Motor Design

[tmacdonald]

I have a project and need some help. I need to build a small motor capable of generating 6-12v and 2-8amps from one of the kits you have here but I need it to only spin from 1000rpm to 3000rpm. Is this possible and what winding difference would I need to do.

Thank you
Tim

[Fourdan]

I have a project and need some help. I need to build a small motor capable of generating 6-12v and 2-8amps from one of the kits you have here but I need it to only spin from 1000rpm to 3000rpm. Is this possible and what winding difference would I need to do.
Thank you
Tim
Hi Tim
3000 rpm 12 V that is roughly Kv = 250 rpm/V
12 V * 8 A = 96 watt
That is easily feasable for an outrunner kit direct drive.
The difficulty is that low Kv induces small wire and moderate current.

A 2215 is probably short in size (about 43 turns per tooth, thin wire)
but a 2814 or 3014 could do the job, with more ease.

For example a Scorpion 3014 with 21 turns per tooth, Star connecting
(42 wires per slot).
See Innov8tive
Louis

[tmacdonald]

I have been reading this site but I am having some difficulty understanding some thing. This is a newbie question. What is the voltage and amperage difference between larger 14g wire than say 32g wire. I know with smaller wire you get more turns but you still have the same amount of mass in copper wound around the stator so what do you get with larger or smaller wire.

Tim

[tmacdonald]

I am trying to get the most voltage and amperage out of a 2 to 3 inch engine spinning around 1000-3000rpm and need a little advice.

[Fourdan]

I have been reading this site but I am having some difficulty understanding some thing. This is a newbie question. What is the voltage and amperage difference between larger 14g wire than say 32g wire. I know with smaller wire you get more turns but you still have the same amount of mass in copper wound around the stator so what do you get with larger or smaller wire.
Tim
Hi Tim

With the same total area of copper per slot you have one freedom degree
1) thin wire + more turns = low Kv , high torque, big prop (3D or glider)
2) thicker wire , less turns = high Kv , low torque, small prop (racer)

For a good tutorial on electric motors, read "De Mulder" papers , here:
http://www.southernsoaringclub.org.za/
Louis

[Ron van Sommeren]

Excellent motor building articles by Brian Mulder, a must read, will prevent you from asking a lot of questions you even did not know you were going to ask ;) ;)
http://www.southernsoaringclub.org.za/
-> Articles by SouthEasterners.
-> Electric Motors - part 1-5

Do-it-yourself motor homepages, manuals/tutorials, checks and tests in this motor builders tips and tricks thread. The checks and tests may save you from frying your controller or motor. Thread is active, bookmark it for future reference and subscribe to it:
http://www.rcgroups.com/forums/showthread.php?t=240993 (sticky thread, at top of subforum)

Two instructive motor winding/assembly videos, 14 & 10Mbyte respectively.
http://www.utahflyers.org/
-> Motor Winding #1 & #2

Prettig weekend ;) Ron

[vintage1]

I have been reading this site but I am having some difficulty understanding some thing. This is a newbie question. What is the voltage and amperage difference between larger 14g wire than say 32g wire. I know with smaller wire you get more turns but you still have the same amount of mass in copper wound around the stator so what do you get with larger or smaller wire.

Tim


Actually what you get with more turns of thinner wire is a motor that needs more cells to deliver exactly the same power at exactly th same RPM and efficiency.

OR if you run it on the same cell count, it turns a big prop slower at less power and whatever efficiency..it happens to arrive at!

Sometimes that means you can utilize a prop that is more efficient, so its not all a loss.

But what you CANNOT do, and this is a fundamentally misunderstood point, is to rewind a motor and get it to put out the same power and efficiency at lower RPM, than it does when set up for its best power and efficiency.

THAT is not a function of the winds: Its a function of the magnets and ironwork. They will deliver a certain torque, and that's it. All you can do is use that torque times RPM to get the power you need, and fill the thing with as much copper as possible to get the winding resistance down.

All the motor losses that affect efficiency are down to the copper fill ratio and the iron and magnet quality, and the RPM. None of them are related to the turns directly..

[tmacdonald]

Hi, all. Thanks for the information. I got a lot out of it. I bought a small kit and will try different windings. I am making a generator out of them so that is why I wanted to know about getting the max in v and amps.

Tim

[kf2qd]

for a generator - the higher the number of turns, the higher the voltage. the faster the magnetic flux changes, the higher the voltage.

On the other side of the equation - the faster the the magnetic flux reverses the more IMPEDANCE there will be. (IMPEDANCE is a term that describes the effect of Alternating current in a circuit) a coil has higher impedance (which in this case is like resistance) at higher frequency.

Our little motors are not designed to be generators(small wires and not much of it) as they are designed to drive something rather than be driven by something. For a usable small enerator you would probably do better to look at using a BRUSH type motor as they are designed for lower RPM and thus will produce more voltage at lower RPM

For a decent small generator from a brushless motor you need a very low KVA rating and lots of windings. Our small motors tend to be just the opposite - High KVA and few windings.

[tmacdonald]

I know that the motor for the RC group is not quite right but it seems to be in the middle for what I want to do. My motor needs to be small say 2 to 3 inches. I need to attach a fan to it like a computer cooling fan. It needs to fit into a small space say a housing 6" long, 4 " tall and 3" deep. I did some testing with a computer cooling fan rated at 12v /.16amps at 3500RPM and easily attained this with my test wind speed of 45MPH. That cooling fan motor was only a 4 tooth stator with really small wire and only 2 poles. I am going to build a motor kit and try to wind it with .20g wire and get as many winds as possible. I appreciate all the help.

Tim