Variable frequency motors

    Jun 08 2011 | 8:16 pm
    Hello everyone, I am planning a prototype project and could really use a little help with the feasibility. The idea is to use haptic feedback to communicate a variety of frequencies through a material so that audience members can "hear" them with their hands. If I wanted to excite a metal plate or tube at a variety of different frequencies without any audible sound, what would be the best way to do it? I have found this: but it only vibrates at 183hz, I'll need a broader range of frequencies to make my project effective. It would also be desirable to effect the amplitude of the resulting vibrations. Do you think this is feasible? Many thanks in advance.

    • Jun 08 2011 | 9:13 pm
      for your variable frequency requirement, sounds like you will be better off with a stepper motor controlled by a arduino. then check out the udp libraries to get arduino to work with max's [udpsend] object. you can often find free stepper motors in old hard drives.
    • Jun 08 2011 | 9:48 pm
      All those motors, coin cell, stepper, offset cam and so on will only vary in speed not amplitude as you have suspected. There are other ways to achieve this depending on your budget and fabrication needs. - Does it have to take weight or just a touch?
    • Jun 08 2011 | 11:14 pm
      Just a touch, I was considering positioning dampeners under it controlled by servo motors, what other ways were you thinking of Simon? Thanks for your replies!
    • Jun 09 2011 | 8:26 am
      Just to amend this slightly, I think this project will work better if there are a variety of different motors, each operating at different fixed frequencies i.e motors at 500hz, 550hz, 600hz, 650hz and so on. I then only really need to vary the amplitudes. What do you think would be the best way to achieve this array of different frequencies? Do you think its feasible getting up to 10000hz with this? Many, many thanks.
    • Jun 09 2011 | 1:18 pm
      The trouble with motors as I said before is that really all that you can do is turn them on or off, you can't change amplitude of speed of vibration much. There are a couple of commercially available actuators that you might use depending on your budget one being the (horribly named) Buttkicker Although this is somewhat crude & will only produce vibrations in the 5-200Hz range.
      I think this is probably getting a bit OT for the Max list , so maybe email me privately for more info
    • Jun 10 2011 | 4:44 am
      The buttkicker and friends are called "tactile transducers". David Tudor used similar drivers for the "Rainforest" installations, but they are sold nowadays to supplement subwoofers without adding volume.
      They are basically a speaker with a piston in place of the cone. Very fun to play with. I've used several different sizes from (search for "exciter" and "tactile transducer") Also check out the Nic Collins book "Handmade Electronic Music" for a small-scale version that uses a piezo disc and a small audio transformer. Cheap, flat, paintable, but not as much amplitude as the speaker-style ones.
      Caveat: if you are vibrating something at audible frequencies, you will hear some sound... unless the thing you're vibrating is extremely non-resonant (ie - not sheet metal.)
      Here's an example of some tactile transducers rippling the surface of a water tank, via low-frequency tones generated by MAX/MSP. (see it's back on topic!)link
    • Jun 10 2011 | 11:46 am
      Yes,check out this 'soon to be released item. Which looks like a rip off of the Aura Interactor from way back. Although now it has acquired a new name 'acousto-haptic technology' Ha ha!
      And as zlp quite rightly says , its all in the mounting
      Chladni Plate, Chladni Plate I cry
      & that is on topic !
    • Jun 10 2011 | 12:52 pm
      In the acoustics, structural dynamics and scientific world what you're trying to do is called shaker excitation. It's widely used for modal analysis of surfaces.
    • Jun 12 2011 | 9:10 am
      Thanks for the fantastic responses, this forum never ceases to impress me in regards to its creativity, knowledge base and willingness to help! I found this It looks like it may be useful, possibly use an Arduino as a function generator.
    • Jun 12 2011 | 2:52 pm
      That Vibration Generator is just a loudspeaker with a piston, as has been mentioned before
      -From the data sheet 'The vibration generator consists of a loudspeaker fitted inside a stable plastic housing. A mounting pin with a 4-mm socket is attached to the speaker to trans- mit the oscillations.'
      Be careful, for a touchable object I doubt that it will take any direct weight, and will probably be destroyed by applying too much pressure. That, is the major disadvantage of this type of actuator. Perhaps some scope for clever mounting though