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Member postings for Swissflyer

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

Thread: What's the main radio brand you use 2017?
02/08/2017 19:18:12

Well here is a slightly different slant. As an electronics engineer I am very conscious that the movements of my thumbs & fingers are translated into electronic signals by potentiometers.

Over time, and depending on the quality of the potentiometers, the tracks in those potentiometers wear and can create spurious noise that does not help flying at all (maybe you have heard a noisy volume control on a radio to understand the point?)

Let’s just say that I trust more the quality of the Japanese potentiometers in my two Graupner/JR transmitters over the more modern production of a neighbouring nation.

So when 2.4GHz came along I just replaced the 41MHz RF links with the “cleanest” 2.4GHz modules I could find. That let me keep those high quality Japanese potentiometers, all the settings in my two transmitters AND enjoy seven years of glitch free flying - wonderful smiley

I do have one model on 41MHz, it does suffer glitches where my 2.4GHz models notice nothing.

So I can happily focus on improving my flying ...

08/02/2017 12:38:08

Getting a buzz?

Well, being an impoverished teenager back in February 1969, I did build a home brew two channel version of the RCM&E digital proportional radio system that was featured back then (see “The Way We Were February 1969 article). It worked and for a teenager that was truly heady stuff.

Yes, it was only two channels as the “impoverished” budget would only stretch to two servos! Many of the electronic components were donated by the local electronic repair workshop where I made holiday money by repairing six transistor radios. Remember them?

These days radio gear is so cheap that doing a DIY job would make no sense.

I have used HiTech, Futaba and Graupner/JR, the two Graupner transmitters upgraded beautifully with drop in 2.4GHz modules. That saved a lot of re-programming.

I have to say that I have not had a radio glitch since moving to 2.4Ghz.

My next step is to test out my new, nicely engineered, Chinese transmitter that offers downlink telemetry and promises to buzz/vibrate in my hands when the flight batteries are flagging.

Now who would have imagined that back in the ‘60s?

Happy flying

Mark

Thread: Multiplex Space Scooter
31/10/2016 22:54:50

My original Sky Scooter had a Mabuchi 380 (Speed 400) motor driving a 9 x 6ish folder through a 3:1 (I think) gearbox. The useful point is that Multiplex used the same drive train for their Easy Glider and there is plenty advice on how to do brushless conversions on Easy Gliders (I have one of those too & did do a brushless conversion)

If you can find a 2'000-2’400 kV brushless motor 20-28mm diameter with a 2,3mm shaft you can think about moving the pinion from the original motor onto the new one.
That would be OK for a 3S configuration, a 3’600 kV motor should be OK on 2S.

Although the Easy Glider did need more power, I have no plans to modify the Sky Scooter as it flew just fine with the original brushed motor.

Good luck with the conversion.

Thread: Hobbyking
27/10/2016 20:11:15

I noticed that HK is installing software to try and protect themselves from DDOS attacks (as per the attack using video cameras etc that blocked access to major US Websites last week). I would draw a couple of conclusions from that:

1) HK is suffering from DDOS attacks.
2) Maybe the people instigating the DDOS attacks are trying to blackmail HK “We will stop flooding your servers if you pay us a lot of money every day”?

For anyone who does not know it, please be aware that Web criminality is a huge, growing and very well organized global business.

So if you are having issues with the HK Website, the chances are that HK have bigger ones!

Thread: Safe Discharge Dodgy Lipo
14/02/2016 16:03:26
Posted by Tony Smith 7 on 13/02/2016 13:45:27:

I've done nothing with my models for quite some time, and today trying to get one of them airworthy again I find I have a dodgy LIPO. It's a bit puffed up, and squishier than the other one, and one cell reads almost flat compared to the others. At the moment, after an abortive flight resulting in loss of power, the cells read 4.08/4.08/2.92.

Hi Tony,
May I point out that the recommended storage voltage for LiPo’s is 3.80V?

I discovered that some years ago after an expensive 3S LiPo pack had one cell exhibit high internal resistance after storage at 4.08V (yes it did that in flight). Since then I always store LiPos cool at 3.80V and my LiPo attrition rate has dropped dramatically.

Pity to throw away your pack when it is 2/3 good!
I do own 2 x 2S packs that started as 3S packs angel

Good luck
Mark
PS Before I start flying again this year (too cold right now) I will be checking the internal resistance of my LiPos under moderate load. That way I could have avoided the failed flight.

Thread: 2016 RCM&E Autumn Special- Free Plan Modellers Choice
13/02/2016 11:48:41
Posted by Alan Gorham_ on 12/02/2016 15:16:43:

Mark

Well, a 60" very scale MC-72 would get my vote!

I built a pseudo MC-72 a few years ago and it was a good flyer:

Hello Alan,

Glad you would vote for a MC-72. Also congratulations on yours, your photo captures exactly what I have in mind, a model that looks great to start with and can be a platform for as much detail as one wants to add.

Yes, I have seen Tony’s S6B plan somewhere that shall not be named wink

My post did have an element of competitive mystery behind it...

Years ago Tony did a twin engine, airliner project for RCM&E and was happy that it was considered to fly better than a Twinstar. I think he even admitted in the article that this had been his objective.

Now my favourite flying spectacle is slow speed aerobatics by a beautiful scale model.

Since we all know that Tony can design beautiful scale models, maybe I was hoping to prod his competitive instinct into a design that would both be beautiful and at least equal Seb’s model in performance?

Mark

Thread: Do you think some sort of registration system would protect the hobby from rogue flyers?
12/02/2016 15:35:07

When I wanted insurance here in Switzerland, the insurance company told me that I had to be a member of a registered model flying club.

The club shares the airfield with full size, light aircraft and has a strict procedure.

They asked me to put in six appearances and fly with the supervision of a senior club member, there was strictly no flying alone at the club site during that phase.

Once that was done & they were sure that I knew the procedures for giving priority to full size aircraft, they gave me the forms to apply for insurance and club membership.

So is this a “Win-Win” procedure? To my mind “Yes”.

The insurance company knows that insurance is being given to “checked out” pilots.

The club knows the capabilities of the new member well and the airfield knows that the club members know the local procedures.

The new member meets experienced local pilots, they are nice guys who really help.

It also means that most of the modelling community is in a club; however, the insurance is world wide so I can also fly with insurance cover in the field outside my front door.

This also means that any “apparently irresponsible” flying by uninsured, unqualified people can be checked as the friendly policeman will check your insurance card to be sure that you have been checked out.

And of course he can take away your model on the grounds that you have no insurance.
So yes, there are rogues, but they don't seem to last long...

Thread: 2016 RCM&E Autumn Special- Free Plan Modellers Choice
12/02/2016 14:59:10

So how about a beautiful, 60 inch wingspan, racing seaplane?

You can see one original plan here:

**LINK**

It is definitely for balsa bashers & shows fuselage construction as 3mm sheet balsa on 3mm ply formers, I would let RCM&E sell me those formers together with the wing ribs & main spar laser cut.

The wing is parallel chord with symmetrical ribs dropped onto a slotted main spar so we are well away from tip stalling issues and the aerobatic performance may startle you, watch the video to check that out.

If I am providing some translation, you might be guessing that we are talking about a foreign design.

If I am talking about beauty, you can probably guess which nation (apart from the UK) made beautiful racing seaplanes?

So why not? Surely Tony could breathe some British genius into his own version; a 40-48inch span would suit well from the power train budget but still be big enough to have real presence in the air.

Or got to YouTube & search for watch?v=rvacC694QZo to see a great pilot flying his version of this aircraft.

At minute 3:30 on that video, you can see how the model would work at your local grass patch…

Hope you enjoy it
Mark

Thread: Understanding outrunner motor specs.
10/02/2016 13:35:54

Hi David,

Thanks to Toni for his support and compliments to you on your tenacity.

Of course there are no dumb questions, only dumb answers.

So as to your question: “Is it that power is fully on for the cells chosen and the current is the result drawn for a particular prop?” The answer is yes, and that is a very useful conclusion as you can experiment with different props and voltages (2S, 3S, 4S LiPo packs etc) to find a good solution for your application.

A very practical way for you to move forward would be to download and try DriveCalc (it is free of charge). Then you could look up the Hyperion motor we have been discussing, set the voltage to a “constant voltage” 14 Volts and play.

**LINK**

Hopefully you will then discover that the curves are always the same, however, different props will load the same motor in different ways.

If you have questions, please ask.

Mark

08/02/2016 21:44:38

Hi David,

Great, you are spot on with your understanding of the green efficiency curve & the red power curve (I guess that you noticed the scales are on the right hand side of the graph).

On the left hand side of the graph you can see a blue scale called n (rpm) and that is what the blue line is. It says that with no prop, the motor will turn close to 12’500 rpm, the bigger the prop you put on the motor, the more the rpm will fall.

In the case that Drive Calculator is showing you, an 11 x7 APC E is “slowing” the motor down to 10’120rpm. Put on a bigger prop and you will go further down the blue curve to the right (lower rpm).

Do let me know if all this is clear to you?

If you would like to, we could also look at how to avoid the “max power” trap that some unscrupulous vendors use to relieve the unwary of their hard earned cash?

Mark

Thread: 2016 RCM&E Autumn Special- Free Plan Modellers Choice
02/02/2016 20:22:38
Posted by Erfolg on 26/01/2016 15:47:27:

As for the DH Rapide a total waste of time, wings far to pointed, then there is the issue of rigging, if a thin aerofoil section were to be used. Beautiful to look at.

Hey Erfolg, washout & low wing loading can manage tip stalls.

**LINK**

Once the current Stearman PT17 is finished, my Dumas Rapide is next.
If its got two wings, let’s have two engines as well and put one on Tony’s list for 2017 smiley

Thread: Understanding outrunner motor specs.
29/01/2016 17:08:04

Christian Persson, the main author of DriveCalc knows about these deficiencies and designed DriveCalc to “choose between several motor models for the computation, depending on what measurement data are available, to achieve the best possible accuracy”.

I do confirm (from practical experience) that DriveCalc adapts its accuracy according to the quantity & quality of data you put in and its accuracy, with good data, suggests that it goes one or more steps beyond the 3 constant model.

Better still, Christian Persson built tools into DrivCalc for estimating the motor (& prop) calculation reliability. If you look at the extended version of the Hyperion HS3026 data (below) you will notice Motor Calculation & Prop Data Reliability at the bottom right.

The motor calculation reliability is derived from the “Measured Data” on the left.

You can see that DriveCalc indicates -13.57% and +17.09% swings in the measured data and says expect only low to medium reliability from this data.

Whoever measured the data for the Turnigy 540S did a much better job and is told to expect medium reliability, I guess that DriveCalc had enough good data to choose a better algorithm.

I used exactly this motor to power my Ripmax Spitfire some years ago, with the weight gain from moving from NiCads to LiPos and the power gain of the brushless motor it flew like a dream.

If you look carefully, DriveCalc says you can be quite confident on the motor results but not with the prop. DriveCalc relies on us (the modelling community) to supply that prop data and no one has said much about a Graupner 9x6 folder on a 45mm hub.

I switched to some well known 10x6 props APC & GWS HD. Then DriveCalc told me to expect 22.6 Amps current draw at 11.25 Volts, my Wattmeter measured 22 Amps at 11.25Volts so I was comfortable with that.

Christian Persson says if you find an error of more than 3% relative to the DriveCalc prediction, look carefully for the reasons. I have followed that advice over the years and found a 12 turn motor missing a winding i.e. 12:12:11 turns, LiPo battery packs with a rogue cell hidden in the middle, faulty ESCs and motors with Kv labelling that is just wrong etc.

In summary, yes, there are traps and many variables with electric motors.

However, well measured motors in the DriveCalc database let you check what you are seeing against a calculation reliability scale & home in on anything that looks odd.

If it looks odd, it probably is and be sure that you understand the cause.

Happy flying
Mark smiley

Hyperion HS33026 0880 with calculation accuracy data2016 01 29 turnigy c540s with calculation accuracy data.jpg

29/01/2016 17:07:03
Posted by David Hall 9 on 27/01/2016 09:38:02:

Thanks all for such detailed replies. There's a lot of technical info here for me to work on. The performance graph is really interesting.

Hello David,

Good to see that this thread is useful to you, thanks for the comment on the efficiency curve; yes those curves have helped me enormously. Ready for another step?

Since this thread is about understanding electric motors, I think BEB’s point on “Why is my fag packet so good?” needs to be addressed.

On the one hand an electric motor, especially a brushless one, looks like a simple piece of kit but why do so many calculators fall down and fag packets work?

Please allow my to tell you a little about me and radio controlled models as part of the answer comes from there. Basically I grew up in the 50’s & 60’s with a wartime flight engineer and pilot for a father. He gave me his Mills 1.3 and later bought me a Mills 0.75, I scaled up (doubled) a Keil Kraft Playboy plan and spent my life savings to buy a McGregor single channel RC with a rubber sequential escapement.

That became a “galloping ghost” and soon I learnt how to strip components off computer boards to make my own RC gear. Grown ups in those days could afford 10 channel reed outfits!

At university, our professors instructed us in the 3 constant model for electric motors, that is where I met our good friends :

Rm (Motor Winding Resistance)

Io (Idle current assumed independent of voltage applied to the motor)

Kv (The motor internally generated back emf when rotating)

All was well under I returned to modelling at the end of the 90’s and jumped into the electric end of the spectrum. In those days the batteries were very heavy and the Speed 400/600 motors were not so efficient.

I quickly found those old equations from university posted on RC Groups by Joachim Bergmeyer. All seemed well; they said increase the operating voltage, set ground rpm about 20% to the right of the peak of the efficiency curve (see my first post) and things will improve.

They didn’t and although Io is supposed to be constant and independent of applied voltage it wasn’t and the promised efficiency gains didn’t come!

So was it back to fag packets? Or did the 3 constant model need improving?

Various experts dug into this and realized that the 3 constant model takes no account of the eddy current losses between the laminations (and other secondary effects). Worse, eddy current losses increase with the square of the current.

In concrete terms, increase your operating current from 10 Amps to 20 Amps and your eddy current losses multiply by 4.

So called 4 constant (and maybe more) mathematical models were developed that incorporated the eddy current effects and gave an excellent fit between theory and practice.

Peak efficiency in a 4 constant model happens at a lower current (less eddy current losses) than in the 3 constant model. However, if you choose propellers to maximize the in-flight efficiency, you will be helping to minimize the eddy current loss effect.

If you look at the efficiency curves you will see that a motor close to peak efficiency in flight will only draw about half the maximum recommended current so will be creating 4x less magnetic eddy losses (remember to square the electric currents).

However, and here is where the fag packets win, most of the calculators (freeware or paid for) that are out there use the 3 constant model so beware if you trust them too much.

continued in next post

26/01/2016 18:34:41

Hello David,

Yes, Drivecalc & WebOCalc make it all rather easy as others have already commented. WebOCalc will get you in right ballpark from the flight perspective but first you need to have a grip on motor kv etc.

DriveCalc exposes what the real rpm/V of motors is and lets you see if you will be operating with good efficiency towards the top of the efficiency curve.

In the jpg below you will see that I am thinking about a 4S setup (14 volts is a conservative number) turning an APC 11x7 E prop at about 10’000rpm.

The blue line here shows the motor at 10’210 rpm.

The green curve shows the motor efficiency 77.4% at that prop speed.

You should also notice that the pitch speed is 109 km/hr (about 70mph) and thrust at 2.4kg – powerful.

Now for the magic, you will probably remember, from David Burton’s excellent series, that a propeller running on the ground is pretty much stalled and will only start “flying” correctly with some airspeed under its belt.

As the propeller “unstalls” it produces less drag so it can speed up.

In the days of Speed 400 can motors we used to call it “unloading”, typically a Speed 400 would unload by about 20% in the air, they were low on torque.

A good, modern brushless motor, with a well chosen prop, will unload by about 10% (these days you can check that in real time)

So now look back at the blue line and imagine that our motor unloads in flight from 10’200 rpm to 11’200 rpm.

Now look at the efficiency curve, you will see that the motor has moved to the top of the efficiency curve at about 80%.

You will know when you have a motor set up this way as you seem to get more power appearing by magic as you power up going into up into a big open loop it is a glorious feeling and you will be amazed by how many mAh are left in your battery at the end of the flight.

A couple of health warnings!!!

Do remember the old pilot’s adage about burning fuel to carry fuel.

An efficient set up will let you fly longer with a lighter LiPo, however, the system I am describing is drawing nearly 600 Watts (one bar of an electric fire), thankfully, most of it is being used to fly the model and you only have to get rid of 120-130 Watts (a good sized light bulb) from your engine compartment.

I have seen models (and read too many reports) of models that are incorrectly set up and so produce 300-400W in the motor body and engine compartment, and then…

Unfortunately a Watt meter will only show you that the total energy drain is 600Watts and you may only get the bad news in the sight of blue smoke and a crash in the visitors car park (the RC Groups report was terrifying).

So my second request is please avoid motors that are not in the DriveCalc database until you know how to measure the efficiency and set up power systems safely yourself.

The good news is that the predictions of DriveCalc will correspond very closely to your Wattmeter and you can fly feeling safe & really enjoy the magic of high efficiency electric flight.

Enjoy it

Mark smiley2016 01 26 understanding bl motors hp hs33026 0880.jpg

Thread: Step craft CNC machine
26/01/2016 17:10:19

And I am enjoying it too.
Thanks for taking the trouble to post your experiences.

Mark

Edited By Swissflyer on 26/01/2016 17:10:50

Thread: 2016 RCM&E Autumn Special- Free Plan Modellers Choice
26/01/2016 16:46:31

Please avoid any current ARTF's, it would be a pity to craft a beautiful model and have a clubmate tell me he saw it for £50 on a Website surprise

Gloster Gladiator - if you do an IC version, I will do the electric one

Concorde - but maybe Cyril Carr will oblige, his normal choice of materials would let me afford to power it!

Lockheed Constellation - for the sheer beauty of seeing it in flight

Or maybe we should do a mass build of Stearman PT17’s and persuade the British lady who just flew one to Australia to come to the event along with a lot of media coverage?

smiley

Thread: Electric Set Up for Ballerina
05/12/2015 13:50:56

So how about this for an idea :

  • Fly Electric is dead as electric is now mainstream
  • Electric vs IC preferences are equal according to the current poll.
  • Peter’s designs are gorgeous & many electric folk would like to build relied & tested electric versions (just look at the interest on this thread)

So would it not be possible to have a RCM&E guru (plenty on this thread) to work with Peter to make the next plan, or an existing one, dual purpose?

If Asian designers can offer ARTF’s with an F1 option for IC or electric motor mounts, I am sure that Peter can.

The “honoured” electric guru from this thread can contribute the “electrify” appendix to the main article and we would have two models to drool over on the RCM&E cover photo.

Better still RCM&E would have a chance of doubling its sales of plans & wood packs.

And the number of mass build participants could potentially double as well.

Happy mass flying smiley

Edited By Swissflyer on 05/12/2015 13:53:36

04/12/2015 17:57:21

twister electric conversion enlarged rudder.jpgtwister electric conversion early tests.jpg

Fascinating thread, thanks to all. I have often thought about electrifying an IC model (including some of Peter’s) but only did it once. The in-flight results are fantastic; the Black Horse Twister (with a larger rudder for knife edge authority and an unintended 700Watts up front) has impressive authority and flies the book.

7-8 minute flights take about 1’600mAh from the 3’600 mAh 4S pack so I often squeeze two flights from one charge.

The undercarriage is a nice springy affair made of high quality carbon fibre, anyone have a good European source for those please? My two current builds both need them.

Would I do it again? Not so sure. With a 50:50 balsa:foamy fleet I have to say that as I modified the Twister I was constantly noticing weight saving possibilities.

Of course the strength (and weight) were there to handle an IC engine, however, my thoroughbred acrobatic foamies (is there such a thing?) just don’t have that weight penalty in the first place and show corresponding performance benefits.

So in conclusion I would say if you really want a particular model that is only available in an IC version, go for it (use our old schoolboy moments formula measured from the designers CG to calculate if the electric motor + battery moments will fit in the fuselage without major surgery)

If flight performance is your thing (it is my thing) a dedicated electric design would be my choice.

And as BEB comments in his post, three years later, the model is still clean.

So Glyn, I hope you jump in and enjoy it, it will certainly fly beautifully.

Thread: electric motor mount
15/07/2015 18:02:07
Posted by Simon Chaddock on 12/07/2015 12:09:59:

I know it is simple and easy way achieve the desired result but with my structural engineering hat on I always cringe at the sight of a substantial rotating mass supported on the end of long bolts.

Now if you were trying to design a mount that would respond to any out of balance forces...........

Structurally it would so much better to bring the motor bulkhead forward. wink 2

Fully agree Simon, however, if the motor has to be mounted that way, it is worth remembering that that one can reduce the vibration & noise of the set up by positioning the prop so that dynamically counter balances the motor.

i.e. apply the EDF dynamic balancing technique to a conventional motor & prop set up.

Happy flying - Mark smiley

Thread: Remember this? The HP115
09/06/2015 11:05:15
Posted by Simon Chaddock on 05/06/2015 19:20:53:

My intention is to build it very light in Depron (again! ) in order to fit an EDF within scale rear fuselage dimensions although I will allow myself an over size jet pipe.

The problem is its polished aluminium finish which is very hard to duplicate in anything but ..... polished aluminium! It also adds about 25% to the weight.

Simon,

If anyone will make it fly it will be you.

Speaking from memory (which may be old and shaky) Graupner used to have a built up Junkers JU52 “Tante-Ju” which they offered a lightweight simulated “aluminium” covering material for.

**LINK**

Maybe someone has some?

KR Mark

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