variables in motor construction

[drfish]

I am sure this is documented somewhere, but in a quick pass of the stickies, I didnt find anything..

Each variable in motor construction (ex stator pole count, turns, wire guage..) has specific effect on the outcome of the motor (this is electricity, so things should be predictable, at least in relative terms)

So, it stands to reason there should be a set of standard rules for what changing one of these paramters is. I have been able to glean a few, but it seems there should be a big sticky with this info - can anyone point to one, or if not, fill in the details:

Here is what I have found so far:

more turns = + kv
taller stator/rotor = + torque, -kv,
heavier wire = + current handling

so some of the variables I am aware of, but dont know the effect
more stator poles=?
more mag poles = ?
other effects of wire gage?
number of strands (multi strand wiring)
how to increase current draw? (ie pull more current at same voltage/load - I think this is taller stator/rotor?)

Any other variables that are predictable outcome?

[BlazerB52]

Trying to make a chart right now on the subject you have. Will post it when I have someone more knowledgable to double check it. Have contacted someone to look it over. Waiting to e-mail it to him. Still trying to grasp everything but my chart will help I hope.I am a newbie.But learning!!! Hopfully shows how everything works with each other and what changing a parameter does.

[fly_boy99]

Comments inline

I am sure this is documented somewhere, but in a quick pass of the stickies, I didnt find anything..

Each variable in motor construction (ex stator pole count, turns, wire guage..) has specific effect on the outcome of the motor (this is electricity, so things should be predictable, at least in relative terms)

So, it stands to reason there should be a set of standard rules for what changing one of these paramters is. I have been able to glean a few, but it seems there should be a big sticky with this info - can anyone point to one, or if not, fill in the details:

Here is what I have found so far:

more turns = + kv
taller stator/rotor = + torque, -kv,
heavier wire = + current handling

so some of the variables I am aware of, but dont know the effect
more stator poles=?
More torque and copper
more mag poles = ?
More torque
other effects of wire gage?
larger guage - lower Rm better heat dissapation
number of strands (multi strand wiring)
more copper per stator fill - sometimes
how to increase current draw? (ie pull more current at same voltage/load - I think this is taller stator/rotor?)
taller stator will make a lower Kv - you need a higher guage wire with less turns and fill as much of the stator as possible.



Any other variables that are predictable outcome?

[drfish]

A correction to myself

more turns = -kv

[ScubaSteve]

Try this: http://www.gobrushless.com/kb

Click Articles, then Brushless 101. Excellent article by Brian Mulder.

[BeavrdamElectric]

so some of the variables I am aware of, but dont know the effect
more stator poles=?
more mag poles = ?
other effects of wire gage?
number of strands (multi strand wiring)
how to increase current draw? (ie pull more current at same voltage/load - I think this is taller stator/rotor?)

Any other variables that are predictable outcome?
I'm a little fuzzy on the effect of different # of stator teeth. If you look at Ralph's (Powerditto) table ( http://www.powercroco.de/Kombinationstabelle2.html ) the magnetic "gearing" doesn't depend on the # of teeth on the stator, but on the # of magnet poles. The magnetic gearing refers to how many controller cycles it takes to turn the motor one revolution. More cycles makes more torque, less Kv.

Thicker wire guage will handle more power and have less resistance. The lower resistance motor (same Kv) will draw more amps and sag less under load. Multistrand may be easier to bend around stator teeth but has no other advantage in most situations over single wire with the same cross section.

To increase the current with the same voltage and prop* you can use heavier wire (reduce resistance), more Kv (fewer turns), or a combination. A larger (diameter or length) stator with the same wind would reduce the Kv and output.

*I assume you mean a prop, which is a variable load. Increasing the wattage going to a fixed load would indicate less efficiency.

Here are some words of wisdom from another poster. Sorry I can't remember who. :o

A running motor acts as a generator and when it reaches the speed where the generated voltage matches the battery voltage, the motor's speed no longer rises. If the motor is forced to turn faster than that speed, the motor's voltage will be higher than the battery's voltage and the amps will reverse causing the motor to act as a brake and recharge the battery.
The resistance of the entire system, including the internal resistance of the battery, will determine amount of amps that the motor will draw when not rotating.
If you have a motor that has a Kv that runs 11000 rpm with 11 volts no load but you load it to the point where it only turns 10,000 rpm, then the motor's generated voltage will be 10 volts, one volt less than the battery's voltage and that one volt difference divided by the motor's resistance will be the amp draw. The lower the resistance, the less the rpm will sag under load.
The first part explains Kv. The more turns a motor has, the less RPM it needs to equal the input voltage. The last part explains the resistance thing.

Good Luck!

[drfish]

Thanks! Excellent info! especially that gb article, and Beavrdam, those little snippits are great!

[Ron van Sommeren]

Always use the thickest wire possible for the number of winds you want. Better for efficiency. Wire thickness has no effect on Kv (apart from the sagging under load).
Normally, the number of teeth depends on the stator diameter, imagine a 6 teeth stator with a diameter of 100mm ;)

DIY motor building tips & tricks (http://www.rcgroups.com/forums/showthread.php?t=240993)


Vriendelijke groeten ;) Ron
• diy brushless motor discussion group (http://www.yahoogroups.com/group/lrk-torquemax)
• Drive Calculator (http://www.yahoogroups.com/group/D-calc/) download & discussion group
• int. E fly-in & diy outrunner meet (http://home.hetnet.nl/~ronvans/), Aug.26 2007, Nijmegen, the Netherlands

[Ron van Sommeren]

Higher efficiency does not only mean that the motor makes better use of the batteries' power, it also means the motor is able to handle a higher power input before hitting its maximum temperature mark.

An example:
Say the motor has an efficiency of 70% and it can handle 50Watt input. That means it can get rid off 0.3*50=15Watt excess heat. Now, by cramming in thicker wire, efficiency increases to say 75% (I'm a bit optimistic here). The motor's ability to loose those 15Watts has not changed (by radiation, convection and conduction). This means the motor now can handle 60Watt before it hits the 15Watt (0.25*60Watt) losses mark. An efficiency increase of 5% gives an increase in the power to weight ratio of 20%. That's why efficiency plays such an important role, in any motor design: efficiency governs maximum power.

Of course there are more methods to increase efficiency:
* better iron lamination quality (lower losses per Hertz for certain magnetic field value)
* thinner iron laminations (up to a certain point, to relative amount of insulation increases of course)
* stronger magnets (less winds needed to get same Kv and Kt) Iron losses may increase though

[powerditto]

:confused:

[BlazerB52]

Made these charts as general reference and not to be taken as gospel.
If anyone see's flaws please let me know so I don't pass on bad info.
Amp chart was made using Drivecalc for single strand wire.

Thanks.

[BeavrdamElectric]

Blazer, in your first pic it looks like a 20 turn single will have 3000 Kv and a 5 turn triple would have 1000 Kv. I'm not sure how to make that clearer in your format.

Switching from 12 to 6 poles will not usually double or halve the Kv exactly due to changes in coverage and pole/hammerhead width ratios.

24t GBv with 12 poles - 1192 Kv
with 6 magnets/poles - 2188 Kv
with 12 magnets/6poles - 1853 Kv

Good Luck!

[BlazerB52]

Was not trying to be exact on figures just trying to make a chart for guy's at the field to show them relationships of what happens when you change parameter. Any advice is extremely welcome because I don't want to give out bad advice. Wanted to show them in easy terms of what goes on with motor and changing one parameter at a time.

Thanks for replys and help!

If a person uses this chart to get a idea of what is going on with a motor will it hurt them in the end or give them a little more insight as to what is going on with changing one parameter?

BlazerB52