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I am building an autonomous robot for robot swarm reasonably small in size (say 30mm x 30mm). I was analyzing such robot's locomotion and found that coin vibration motors are used widely as opposed to generic DC motors with wheels. I get that the the coin vibration motors are very cheap and can keep the overall size of the robot fairly small, whereas with DC motors, wheels will be involved which will make the overall body size of the robot bigger compared to using vibration motors.

My question is how do coin vibration motors create forward motion. Say a robot uses two of these motors. How can it be determined which direction the robot will travel and WHY? Is this something to do with centripetal forces?

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  • \$\begingroup\$ Possible related to this? \$\endgroup\$ – sherrellbc Jun 24 '14 at 1:58
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    \$\begingroup\$ Look for these robots under the generic names "bristlebot" and "vibrobot". Bristlebot, for example, uses toothbrush bristles to get linear motion out of the vibration; there is more friction one direction than the other. \$\endgroup\$ – Ken Shirriff Jan 7 '17 at 0:55
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Vibration does not in itself create continuous motion in one direction- the center of mass stays exactly fixed in the same place in the absence of external forces (assuming it was not moving to begin with).

If you have feet that slip more easily in one direction than the other then vibration can cause motion. There are other options, but it's the interaction of the object with the environment that causes motion.

Here is a paper on the subject. Link expired, new link

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  • \$\begingroup\$ Thanks for your answer. I was reading on Eccentric Rotating Masses and came across the term fictitious force. I guess that plays a big part in motion? What I find interesting is how a rotating mass creates motion. \$\endgroup\$ – David Norman Jun 24 '14 at 2:15
  • \$\begingroup\$ @DavidNorman These sort of nonlinear effects have fooled people into thinking that they violated Newton's 3rd Law. See, for example, the Dean Drive, a purported reactionless drive: en.wikipedia.org/wiki/Dean_drive \$\endgroup\$ – Spehro Pefhany Jun 24 '14 at 2:32
  • \$\begingroup\$ Rotating a mass creates both vertical and horizontal vibration. Vertical vibration adds oscillation to the robot's weight and this way to the friction force. Horizontal vibration can make the robot to move if the friction force is different enough (because of difference between static friction and slip friction, because of a surface designed to make friction non-isotropic, or because of vertical vibration). The last case is much like "synchronous rectification" in electronics. \$\endgroup\$ – motoprogger Jun 24 '14 at 5:16
  • \$\begingroup\$ @motoprogger, I have been reading on centrifugal forces and what makes vibration motors desirable for precision movement. But I'm still not sure how TWO vibration motors can cause an object to travel in a certain direction. \$\endgroup\$ – David Norman Jun 24 '14 at 6:05

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