Snubber

A comment was made about a capacitor seen across the inertia wheel motor in this post. Just so you know, that was for test purposes only; don’t go putting 100 nF across your 20 kHz MOS driver outputs!

The VHNH2SP30 driver can operate at a supply voltage of up to 16 V, though the maximum rating is 41 V. If 16 V is exceeded, the device shuts down which causes erratic behavior if ignored.

The Mabuchi RS-555PH motor I use has an armature resistance of about 1 R, so with an 11.1 V LiPo @ 0 RPM, that causes what would seem like a relatively large current for such a small ‘bot, but it’s needed for the torque. Anyhow, when the motor commutates, especially at low speeds, all the resulting stored energy gets dumped across an unloaded H-Bridge causing some large voltage transients that shut down the driver. There isn’t much voltage margin to play with so my solution was plonk a 15V TVS across the terminals.

An RC snubber compliments the TVS’s clamping ability by reducing the dV/dt. The resistor was selected to produce < 16V with maximum motor current. The capacitor was chosen quite conservatively to limit power wastage in the resistor to 1W @ 20 kHz. It should help to reduce noise that might interfere with the Bluetooth transceiver but I’ve not verified this.