Where have my watts gone?- advice please

[Dave Rose]

I have recently bought second hand an Extra Sport plane,63 inch, 7lb all
up weight including battery.The motor with it is a Thumper 5065,--
 Specs1400 watt,- 380kv, - prop recommended is from16x8. -- Recommended, 3-8
Lipoly..
 The controller is a Tower Pro 70A.  I have got a 3700 4S lipo.

I tested the set up with a Watts Up wattmeter.

Using a 16 x 10 prop, I have got very low readings.  At full throttle I have
Max watts of 273.  Max amps  17.  The meter shows 16v.

Until I thought about it, I  expected a lot higher watts- certainly I need a
lot higher!  .
I would appreciate advice please, as to what the reason is and what I need
to do to get a viable power for this model.

My thoughts on it are that the motor has a very low kv , (and i think this may be the key to the problem -/) which  causes not many amps to be drawn- 17 is extremely low.
Seems the only solution is a bigger prop, both in length and pitch.
(Required clearance means the limit is 20 inches.)

That,  or a  different motor with a bigger kv.?

I would appreciate some guidance from the experts please.

Thanks

Dave 

[Brian Lambert]

You are running at the low end of the voltage range for this motor, I would try more volts. There will be an expert along soon I am sure.

Brian 

[birdy]

The motor is designed to word at higher voltages. Try a way bigger prop, and try and get about 80 amps, but you will need to get a new esc - around 130amps? - or raise the cell count, to I would reccomend 6, since someone with a lipo that big is lightly to have some 3s lipos they can put in series, and try and get about 50-55 amps at full throttle! And I'me not the expert - thats timbo!

[Tim Mackey]

Well first off, I do actually think that FOR THIS MODEL the Kv is too low - it is a sport 'plane and should fly at a decent speed. I have a 400 Kv ( not much higher really ) motor in my Sopwith Camel and I run that on a 4s Lipo, and an 16 X 10E prop too - but thats because I want a fairly slow pitch speed for WW1 scale speed. However there is something amiss with your setup because on my setup I am getting 40A static with 600 watts - which is fine for the flying style of this model - My volts hold at 15V (approx 3.75 per cell ) but thats because I use 2 x parallel 3200 mahr packs giving me 6400 mahr.

For your 3700pack to be holding 16V under load says to me that the motor is just not right.....and one thing I wondered is whether you have "trained" the ESC to recognize your particualr throttle settings? Check the ESC instructions and ensure that you teach it your full throttle range, and also ensure you have it set to hard timings for an outrunner.

Even when you find out why it is not working properly, you are still left with a very low Kv motor for a sport 'plane, and the only way you will achieve the sort of power you need ( at least 700 watts and preferably nearer 1kw ) will be to up the volts. Running the same 400Kv motor ( with a 14" prop ) on 6s Lipo gave me 910 Watts at 42A and of course a much higher pitch speed ( 9600 RPM ) which would be nearer the mark for your model.

[Tim Mackey]

80 A is way too high...and unless you have a HUGE capacity battery will result in very short flights, and hot ESCs and motors.  Go up to higher cell count by all means but you will have to drop the prop size.

[birdy]

I was thinking that too, but then thinks I can you get over 100amp speed controllers. I once saw a 150 amp esc(!) and I wonder who might use it. Anyway that is not the point, and I should have mentioned the lipos C ratings to. Sorry!

[Tim Mackey]

Indeed very large currents can be used but these are normally in very large and heavy models, where high voltages also combine to give HUGE power input. The model here is only 7lbs AUW. Also, many people prefer to have a lot in reserve in their ESC capability....

And its  not really just about C ratings of LiPos either - more about the actual cell capacity - C ratings are ...well ... err.....over-rated

[Mike Rolls]

As an illustration of what is being said, here are the bench test results from a 650kv 4120/6 from Giantcod:

E-tek 3S

Jeti 40APC-E 12x823.02406700Sharkpower 4SJeti 40APC-E 12x830.04007800Ecolite 6SJeti 70APC-E 12x852.0130010500

The first number is Amps, the second Watts, the third RPM. The 6S is a bit approximate - the power was so much that the 1/2" ply mount was bending under the thrust, so I quickly shut down.

Mike

[Mike Rolls]

AH, those figures shoulf have been in a nice clear table!

they were

3S 23A 240W 6,700 rpm

4s 30A  400W  7,800rpm

6S 52A  1300W 10,500

For an IC comparison - I used to run my ST 51 on a 12x6 and get 10,000 rpm.

Mike

[Mike Rolls]

And the prop was a 12x8 APC-E

[Tim Mackey]

And of course, that motor is quite a lot higher Kv - remember dave, that very generally speaking, high Kv means high Amps and high revs, whereas low Kv means the opposite.

[Frank Skilbeck]

I ran a 370kv motor through drive calc using a 16 x 10 prop and it gave these results

4S - 23A, 4700 rpm, 2029g static thrust

6S - 45A, 6550 rpm, 3949g static thrust 

So looks like you need a 6S battery (or 2 x 3S in series) and your ESC would be fine.

Note I substiuted your  motor for a similar one as the Thumper motor was not in the data base. If you went to 8S you might have to prop down, say 16 x 8

[Mike Rolls]

Frank

To keep the current draw around the same with an 8S pack instead of a 6S, I think a considerably smaller prop than a 16x8 would be needed. The motor I quoted above - to go from a 3S to a 4S pack on a 14x10 saw the amps jump by 30%.

Mike

[Dave Rose]

Gentlemen

Thank you for your prompt  and informative replies. Things are a little clearer, but please bear with me if i don't grasp matters the first time.  I'm new to this electric lark

( otherwise I might not have bought the plane with this motor.However, having said that, is not the setup of the Sebart Angel as reviewed in this months RCME page 114, using a similart Kv motor in a similar weight plane?- Using a 6S battery, I see.) 

Timbo, your point about setting up the esc may be highly relevant- though what i can do I'm not sure.I did attempt to program the esc using a Tower Pro programming card , but I couldn't get it to work. It seems you have to decide whether you are using BEC or Opto- there is a wiring sequence for the programming card, foreach, depending on how you are set up. The setup I have is that I am using a separate receiver battery, with a non opto esc, having the red wire to the throttle input of the receiver disconnected. So- am I using BEC or opto.as far as the programming card is concerned. ? I think  the former, but please advise.  Mind you I tried both methods, but couldn't get it to show connected in either method.

So I tried the throttle setting and music method .  I thought i had set it to 4S and I thought that was confirmed when i saw that my watt meter showed 16 volts ( the 4S battery was fully charged) .?   Please advise on this one too, timbo, if you would be so kind. Have i got it set to 4S?

I didn't go beyond that to programme the other settings you mention,  so maybe  I have problems there- ( I didn't think they were relevant  to vital performance. ).

Please confirm whether I have the choice  of two  or more ways to go., even if i have an  inaccurate esc programming , ( which I shall correct,hopefully- these things ar so difficult  to get right-lol)

1. Get two 3S 4200 batteries and use them in series,

2 Get another Thumper motor with a higher Kv  - there are two capable of  700 watts and with KVs of 900 and 600. 

3. Open to suggestions on motor.  

I certainly don't want it to fly slowly-  but, as i say, the Sebart Angel power train isn't too far away from if i go the first option route , is it? 

Sorry i've gone on a bit, but hope you can help

TIA

Dave 

[Frank Skilbeck]

To get 700 watts from a 4s battery you will be pulling over 47 amps, thats about 13c on your existing battery so shouldn't be a problem. But you would only get 4.6 mins at wide open throttle so allowing for flying at less than full throttle you would need to set your timer for less than 7 mins.

I would think 2 x 3s batteries you mention above would be a better way to go with this plane, 700 watts on a 6s is going to be around 32 amps which is kinder on your batteries and gives a decent flight time, well over 10 mins.

 I've got one of these

https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2099&Product_Name=TR_42-50A_700kv_Brushless_Outrunner_/_720W

Gives 8900 rpm on a 13 x 6 at 36 amps on a 4s battery, about 550 watts, you could probably put a slightly larger prop on it and draw a bit more current.

[birdy]

Your esc is opto. I cant comment on the programing kafufle though!

[Tim Mackey]

Timbo, your point about setting up the esc may be highly relevant- though what i can do I'm not sure

It normally involves switching the TR on first with throttle set to high, connecting the ESC to the battery, and then waiting for na beep sequence - this means it has learned the high position.

Am I using BEC or opto, as far as the programming card is concerned.

I would say Opto - but it shouldnt matter as far as the above is concerned anyway.

I thought i had set it to 4S and I thought that was confirmed when i saw that my watt meter showed 16 volts ( the 4S battery was fully charged) .?   Please advise on this one too, timbo, if you would be so kind. Have i got it set to 4S?

The reading on the wattmeter has nothing to do with whether the ESC has correctly identified the battery cell count - and this part of its programming is only relevant to the LVC figure anyway. 

Practically speaking...yes you have 2 x choices - and this depends to a large extent on your budget. A new motor with a more suitable KV ( around 600 or so ) would be whole lot cheaper than 2 x new large capacity 3S batteries.... suitable high wattage motors are available for around 20 squid.....however its still debatable whether 4s would be the right configuration, because the current consunptiuon will go up with the higher Kv motor, and as pointed out to get 700 watts ( which is the MINIMUM for this model IMO ) from a 4s battery requires around 50A static and this will mean short duration.

I think in all honesty I would get 2 x large capacity ( 3500mahr  minimum ) 3s packs and use them in serial with  the existing motor and a smaller prop - experiment with props and the wattmeter to get the right sensible current draw, decent pitch speed, and the required watts. This way you have the 3s packs for other projects too.

One problem with going to 6S lipo is whether the ESC can handle that amount of voltage ( 25+ ) - I think your ESC is just about rated to 25V so should be OK.

HTH 

[Frank Skilbeck]

Dave, just a thought your ESC has a BEC and will use the BEC to power the programming card when you connect it to the ESC, if you've disconnected the red wire then it won't  power the programming card. I have a Turnigy one which I think is the same as the Tower pro type and it does have provision a separate power supply if you are using an Opto ESC.

But maybe to program the ESC with BEC the ESC has to power the programming card, have you tried reconnecting the red wire when you are using the programming card. Note as Timbo says though the lipo setting won't affect the max power sent to the motor just the low voltage cut off  point.

[Tim Mackey]

Yeh, thats a good point about the card power there Frank

[Dave Rose]

Thanks again chaps for your time and advice on this.

Frank - Yes, the esc does not say Opto on it. I did, however, decide to use a separate receiver battery so I did disconnect the red wire. I took out this connection and replaced it, pro tem, with a lead with red wire and connected to the esc intending to try the programme card using the BEC sequence. But there was zilch from the card and the esc made continuous beeps and none of servos worked - so I figured no power was getting to the receiver - ( duff temporary lead?).lol

I went back to my original set up and all worked as before. I'll play around with the manual tuning of the esc - beeps et al.Thanks for the heads up re the motor.

Timbo - Yes, I'm leaning towards getting two 3S batteries . I've got two 4200s lined up to buy. As you say, if I have to go the other route eventually, I still have two 3s batteries for other models. This esc is rated for up to 6S, it says 70A but no mention of Opto on it.

The sheet givng the set up menu is headed "Brushless motor controller Setup menu for 50A and 70A No Power output to receiver." (Italics are mine ). Not sure how that relates to my setup, frankly. I got it from the tower Pro website and figured it was relevant to my esc. Certainly the beeps seem to work in the order given on the sheet- I just have to try to keep up with them-lol.

  On the sheet it gives options for Timing Mode Set,then gives four settings which it calls 3 degrees;8 degrees;15 degrees and 30 degrees. Which should i choose?  Is it important?

Again, Thanks to all. I shall print and keep this thread for ny future reference . there is some good info in it. 

[Tim Mackey]

Most outrunners prefer hard timing - IE: 15 or 30 dgrees in the case of your ESC. Won't make a huge difference to power and is unlikely to be the reason for yoir very low power figures - have you done a RPM check to see whether maybe it is the throttle sensing that is not right ?

 "Brushless motor controller Setup menu for 50A and 70A No Power output to receiver"

Sounds like they mean no BEC then, so its an OPTO version...as most of the larger ones are.

 

[Frank Skilbeck]

Timbo, I've just got a Turnigy 60A ESC with a built in SBEC rated for 3A continuous, 5A peek. I think Turnigy and Tower Pro are just rebadged versions of the same.

If i understand Dave correctly he might have an ESC with BEC and has disconnected this to use a separate battery. The problem with then using the programming card is that the BEC probably provides the power to the control electonics in the ESC and programming card, with an OPTO ESC the power for the control electronics probably comes from the Rx battery. So if the red wire is disconnected then there is no power from the BEC to the programming card.

Dave I didn't understand your comment about the other servos and Rx when you were using the programming card, to program my ESC I have to unplug it from the Rx and plug it into the programming card.

[Tim Mackey]

Yes I know that Frank...but the stated that the instructions say " no power to the receiver" which suggests its an OPTO. The best way to tell would be to hook it up to the battery, and use a DVM to see whether there is any output on the red wire /pin on the receiver throttle plug.

[Dave Rose]

Frank - Is this the bit you didn't understand ? "

and replaced it, pro tem, with a lead with red wire and connected to the esc intending to try the programme card using the BEC sequence. But there was zilch from the card and the esc made continuous beeps and none of servos worked - so I figured no power was getting to the receiver - ( duff temporary lead?).lol

What this means is - I had setup the system so that I could use a receiver battery to power the servos etc , independent of the lipo battery. ( I try to use that system in all my planes now, rather than rely of the BEC.). If I think it is not an Opto controller ( as i thought in this case ) then I can only do that by disconnecting the red wire in the throttle (esc ) lead, yes?

Anyway, because I was trying to use the programming card following the sequence given to be used for a BEC controller, I disconnected the lead from the receiver battery, and I replaced the throttle lead ( which had no red wire ) with a lead from the esc to the throttle which had a red lead.

So, now i expected, when connected up to the lipo, that power would be given to the sytem and the servos should have worked!  But none did- nor did the programming card when I tried to connect that. What's more, the beeps made a continuous sound as if telling me there was no power getting through from the lipo.  When i went back to the receiver battery system, then all worked including the manual setting up of the esc using all those musical tunes.

Timbo - I'll have another go with the manual menu and set the timings to hard. However, I'm not sure what I have to check to see if i have full throttle range ( which you suspect i haven't ?).  I follow the menu but it doesn't say anything about the throttle range.

If I may, I'll send the instructions to you in a PM- they aren't overly long, but too long for herel

cheers 

 

[Frank Skilbeck]

OK I wasn't sure why you were disconnecting the red wire if you though the ESC didn't have a BEC. I agree it's probably best to use a separate Rx battery  than a regular BEC, the new ESC I've just got uses a switching BEC which can drive a full compliment of servo's.