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My project deals with simulating a fixed frequency tremor and process it. The required tremor range is 5-20Hz. I have been trying to generate this vibration motion with a vibration motor, but all i get is a frequency greater than 30Hz ( measured using accelerometer).

Is there any other way in which i can generate a 5-20Hz mechanical vibration?

OR Is there a way of reducing this frequency generated by the motor?

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    \$\begingroup\$ How about using an ordinary DC motor (like from an old cassette player) powered through a rheostat with a small off-centre weight attached to the shaft? Or, do you have a signal generator and a loudspeaker? \$\endgroup\$ – Andrew Morton Jun 28 '16 at 10:03
  • \$\begingroup\$ @AndrewMorton, I am used DC motor with rheostat control, PWM control, voltage control, however, nothing seems to work. How do you propose using loudspeaker and signal generator? \$\endgroup\$ – user5089054 Jun 28 '16 at 10:17
  • \$\begingroup\$ Check the output power capability of the signal generator. If it is suitable for driving a loudspeaker directly, do so. At a rough guess, a 10 cm diameter speaker would be enough for small amplitude vibrations. By "vibration motor," do you mean one of those tiny things used in mobile phones? \$\endgroup\$ – Andrew Morton Jun 28 '16 at 10:27
  • \$\begingroup\$ @AndrewMorton, Yes. I have tried using the normal DC motors that we have as well as the ones used in mobile phones \$\endgroup\$ – user5089054 Jun 28 '16 at 10:30
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    \$\begingroup\$ You can get gear motors with relatively low gearing (3:1 or 4:1) that should run nicely at the speeds you,re interested in. These should be considerably more efficient than a loudspeaker at such low frequencies. \$\endgroup\$ – Brian Drummond Jun 28 '16 at 10:32
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You don't say how big the vibration needs to be, or what your cost parameters are, but I'll throw in with a voice coil actuator

voice coil

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  • \$\begingroup\$ This is too epensive; my budget is not more than $15... \$\endgroup\$ – user5089054 Jun 28 '16 at 11:08
  • \$\begingroup\$ Wow. I was going to suggest a few things (using motors), but nothing would be in that price range. \$\endgroup\$ – Mark Jun 28 '16 at 21:35
  • \$\begingroup\$ Funny frequency point. If you need great precise control in this range, these are a great way to go \$\endgroup\$ – Scott Seidman Jun 28 '16 at 22:53
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    \$\begingroup\$ Grab a speaker? \$\endgroup\$ – Someone Somewhere Jun 29 '16 at 12:58
  • \$\begingroup\$ @SomeoneSomewhere -- for sure \$\endgroup\$ – Scott Seidman Jun 29 '16 at 14:49
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Your attempt with a vibration motor is a good start, but obviously you cannot control the vibration frequency precisely using an ordinary motor. You should try to mount and off-center weight on a stepper motor and control that. Note that most stepper motors can rarely go above 500-1000 RPM. You need 1200 RPM, perhaps you'll find a motor which can do it. Otherwise you'll need a small gearbox to increase the weight's RPM.

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