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BLHeli ESC Settings for 1306 Small High KV motors
#1
When running 4000kv motors (and similar ranges) on a mini quad, what specific demands are needed in an ESC (BLHeli/OneShot/Damped Light) to be able to properly operate on 3s and 4s?

I hear so many people talk about sync issues on these high kv micro motors when using some of the standard multicopter ESCs.

I am in a crunch on a build and wish to use a 4-in-1 ESC combo board, but I need to know it will be able to keep motor timing and such on some 1306 4000kv motors with 3" props.
#2
The smaller motors have fewer poles than the big motors so if you are worried about maxing out erpms on the ESC's, you shouldn't.
Plenty of people run 4s with 3" props with no issues.


You shouldn't get desync issues, I've got the RMRC 4in1 ESC and have run 3s and 4s on 4045 on the 1407 3200kv and it was perfect.

You can play around with timing if you'd like, but feel the motors and ESC's often to make sure they aren't getting hot. I didn't really notice a difference between medium and high though.

Tuning can have an adverse effect on performance as well. Too high P gain can cause oscillations which will work the escs and motors to death so be careful of that as well.

On my 160mm frame the default rewrite pids worked pretty well. I haven't bothered to tune it further. Luxfloat seems to be harder on components as well. I tried it once and could never get a good tune so went back to rewrite.
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#3
(08-Apr-2016, 12:48 AM)Multirotor Army Wrote: The smaller motors have fewer poles than the big motors so if you are worried about maxing out erpms on the ESC's, you shouldn't.

Thank you for the answer that's good to know... but about the number of Poles and eRPMs, it's still possible to max out on a micro motor on 4S i think...
if you do the math, a 4000kv motor at 4S and 12 poles will still max out both an F330 and the Atmel MCU.
14.8v x 6 magnetic phases x 4000kv x 70% efficiency is still almost 250,000 commutations per minute (eRPM), which is right at the limit of F330s, and above the limit for Atmels.
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#4
(08-Apr-2016, 12:51 AM)SonicCopter Wrote: Thank you for the answer that's good to know... but about the number of Poles and eRPMs, it's still possible to max out on a micro motor on 4S i think...
if you do the math, a 4000kv motor at 4S and 12 poles will still max out both an F330 and the Atmel MCU.
14.8v x 6 magnetic phases x 4000kv x 70% efficiency is still almost 250,000 commutations per minute (eRPM), which is right at the limit of F330s, and above the limit for Atmels.

Hi,
I stumbled on this thread lookin to learn something about this matter so it's safe to say I'm no expert when it comes to BLHeli parameters or chip specs but as an engineer I do have a fair bit of understanding of the technical factors and a whole lot of experience with brushless motors.

I recently started winding my own brushless outrunners and I'm currently working on a set of cheapo-chinese 1306's that I use as a mechanical basis but i'm completely overhauling them after a full out melt-down of all four motors.
(in case anyone is left wondering howSmile (if not, skip to next paragraph)
the hair thin windings of at least one phase group in every motor had just melted into solid blobs of molten copper/insulation gun during an intense maiden that ended in a reversed failsafe situation. All ESCs (i think they were littlebees 16A BLH) burnt out after a full out throttle punch fly-away deal on 4S 65C in just a couple of seconds. I had Gemfan GRP3030 straight tip bi-blades on the originally 3300kv 1306's. I did the new windings with thicker wire gauge and fewer turns on each pole, dropping my KV value and allowing me to go 4" on 4S for the rebuild of that 160 quad. Aaaanyways what im trying to say is that i have some experience lol

But, reading this thread raises a few questions about what you doing with the math there so I was hoping to pick ur brain a lil on that...
In your calculation you are determining eRPM for your ESC's correct? But from what i understand the concept of eRPM is basically the actual mechanical RPM (revolutions (=angular displacement around center axis until fully returning to starting position) per minute) but when considering the electrical "fully returned" situation, this has occured at a number of degrees that is just a fraction of a full revolution of the rotor. (north and south poles of the magnets correspond to the same coil phases magnetic fields from the stator, just a few theeth over) Now, pls bear with me as i sum up everything i can think of that may be of influence on the math:

- The eRPM value is a unit of is electrical "cycles" per minute. (this is a fixed ratio to the mech. revolution)
- Commutations are the steps that an ESC uses to time it's back-EMF readings over the length of 1 eRPM cycle. it is used in a unit of frequency, noted as Hertz (= occuring intervals per second) The purpose of commutations is to keep the activated magnetic field at a approx 90deg angle to the closest magnetic counterpole moving around the coils as the bell spins.
- Cogging steps are all the possible rotor-stator positions relative to each other that cause a direct radial orientated magnetic force which either applies no rotational displacement or max displacement. (in other words, the mag field is directly in front of the active coil, or right in between the little gap between 2 magnets in the bell.) when a motor is not powered it will immediately try to snap to any cogging position and when hand turned you can feel the clicks)
- kv rating is simply the RPM increase per applied Volt. (this will happen without any load and needs time to accelerate to that speed) When load is also considered in the equation, thats where it becomes tricky as you can imagine that the inertia of the prop's mass is in fact dragging the motion of the rotor somewhat dynamically under acceleration/decelleration conditions and your ESC's will start to "fire" the phase groups slightly ahead its optimal moment. This is what you can detect as performance decrease and often mentioned as de-sync effect. This is inherit to a brushless motor and good ESC's will quickly make changes to the timing to adjust itself back to the sweetspot. However, too much of this "error" for too long and ur motors will get so hot that it causes a chain reaction of effects that kill your precious motors, often resulting in a short and when that happens you get to say goodbye to your ESCs as well.
- A 4S Lipo when fully charged will put out approx 16.7V, not its nominal rating of 14.8V
- To my knowledge, all 1306 outrunners are built as 9n12p configurations, meaning they have 9n / 3phases =3 groups of three teeth, typically wired in Delta.
- with a stator diameter of 13mm to devide over 9 teeth and assuming your 1306's also have 12 magnets, that would give you 36 cogging steps.

My question to you is,
What is "the math" you used to get to the 250000 number and is a chip rated in commutations like that?
by magnetic phases, are you referring to magnet pairs? or coil fields?
what is the 70% efficiency for and how does that work?
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#5
(25-Dec-2016, 11:48 AM)Link0ne Wrote: what is the 70% efficiency for and how does that work?

I'm no expert at all and tbh i understand probably less than half of what you're talking about, but i guess that's just accounting for prop load. The motors won't reach their theoretical max rpm, ever, under load.

I have one quad running a setup that in theory would exceed esc specs (2300kV 14-pole motors, 4s battery, 200'000erpm esc) but in practice does not show a problem. KV rating * max voltage is ~38000 theoretical rpm, while the esc's limit would be ~28000 real rpm.

I think the 70% is a good guess. Difference could be less though with light, low-pitch props. No guarantee from my side. Wink
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#6
fftunes
I'm no expert at all and tbh i understand probably less than half of what you're talking about, but i guess that's just accounting for prop load. The motors won't reach their theoretical max rpm, ever, under load.

I have one quad running a setup that in theory would exceed esc specs (2300kV 14-pole motors, 4s battery, 200'000erpm esc) but in practice does not show a problem. KV rating * max voltage is ~38000 theoretical rpm, while the esc's limit would be ~28000 real rpm.

I think the 70% is a good guess. Difference could be less though with light, low-pitch props. No guarantee from my side. Wink
---

Thanks for your input,

Reading back my own post now, i realize i have made it more complicated than necessary by getting my forums mixed up a lil bit lol, sorry about that. I was having a different discussion on a similar topic on rcgroups.com so im talking about irrelevant stuff in this thread like cogging steps and whatnot but pls just ignore all that haha. My knowledge about IC's is where i fall short so i'm curious how you guys go from the chip rating to the rpm.

My best guess was that it was either a max possible efficiency type of thing for calculations regarding IC's or perhaps a safety threshold/margin to prevent running your hardware too close to breakdown speed...
but the next question would have been: why 70%?
Is it a approx rule of thumb value that is found to be generally true in most common situations or should i somehow determine what that factor would be, depending on the components in the setup in question?

When i consider your suggestion, something doesn't quite fall in place yet in my mind.
If I understand what you're saying correctly (not sure if i do) that would mean that taking the props off your motors and spinning them at full throttle should trip out your ESC's as soon as you reach the chip's limit. right?

Bewaren
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#7
(29-Dec-2016, 07:18 PM)Link0ne Wrote: When i consider your suggestion, something doesn't quite fall in place yet in my mind.
If I understand what you're saying correctly (not sure if i do) that would mean that taking the props off your motors and spinning them at full throttle should trip out your ESC's as soon as you reach the chip's limit. right?
Bewaren

Yes, i guess. Spinning motors at full throttle without load (props) is something that's generally not recommended, probably also for this reason. Smile But the prop weight also acts as some kind of dampening, which prevents too quick changes ("oscillating") of motors.
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