Issue 2 of 2016_06_11
Here is an outline schematic illustrating one approach for controlling your vibration motors. You would need three of these circuits to provide the capability of driving 3 x 16= 48 vibration motors which will meet your requirement for driving 40 vibration motors.
ERRATA
(1) Fit rectifier diode (to be defined) cathode to drain and anode to 0V for each PMOSFET (catching diode to catch voltage under swing caused by motor inductance when PMOSFET turns off).
NOTES
(1) The basis of the design is from ronsimpson's summary of the vibration motor current consumption: start current = 680mA, run current = 250mA.
(2) Two LiIon batteries, connected in series, and one PCA9685 chip
or module to drive 16 vibration motors via a PMOSFET for each motor.
(3) At a first approximation, the battery duration will be an hour with all sixteen motors running at full power.
(4) The capacitors play no part in the basic operation of the circuit, but are decouples to help eliminate frequency instability.
(5) The 10 Ohm resistor plays no part in the basic operation of the circuit but is a gate stopper to stop the PMOSFET from oscillating and to improve the gate drive. The 10 Ohm resistor should connect directly to the PMOSFET gate terminal.
(6) The batteries under consideration are:
(6.1) Panasonic, NCR18650GA, 3.4Ah, 10A max
(6.2) Samsung, INR18650-30Q, 3Ah, 15A max
(6.3) LG, INR18650-HG2, 3Ah, 20A max
(7) The Switch Mode Power Supply (SMPS) is as described in ronsimpson's post #10, or similar:
"DC-DC, 12A adjustable buck-board module"
(8) The non polarized capacitors are ceramic types with X7R dialectric
(9) C2, 2m2F (2200 uF), is an aluminum low-loss type.
(10) All capacitors are minimum values. Higher values will also be suitable.
(11) The PMOSFET under consideration is, ON, DMP4015SK3
(12) R8 (470 Ohms) speeds the PMOSFET turn-off, as the PCA9685 outputs have very low source current capability.
Data Sheets
(1) NXP PCA9685
(gives function of module)
**broken link removed**
(2) Panasonic, NCR18650GA, 3.4Ah, 10A max
https://www.nkon.nl/sk/k/ncr18650ga.pdf
(3) Samsung, INR18650-30Q, 3Ah, 15A max
https://www.nkon.nl/sk/k/30q.pdf
(4) LG, INR18650-HG2, 3Ah, 20A max
https://www.nkon.nl/sk/k/hg2.pdf
(5) PMOSFET ON, DMP4015SK3
**broken link removed**