nickd

Hello I am a coming over from the car and airboat section of the site so I am not too familiar with electric plane gear.
I recently bought this motor esc prop combo from united hobbies
https://www.unitedhobbies.com/UNITED...idProduct=4711
I am wondering if it is ok to extend the wires from the esc to the motor? I know how brushless esc's work and just want to make sure that extending the wires will not increase resistance too much and lower the signal/power to the motor.
The wires are currently soldered together until I get connectors and the total distance between the esc and motor is about 4 inches, I would like to double that by adding in another 4 inches or so.
I actually have another problem with prop mounting that I figure I will ask now as well, the prop is meant to mount over a nut on the motor (hex in back of prop goes over hex of nut), First time I tried it like this the hex in the prop stripped and the prop free spun. I bought a prop adapter that uses an elastic o-ring to secure the prop, it is screwed to the shaft with screws on the side similar to a pinion gear. The screws dont hold the shaft very well and come undone very easily, should I dremel a groove (like a keyed shaft) for the screws or will this weaken the shaft too much?
Thanks in advanced, Nick

rmenke

My Feedback: (13)

nickd:

You should not have any problems with a overall lingth of under 12". The differences in distance you are talking about can be measured with good instruments, but you would not be able to tell the difference in actual use, IMHO. Typicaly, electrical line lingth in normal electrical wiring electrical scales provide line size increasees necessary for every 100 feet. Just keep in mind to keep things close and tidy, I can't imagine any installation needing more than 12" from battery to ESC. ENJOY

nickd

I am hoping to lengthen the 3 signal wires from the speed control to the motor, not the battery side.

mrasmm

you should be able to lengthen them, but you'll need to figure out what gauge you need. First I would figure out what the stock volt drop is with the stock gauge wire and length. Then you want to figure out what gauge of wire you'll need to get that amount of volot drop or less over that length of wire.

Brushless motors work on the A/C principle, so it shouldn't matter quite as much, but you might just go up like 2 steps or so, so if it is 22ga then go up to 18 ga, that would be my best guess

pilotpete2

Just make sure the wire gauge you use is equal to or one size heavier (lower number) than the existing wires, also it is definitely better to lengthen the motor power wires rather the battery wires.
On a technical note, the motors we call "brushless" in the hobby are actually brushless DC motors, and have absolutely nothing in common with normal AC motors, the only difference between a brushed permanent magnet motor and a "brushless permanent magnet motor is that the ones we call brushless are commutated electronically, rather than mechanically.
Pete

jooNorway

Good point from Pete.
A lot of people compare brushless motors for RC with AC-motors... This is wrong. On an AC-motor you could literally have 100 meters of wire to the motor, since it just runs at a RPM related to the AC frequency... Our motors have to keep up the synch to perform best.

The wires between battery and ESC can also be extended, but to make sure you don`t blow the electrolytes at the ESC input more capacitors have to be added when we go much above 20-25cm. This is not easy to do if you don`t know what to do. Usually a combination of electrolyte and tantal is needed and you should be able to measure what happends.

mrasmm

ahh, ok =) thanks for the info

where is the power fluctuated? In the motor or in the ESC?

pilotpete2

The current is "commutated" in the ESC based on feedback from the motor, it's a closed loop design, so the ESC must be considered as part of the motor, as neither will function without the other.
The brushless motors we use can be used in some applications with a variable frequency AC drive (they are useless on fixed frequency AC), but that would not be practical for our use as they then would operate as a pure AC synchronous motor, very unfriendly operating characteristics as opposed to the more familiar asynchronous induction motor or brushed commutated motors that run so much of our world.
Regards,
Pete

mrasmm

so the current that is sent over the leads from the esc to the motor is an a/c current then? Or am I still missing something? BTW thanks for taking time to help me understand.

pilotpete2

It's switched DC, but the switching results in current reversal so in effect it is AC, this is identical to what happens inside a brushed DC motor, you would see the same form of AC (damn hard to get those scope probes in there) with brushless motors the motor leads in effect are the same as the armature coil wires that are connected to the commutator segments, but since the commutation is done electronically it can be done with an external controller. The brushless DC cooling fans in our PCs actually have the electronic switching done internally and just as in our brushless motors you can't reverse them by changing the polarity of the DC input, well at least if you ever want it to work again
Regards,
Pete

mrasmm

hehe, gotcha =) That's what I thought they were, so I just called it a/c, I guess the more technical term is switched DC. Isn't it switched like 2000 times per second? If that is the case would the conductors be calculated more on the a/c charts or the d/c charts as far as current and circular mills?

pilotpete2

Well you have the PWM part of the controller that switches the DC at 8 to 13Khz (still DC, no current reversal) for most outrunners, then that is commutated or switched by the controller based on the back EMF from the phase of the motor that is not energized at that instant in time, at idle that commutation rate can be a very low frequency as a brushed or commutated motor creates its own AC frequency to match its the speed of its rotation, so technically speaking a Graupner can motor running off a couple of D cells internally is an AC motor, but we call it a DC motor because that's what we feed it.
Now as to the sizing of the conductors based on AC or DC[X(] [&o], got me there I suspect (sounds better than assume) that it isn't critical, but then you do have to watch out for that skin effect with AC[8D]
Pete

mrasmm

hehe, alrighty =)

thanks for all the help and the input

mrasmm

I did a little more digging and found this post, apparently it is more of a squareform AC, but it is still AC from the ESC (which is a DC device, just like the comm), the actual wave form ends up being trapezoidal, check here
http://www.rcgroups.com/forums/showt...16#post1920716

the other info is here in this post, and in the containing thread =)
http://www.rcuniverse.com/forum/fb.asp?m=1627084

looks like you would do the calculations on AC, so the gauge of the wire isn't going to matter too much (needs to be atleast the original size though), on brushed motor ESCs, the slower ones are 2kHz or 2000 times per second, so I imagine brushless esc's are probably somewhat comprible, and that's vs like 60hz in your house.

From what this guy who builds them was saying is it's basically 3 phase AC, I don't think he mentioned delta or wye though

Anyways thanks for the replies and helping me figure it out =)

carguy1994ca

Hi !

I'm new to brushless motor but I have a question. I will be converting a Park Zone f-27 stryker to brushless motor and for that I bought an e-flite six series brushless motor and speed controller. Since this plane is a pusher, I either need a pusher prop so the motor spins in the usual conter clockwise direction or I need a regular prop but then the motor must be run in reverse. The prop they recommend is a normal rotation prop and would need the motor to run in reverse.

My question is: Can the motor be run in reverse ? In the six series manual they just say that if the direction of rotation is not correct, just switch the leads from the speed controller. They also say that the wires from the motor can be connected to the wires in the speed controller in any order. Is that true ? I don't want to mess a 80 $ motor !!

Thank you very much !

mrasmm

yup, that's true. Hook up the 3 wires in any order between the esc and the motor, if it runs the wrong way, swap any two of the wires =) Good luck!

carguy1994ca

Thanks mrasmm, but just for me to be sure, do you mean that the motor can run in both direction of rotation without damage ?

nickd

Sorry I did not reply it seems you guys had a good discussion on the motors workings while I was gone (3 days in the hospital )
So basically what I gather then is that I can extend the motor side wires as long as I use at least the same gauge as what is there, It has 2 different sizes, lager on the esc and smaller on the motor aprox 18 an 22 I think. I will just add in another piece of 18. Any one have any recomendations on what size bullet connectors with this size wire.

And in response to carguy1994ca as mrasmm had said just switch any 2 wires, the nice thing about the brushless in unlike the time advanced brushed motors from rc cars the brushless motors rotate the same rpm in either direction.

carguy1994ca

Hey thanks a lot guys !

Btw, my motor is rated for 3 li-po cells. Will it run on 8 cell ni-mh (9,6 volts). I know it is less than the 11.1 li-po but if it is like brushed motor it should run anyway, only slower. I want to try it with the same batteries as my speed 480 brushed to see the increase in performance with just the motor.

nickd

car guy - yes it will work just fine, the 3 cell lipo rating is the max voltage and often most efficient, that actually reminds me I want to try the same to see what my motor is like on a 6-8 cell ni-mh pack.

carguy1994ca

Me again !!

I was also wondering about li-po and balancing connectors. I saw there not the same for every brand, but is it possible to balance any li-po baterry with any charger, like with connector adapters ?

mrasmm

yeah it is =) just as long as the chemistries match (ie lipo charger/balancer and battery)

check out www.commonsenserc.com under their adaptor section for a good selection of adaptors

carguy1994ca

Thanks for the link ! Now I just want my parts to arrive so I can join the fun of brushless and li-pos !

pilotpete2

Hi nickd,
Hope your hospital stay was a minor one.
Just a note on the timing advance with brushed motors, brushless motors also have timing advance that in many cases is adjustable in the ESC, but unlike with the brushed motors where you have degrees of advance from zero that must be set with regard for the direction of rotation, in the case of brushless operation reversing the wires between the ESC and the motor windings results in the motor still having the same degree of advance even though the rotation is changed. In the case of the brushed motor you change rotation by reversing the current before commutation, with brushless you are reversing the connections after the commutator in effect.
It's amazing how similar the timing principle of a commutation mode motor, brushed or brushless equates with ignition timing in a gasoline engine[8D]
Regards,
Pete

nickd

thanks pilot pete I did not know that, I have linked the similarities with gas engine timing.
Since you seem to know quite a bit about the workings of brushless esc can you comment on extending motor wires. I am still unsure of the size of connectors and the best way to link in the extended wire (solder or connection etc