Motor formulas - Page 3 - RC Groups
 This thread is privately moderated by fly_boy99, who may elect to delete unwanted replies.
 Feb 02, 2009, 05:25 AM Impossible? Hah! The diameter affects torque in two ways. First, the diameter relates to the radius and this affects torque linearly by simply providing more "leverage". Secondly, the larger diameter linearly increases circumference which in turn allows for more magnets or magnetic material. Together theese two make up the D^2 component. You do not have to change number of slots, nor do you have to change the magnetic pole-count. It's just scaling like with the L. If you do change polecount, or the width of the teeth for that matter, you are obviously changing more than just D and then k would change. Same goes for changing thickness of magnets of airgap.
 Feb 02, 2009, 11:53 AM Registered User Kreature I agree with you if you increase the magnets volume (could be generally via the width along the circumference). In my post I was writing "keeping the same magnets" for linear relation to diameter D Regards Louis
Jun 27, 2009, 11:37 PM
Flying motor mount master

Folks,

It has come to my attention that this thread is getting off topic. So I will reiterate what this thread is NOT:

1) Not a place for "hey what's this motor?"
2) What motor can I use to fly a 250g heli?

It is for motor formulas that are helpful for those who want to learn and understand the underpinnings of brushless motors.

I will update the formula list as needed and I will delete those thread which do not belong here.

Thanks,
Bryan
Sep 10, 2009, 03:20 PM
Registered User

# got iron dimensions, lack of electric related informations

Is there a way to calculate (or roughly guess?) what can you expect of
DIY motor, if you have following informations
1.dimensions of stator (diameter, thickness, number of poles, ...)
2.bell diameter
3.dimensions of magnets

For example, I got these:

1.
stator diameter 20,7mm, stator thickness 4mm
bell diameter 27,5
magnets 12pcs 6,5x5x3mm
total weight 28gram
very small airgap
you have to force stator to turn with formidable force
stator is not wounded yet, but I can get my hands on wire of any thickness

2.
stator 22,2mm, thickness 4mm
bell 27,5mm
magnets 12pcs 6x4x2,5mm
weight 26gram
very small airgap
you have to force stator to turn with formidable force
not wounded,

3.
stator 22,2mm, thickness 4mm
bell 27,5mm
magnets 6pcs 5,5x4,5x2,5mm
weight 24gram
very small airgap
you have to force stator to turn with formidable force
not wounded,

4.
stator 22,5mm, thickness 4mm
bell 28mm
magnets 6pcs 5x5x2mm
weight 20gram
bigger airgap
you have to force stator to turn with smaller force
not wounded,

I have 0,325; 0,4 and 0,5mm insulated wire for transformer windings, but I could easily get any wire.

I think this is a bit awkward approach, but, any ideas?
Sep 10, 2009, 04:20 PM
Suspended Account
Quote:
 Originally Posted by fly_boy99 Folks, It has come to my attention that this thread is getting off topic. So I will reiterate what this thread is NOT: 1) Not a place for "hey what's this motor?" 2) What motor can I use to fly a 250g heli? 3) General disagreements about formulas It is for motor formulas that are helpful for those who want to learn and understand the underpinnings of brushless motors. I will update the formula list as needed and I will delete those thread which do not belong here. Thanks, Bryan
Thanks Bryan, for keeping this thread clean and lean, and packed with great motor formulas. And please feel free to delete this post too. Just wanted to say I enjoy and learn a lot from these formulas.

Chuck
 Sep 14, 2009, 08:55 PM Registered User guys, this looks like graduate level formula talk how about a simple formula to work with since most of the data bases are way out of date. Very simply, I have a 2505 ... 12 poles/14 magnets ... I'll wind dlrk. I want to turn a 10" SF GWS prop on 2 cells, on a 10 oz 3-D foamy. I'd like around 10 amps. In my mind a formula would be # of turns ... awg wire ... and termination. Now that would be a formula I could get my mind around and use. Any help ... please
 Oct 17, 2009, 05:47 PM Registered Aircraft Offender People are always asking about turns and Kv. Here's the equation that relates # of turns (Tx) and Kv (Kvx) for a given motor and termination: Kv1*T1 = Kv2*T2 = Kv3*T3 =...= Kvx*Tx = Constant Some common simplifications used by those who rewind motors: T2 = Kv1*T1/Kv2 Kv2 = Kv1*T1/T2 ...and to be sure, the constant is different for different motors. Different magnet numbers count as different motors here. Different terminations can be related with the root(3) rule, which relates delta Kv to Y Kv. The root(3) rule is already listed in the first post. Cheers, Kev Last edited by Truglodite; Oct 17, 2009 at 06:13 PM.
 Oct 30, 2009, 04:55 PM made of foam What's the kV of a 22mm dia 8mm thick 18turns per pole 12 pole 14 magnet lrk delta wound motor?
Oct 30, 2009, 06:39 PM
Registered User
Quote:
 Originally Posted by appa609 What's the kV of a 22mm dia 8mm thick 18turns per pole 12 pole 14 magnet lrk delta wound motor?
Hi
If you mean true LRK 6 coils (on 12 slots)
with 14 magnets (14 poles) steel ring
Scheme A-b-C-a-B-c-
Delta connecting
I would say Kv roughly 2000 rpm/V for 2208 stator size

But the real world Kv depends also of magnet total volume and airgap

if you mean dLRK 18 turns per tooth (36 wires per slot) Kv around 1000
Louis
Nov 01, 2010, 01:42 PM
Registered User
Quote:
 Originally Posted by Truglodite People are always asking about turns and Kv. Here's the equation that relates # of turns (Tx) and Kv (Kvx) for a given motor and termination: Kv1*T1 = Kv2*T2 = Kv3*T3 =...= Kvx*Tx = Constant Some common simplifications used by those who rewind motors: T2 = Kv1*T1/Kv2 Kv2 = Kv1*T1/T2 ...and to be sure, the constant is different for different motors. Different magnet numbers count as different motors here. Different terminations can be related with the root(3) rule, which relates delta Kv to Y Kv. The root(3) rule is already listed in the first post. Cheers, Kev
Thanks Kev, what is the meaning of Kv and T?
 Nov 02, 2010, 01:30 AM Registered Aircraft Offender T is the number of electromagnetically effective turns wound around each stator pole. For example, a multistrand wind with 3 parallel strands may physically have 36 turns of copper on each stator pole, but you would use 12 turns in the equation (to be consistent with EM theory). Same rule counts for half parallel and full parallel winds. Physical turns equals effective turns for a standard wind. Kv is the specific speed constant of the motor (in RPM/V). One of the three fundamental constants that define motor performance. Kev
 Dec 01, 2010, 07:00 AM Registered User I've looked at all these formulas and I never see anyone take into account the phase shift beteewn I and E and we know that as rpm increases so does the phase shift so it's no longer I times E as you nwould figure in a simple dc circut
 Dec 01, 2010, 10:57 AM Impossible? Hah! Well, RMS handles that...
 Dec 04, 2010, 02:20 PM Registered User who has a clear and simple motor/prop thrust /amp draw/cell count chart thanks a bunch! Greg T
Dec 04, 2010, 03:41 PM
Registered User
Quote:
 Originally Posted by rcsuperhero who has a clear and simple motor/prop thrust /amp draw/cell count chart thanks a bunch! Greg T
Hi Greg
Try free Scorpion Calc here