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### Topic: Seeking help on acheiving rapid back and forth oscillations (Read 190 times)previous topic - next topic

#### VLetrmx21

##### Sep 14, 2018, 04:22 pm
Hi everybody, I have a few questions regarding a setup for project that I will be engaging in and I need some feedback. When it comes to electronics I am a newbie so I may ask some questions which may sound stupid so bear with me here.

The project I am working on involves oscillating the upper wingspan of the blades of a small scale horizontal axis wind turbine (to clarify, the whole blade doesn't oscillate, only 60% of the blade does while the other 40% is fixed) in order to achieve higher rpm at low wind speeds and hence generate more electrical power. Previous experiments on the project have managed to achieve a maximum 18.8 Hz oscillating frequency with the oscillating blades. These oscillations occur back and forth along a certain angle and amplitude, theoretically the faster the oscillation the faster the airfoil moves and higher amounts of power can be extract from the wind at low wind speeds.

I would like to increase the oscillation frequency for this setup beyond 18.8 Hz but I am a bit lost on what kind of setup I should use to achieve higher frequencies. The previous study involved using a DC servo motor with 11.00 kg*cm torque and a 0.16 sec/60° @ 6.0 V specification which was controlled by an Arduino Uno. I am planning on using a high performance BLDC servo (Brushless DC) used for RC racing (Such as the Blue-Bird BLS 29-A) but to be honest I am not too familiar with how the installation scheme should be like. I have been reading up on BLDC motors and it's always mentioned that an ESC (Electronic Speed Controller) must be used to convert the DC voltage from the battery into pulses to run the motor. Do I always have to embed an ESC in the setup to be able to run the BLDC?

I have also thought up of using different setups involving smaller AC servo's but those servos need servo drives and extra wiring which take up space and I have some space limitations in terms of what I can fit into the nacelle of the system and I want to take a simple and practical approach to this. It would be highly appreciated if you share your ideas and suggestions.

#### slipstick

#1
##### Sep 14, 2018, 05:18 pm
BLDCs don't generally oscillate, they rotate, often quite fast. Are you planning some sort of mechanical linkage to convert that into back and forth movement? A picture of what you're talking about might help.

An ESC (or some fairly complex code that's a bit much for an Arduino) is needed because, being brushless, a BLDC needs electronic switching to replace the commutator in a brushed DC motor.

Steve

#### Robin2

#2
##### Sep 14, 2018, 05:55 pm
A picture of what you're talking about might help.
+1

I reckon a picture or diagram is essential.

I also reckon that if the wind power cannot directly cause the required oscillations then the oscillations are of no value. Feeding electric power INTO a wind turbine seems counter-productive.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### WattsThat

#3
##### Sep 14, 2018, 08:10 pm
Quote
Feeding electric power INTO a wind turbine seems counter-productive
A large percentage of the commercial turbines presently installed do exactly that. You'd be gob smacked with how much energy is actually pushed into the generator. This good news is that almost all of it comes back out.

https://en.m.wikipedia.org/wiki/Doubly-fed_electric_machine
Vacuum tube guy in a solid state world

#### Robin2

#4
##### Sep 14, 2018, 11:21 pmLast Edit: Sep 14, 2018, 11:24 pm by Robin2
A large percentage of the commercial turbines presently installed do exactly that. You'd be gob smacked with how much energy is actually pushed into the generator. This good news is that almost all of it comes back out.

https://en.m.wikipedia.org/wiki/Doubly-fed_electric_machine
That's for an entirely different purpose than making parts of the blades wiggle. Power will be needed to energize the motor coils whether it comes from within the turbine or from an external source.

If you imagine the turbine charging a battery bank then the power for energizing could come from the batteries and still leave power for export after charging the batteries. If the power for the wiggling blades can do likewise then it may make sense - but I am sceptical.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

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