Servo Controller

[WXYZCIENCE]

The VPSC ( Variable pitch servo control) is working, thanks to the R&D of my brother Bill. This unit has high and low setting for the position of the servo and a math unit that calculates a factor of divisions in that range. The unit is set with 16 positions in 90 degrees. It has an adjustable input gain for wind speed input devices. The display shows wind speed, servo position and low / high settings.

Our servo is a worm gear type but the output could be adapted to other types.


The computer is a Motorola 68HC908 Flash program micro-controller. In operation mode the power draw is 40ma at 5v. and can be powered down in sleep mode. Questions?


Joseph.

[SamoaPower]

Great Joe! Looks like you and Bill make a good team.

I'm not sure what the operational algorithm is from your description. I assume you have positional feedback from the pitch serveo. Are the mentioned 16 positions evenly spaced over 90 deg? If so, I'm afraid that will be much to coarse for the usual speed range. I would expect the normal operating pitch range to be less than 10 degrees. Of course, you need a larger range for start-up and feathering.

Is rotor rpm an input to the controller? I would think you would need that to be able to run at a constant TSR.

Would be interested in more algorithm detail.

Congrats on not being afraid of complexity. You're one of a few.

[Flux]

I thought it was a means of setting angles for test. From what I saw of the operating mechanism it didn't look as though it would last long as a normal pitch controlled hub.

If this is the case then the angles should be ok.

Flux

[WXYZCIENCE]

SamoaPower, If I set the low to zero degrees and the high to 16 degrees then the 16 positions would be one degree each. In my case it is not so much feathering I wanted to obtain but start up position, run position and high wind shut down. The options that the controller has will only be understood fully when the mill is up and flying. Thanks for your interest. I will keep posting the results. Joe.

[WXYZCIENCE]

Flux, due to the wind conditions that we have here, the pitch settings should allow me to protect larger blades. Time will only tell if my design will withstand the elements and the forces that the wind can put out. This was one of the big hurdles in this project. The yaw control and the tower are next. Joe.

[RP]

One idea to consider would be modifying the servo system to be (for instance) 0-15 degree with 1 degree resolution PLUS a 90 degree setting for shutdown.  If this is a microcontroller device then it's just a matter of tweaking the firmware.

[SamoaPower]

Oh, I see, the 16 steps are between the high and low set points. Hmmm, but I see a 90 degree range being necessary. Operating, maybe 1 to 10, start-up about 45 and feathered - 90.

"In my case it is not so much feathering I wanted to obtain but start up position, run position and high wind shut down."

But, shut down IS feathering.

[willib]

hey Joe ,how does it work..

or what is that knob for to the right of the on off switch?

those labled High & low , are they knobs too?

details ??

[BigBreaker]

This was my immediate thought as well.  Micros are wonderfully flexible and I doubt the 16 positions are hard limit.  Certainly the positions don't need to have equal angle portions.

One reason to "quantize" the angles is to avoid too much searching or cycling by the algorithm.  Even though you lose some small amount of efficiency, you save a lot of wear on the servo and debugging time.  If 16 works, he can always flash a new program and try for something different.

90 degrees is better than zero for two reasons.  First the servo or structure might fail slightly to leave some pitch in the blades.  Secondly the tower and blade loading is lower.

Was their any comment on the inputs to the micro?  Is it tacho, wind speed, or both?  There is something to be said for doing tacho, current (AC and all phases) and wind speed.  That protects against a lot of failure modes.

[canadianfred]

If this fails, does it fail in such a way that your windmill doesn't self-destruct in high windspeed conditions?

[WXYZCIENCE]

Fred, the mill also will have a servo yaw control and in the event that circumstances cause pitch failure, the mill can be furled. If this fails I guess she will be at the mercy of the elements. Joe.

[WXYZCIENCE]

Willib, here is a block diagram of the servo driver.

The knob beside the switch controls the wind speed cross over point, or a calibrated setting for the run position of the blades. (ie. Gain Control.) The over speed is set by a lookup table and is set for maximum RPM, we are using the frequency of the alternators AC output. Much of the test data that this unit provides will become the firmware in the future model. We can read the A/D converters many times per revolution of the blade. But we will update every 5 seconds for servo stability. We can also manually control the pitch, this will allow us to tweek the setting for any wind condition. Theory is useless without real testing me thinks. Joe

[WXYZCIENCE]

That is very close to how the unit works. Example: The stopped position, 45 degrees, the run position, 12 degrees. Wind speed low set to 5mph, the high set to 18mph. The gain can now be set between the low and high. At the cross over point the blades goes to run position. This is one example of the flexibility that we have wanted looking up at a stopped windmill. Joe.

[redsand]

Congratulations on a job well done. But the casing looks a little flimsy. I could be wrong though.Not much to test its solidity through pictures. But from what I've read so far, it seems to be a great piece of work. Any more information we should know? Thanks!