Sourcing Motor for High-Frequency ~30 deg Oscillations

Hi! My current project involves creating and sending pulses of air down a 1 square inch tube. My idea is to oscillate a fin attached to a motor, and this "flapping" will create the desired pulses of air. I am looking for assistance in finding the appropriate motor, which satisfies the following requirements:

  • 5-20 Hz frequency of oscillations
  • Very accurate and repeatable motor-arm movement
  • Resistance to displacement by external forces
  • Lightweight
  • Small
  • We are only pushing small volumes of air, so I doubt torque requirements will be very high.

I was playing around with the TowerPro SG90 9G Mini Servo that came with my Arduino Uno starter kit, but couldn't get it to reliably oscillate at a high enough frequency. Is a servo a good motor to use? I was looking online at some servos used in RC Helicopters as potentially applicable for my project. The HKS-9257 High Speed Servo 4.5kg/ 25g/ 0.07sec seems like it might work, but I am concerned with the precision of the servo movement, as I require a high tolerance on the volume of air displaced by my fan. Is this a valid concern?

Am I on the right track with looking at servos? Would a stepper motor be better for my application? Would a piezoelectric bimorph actuator be a good possibility?

Thanks for your help!

5-20 Hz frequency of oscillations

That implies large forces and torques, if operating a reciprocating mass. The mass of the air may also be significant at those frequencies, force depends on the square of frequency for a given displacement amplitude.

For instance a 5g mass vibrating at 20Hz with an amplitude of 1cm requires a force sinuisoid of 0.8N amplitude - or put another way its accelerating at about 16g

We are only pushing small volumes of air, so I doubt torque requirements will be very high.

If you want low forces you need to reduce the reciprocating mass as much as possible - you are designing a high-travel bass speaker without realizing it - a diaphragm and moving coil is a good technology for that, but tricky to use for this application.

Hobby servos aren't fast enough or accurate enough. A commercial servomotor system is a possibility, not small, not light, not cheap.

A repurposed disc drive head assembly might be worth looking at, they are designed for fast accurate reciprocating movement - but you'll need some sort of encoder to sense position and a very fast control loop...

A fast solenoid might work...

Or a compressed air source with a solenoid valve....

regards

Allan

MarkT: you are designing a high-travel bass speaker without realizing it - a diaphragm and moving coil is a good technology for that, but tricky to use for this application.

Thanks for your input. Can you tell me why using a high-travel bass speaker would be tricky to implement? Also, does anyone have any recommendations as to where I can find some smaller/lighter high-travel bass speakers?

Thanks

High travel bass speakers down have square tubes intersecting their cones!