< > [Motion](../../motion) > Voice Coil Actuators
## Linear motors
#### High speed, large travel
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A linear motor is simply an unrolled rotary motor. As such, there are many types.
### Linear synchronous motors
The video below explains some basic concepts for a 3 phase linear synchronous motor (perhaps the most common type).
[](https://www.youtube.com/watch?v=0_QBl6-_jJU)
### Comparison to linear actuator
In contrast to a linear actuator (I know, the names are confusing...) like the one shown below, linear motors will move faster and with less backlash, but with potentially less force. Linear actuators have a transmission element (usually a belt or leadscrew) that turn a rotary motor's output into a linear movement.
The video below shows a comparison between linear actuators and linear motors:
[](https://www.youtube.com/watch?v=XlLoEWoQ7sI)
The form factor shown above with magnets and backiron on the stator and coils and backiron on the rotor is fairly common. Another form factor is the <a href='http://www.nipponpulse.com/catalog/document/51c4719fa5ce2_lsm.pdf'>"linear shaft motor"</a>, which (as the name suggests) moves a shaft back and forth.
### Linear induction motors: efficiency at high speed (+ levitation)
Induction type motors can (and often are) made linear. The advantages include no coils or magnets on the rotor -- just a conductive plate! If designed correctly, linear induction motors can levitate the rotor, making very low friction bearings possible. In fact, <a href='http://web.mit.edu/mopg/www/papers/MITHyperloop_FinalReport_2017_public.pdf'>MIT's hyperloop team took advantage of this in their prototype to create an electrodynamic suspension without any additional infrastructure on the track</a>. <a href='http://drivesncontrols.com/news/fullstory.php/aid/4068/Linear_motors_will_drive_Musk_92s_1,220km_h_Hyperloop_system.html'>More here</a>.
[](https://www.youtube.com/watch?v=bJD5d2-b5ZI)
### Linear stepper motors: open loop precision
Linear versions of stepper motors can also be made, for most of the same advantages as stepper motors in the rotary case. Most notably, open-loop precision and direct drive. The image below shows a hybrid linear stepper schematic.
### How to use linear motors in your projects
Linear motors are expensive to buy! Mostly I think this has to do with not being commoditized like their rotary coutnerparts. But, linear motors are relatively easy to make (perhaps easier than rotary motors?).
<video controls src="linear-motor-testing-3-small.mp4" width="640"></video>
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