What servo motor to use???

[amiklic1]

I would just like to hear from someone who allready tried something to do with factory servo motor. What type of motor to use? I would like to buy new motor, servo ) or stepper, if I can use it), but I don't have the chance to experiment with all the options. What data to look for. How many HP to look for. I just know that I need to find some 12 V DC, but do not have an idea how many rpm. Also, can I use some motor that is rated 80V DC / 1800 rpm. Also, how much torque to look for???

To many "???", but I would appreciate some info, and maybe some places to look for to buy. I need international shipping, as I live in Croatia (mid/east Europe).

Thanks to all of you who are encouraging me to learn more and more, and are changing knowledge with us who are just at the beginning!!!!

Best regards from sunny Croatia!

[ghurd]

I will say the bigger the better.

The lower the coil resistance, and/or the higher the rated amps, the higher the rated volts (24 to 48V for 12V battery charging), the higher the HP or watts, the lower the rated RPMs without a gearbox... the better!

I have many kinds (30 to 50 kinds) of stepper motors here, but none will make 2W at 12V in a good wind. My bigger (2.5kg) stepper motors are usually the worst and some make 0V open circuit.  People claiming 6W with small stepper motors are not informative about anything specific to the motor used. Possibly my luck in buying stepper motors was exceptionally bad?

I have a few very small servo motors, but most will not reach charging voltage. Those that do make very little amps at 12V, like under 50ma. Most make less than 1V open circuit at 1000rpm. But these are very small servo motors.

I must suggest a TDM or treadmill motor for limited funds, and a far better chance of success.

G-

[Norm]

    Yes I agree with G- treadmill motors if only

you could buy them without that heavy cast iron

flywheel...

http://www.fieldlines.com/story/2005/3/11/193835/821

http://www.fieldlines.com/story/2005/3/23/225230/317

                   ( :>) Norm.

[kenputer]

  I look for high VDC and divide the voltage by the rpm and if it under 20 then I'll use them. just my way of doing it :-)

[cr8zy1van]

Well I bought 2 of those motors. The heavy cast iron flywheel ended up being a blessing in disguise.. NO matter where I went (hardware stores, bolt supply stores you name it) I could not find a nut to screw onto the shaft. In desperation I took my hacksaw to one of the flywheels and cut off the pulley that had the threading in it. I machined the sides into a hexagon. I have one of the motors hooked up to a drill press, slowest speed about 500 rpm, and it puts out about 160 watts.

Since the threading is left handed, I am making my turbine blades run counter clock wise.. Or if you plan on running purchased blades, you could probably run a downwind setup.

One worry is that the motors have brushes that will eventually wear out. Since this is my first generator and I still want to experiment, I see this motor as a temporary solution.

[richhagen]

You need a high voltage stepper motor.  A 2 or 3 volt stepper motor would have to spin incredibly fast, faster than it would in a hurricane, in order to generate enough voltage to charge a 12V battery.  A lot of amps at 3 volts will do little to charge a 12V battery without a dc/dc converter or something to boost the voltage.

For servos, to a point, the higher the voltage the better.  I've read where people use 30V motors successfully, but I think even then, depending on the nameplate rpms, it would likely take a pretty high rpm to make 12 volts.  You want something that you can build blades to match in both the rpm and the power.  I tend to think that a high tsr machine would put more wear and tear on the bearings.  

For example, if I understand correctly:

If your servo motor can make 3 amps at 15 volts at 300 rpm, then you need to be able to make blades that can approximate this.  The power your taking out would be about 45 watts.  If you are trying to make this at a 12MPH wind speed then, if we can expect to extract about 1.75 watts per square foot of swept area at this speed, based upon roughly average performance of machines posted on this site, then we would need to sweep about 26 square feet.  We would need to have a rotor diameter of roughly 5 3/4 feet.  The tip speed would need to be about 300 * pi * 5.75 / (5280 feet/mile)*(60 min/hour) = 61.6 mph  this would be a tsr of 61.6/12 = 5.1, which is, I believe, what we would plug into Ed's blade calculator or Hugh's formulas to calculate the dimensions of the blade required.  

The power out is generally less, often significantly, than the nameplate power in at a given rpm so emperical data is best.  If you are looking at a 3 to 5 foot machine, and you calculate it out to require about a tsr 5 to 7 blade, then I would think it would be a pretty reasonable motor.

Take all of this with a grain of salt as I only have limited practical experience applying these principles.  I would be curious to hear others perspectives.

Rich Hagen

[FrankG]

I'm currently in the process of experimenting with Stepper motor/gennies, and the results are rather poor to this point.

I've mounted 2 bipolar (4 wire) steppers that are somewhat larger than what are typically found in a generic dot-matrix printer. Coils are 2ohm, rated at 4.1V, bench tested each coil produces approx 10VDC (after a bridge rectifier).

With both coils bridged and wired in series 18VDC when spun @ 950RPM.

The blades are approx 18" across and recovered from commercial "Box-Fans".

Over the last week or 2 we've had some windy periods, but I have yet to see more than a few mAmps flow into the batteries... Though I've measured over 20VDC (OPen circuit) and 400mA (short Circuit or directly via the DVM). But it would appear that all that is meaningless as I have yet to fully charge a 12V battery, and that is a real-world test.

My experience is certainly counter to some of the claims I've read on the internet, and will move-on to either TDM (tape drive motor??) or plunge right into the true home-brew gennies similar to smaller models featured on the "Other-Power" site.

[ibedonc]

you can get the nuts from www.mcmaster.com

[ghurd]

Frank,

I am glad I am not the only one having no luck at all with steppers!

Not sure why, but it makes me feel a lot better.

And I had much better luck with little tiny (like 1/30HP) conversions.

Even when they were very poorly done.

G-

[Epower]

With both coils bridged and wired in series 18VDC when spun @ 950RPM.

Steppers come with different resolutions. Virtually all steppers are either 1.8° or 7.5° per step; (200 steps or 48 steps per revolution). The 1.8° ones are better for generating at really low revs, but also tops out lower and beyond a certain speed the output frequency gets so high that the impedance of the coils starts to become significant and limits the current. When using a stepper motor as a generator, you need to keep the motor speed to around a couple of hundred revs per minute. I myself have been lucky with steppers. I have built a "stepgen" generator in which I have published on this site. I wired the coils of the stepper motors in parallel along with a bridge for each coil and then I connected all of them to a capacitor bank. The output was in the range of 16 volts x 2.5-amps (40 watts) at approximately 200 rpm. The steppers I used was made by Japan Servo Co. and the number was KP56LM2-097 x 6-volt x 1.8 deg.....Epower    

[ghurd]

The 'Stepgen' is EXACTALLY what pushed me over the edge to wind power!

I can use 250ma, but not 50A of wind power.

And you gave part numbers even if I can't find the parts.

But that is 10 stepper motors, so 3.3W 250ma each into a battery.

Others have claimed 8W (each). Maybe more. But they give no specifics at all.

Inductive or leakage reactance will limit the amps more as the step angle decreases.  I think.  My motors go from 0.9 to 18 degrees per step.

Honestly it was cheaper and easier to get 30W from an old box fan and 4 magnets.

G-

[Epower]

The maximum I`ve ever got out of the steppers was around 5 watts each. I was running them between 300 to 400 rpm, but I think that was the limit. I am now in the process of building a "one of a kind pedal generator" in which I have designed that will be displayed at a mall near by for engineering week here in Toronto of next year. When I finish building it, I will post some pictures along with the output. I am also looking for a motor to be used a a generator that has a good output and a running speed of around 1200 rpm or so and not to large in size. This is to be used on a pedal generator, any ideas...Epower