, reports indicate that the two internals are better than the single external. However, my own experience with several single external antenna transmitters indicates there is no problem here, provided you can angle it suitably. On my Taranis (an early one) this movement is restricted, and I can't get it into the position I would prefer. I still haven't had a problem with it, though.

At the end of the day, it will come down to your personal preference. If you need to display a lot of info, go for the X10S. If you prefer a smaller, lighter transmitter, go for the Taranis. In either case you will be well satisfied.



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