how to determine what esc needed for a 6384 brushless ?

[Mariestad1066]

Hi all,Just joined Endless Sphere and have a pressing question.I scooped an e-zip 4.5 for $20 and would like to
mod it.I bought a 6384 120kv 4600w sensored motor on ebay.I need a brushless esc that is correct for this motor.
Here are some questions I have: The motor has 5 hall sensor wires,must they be used,or can I leave them
unconnected? the esc's I've seen on ebay have no connectors to attach to.Most esc's I see are rated 6S or
some number followed by the letter "S".My guess is that means the battery voltage? None of the esc's I see are
rated for 12S ? I plan to make my own Li-ion batt. pack,but don't know what voltage to shoot for?
So, Where do I buy an esc? and how do I size it for a 6384. Any and all help for a noob would be great.
I have been lurking and following threads on ES for some weeks now and am blown away by your knowledge.
Hope I can get my questions answered.Thanks to all. John

 

[amberwolf]

it's not quite as simple as just buying a random motor, then deciding what battery to use, then the esc, etc. you'll need to match the motor kv to the system voltage and the rpm you need to get the speed/power you're after, etc. you'll need to match the power need to what you need the system to do for you. you'll need to match the battery to the needs of the motor/controller (esc), which means what you need the system to do for you, and how much range you need out of it, etc.

so i would recommend first reading the eskate / board threads, and any kickscooter threads, most of them in this forum
https://endless-sphere.com/forums/viewforum.php?f=35
where people use similar rc motors to drive the wheels. there's more than a few, some even using the same general size of motor (though the kv or other details might be radically different). evne the ones not using rc motors will have useful information for you in how to decide what you want it to do and what kind of parts you might want to use.

these should help show you why certain things are done certain ways, or why they arent' done some ways, and help you get the idea of what you need to figure out before you buy parts.

you're also going to need to decide exactly what you want the ezip to do for you, and under what circumstances. that will tell you how much power, at what speed, and for how long, to go how far, that you will need the system to have. knowing those things will then help you pick out which and how many cells to use for the battery (and whether it will fit on the ezip or if you'll have to use a backpack), etc.


i don't know enough about what you want to do, or the rest of the unit you have, to know for sure, but it is also possible that the motor you have might not be suitable for your purposes...so don't buy anything else until you know for sure that's what you need.



while it isn't specifically setup for your purposes, it can be adapted for it (has options for some things you need to figure out), the http://ebikes.ca/simulator is very useful for learning the relationships between motor, controller, battery, wheel size, gearing, wind resistance, etc. so i would reocmmend going there, reading the *entire page* to learn how it works and what options do what, and then playing with various systems to see the relationships between the things you change. it doesn't really matter that you're playing with "ebikes" on it rather than scooters/etc.; the concepts still directly apply.

 

[Mariestad1066]

Amberwolf... Thank you so much for your clear and helpful advise.I guess I have a lot of work to tackle.
Thanks again. John

 

[DogDipstick]

When sizing an esc for an application: Your variables are the voltage you run at and the PWM throttle input ( 0-100%) of the throttle input. Typically you want to size your installation so that under load you are runnning in the 60-100% pwm region and not lugging the drive. Size the drivetrain reduction for this. For instance, good example, simple:


RC heli example.. ebike is similar but different in many ways but basically:

I got a rc toy helicopter. If it runs at 50% ( 1100 rpm rotor speed) the esc will overheat and blow up. If I run at 100% I get the headspeed I need. 2200. The reduction on my heli is 10:1... so for every 100 rpm of the ( 500Kv) motor, the main shaft turns 10rpm... At 12s ( 44v nominal, 12 cells in series, ) (500Kv/volt, 44v, motor turns at 22000 rpm..) and at a 10:1 reduction, the main rotor turns at 2200 (good high power flight) ...

Now if I gear that ( through pinion on motor) much higher ( with say a 12T pinion, not a 10T.. ) , the ratio is now 100/12 = 8.33:1 ratio that the esc is trying to push.. and a final headspeed ( attempted) of ( @ the same 44v) (500Kv @ 44v = 22000 at a reduction of 8.33:1 (22000/8.33) 2650 rpm on the main rotor shaft... Way to much with the heli I have.. and the power to push that would be more than my esc can handle... and it will lug and push current that it cannot really handle ( power demand > power available) .. it will (try to) run at 100% ( trying to push the high ratio reduction) but load up and lug when it doesnt have the power.... ( plus would fly like shit at 2650rpm.. if it had the power.... to fast...) It will sit where it can push all the current it can, and this may not be the 100% you need but much lower.. say it can only push 2350rpm with the power, it is there trying to output the requested 100% but will load up around... 90%.

No lets look at that the other way, if radically gear the other way, with the pinion: 8t instead of 10t.... a 100/8= 12.5:1 ratio... and when on the 500Kv motor, on 12s (44v) the motor turns its pinion 22000, reduced to a headspeed of 1760 rpm...: good for gentle flying. It (esc) will run at 100% at this 1760 rpm.


OK: That is just the beginning.

Now with my original setup, 10:1, and go to the field, ready to fly. Setup for 100% at 2200rpm... full power and speed...

BUT..

.... there are some old ladies at the park that day, and I dont want to scare them. So I want to fly 1760rpm ( not the 2200 setup for) ...

I have two options:

Take the heli apart, change the pinon from 10T to the 8T, and fly at 100% pwm... and the 1760rpm headspeed.

OR:

Just lower the throttle to 80% of the 2200... and that is now 80% of 2200 = 1760 rpm.. I am happy and just changed the throttle on the Tx and did not have to take the heli apart. Great, right? .... Well, yes and no. 80% is generally fine, but say I see the old ladies still worried and wondering what this toy helicopter is doing making all the noise over there... and.. I decide I want to lower it further... to say 1250 rpm, for some nice low head speed flight.. I have two option again...

Change the pinion, or lower the throttle in the Tx that day. Option 1 & 2.

I lower the throttle.... and... now for the 1250 rpm I have to output only about 55% on the ESC throttle forthe target headspeed... and.. this is not good.

Running low PWM to get the speed is what destroys hobby grade ESC on high loads.. ( power) . Ebike ESC have what is called "syn·chro·nous rectification", or electrical ( active or passive) freewheeling, to combat this ... and only the really good 400$+ hobby esc have this complex algorithm. Without it you shortly blow the ESC up. Hobby ESC DO NOT LIKE part loads, or running at less than 60% throttle. One of the reasons ebike esc are so much bigger and bulky. To handle the part load... low throttle times.

So size the ESC (amps) so that you spend alot of time in the 60%-100% region, and it will be better (cooler and longer lasting) . Always better to run near the 100%, rather the 50%, on a hobby ESC... Low pwm is worse than high pwm, in that the flyback is worse at part loads on a high power esc...

Hope this helps in showing you how the reductions work and whatnot... and choice of reduction ration.

Size the reduction based on your speed, power, and rpm goals.

 

[Mariestad1066]

DogDipstick: Well thanks for your advise,It's hard to sort it out as I'm not technical at all.
I will have to re-read all that you have said,but the good part is you have already answered
a couple of my questions.This stuff is not really plug n play like I first thought. I need to follow up
on the advise from both you and Amberwolf. But I am grateful for your response.I'm 75 yrs old and
find it hard to pick up on this new tech stuff. Thanks again John

 

[Mariestad1066]

DogDipstick: Well thanks for your advise,It's hard to sort it out as I'm not technical at all.
I will have to re-read all that you have said,but the good part is you have already answered
a couple of my questions.This stuff is not really plug n play like I first thought. I need to follow up
on the advise from both you and Amberwolf. But I am grateful for your response.I'm 75 yrs old and
find it hard to pick up on this new tech stuff. Thanks again John