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Resurrecting A Classic Matador.....


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I have fitted the brush-less motor to replace the brushed geared motor and carried out a current check as indicated in the photos below.

Matador Brush-less Motor

Matador Current Test

The current test with the 10.8 volt battery pack showed a marked decrease in the current demand compared with the brushed motor and at about 1/2 throttle just under 15 amps was indicated on the ammeter. I did not try full throttle. Further tests with the somewhat discharged 9.6 volt packs showed a maximum of 15 amps at full throttle and sufficient power to fly the plane comfortably.

Deans connectosr to be fitted next.

MJE

Edited By Mike Etheridge 1 on 11/05/2012 12:51:36

Edited By Steve Hargreaves - Moderator on 11/05/2012 13:35:39

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Hi Mike,

As Chris says if your using 22 amps at 9.6 volts It'll be 22 x 9.6 = 211 watts and the Matty will be going like a bat out of a really hot place. At 15 Amps on the same battery pack It'll be turning out 144 Watts, and if you could reduce the power by removing some of the cells from you battery pack you will obviously reduce the wieght as well requiring less power to fly well. I recon that 100 watts is a good power level for the Matty. if you aimed for 13 Amps on an 8.4 pack (7 Cells) you'll have a bit to spare and a sweet flying model.

Cheers,

Chris.

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Looking good Mike.....Remember you can alter the power consumed by the motor considerably by changing the prop.....I'm thinking maybe a 9x4 slo fly prop on that motor/battery combo will be good!!!

When you get to fly it then make a note of the throttle stick position when cruising & then, when on the ground, set up the ammeter & see how much current is drawn at this setting....I think it will be interesting to all the other Matty builders out there....wink 2

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Chris, Chris & Steve,

Thanks for the responses.

The motor is the EMAX BL2215-20 so the maximum rating is 22 amps for one minute. I have just got back from a quick trip to Croydon town centre and was thinking also that I did not need a battery pack rated any higher than 9.6 volts on the strength of the tests. I do have about 4 to5 no. 9.6 volt battery packs so will retain those and change the connectors. I also have three 8.4 volt packs so can also utilise those as well. All the packs need charging at present.

Other than for taking off you are quite right the Matador should not need a lot of power and was never intended to fly like a 'bat out of hell'. However I do have an unmade Weston Velocity 50 I won in the club's raffle last year. It's supposed to be capable of speeds up to 200mph----not sure I am going to cope with it!

Steve, a good idea on the flight/ ground test----the club members will be very impressed with the ammeter or will they?

Mike

Edited By Mike Etheridge 1 on 11/05/2012 13:41:24

Edited By Mike Etheridge 1 on 11/05/2012 13:42:41

Edited By Mike Etheridge 1 on 11/05/2012 13:45:20

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Posted by Mike Etheridge 1 on 11/05/2012 13:40:36:

Steve, a good idea on the flight/ ground test----the club members will be very impressed with the ammeter or will they?

Mike

I suspect not Mike.....they will probably say "What on earth have you bought one of those for....? You can get a proper wattmeter for less thah £15 you know"

At least ...that's what I said when I saw you'd bought that ammeter.......teeth 2party

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Good point Steve----I think I will mark the transmitter at the flying club and carry out the current measurement at home!

No progess this afternoon the grass needed cutting in the garden---my wife after a hard day's work teaching I thought  would appreciate that more than me buying a 9x4 prop at Avicraft and soldering-up the Deans connectors.

I did find the gold connectors very easy to solder and insulate-very impressive.

Mike

Edited By Mike Etheridge 1 on 11/05/2012 17:35:39

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Went to Avicraft today to buy rubber bands and replacement prop. However Ii could only buy a 9x6 prop so I have ordered a 9x4. However they did have a red and yellow spinner as shown below. I have tested the motor with the 9x6 prop and a 9.6 volt battery pack. The plane should fly Ok with this set up but I think the 9x4 prop would improve the performance.

MJE

Matador 12-05-2012

Matador 12-05-2012

 

Edited By Mike Etheridge 1 on 12/05/2012 14:41:24

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Hi Mike...looks really smart...hope you get it into the air soon....

Can I just add (& I apologise if you already know this) that you can't swap propellors around willy nilly on an electric motor.....an electric motor is essentially a single speed machine & will always try & spin at a speed dictated by its design (windings, number of poles etc)....to achieve this speed it will simply draw as much (or as little) current as it needs to achieve its design speed. Swapping from a 9 x 4 to a 9 x 6 won't slow an electric motor down in the same way as it would an IC motor....it will simply create more thrust. To do this the motor will simply draw more current......& so on ad infinitum until something melts..... The propellor is probably THE single most important part of an electric set up so please don't go swapping them around on a whim. Check each set up with your meter to make sure that none of the components are beyond their capabilities.....this is the main reason why a Wattmeter is so useful...nay essential....

PS some of the details above are not 100% correct but they are correct enough to explain the concept....wink 2

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Steve and Chris,

Thanks for your responses.

Steve,

Thanks also for the advice, of course at college many years ago we had to learn about the speed of all motor types and the formulas always involved 'pairs of poles' and voltage,but to date I have been too lazy to check them out so thanks for the reminder. i did go specifically to the model shop to buy a 9x4 prop for the plane as it appears to be the size recommended somewhere although the motor specification also suggests up to 10 inch props. I had to settle for a 9x6 prop that is currently fitted to the plane.Due to your encouragement I am carrying out load tests on the props and batteries prior to going out to fly the plane. i looked also at the one wattmeter available in the model shop but thought  there were better models on offer so may buy one 'on-line'.

The 9.6 volt Ni mH batteries seem OK now after 5 hour trickle charges but I do have a concern still about fast charging them. I currently have no confidence that the concept of fast charging Ni mH batteries is good idea and this applies to my 4.8 volt flight batteries in all my IC models. On the strength of it I have ordered a battery monitor for the IC models but may also invest in a new charger. My current charger is a Ripmax Pro Peak 2500VP which I bought in late 2003.

I have resisted Lipos to date but may eventually take the plunge and increase my fire insurance! I will look closely at your recommendation.

Regards,

Mike

 

 

Edited By Mike Etheridge 1 on 14/05/2012 13:49:55

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CROYDON AIRPORT 17-05-2012.

As the weather seemed OK today I though I would take a quick trip to the airport to test out the brush-less motor. Sure enough the one 9.6 volt Ni mH battery I tried let me down with two failed hand launches. I then installed the 10.8 volt pack which provided more than enough power and the plane flew OK. I tried a few right hand turns which proved more difficult to achieve than left hand turns. Whether this was due to fighting the dihedral I am not sure but throughout a lot of rudder work was necessary to keep the plane on an even keel. I thought perhaps a little more nose weight might improve things, however with the power off the plane glided nicely and was easy to direct on to the landiing- strip. I must pick-up the 9x4 prop from Avicraft tonight together with the in-flight battery monitor.

I spent some time looking at the theory of brush-less motors this morning as I thought it was about time to add the theory to what I have been practising. I had not realised they are 'synchronous' machines in other words as Steve mentioned before they try to achieve the same speed regardless of the load. This is similar to an AC electric clock synchronous motor,however a clock motor produces very little torque unlike the DC brush-less motor. I assume that with too much load with a DC brush-less motor then a volt drop on the battery would occur causing the motor to reduce speed. With AC machines of course the voltage is usually considered to be a constant. I was interested to note also that with some brush-less motor controllers 'Hall sensors' are used. Recently I had a 'Hall sensor' fail on the distributor on my wife's old VW Polo Ranger.

MJE

Edited By Mike Etheridge 1 on 17/05/2012 16:53:46

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Ooo Mike....you have lifted the lid just a fraction too high & now the worms are crawling all over the bench.....wink 2

Right...lets get a few bits of theory out of the way first......the brushless motors we use are DC brushless motors....synchronous motors are usually AC & the rotor is "sychronous" with the AC frequency (usually 50Hz). This produces a fixed speed depending on the number of poles of the motor......to vary the speed of these motors we need to vary the frequency of the supply & use a VFD or Variable Frequency Drive. The brushless DC motors is just that...a DC motor that instead of using brushes rubbing on a multi segmented commutator to switch the current to the coils on & off at the right point it uses "back emf" (effectively the ESC monitors the voltage waveform produced by the motor & "learns" where each coil is in relation to each other!!) to know when to switch the current to each coil on & off. It does this around 8,000 times per second for (possibly) 14 poles (& you complain that the ESC costs nearly £20!!!!). The speed is varied by the voltage applied.....

Now...Hall Effect sensors....these are basically little magnetic switches that are used in DC brushless motors to tell the ESC where each pole is in relation to each other.....they feed back a signal to the ESC to allow it to determine where everything is. They take the place of the back emf sensing explained above. Rarely used in the motors we use but very common in full size brushless motors & also in brushless motors used in RC cars. Hall effect sensors are also used in full size car ignition systems & take the place of points as you found out on your wifes car.....

So...to the model....what prop are you using currently? I wonder if the 9.6V batteries are simply sagging under load & the voltage (& hence the speed of the motor) is dropping away.... Alternatively the 9.6V batteries may not be able to spin the prop fast enough to produce a nice amount of thrust & you might need a bigger prop for the lower voltage battery. Remember that the 10.8V battery will make the motor spin at 1.2Volts x the motor kv faster.....as I recall you have a 1200kv motor so an extra 1.2 volts will equate to 1.2 x 1200 = 1440 rpm more......quite a lot.... Have you taken any readings of the voltage & current under load? A wattmeter would tell you all you need to know here & would guide you to the correct solution.....wink 2

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Steve,

I wondered whether there would be any reaction to my last comments and somehow guess you guys are harbouring electronics degrees or similar! I must admit I read a few paragraphs on brush-less motors on the internet and you can probably guess how much of the information has filtered through to 'the old grey matter'.

However I much appreciate what you have written and would guess that others reading it will find it most interesting as you appear to have covered most of the technical issues regarding brush-less motors we use,thanks very much for the effort!!!---do I deserve it?

As regards the Matador once it was in the air my throttle setting was probably less than 50% with the odd burst of extra power necessary when the plane lost a bit of height. At present the plane does not appear to fly 'hands-off'' which is a bit disappointing as most former 'free-flighters' do.

If Santa Claus does not bring me a wattmeter this year I will be most disappointed,but I have now got a selection of props to experiment with including a 9x4

Best Wishes,

MJE

Edited By Mike Etheridge 1 on 18/05/2012 10:35:58

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Electronic Degree....nah! I'm just a natural genius........teeth 2

Mike, we are all standing on the shoulders of giants really....I didn't invent any of this stuff & take my hat off to the guys who did. For me the understanding of how things work is important....I like to know (& have several Anoraks to prove it...wink 2) & I believe it helps get more out of the hobby & makes you a "better" modeller more able to understand potential problems & get the best of your models be they IC or electric. If you are going to experiment though it is even more important that you understand some of the principles involved or you will never understand why such & such a thing happened.

What little knowledge I have gained during my disorganised wanderings through life I am very happy to share in the hope that it helps others.....payback if you like for all the times others have helped me....smile

The flying characteristics of the Matty are probably down to the airframe.....it doesn't really care where the power comes from after all....I do wonder if all these NiMH cells might be a bit heavy...my learned colleague Mr Bott is close to finishing his Matty & thinks he will be around the 1.5lb mark AUW....a good bit less than yours....

Waiting for Santa to deliver your wattmeter might mean that you miss all that summer flying.....which would be a shame...sad

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Dear DH 82A,

I have currently introduced a fair degree of right side thrust (not measured to date) and some down-thrust. I will replace the 9x6 prop with the 9x4 next flight to see whether there is any difference from a torque effect point of view.

I can't suggest the structure is completely true but there could be a wing issue but nothing extensive. Also stubby little planes with low wing aspect ratios all seem to have similar characteristics.

I must dig out soon some of the other planes in the loft as the Matador has taken upmost of my modelling time lately.

Regards,

MJE

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THE CURSE OF THE MATADOR!

I have just emptied the boot of my car of planes from yesterday's flying session at Bartons Point.

I have put the planes for the time being in my garage, and have returned the Matador to the drawing board top. As I was leaving the garage I spun the propeller and noticed eccentric movement. After dismantling the prop it was evident the motor shaft was creating the problem as it appeared bent. I can confirm the plane has landed nose first a couple of times at Croydon airport with abortive launches, and it turned over once on landing yesterday. The plane suffered no structural damage on any occasion.

So there it is after no more than four full flights,one with a brushed geared motor and three with the brush-less motor the plane has effectively failed!

What are these brush-less motors made of such they cannot withstand the rigours of flying a 32 oz balsa and Solarfilm aeroplane?

MJE

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I have checked the internet for information on problems with bent drive shafts on brush-less motors. It would seem to be a common problem especially with the smaller motors. Various solutions were indicated including replacing the shafts. However another idea illustrated on 'You Tube' showed a straightening method in which the drive shaft is tightened within cordless battery drill chuck and the drill turned to apply pressure on the shaft. Having nothing to lose I have tried this on the Matador motor with some success such that another flight is possible.

I have to admit though the plane does not fly well especially in a breeze as illustrated on Peter Bruce's

video shown on the BPMFC website. Some trim / GC adjustments appear necessary

MJE

Edited By Mike Etheridge 1 on 26/05/2012 20:59:55

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