DC Motor Pump Guide¶
One option for creating self-contained or wearable pneumatic systems is to use small pumps driven by battery-powered DC motors to inflate and deflate small pneumatic actuators. The fill rates are relatively slow, but the total volume is only bounded by time.
Following are notes on the pump mechanical and circuit considerations. For sample code, please see Motor Pump Examples - Adafruit Circuit Playground Bluefruit.
Contents
Adafruit 2.5 LPM Pump¶
One option for operating wearable inflatables is the Adafruit 2.5 LPM Air Pump.
We tested the motor using a four-cell NiMH battery pack measured at 5.1V and observed a motor current draw of 350 mA with no load, climbing to 500 mA with the output capped (max load). This magnitude of current requires a motor driver circuit to control the motor from a microcontroller. Pulse-width modulation at 20 kHz was effective at controlling motor speed over a range from 100% to around 75% duty cycle, at which point the motor stalled.
The output port is a cylindrical tube extending axially from the end. The input port on the side includes a cylindrical base which is wider than the tube extending from it.
The motor leads are copper tabs extending from the base. We recommend soldering permanent wires to these tabs and using tape or a wire tie to secure the wires to the motor body to relieve strain on these tabs. Otherwise these types of tabs tend to break off from the repeated strain of alligator clips or long unconstrained wires.
Dimension |
Value |
---|---|
output port external diameter |
4.3 mm |
output port length |
5.6 mm |
input port external diameter |
4.3 mm |
input port length |
6.5 mm |
input port base diameter |
5.8 mm |
input port base length |
2.7 mm |
Motor Driver Circuit: MOSFET¶
The left image shows a MOSFET power transistor in a TO-220 package. Please note the pin layout: as viewed, the gate input is on the left, the positive drain terminal is in the center, and the negative source terminal is on the right.
The center image shows a sample breadboard implementation of the MOSFET driver. The recommended resistors and diode are omitted. The blue wire carries the PWM signal from the microcontroller to the left ‘gate’ terminal. The yellow motor wires connect between the center ‘drain’ terminal and the red battery lead. The black wires from the microcontroller and battery connect to the right ‘source’ terminal.
The right image shows a sample physical breadboard implementation.