Motor Driver

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A term used when referring to a device or circuit that is essentially current amplifier; the function of which is to take a low-current control signal, and turn it into a proportionally higher-current power source that can drive a motor.

It should be noted that the control signal is likely to be on the order of 10 mA, while the motor may require several 100 mA, or even a few amps, to make it turn.

[edit] What they are, how they're used

You can think of a motor driver as an interface used to connect a control circuit to a motor. It can be view very simply, as a "wrapper" around the motor. Schematically, the arrangement would look something like this:

There are a wide range of motor driver designs available to meet most any robotic need -- they all vary in the requirements they try to meet (so read their descriptions very closely).

There are some things to look for in a driver design, based on your requirements (bear in mind that there are always trade-offs):

Output power capability -- as a rule you don't want overkill here; higher-gain drivers generally also have higher power consumption, among other costs

Number of circuit connections -- this is a good indication of how difficult it will be to build the circuit. This is particularly important if you're making your own PCB, since drilling lots of holes can be a pain if you don't have a drill press (and honestly, it can be a pain even with one).

"Smoke proof" (or not) design -- unless you're amplifying a signal from a bicore, your bridge design needs to be "smoke proof". Drivers generally have two control inputs; "smoke proof" designs won't self-destruct if both control inputs are "low", or if both inputs are "high".

Cost and availability of parts

Size -- more-compact designs are easier to fit into an arbitrary BEAM bot design

Reversability -- most (but not all) motor driver designs allow your motor to run in both forward and reverse

Output voltage -- some drivers provide (or at least allow for) output voltages higher than the input (control signal) voltage

Braking circuitry -- if you are using really good motors, you'll need to provide an electronic motor brake to keep the motors from moving around when no control signal is being applied.

For a list of various motor drivers that have been used for BEAM robots; be sure to check out the Motor drivers section of the BEAM Circuit Assemblies page of this wiki.