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Feb 17, 2021, 03:12 AM
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BillzillaAus's Avatar
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Rules of thumb for designing/building a BLDC


As the title says, are there any reasonable rules of thumb for making a motor? Things like wire thickness, number of turns, magnet size, etc.
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Feb 17, 2021, 11:41 AM
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Fourdan's Avatar
Quote:
Originally Posted by BillzillaAus
As the title says, are there any reasonable rules of thumb for making a motor? Things like wire thickness, number of turns, magnet size, etc.
Hi
Yes ... a lot
Rule of thumb n°1 : consult a BLDC guru
Louis
Latest blog entry: Scorpion Calc
Feb 25, 2021, 10:54 AM
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Quote:
Originally Posted by BillzillaAus
As the title says, are there any reasonable rules of thumb...
Keep your thumb safely away when putting motor together. Other than that the only rule is more copper the better.
Last edited by Hummina; Feb 25, 2021 at 05:28 PM.
Feb 26, 2021, 09:34 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by BillzillaAus
As the title says, are there any reasonable rules of thumb for making a motor?
Things like wire thickness ...
Wire as thick as possible, for a given/desired number of turns: results in lowest resistance and temperature, highest efficiency and highest power handling capacity.

Quote:
Originally Posted by BillzillaAus
... magnet size ...
Magnet size, if not a given already, 75-85%%, not critical.

Quote:
Originally Posted by BillzillaAus
... number of turns ...
Number of turns (and o.a. airgap, magnetstrength, star or delta) determines kv.


Note that the velocity konstant kv says nothing about max. power, max.current, torque, rpm, quality. It only tells you how fast motor tries run, not whether it can run that fast.
The higher number of turns, the lower kv, and vice versa, they are inversely proportional:
#turns × kv = constant
#turns_new = #turns_old × kv_old / kv_new

also
kv_delta = √3 kv_wye
Most builders start from an existing motor, consertive rule of thumb 3-4watt gram motormass for conservative power. Since kv and number of turns are know, it's now very simple to determine new number of turms.


A good start by RCG user skylar
www.bavaria-direct.co.za


If you want to use/(re)wind an existing motor.
Do you want more power?
Why/what for do you want to change Kv?

Don't remove the windings yet, we/you need a bit of information first.
  • What is the original Kv_old of that motor?
  • Desired Kv_new?
  • Are the three phases terminated in delta or wye?
  • Maybe it's not necessary to rewind the motor, just changing it from wye to delta termination will multiply Kv by √3.
    Conversely, going from delta to wye will divide Kv by same factor √3.
  • What is the number of magnetpoles?
  • Number of statorteeth?
  • Number of coils?
  • Pictures?

Once you know all that, you can remove the windings.
  • Don't damage the stator insulation.
  • How many parallel wires?
  • (Single)wire thickness?
  • How many winds in a coil? Parallel wires count as single one wire when determining number of winds.


Prettig weekend en wees voorzichtig, Ron
• Without a watt-meter you're in the dark ... until something starts to glow •
E-flight calculatorswatt-metersdiy motor tips&tricksCumulus MFC
Last edited by Ron van Sommeren; Feb 28, 2021 at 01:54 PM.
Feb 26, 2021, 03:28 PM
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BillzillaAus's Avatar
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Thanks for that. I may have to build the motor from scratch, not sure yet.
Feb 26, 2021, 08:15 PM
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“from scratch” in my mind includes designing the stator and maybe gluing the laminations. Getting more “from scratch” than that have to get in neodymium mine.
Feb 28, 2021, 07:11 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by BillzillaAus
Thanks for that. I may have to build the motor from scratch, not sure yet.
What do you already know about the motor Bill?
What is purpose of motor, application?

What power and torque?
What rpm and voltage?

Vriendelijke groeten en wees voorzichtig, Ron
• Without a watt-meter you're in the dark ... until something starts to glow •
E-flight calculatorswatt-metersdiy motor tips&tricksCumulus MFC
Last edited by Ron van Sommeren; Feb 28, 2021 at 01:53 PM.
Feb 28, 2021, 06:07 PM
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BillzillaAus's Avatar
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I need something about 80 kW with lots of torque and up to about 8,000 rpm.
At the moment it's just a thought project for one of my racing cars, it would have one of those motors on each corner.
Feb 28, 2021, 06:14 PM
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Fourdan's Avatar
Hi
Maybe EMRAX 208
https://emrax.com/e-motors/emrax-208/
Louis
Latest blog entry: Scorpion Calc
Feb 28, 2021, 07:17 PM
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BillzillaAus's Avatar
Thread OP
Not really powerful enough with one motor per wheel unfortunately.
I was looking more seriously at the Neumotor 18050 though.

https://neumotors.com/motors/neumoto...o-80000-watts/
Feb 28, 2021, 07:20 PM
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BillzillaAus's Avatar
Thread OP
Although now I look at more of their motors, one of the larger ones might be a good think. Thanks for the link.
Mar 01, 2021, 08:46 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by BillzillaAus
I need something about 80 kW with lots of torque and up to about 8,000 rpm. ...
Haven't seen that size in this subforum. Yet
2-3kW continuous power, iirc.

www.plettenberg-motoren.net ?
Lehner, Kontronik, Hacker?


Vriendelijke groeten Ron
Last edited by Ron van Sommeren; Mar 01, 2021 at 08:52 AM.
Mar 04, 2021, 06:43 AM
Entropy is happening!
Jim.Thompson's Avatar
The ESC logistics for motors of that power category are frightening!.......................To my mind anyway............
Mar 04, 2021, 06:50 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by BillzillaAus
I need something about 80 kW with lots of torque and up to about 8,000 rpm.
At the moment it's just a thought project for one of my racing cars, it would have one of those motors on each corner.
An e-traction forum, scooters, bicycles, motorbikes, cars
www.endless-sphere.com

APD controllers from downunder
www.powerdrives.net



Vriendelijke groeten en wees voorzichtig, Ron
• Without a watt-meter you're in the dark ... until something starts to glow •
E-flight calculatorswatt-metersdiy motor tips&tricksCumulus MFC
Mar 04, 2021, 05:45 PM
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BillzillaAus's Avatar
Thread OP
Thanks for the links.


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