Turnigy motor - odd behaviour

[TonyS]

Hi everyone....

Quick question. Anyone experienced a strange stuttering behaviour from their electric motor. I've recently bought a Turnigy 35-30C 1100kV motor. It felt a little odd when I got it (it didn't spin smoothly). I've rigged it up to the receiver and an ESC and it doesn't work. It bleeped, played the tune as I expected bu then at any throttle setting just stutters with the prop moving only slightly backwards and forwards in a jerky way.

Anyone experienced this before?

Thanks

[Robert Bromwich]

Hi Tony

sounds like the ESC ,what voltage are you using to power,test it ?.

if the ESC is set at 3 cells and yr only using a 6 volt rec pack then the cut off will be active.

 

rob

Edited By Robert Bromwich on 24/07/2009 18:51:39

[ken anderson.]

hello tony-timbo is your man for this prob---send out an sos..he'll sort it for you..

 

              ken anderson..............,

[paul@scc]

I have had a similar problem. It turned out to be a bad solder joint on one of the gold connectors from the motor.

The strange thing was, if I removed the prop the problem disappeared.

[Tim Mackey]

More likely a timing issue - most outrunners prefer hard timing - check to see what your ESC is programmed for. Also try altering the start up options... soft / medium/ hard etc.

When you say it didnt feel smooth when you got it... do you mean sort of "notchy" as you turned it ...cos if so, thats perfectly normal - it s the rotor magnets field effect as they pass over the stator.

[TonyS]

Hi Guys,

Much food for thought....

Additional info. The ESC is a SKYARTEC BMC-18A.

The battery a newly charged Overlander 1700mAh 11.1V 3S (Extreme 35C).

I did notice this got quite hot after being plugged in for only a short time.

I also tried it with aHi-Energy 7.4V 1000mAh battery - same results.

It could be the soldering (I'm not the world's most experienced!!)

Thanks

T

[TonyS]

Update!

I re-programmed the ESC for soft start and 'middle' timing and hey presto it now works so thank you for the help. Now, the new problem I have is that I think I've over-sized the whole set up.

The plane is a Simply E-Zee trainer. The prop is an 8x6. On full throttle it feels like the motor could pull my arm off.....

If anyone understands motors / ESC's props etc I'd welcome a view on the appropriateness of these for the plane.

Thanks

[TonyS]

Posted by Tony Stein on 24/07/2009 19:29:42:

Hi Guys,

Much food for thought....

Additional info. The ESC is a SKYARTEC BMC-18A.

The battery a newly charged Overlander 1700mAh 11.1V 3S (Extreme 35C).

I did notice this got quite hot after being plugged in for only a short time.

I also tried it with aHi-Energy 7.4V 1000mAh battery - same results.

It could be the soldering (I'm not the world's most experienced!!)

Thanks

T

 Sorry, just re-read. What I meant was the ESC got quite hot not the battery.

[Robert Bromwich]

i would try a 8x4 prop if there's lots of power with a 8x6

also if you have a watt meter use that will give you amps,watts voltage of battery and setup etc

nice and shiny the solder joint should be if they are newly done

 

rob

Edited By Robert Bromwich on 24/07/2009 20:10:12

[Merlin spit]

a wattmeter will save you £££ in the long run ,it could be the amps are getting near the 18a rating of your esc and you then you  risk burning it out .a good rule of thumb is to alow 25% head room with a esc

Edited By austen rover on 24/07/2009 20:11:00

Edited By austen rover on 24/07/2009 20:12:02

[TonyS]

Thanks chaps. A wattmeter and a smaller prop it is then.....

I know that this will sound really really dumb but....

Is it the battery or the motor that will determine the ampage through the ESC i.e. if I put the smaller 7.4V battery on the set-up will this save the ESC or will that make no difference?

Thanks

[Frank Skilbeck]

Tony ran your combination through drive calc (well similar 3s battery), this is quite a powerful motor and on a 8x 6 it is pulling over 20 amps, see below output from drivecalc

 

8X4 prop will drop the amps to approx  14A and static thrust to 821g, vopt to 52 km/hr and power out 110w.

 

How big and heavy is the plane for a trainer type model then 80 watts per lb should be enough. If you need more power then a 8 x 6 (or bigger prop) and bigger ESC is needed. Don't overload the ESC nasty things can happen

 

 

[Frank Skilbeck]

  A watt/amp meter is a a very good idea. The motor rpm is governed by the volts and load on the motor and power is basically proportional to the square of the speed, i.e. if you double the rpm on a given prop then it will take 4 times as much power (or twicw the volts and amps)

 

On a 2s and 8 x 6, the motor amps drop to  11A and power be down around 60w, so if you went to a 2s a larger prop might be needed, e.g. a 10 x 7 gets you to 18a and just over 90w.

 

You can download drivecalc for free and while it is not real replacement for having a wattmeter its a good for getting the starting point. www.drivecalc.de best of all its free and they keep updating the motor,prop and battery database.

[TonyS]

 

I have to say that piccy proves to be a very convincing argument. The graph I'll need to study before I properly understand what it's telling me. (Is the 35-42 motor the same as the 35-30?)

The plane is 20 oz all-up weight so at 80watts per lb that's 100 watts required. If I get what's going on then at a draw of 20 Amps and, on an 11.V  battery that's 222 watts or 120% over what I need?

I think I need a smaller prop   .

Thanks for the help it's much appreciated. I will get to grips with this eventually I promise. In the meantime I thank my lucky stars that I found this site....

 

[Robert Bromwich]

Tony is this the model you have :E-zee trainer

[TonyS]

Hi Robert,

Yes, that's the wee chappy!!

[Merlin spit]

tony its mainly the size of prop you use that effects amps,the kv rating of your motor will effect this also a 800kv motor for example will turn bigger prop with less effort producing less amps ,a higher 2000kv would turn a smaller prop faster or say  a EDF  , a 1100kv motor is a good middle ground motor and so id use a smaller prop to reduce amps .

 

amps x volts = watts      for example 15amps x 10.5V (3s battery under load) =157.5 watts

 

if you wanted more power but wanted to keep the amps the same you could use a higher voltage battery( if your motor and esc are rated to do so)

 

15a x 14V (4s batteryunder load)=210watts

[TonyS]

Hi Austen,

Thanks for this. I don't think I'd have got this intuitively. To me, a bigger kv would mean it would turn a bigger prop easier... . I'm slowly getting to grips..

So here's a question...

If I set my transmitter to max out the throttle at say, 75%, will this safely limit the load on the ESC even if I leave the 8x6 prop on?

T

[Merlin spit]

ive never tryed it myself but yes it should, also while static testing the prop will pull more amps this will unload to some extent in the air with would add to your safty net if you went with the 75% thottle idea,the best bet is to get setup with a wattmeter as it takes all the guess work out .there are some very good sticky theads in the electric flight section id reccommend reading them ,i learnt a lot from them and timbo is the real expert on here.

[TonyS]

Thanks Austen.

I'll look up the sticky thread...

Anyone recommend an idiot-proof wattmeter  ?

[Merlin spit]

a watts up meter here is superb ,you may find it cheaper elsewhere but this guys ok sells the hobbycity stuff at a good price

[Merlin spit]

Model: TR35-30C
Input Voltage : 7.4V~11.1V (2~3S Li-po)
KV : 1100 rpm/V within 10%
Max. efficiency current : 10~15A
Dimentions : 35mm X 30mm / 1.38in X 1.18in
Shaft diameter : 4mm / 0.16in
Weight : 77g / 2.72oz
Number of poles/magnets : 14
Recommended model weight : 600~1300g / 21~45oz
Power equivalent : .12,2stroke

Stator Dimentions: 28-08

 

Tony,please dont use a 4s battery as in my example this would burn out your motor  ,it  is rated as above. so stick with a 3s batteriy also as you can see max current is 15A  so on a 3s battery the max power ratting would be 15A x 10.5V(3s) 157.5watts ,so when youve got your wattmeter this would be a good max figure for your setup .

 

whats the all up wieght of e zee trainer Tony

[ken anderson.]

http://www.brchobbies.co.uk/?page=shop&action=additem&item=664

 

 

hello tony-try something like this--it will take out some of the guess work and will save you burning out anything......

 

there are several other's which are just as good as well......

 

 

         ken anderson.......

[Merlin spit]

thats a good spot by ken ,its got some good added features and brc are a good firm

[TonyS]

Excellent info chaps.

Supposedly good weather tomorrow so off to the club.

Will order the BRC wattmeter etc - looks like there are lots of features to assist.

I shouldn't think the little E-Zee has ever had so much thought go into setting up  

Thanks chaps.