Jump to content

Smoking....


Recommended Posts

Hi Roger, I've been reading this thread with some interest as I too am new to electric powered flight, and still love the sound and smell of ic motors smiley

Also seems we've had a similar past, I started with Rediffusion ( remember them? ) in 1970 mainly on cable systems but with a bit of TV repair thrown in for good measure. Then many years in various different companies from marine electronics to working for Flight Refuelling Electronics.

I too have a PPL and fly from Bournemouth in a Grumman AA5b Tiger and am a member of Wimborne Mac.

Having said that I do find model electric motors and esc's an absolute minefield, there are just so many different types and numbers that, to me at least, make no logical sense...……..

Every day is a school day as they say and I'm learning quite a bit from this thread.

All the best and happy flying.

Davey

Edited By DaveyP on 07/05/2020 18:34:39

Link to comment
Share on other sites

Hi Davey,

Nice to hear from you. My word, we did have similar backgrounds didn't we. I well remember Rediffusion. One on my pals was an engineer for Radio Rentals. Do you remember that one too. There were quite a few television rental companies around back then. We don't seem to see many any more.

I packed up full size flying in October 2018 and returned to model flying. I used to fly for some years from Coventry, but from 2009 flew from Wellesbourne (Warwickshire) as a member of South Warwickshire Flying School. I used to fly rental aircraft which included PA28's, Cessna 150's, 152's, and 172's. I'm still an honorary member and pop in on Thursdays for a chat and a cuppa with some of the other honorary members. It's like 'last of the summer wine'.

My model club is 'Heart Of England Aeromodellers' (HOEA) and is based in Meriden (near Coventry). I'm with you on model motor specs making no sense. Still, I've learnt lots about electric flight and it's components over the last few weeks so that has been really good experience.

Happy flying.

Roger

Link to comment
Share on other sites

I've never been a fan of the databases that predict what motor and battery one should use. Usually because they never featured the motors I use. Instead I made a simple jig on wheels, secured so it couldn't go flying off, linked it to a set of small luggage scales, and bolted the motor ESC and battery to the jig via a wattmeter. Then I simply used a servo tester to alter the throttle. It was published in RCME a few years ago.

Experimenting like this with different batteries and props gave some very interesting results when looking at the static thrust. I usually take about 5-10 readings from 0 throttle to full throttle. Many have said static thrust is of little use as the thrust changes once the plane is in the air, so I tried another experiment. I waited until we had a really strong gale blowing, 25-30mph, and faced the prop into the wind, and then with the wind. There was less than 10% difference between the two, and with every motor combination the thrust curve was identical. In reality most of my models will fly at 50-60mph on full throttle, so this was a really good test, as the airspeed difference was about that. Also, the one time when you really need full thrust is when the plane is static on the ground, especially, if like me, you fly off a grass strip. Thus I have been able to easily select a motor/battery setup that I know will work in the plane. My own rule of thumb is to ensure the static thrust at max is always more than the fully laden weight of the plane.

Telemetry readings in the air tend to back up the static tests I have done.

The final thing with electric I quickly discovered is to standardise. I only use about 4 sizes of batteries in all my models, and tend to use the same motors wherever possible. If the model doesn't fit one of my battery sizes, I don't build/buy it!

Edited By Andy48 on 07/05/2020 20:20:47

Link to comment
Share on other sites

Interesting to see that all you electronics based guys have trouble with model motors, me too. I started life as a BT (sorry, PO) engineer but after 28 years got replaced by microchips. I worked shifts as an emergency engineer but on my occasional fill in days I would repair some of the very nasty voltage converters. After a break elsewhere I got a job with a manufacturer of cellphone Tx/Rx equipment and was involved with testing some power supplies made by as it turned out the same manufacturer as the BT ones, but during the break I replied to a job advert in Ilfracombe made again by the same people. They did not even bother to reply, despite the fact that I was experienced with their wares and lived only 30 miles away. Just who did they expect an application from?

Before retiring I moved to CCTV in emergency vehicles, much more interesting because I had to design the bespoke installations, many of which were very covert.

Hope I have not bored you to tears with this.

Link to comment
Share on other sites

Andy: That sounds like some useful gadget to built there. I have always used a loop of string around the tail of my aircraft with luggage scales attached to test my torque. With the electric, I also include my wattmeter. I used to use this method when experimenting with different sized props too.

Like many things, once we have compiled endless amounts of data from all sorts of experimental scenarios we usually end up with just a few choices that 'fits all' that we are happy with.

Martin: Thanks for the interesting story of your career. I always find long careers fascinating. I've found that as I've got older and have lots of older friends, that between us all we have a massive amount of different experiences from life and work gathered from our past and it is rare when asking around about a particular problem, that we cannot find someone who knows the answer to it or can advise.

Link to comment
Share on other sites

Martin, I was also a P.O. Telephones engineer in the 70s but by 77 - 78 I felt I could do better so joined my friend servicing VDUs and Printers for large banks in the City. Through luck and judgement (good and bad) via systems engineering, Project Management and network design I ended up as Manager of a European Telecoms and Data network with 35 manufacturing and sales sites.

Po telephones training was excellent and after being an electrician apprentice for five years it was much more interesting - until telephone installations started to shrink in the late 70s and overtime sic was cut.

Link to comment
Share on other sites

Can we get any further from topic? But so what.

I was getting a little cheesed off with the PO and at the time you could walk into almost any job you wanted, but as soon as I was 21 I was offered a shift post in Birmingham Central exchange which meant a 50% increase in pay and model flying almost whenever I fancied. Not everyone`s cup of tea but I loved it. When those microchips replaced me I was again super lucky because they wanted to double up on the out of hours emergency team to look after the next generation of equipment which I was already trained in.

Took Release `92 which preserved what pension I had at the enhanced rate I was earning at the time. So glad I did.

Link to comment
Share on other sites

  • 2 weeks later...

Hi All,

Interesting ending to this thread. I recently obtained a new motor for this aircraft of the same make and model. In running some tests on it, I immediately noticed that the current figures bore no relationship to the figures of the previous one that went up in smoke. With the very same set up the current and power figures were much higher. Almost double in fact. Thinking this was strange, I double checked that my setup was the exactly the same, and it was. Well almost. This time I had used a newer wattmeter that I had purchased about 4 weeks ago. On the motor that burned out I used my other one (purchased last January). So I decided to connect the two wattmeters together in series and repeat the test. This time, the newer wattmeter was showing the same (higher) figures, but the older one was only showing about half. I then decided to raise the throttle from zero and to watch both the displays. Both wattmeters tracked almost identically up to about 20 amps. Then as they went through 20 amps, the newer one carried on in sympathy with the throttle stick but the older one hesitated then fell back to 19 then started to climb again but slower than the newer one. By the time the newer one was showing 39 amps, the older one was only showing 24 amps. Just to make sure I also used a tongue tester (clamp meter) on the setup and the readings agreed exactly with the newer one. So there we are. One defunct wattmeter. I opened it up to look for bad joints etc., but everything appeared fine. So one for the bin. I know that my habits and judgements are not the best in the world but my poor old motor must have been dissipating twice the power (watts) that I thought it was. No wonder it went up in smoke. Just thought you'd like to know the outcome.

Roger

Edited By Roger Dyke on 17/05/2020 14:09:26

Link to comment
Share on other sites

I started on electrics when they were new, 'difficult', and somewhat experimental. When they became easier I largely lost interest but I still make small electrics.

As for glows I use OS, and when they were made, OPS and K&B. In at least 20 years I have never had one stop unexpectedly. It's only those people who constantly fiddle with the settings that have problems.

Mine start as easily as my car and never need their settings changed, no more than my car does.

But there is an awful lot of grossly over-specified cheap junk in the model plane electric world.

Link to comment
Share on other sites

I bought a Wattmeter, branded by a very well known chain of model shops and stopped using it once I realised that there was little relation between the readings displayed and reality. I now use telemetry sensors on new electric models to check that components are operating within reasonable limits, both on the ground and in flight.

And yes, I'm another retired BT engineer (with over 41 years service, man and boy). I was too young for some of the very generous release schemes but I managed to escape to early retirement at the age of 58 what was becoming a very different micro-managed culture of fear environment which was so alien to the probably somewhat over-lax days of the 70s and 80s before the effects of the Civil Service origins diminished in the face of privatisation and competition. I moved in to the very different environment of internet and private network provision in the early days of commercialisation of the internet which was interesting and challenging until it was absorbed into business as usual and progressively de-skilled.

Link to comment
Share on other sites

Posted by Roger Dyke on 17/05/2020 14:05:49:

Hi All,

Interesting ending to this thread. I recently obtained a new motor for this aircraft of the same make and model. In running some tests on it, I immediately noticed that the current figures bore no relationship to the figures of the previous one that went up in smoke. With the very same set up the current and power figures were much higher. Almost double in fact. Thinking this was strange, I double checked that my setup was the exactly the same, and it was. Well almost. This time I had used a newer wattmeter that I had purchased about 4 weeks ago. On the motor that burned out I used my other one (purchased last January). So I decided to connect the two wattmeters together in series and repeat the test. This time, the newer wattmeter was showing the same (higher) figures, but the older one was only showing about half. I then decided to raise the throttle from zero and to watch both the displays. Both wattmeters tracked almost identically up to about 20 amps. Then as they went through 20 amps, the newer one carried on in sympathy with the throttle stick but the older one hesitated then fell back to 19 then started to climb again but slower than the newer one. By the time the newer one was showing 39 amps, the older one was only showing 24 amps. Just to make sure I also used a tongue tester (clamp meter) on the setup and the readings agreed exactly with the newer one. So there we are. One defunct wattmeter. I opened it up to look for bad joints etc., but everything appeared fine. So one for the bin. I know that my habits and judgements are not the best in the world but my poor old motor must have been dissipating twice the power (watts) that I thought it was. No wonder it went up in smoke. Just thought you'd like to know the outcome.

Roger

Edited By Roger Dyke on 17/05/2020 14:09:26

I don't think the wattmeter is to blame for your motor "going up in smoke". Judging by the photo you posted of it the motor was badly wound, it looks more likely that one of the coils had been damaged during winding. If it had been due to overcurrent for the time the motor ran all of the coils would have been discolored.
Also in the OP you say that you had ran another model with the same setup for a longer period without any problem. Why didn't, at least, overheat ?

Link to comment
Share on other sites

Hi Pat,

I agree that when dismantling the motor I too was expecting to see discolouration of all the windings, not just one section. I think it was the bad under-reading wattmeter that really tipped the scales, as the motor was actually taking far more current (and a lot more watts dissipating) than I had planned for and therefore rapidly got a lot hotter quicker than I was expecting. Maybe it was a combination of both,

Link to comment
Share on other sites

Roger, maybe the faulty motor damaged the Wattmeter when you first ran it up. This would explain a lot.

MH, it certainly did change with lower management put on short contracts and the pension scheme for newcomers being no where near what I had. At one time I thought of rejoining the company but after several pages of form filling the last line stated that it was not policy to re employ former workers. Probably because we knew how lax and cosy it used to be.

An engineer I called to fix a fault was rather less than trained and I had to tell him where to look for it. He was running round like a blue tailed fly with a hand held computer following his every move.

Link to comment
Share on other sites

Posted by Martin Harris on 17/05/2020 14:49:21:

And yes, I'm another retired BT engineer (with over 41 years service, man and boy). I was too young for some of the very generous release schemes but I managed to escape to early retirement at the age of 58 what was becoming a very different micro-managed culture of fear environment which was so alien to the probably somewhat over-lax days of the 70s and 80s before the effects of the Civil Service origins diminished in the face of privatisation and competition. I moved in to the very different environment of internet and private network provision in the early days of commercialisation of the internet which was interesting and challenging until it was absorbed into business as usual and progressively de-skilled.

I'm yet another a retired BT engineer, though at 24 I was an adult entrant having served my apprenticeship & worked as an electrician first.
"somewhat over-lax days of the 70s and 80s" is an understatement of PO Telecoms problems, The company was badly resource managed from the top down & lacked real work discipline. Virtually all performance targets and products were base on internal perceptions with little regard to customer expectations.
Because PO Telecoms reaped a healthy profit & subsidised the Royal Mail it was treated as a cash cow by successive governments who starved the business of much needed modernisation investment.

Martin, unfocused over-training was a gross waste of resource in PO/BT right up until I retired in 1995.

Edited By PatMc on 17/05/2020 17:10:25

Link to comment
Share on other sites

Posted by Roger Dyke on 17/05/2020 16:49:14:

Hi Pat,

I agree that when dismantling the motor I too was expecting to see discolouration of all the windings, not just one section. I think it was the bad under-reading wattmeter that really tipped the scales, as the motor was actually taking far more current (and a lot more watts dissipating) than I had planned for and therefore rapidly got a lot hotter quicker than I was expecting. Maybe it was a combination of both,

Then why didn't the other motor suffer the same fate ?
BTW the total Watts dissipated is irrelevant, it's the proportion that are dissipated as heat in the windings that matter.

Link to comment
Share on other sites

Pat: I wasn't driving the other aircraft anywhere near as hard as this one and also because the other aircraft's motor was in the open with no cowl at all. The setup was totally different. Different make and size of motor too. I got lucky.

As I understand (from an electrical background) nearly all the battery power (watts) is dissipated in the motor (windings) apart from a small amount in the ESC and the BEC for the RX and servos. The motor is the main load on the system. Or am I missing something.

Link to comment
Share on other sites

Very interesting thread even if it veered off track.

I must be the only aeromodeller who has never worked for BT - most of my clubmates did.

From the publics point of view BT was visibly hopelessly inefficient in the 70's and 80's. It was legendary that BT engineers came in 3 or 4's for the simplest job. The sight of 3 or 4 BT men walking in indian file down the office was so common people still talk about it. The first man carried a small leather pouch, the second a spare phone, the third carried a larger toolbag and the fourth probably carried a telex machine or perhaps the lunch. Not the mens fault I suppose and the spare men may have been trainees, but it looked inefficient. As a potential customer the cost of installing a phone line to my first house was so expensive I couldn't consider it. My parents had to put up with a 'party line' for years - shared with next door because BT couldn't provide enough lines in the area. Now every child insists on having their own mobile phone. From one extreme to the other. Now when they see their home phone bill many people now question whether there is any need for a hard wired phone line to their home. I am sitting looking at the dangling wire from a telephone pole to my house wondering whether that is really necessary- why isn't it underground? The most modern and essential ( especially in lockdown ) means of communication relies on victorian telephone poles!

However lets remember if it wasnt forTommy Flowers of Bletchley Park fame ( Dollis Hill actually and lack of fame really) we wouldn't be here on our computers and the internet. And we wouldn't have all the modern micro electronic stuff that enables RC to be available. So we do appreciate BT engineers really!

Edited By kc on 17/05/2020 17:51:39

Link to comment
Share on other sites

All the BT people will know this but for anyone else it's worth reading about Tommy Flowers here. Or just read the last line and note that all the companies mentioned are foreign owned which explains a lot about Britain.

Link to comment
Share on other sites

Posted by kc on 17/05/2020 17:44:24:

It was legendary that BT engineers came in 3 or 4's for the simplest job. The sight of 3 or 4 BT men walking in indian file down the office was so common people still talk about it. The first man carried a small leather pouch, the second a spare phone, the third carried a larger toolbag and the fourth probably carried a telex machine or perhaps the lunch.

Did you have some very attractive ladies in your office, perhaps? In my time as a field engineer I worked alone for 99.9% of the time, only doubling up for unusual jobs, training apprentices/new starters or, in my early years when some external work was common, during adverse weather conditions. Maybe things were different in Telex?

I don't think many new builds are fed by overhead lines but wholesale replacement of existing overhead services would not only be extremely costly but would cause environmental damage [remember the fuss over trees being damaged during the mass London cabling programme when liberalisation was launched?] and disruption to pavements and gardens.

Link to comment
Share on other sites

Martin, this was in the City of London in the era when secretaries were considered essential and the more attractive the better.

My wife remembers the same indian file of BT men in her office too, it was normal.

It's a forgotten thing now but Telex used to be an essential thing to international trade. Completely superceded by e- mail now I suppose. As old fashioned as a typing pool.

Link to comment
Share on other sites

Posted by Roger Dyke on 17/05/2020 17:28:51:

Pat: I wasn't driving the other aircraft anywhere near as hard as this one and also because the other aircraft's motor was in the open with no cowl at all. The setup was totally different. Different make and size of motor too. I got lucky.

As I understand (from an electrical background) nearly all the battery power (watts) is dissipated in the motor (windings) apart from a small amount in the ESC and the BEC for the RX and servos. The motor is the main load on the system. Or am I missing something.

Roger, you did say in the OP that you had the other motor at full power for 6 minutes & used the same setup on both albeit you didn't mention anything about cooling. Have I missed something ?

The only power dissipated in the windings is the difference between the applied voltage & back emf (from the motor acting as a generator} times the current. If the resistance of the windings circuit is known (HK give your motor resistance as 33.2mh (presumably they mean 33.2mohm) which is about right for a motor this size & kv) then multiplying by the current sq gives the watts dissipated in the winding. Taking the 25.2A quoted in the OP I make that about 21.6W generating heat.
The rest of the power is of course dissipated as work.

The point to remember here is that if you had been using 4 cells instead of 3 matched to smaller prop that pulled 25.2A the power would have increased by 33.3% but the heat generated would still have been 21.6W.

Link to comment
Share on other sites

Pat: Apologies. In the initial post I mentioned both models having the same set up. What I meant was exactly the same test conditions that they were subject to, not the same components that they were built from. Bad phrasing on my behalf I'm afraid.

I like your analysis reference the motor dissipation, although I'm not too sure about by increasing the voltage (3 cells to 4) with the current remaining the same (with a smaller prop) that the heat generated in the motor wouldn't rise (V squared over R).

As mentioned, I am a novice to model motors so of course I will bow to your superior knowledge.

Link to comment
Share on other sites

I have an original "Whatmeter" bought in the 90's from West London Models, cost about £55 IIRC. I have never had reason to doubt it's reliability though I have never been able to double check using any other method except "Motorcalc" which is usually in the same ball park but seems to read on the high side.

 

Re: BT / GPO telephones.

I was working on "Subs Apps" maintenance in the 70s in a mainly rural area which co-incidentally was also the area where my club field was located. It's amazing how quick faults could be fixed on a nice day to leave space for a couple of hours at the field.

Edited By FlyinBrian on 18/05/2020 08:00:09

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...