"Generally a 0.01~0.1uF capacitor is wired across brushed DC motors to reduce radio frequency EMI caused by arcing between the brushes and commutator. Sometimes two capacitors are wired in series, with the center connection going to the case to 'ground' it at RF frequencies.
For best effect the capacitor(s) should be placed on or inside the motor. In this case a capacitor has been included on the driver board. This makes it less effective at higher frequencies because the wires from the board to the motor will still be able to radiate EMI. Still it's better than nothing, and may prevent misoperation due to interference from an unsuppressed motor getting into the driver and input wiring."
And:
"The capacitor shunts (or "absorbs") the high frequency spikes from the commutation and prevents damage to the driver chips.
A further factor not clear from the schematic is that snubber diodes should be used to prevent inductive kick-back from the motor's inductance causing damage to the driver's output transistors. While the diodes protect the driver, the capacitors take the "edges" off the current spikes and help reduce EMI, etc."
"Generally a 0.01~0.1uF capacitor is wired across brushed DC motors to reduce radio frequency EMI caused by arcing between the brushes and commutator. Sometimes two capacitors are wired in series, with the center connection going to the case to 'ground' it at RF frequencies.
For best effect the capacitor(s) should be placed on or inside the motor. In this case a capacitor has been included on the driver board. This makes it less effective at higher frequencies because the wires from the board to the motor will still be able to radiate EMI. Still it's better than nothing, and may prevent misoperation due to interference from an unsuppressed motor getting into the driver and input wiring."
And:
"The capacitor shunts (or "absorbs") the high frequency spikes from the commutation and prevents damage to the driver chips.
A further factor not clear from the schematic is that snubber diodes should be used to prevent inductive kick-back from the motor's inductance causing damage to the driver's output transistors. While the diodes protect the driver, the capacitors take the "edges" off the current spikes and help reduce EMI, etc."