TommyWatson

My Feedback: (1)

I am helping a friend with a four engine C130. It has 4 Turnigy 3542 1250 motors and four Turnigy Plush 60a ESCs. I have wired the inner motors together to one battery (5000mah 4s Lipo). The outer motors are wired the same. we have extended the wires from the ESC to the motors so the wires from the battery to the ESCs are very short.
Props are 9x6, we have also tried 10x6. The model will need at least 9x6 to fly with any authority

I measured the current from the battery (to both motors) and also each motor seperatly.

At full throttle the combined current went to over 80 amps and of course the individual went to over 40 amps.

Even when limiting the throttle to 40 amps (two motors), the ESC gets hot. By hot I mean too hot to hold for very long. The motors are also getting hot. Hot enough so that if you hold the prop nuts you can feel the heat.

I suspect the problem is the fact we are using 4s batterys.

Can anyone comment on this?


All of the comments on the Hobby City site about this motor are using only 3s battery.

Regards

cyclops2

Do you read any prop & voltage recommendations first ?

It is the right way before you post a question like this.

There are free online motor calculators that will give you plenty of correct combinations for motor / prop / battery cell count.........www.adamone.rchomepage.com is 1.

Rich

TommyWatson

My Feedback: (1)

I understand what you are saying Rich, But the specs of the motors and ESC are well within the parameters of the stuff I am using. The Current from the batt to each esc is only 20 amps and it is a 60 amp esc. The battery voltage is at the upper limit of the esc specs but still within. The prop is also within the published specs. As I have stated above, most users of these motors and ESCs are only using 3s batterys.. We are going to try a 3s battery tomorrow and see what happens.

regards

alaursen

Hi Tom,

With lower voltage of the 3S, you will of course have even higher current for a given power. That leads to higher IRloss and even more potential for heat.

What happens if you just run one motor/ESC off of one battery as a test to isolate the problem? If that doesn't overheat, then the combo shouldn't either unless there is some sort of ESC interaction taking place on the common (Battery) side. Just a thought.

Art

cyclops2

Use 3 singles tonight. Call me in the morning. 3S will draw less than 4S.

If you still overheat all motors & controllers, ask for your money back . Plus all shipping & handling charges.............They would be rejects dumped on the buying public.

TommyWatson

My Feedback: (1)

I am going to my friends place in about three hours. So I will soon know. This model has 4 motors and 4 speed controllers and they all do the same thing. It just mystifies me that if the current is only 20 amps, (measured with a Astroflight Watt meter), that a 60 amp speed controller would get hot.
Regards

cyclops2

Check the battery volts with one running or 4 running.

TommyWatson

My Feedback: (1)

Hi Cyclops,

Well the good news is that the ESCs and the motors run at a normal temp on 3 cells.
By that I mean just slightly warm. Due to use of two battery packs, we could only run two motors at any one time with the meter, however we ran two inner motors on 3 cells and I saw 80 amps between the battery and the escs. That means 40 amps per motor/esc.
It was the same on the outer motors. RPM was over 10000rpm on zinger 10x6 wooden props on both motors. This was at full throttle on the radio. We ran the motors at 30 amps/motor for about 3 or 4 minutes,(simulating crusing flight power), and the ESCs remained just warm. The motors were barely warm.
The final setup will be the inner motors running off on 3 cell 5000mah pak and the outer motors on another 5000mah pack.

The ESCs are in the fuse at the centre of the wing. There is some air coming from the nosewheel and we still need to engineer some exit holes.


My friend is very pleased and is getting ready to fly the C130 next weekend.

So problem solved but I still can't explain the vast difference in heat between the two setups. Can anyone?

Regards

speedy72vega

Tommy, the difference is in the voltage and Kv rating of the motors. As you increase voltage to the motors, ie 3S to 4S, you're increasing the rpm the motors will try to turn.
Kv=rpm/v, so every volt you feed the motor, it's going to try to turn that rpm. For instance, if you're motors are 1000kv, on 3S they'll try to turn 11,100 rpm. 1000kvX3S or 11.1v=11,100. That same motor on 4S will try to turn 14,800 rpms, 1000kvX4S or 14.8v=14,800 RPM, understand? So, to explain the hot ESC's, the motors were trying to turn all that mass (propeller) at a higher rpm. When you dropped the voltage to 3S, the motors were turning at a lower rpm, thus less draw.
In general, when you increase voltage (more cells), you either need to decrease prop diameter or pitch, or both in some cases. Also, as a general rule of thumb, the lower the Kv rating, the larger prop you can run and vice-versa.
So, if you want to stay with the 4S packs, decrease prop diameter or pitch until the draw is within specs. Or you could just stay with the 3S packs. It depends on how much power you want to fly with.

TommyWatson

My Feedback: (1)

Hi Speedy,
It is all starting to make sense now. These motors are 1250 rpv so with 4 cells they were trying to turn the props at 18500 rpm (1250*14.8), where as with 3 cells it was 11.1*1250 = 1387 quiet a difference. I assume the difference between the theretical predicted RPM and the actual RPM that the props will turn is disipated in heat.
If I were to use really small props then the heat would have been OK. However we need 10" props to fly the model.

I was just surprised at the difference 1 cell (3.7 volts) would make. The difference in heat was dramatic.

I am at last startng to understand the dynamics of these little motors.

Thanks to everyone for their help. This forum is awsome.

We will see how it flies next weekend.

Regards

speedy72vega

Now you've got it Tommy, however, you could still possibly use the 10" props, try dropping the pitch and see what the readings are on the wattmeter. Larger diameter with less pitch will give the plane more thrust, but possibly a little less top speed. A C130 isn't exactly a speed demon, so more thrust might be best for it.
Try 10X5E props and see what the draw is.

cyclops2

If you want the maximum power from all of your setup. Send a PM to ........Dr KIWI. He is the best on new set ups.

Rich

cyclops2

STOP using wooden props !

They are way to thick everywhere & waste power. Try the APC E types. Way more efficient than woodies.

Woodies are for the hard banging of piston engines firing at ignition point.

Rich

TommyWatson

My Feedback: (1)

I agree. The bloke that owns the C130 seems to like wooden props. This is his first electric model. I need to convince him to use E props. We are using 10" props now and the current and heat is OK. Just barely warm.

Regards

cyclops2

www.gwsus.com makes 3 bladed 10 x 6 in both left & right turning. It would reall save the plane on loss of power or banking turns in some wind. APC ....www.landingproducts.com ?? makes some sizwe in L & R

Rich

cyclops2

Forget APC. Only 1 biggy

Rich