xmech2k

OK, hopefully not a too stupid question, and hopefully in the right place.

I'm re-powering my Phase3 P-40, and found a 16A motor, 18 amp ESC, and a 1500mah 20 lipo battery I'm thinking of getting. I did the calculations and it should have the watts/lb rating I desire.

So, I understand it's good to have an ESC rated for more than what motor will run. I'm just wondering about the 30 amps the battery can put out. From what I've read in this thread, the ESC just pulses the full power of the battery to the motor, does this mean the motor will get the 30 amps pulsed and fry it?

Turner

The amp rating of the esc is the esc's capacity. Higher numbers have no effect on actual current your system will use. This is determined by the motor and prop and to some degree the battery.

xmech2k

So the battery won't be a killer in this setup, as long as I prop it right? I'm ordering a wattmeter as well, so I'll be checking with that before I install it.

Turner

That's right. The motor and prop are the main factors determining current draw though a higher capacity or higher C rating will slightly increase current over lower cap and C. The only time a larger capacity and/or higher C rating could be an issue is if your system was right on the limit of motor or esc rating with a smaller or lower C rated pack.

xmech2k

OK, thanks Turner. That's a mental breakthrough for me. My credit card is ready to jump out of my wallet now!

AEAJR

Just to add to this discussion of batteries:

Going to a higher voltage battery will spin the prop faster which will cause the motor/prop to draw more amps.

Going to a higher C rated battery does not cause the motor to spin faster so it does not cause it to draw more amps.

Having a battery that has too low of a C rating can cause a drop in amps because it can't keep up with the motor's demands. It just can't deliver.


Same for ESC. Having a 30 amp ESC vs. a 20 amp ESC for a motor that draws 10 amps does not increase what the motor will draw.

But if you have a 20 amp ESC when the motor wants 30 amps, the ESC will be overloaded and burn out.

xmech2k

Thanks Aeajr, that clears it up even more. I think I finally have a neophytes grasp of the electric power system now. Hopefully it doesn't get dislodged from my brain anytime soon!

mred

The biggest reason to go to a higher C rating on the battery is to allow it to run the motor better. The voltage will not sag as much and the current draw from the motor will not heat up the battery as much if it is better able to handle the current draw.

The pulse from the ESC to the motor is is what you are concerned about when figuring the needs for the size ESC you need. Never run a lower amp ESC then the motor will draw. If it is pulling 30 amps and you put a 25A ESC on it and hope to run the motor slower to use less current, it will not work. The ESC is still putting out a 30 amp square wave to drive the motor no matter what speed you run it. The slower the motor runs, the shorter the pulse width, but it is still putting out 30 amps and will burn the ESC out. You need a good watt meter and only take a reading at full throttle. Anything less and you will not get a true reading of the current draw.

I like to give my ESC more head room then what you are using. On an 18 amp motor I will use a 25 amp ESC just to make sure it does not have to work as hard. The closer you get the the upper limit of the ESC the better your cooling has to be. If you are going to use an 18 amp motor with a 20 amp ESC, then you better have good cooling or you can still cook the ESC and burn it up.

If you have any more questions, ask away. There are plenty of people on here to help you out. Don't worry about stupid questions, we all ask simple questions at times, but none of them are stupid.

Ed

juanquy

Hi my name is Juan Carlos :My question is for builders I'm new building electric, I remember with nitro engines they need btw 0 to 3 degree when you mount it to the left and down, Its the same with electric?
thanks
jc

MustangMan

It depends on the airframe, of course. But Yes, in general. Electric power doesn't change the physics.

AEAJR

I thought it was typically down and to the right 1-3 degrees. Left?

juanquy

0-3 degree to the right, so still like that or does not matter ?

thanks
jc

mred

It's still like that. Nothing changes just because you are using an electric motor.

Ed

Rockin Robbins

Ed is a sailplane pilot. For him motors are instruments of last resort!

On my Radian the motor is straight ahead. No down or right deviation of the thrust line. Many sailplanes are the same. But they are very frustrating to try to fly as a powered aircraft. Their motors are to get them to launch altitude and then turn the cursed thing off for the duration! You might run the motor for 30 seconds on a 20 minute to an hour flight.

mred

There is no reason to not have a good flying glider under power even if the motor is only used for 30 seconds. Mine are very easy to fly under power and have down thrust and a little right. The down is adjusted for each plane and the right thrust is about 3 degs on all of them. On a glider you really need down thrust because the high life wing is going to try and do a loop if the motor is not pulling it down all the time. I Adjust mine so that full throttle is neutral and I give it a little up elevator to get it climbing good. It will stay where I put it and not try and go nuts every time I give it power. There is no reason to have a frustrating glider under power and it can be adjusted out if you take the time to do it.......................

Ed

SARG5

Hello Sportfier87
\SARG5 from Kansas
I toooo had hung everything up for some 35 years. Back to flying all E-planes about two years ago. Everyone here are great help.
Take a hard look at all of the Multiplex planes. I like my Multiplex EasyStar. and my Fun Cub.
Also, go to www.headsuprc.com They are a great help. Owner Jeff is a great help
Take care
SARG5
FLYING AND SEEING THE COUNTRY WE DEFEND

AEAJR

It is good to see people return to the hobby.

Scott Jackson

Hello,
I've just finished my first kit; a Pete 'N Poke Sport 40 by Great Planes.

My question with detail following: When using an electric motor on a plane originally designed for glo, is it necessary to install the motor with a right offset as shown in the plans?

I opted to use electric rather than glo for power. Yesterday, I took my plane to our park and asked our club president/instructor to do the first
flight. Thanks goodness he is good!

First, all spec's were checked by he and our Safety Office. Everything checked out right on. On the first flight, nearly the last, the plane took off in a violent rising left turn. After recovery, and reaching a safe altitude, he tried various manuevers which went well with one exception .... it just doesn't want to turn right. It can be forced, requires a lot of rudder and wants to slide.

After this flight, we increased the downward slope of the motor to 5 degrees. Next flight was better but still tough right turns.

I installed the motor with the 3 degree right offset shown on the plans for a glo motor. Since I'm using electric, should the mottor be installed with no offset? I'm thinking the offset is causing the problem.

AEAJR

Motor offset should be similar for glow and electric. The offset is more to overcome the inerta of the prop.

Sounds like you might have a miss alignmnet of a wing or a twist somewhere.

Red Scholefield

AEJAR's diagnosis was the first thing that hit my mind also. Check the wings, make sure there is no washout in left wing or washin in the right wing. Washout is the amount the leading edge is lower than the trailing edge, Washin the amount the leading edge is higher than the trailing edge measured with the wing on a flat surface.

for a good dissertation on washout see:
http://vaillyaviation.com/images/Washout%20_web_.pdf

AEAJR

Also check:

Fuse is not twisted
H-Stab is aligned with wing
Vertical Fin is straight
No warp in ailerons or rudder
CG is on the mark.

These are all things I would expect your experts checked, but they are worth double checking.

Scott Jackson

Yes, 3 "senior" club members with collectively 150 - 200 years RC experience checked all the items you listed. What do I risk by reinstalling the motor with " 0" degrees offset and trying it. I'd like to eliminate the possibility that I have too much offset.
Thx

Red Scholefield

Sounds like you are in good hands with 200 years of RC experience to guide you. They should tell you that offset is not your problem. What does it do in power off mode? , That should tell you a lot.

Scott Jackson

I'm just a bit frustrated. All design specs are good per the plans. My senior guy's last said "we don't know what the problem is. If you mean how does it fly/glide power off.. it does very well. Put it on the runway well out on final.

Does the electric motor have an effect similar to a gyro?

mred

I don't blame you for feeling frustrated, I would be too if I couldn't get help from the Pro's at the club.

First of All, you have to understand what the down thrust and right thrust is all about. Down thrust is to counter the lift of the wing on a high lift wing. With a flat bottom wing, it has a large amount of lift and to keep it from climbing under power, you need the down thrust to keep the plane flying level. This is only set for one speed, as any increase over cruse will give you a climb again. Generally, the cruse speed is not WOT on a plane such as the one you have, so you need to throttle back for cruse. This way, it will have a nice climb under full power and fly level at cruse setting and decend at idle in a nice glide.

Right thrust is there to overcome "P" factor during a climb. That is, the down going blade has more effect then the up going blade in the climb, so you get a left turn induced during a climb. To counter this, you put in right thrust. At cruse speed, it has very little effect, so you can forget about that for straight and level cruse speed.

You say that it had a violent left turn on take off the first time, so you have a warp or twist in the wing some place. Look at the control surfaces. They should all be at or VERY near neutral with the control sticks centered. The gentleman that did your first flight had to put some kind of trim in to counter the left turn, so you should have something trying the turn it right all the time now just to get it flying straight.

Lay your wing on a FLAT surface and gently push it down until it is laying flat on the surface. Look at the trailing and leading edge. They should both be on the surface at the same time, but don't force the wing down flat, just gently push it down. If the trailing edge is up, you have washout and it the leading edge is up, you have washin. Normally, you have washout built into the wing, so check that it is the same on both sides.

If you find a twist in the wing, you can take it out by re-shrinking the covering while holding in a twist in the opposite direction and letting it cool before you let go. You may have to do this a few times and once you get it right, you need to check it again the night before you go flying to make sure it hasn't changed again. After awhile, it will take a set and pretty much stay in there.

Motor offset is the same for any type of power plant you have installed. That does not change just because you are using a motor instead of glow. You are compensating for the thrust of the power plant, not the type you have installed. This is going to be the same regardless of the type of power plant you have installed. You just have a warp somewhere and you need to find it. Some times they can be very hard to see, but I think you will find this one with no problem.

Also check your controls and make sure you have the same movement in both directions. Somewhere you have quite a bit of trim in because of that left turn on takeoff on the first flight. He had to put in right trim in order to get rid of that left turn, so you may not have very much right movement left on the controls. I think your ailerons are trimmed off center quite a bit, so check them and make sure you are close to neutral and they still have plenty of movement for a right turn. That wing is almost flat, so trying to turn on rudder is going to induce a skid. It doesn't look like it has enough dihedral for a rudder turn without using ailerons too. After you get your plane flying right, take the pushrods off the controls and reset the trim on the transmitter to neutral and then adjust your linkages to put the surfaces back where they were with the trim in. This will give you full movement of the servo again.

Let us know what you find and here's hoping you find it quickly.

Ed