eBay Mini-vacuum Pump

Quick version: Hey this little thing works and seems practical for robotics, specifically the Pop Can Challenge.

I had to add “mini” to the title of this post, calling this a vacuum pump seems odd when you’ve played around with big pumps. Which leads me to make a mental note to share some information my industrial vacuum pump sometime; my big pump is currently at the SnoCo Makerspace but it seems it gets used as hold-down weight on glue-ups more than it’s intended use but at least it’s getting some love.

I moved workshops; I swear this is related… The kids are at an age were it’s hard for me to get out to my workshop for very long and Melissa works in the evenings right now so I just wasn’t getting any fun-stuff done. I’ll shoot another workshop video… soon-ish. I’ve been slowly filtering through my bins of incomplete or never-started projects in and sorting through it all to bring some organization into my “inside workshop”. In digging through the bins I recently came across most of this eBay purchase: https://ebay.us/2L8SOa . If you want to skip on clicking the link it’s a small motor/vacuum pump with a suction cup grabber. I bought this for PopBot after the 2019 Robothon. I put this aside because I’ve been working on PopBot and a second marine-based robot platform for the last two months. PopBot is getting a deep drive because the SRS Robothon (2020) https://robothon.org/ has been cancelled this year. The thought is I might be able to grab the PopCan with a suction cup instead of actively grabbing it, or in my case I was going to sort hug it/lasso the pop can; time will tell on this. My initial concern is current draw, thankfully thing only pulls a couple hundred milliamps and then it’ll hold it’s suction fairly well for a while. I noticed a solid drop off in current after the suction was “successful”. I would have thought it opposite but I guess based on looking at current curves on squirrel cage fans and seeing them unload without air flow I’ll accept it without figuring out why. My goal is to grab the can with a pair of suction cups, drop the motor PWM or turn it off once the suction is maintained (as determined by current) and then just provide a couple moments of pumping to maintain suction while transporting the can. For testing I came up with a quick little circuit with a Pololu DC motor driver (#2961) and an Adafruit i2c IN219 current sensor breakout board… don’t mind all the other stuff strapped to the MEGA in the photo below. It was on my bench for some sensor fusion testing. The INA219 is hooked up to the i2c ports (20/21) on the MEGA2560 and the motor driver is getting a PWM drive from Pin 6. I didn’t need to use the enable or direction, I just sunk the enable low. The amount of suction is quite adequate if you’re a 14 year old boy trying to get popular by giving yourself a hickey…. this is not recommended of course and mostly a guess as I have 4-day-old vacation stubble so there is no sense in trying.

The code for testing is at the end of the post, anyone with a couple hours of experience with Arduino IDE could whip this out in 10 minutes but just in case you were hoping to save 9-1/2 minutes…

/*  @chasihler iradan.com
 * 
 * 0.1 2020/08/20 Test
 * 
 * INA219 test w/ Vacuum Pump
 * Most of this is from the adafruit library example. 
 * 
 */


#include <Wire.h>
#include <Adafruit_INA219.h>

Adafruit_INA219 ina219;

int motor_pwm_pin = 6;
int motor_enable_pin = 7;

int int_stop = 0;
int int_lowSpeed = 950;
int int_highSpeed = 1023;

void setup() {
  Serial.begin(115200);
    
  pinMode(motor_pwm_pin, OUTPUT);
  pinMode(motor_enable_pin, OUTPUT);

    if (! ina219.begin()) {
      Serial.println("Failed to find INA219 chip");
        while (1) { delay(10); }
    }
      //ina219.setCalibration_32V_1A();
      //ina219.setCalibration_16V_400mA();
}

void loop()  {
  float shuntvoltage = 0;
  float busvoltage = 0;
  float current_mA = 0;
  float loadvoltage = 0;
  float power_mW = 0;
  Serial.println("No Load Test");
  Serial.print("Bus Voltage:   "); Serial.print(busvoltage); Serial.println(" V");
  Serial.print("Shunt Voltage: "); Serial.print(shuntvoltage); Serial.println(" mV");
  Serial.print("Load Voltage:  "); Serial.print(loadvoltage); Serial.println(" V");
  Serial.print("Current:       "); Serial.print(current_mA); Serial.println(" mA");
  Serial.print("Power:         "); Serial.print(power_mW); Serial.println(" mW");
  Serial.println("");
  
  analogWrite(motor_pwm_pin, int_lowSpeed);
  delay(1000);

  shuntvoltage = ina219.getShuntVoltage_mV();
  busvoltage = ina219.getBusVoltage_V();
  current_mA = ina219.getCurrent_mA();
  power_mW = ina219.getPower_mW();
  loadvoltage = busvoltage + (shuntvoltage / 1000);

  Serial.println("Low Speed Test");
  Serial.print("Bus Voltage:   "); Serial.print(busvoltage); Serial.println(" V");
  Serial.print("Shunt Voltage: "); Serial.print(shuntvoltage); Serial.println(" mV");
  Serial.print("Load Voltage:  "); Serial.print(loadvoltage); Serial.println(" V");
  Serial.print("Current:       "); Serial.print(current_mA); Serial.println(" mA");
  Serial.print("Power:         "); Serial.print(power_mW); Serial.println(" mW");
  Serial.println("");
    
  delay(1000);
  analogWrite(motor_pwm_pin, int_stop);  //stop
  delay(5000);
  analogWrite(motor_pwm_pin, int_highSpeed);
  delay(1000);

  shuntvoltage = ina219.getShuntVoltage_mV();
  busvoltage = ina219.getBusVoltage_V();
  current_mA = ina219.getCurrent_mA();
  power_mW = ina219.getPower_mW();
  loadvoltage = busvoltage + (shuntvoltage / 1000);
  
  Serial.println("Full Speed Test");
  Serial.print("Bus Voltage:   "); Serial.print(busvoltage); Serial.println(" V");
  Serial.print("Shunt Voltage: "); Serial.print(shuntvoltage); Serial.println(" mV");
  Serial.print("Load Voltage:  "); Serial.print(loadvoltage); Serial.println(" V");
  Serial.print("Current:       "); Serial.print(current_mA); Serial.println(" mA");
  Serial.print("Power:         "); Serial.print(power_mW); Serial.println(" mW");
  Serial.println(""); 
     
  delay(2000);
  analogWrite(motor_pwm_pin, int_stop);  //stop
  delay(10000);
}

Programming ESC with Arduino

The story: I hit a break wall with ODrive. ODrive is an open source brushless DC motor (BLDC) driver built with robotics in mind (my application..). I don’t have faith in the project and after months of trying to make it fit my application I’m abandoning it. It’s painful to spend that kind of money on a product (two even!) … but I’m not hopping back on the Stepper bandwagon just yet. I’ll see if I can put my brushless DC motors to use on PopBot 0.5.

First step was deciding on if I could use an off the shelf ESC or buy one. I purchased a RC “rockcrawler” driver as I assumed the firmware would be most compatible with my application. The car and boat ESCs have forward and reverse speed by splitting the PWM servo input in half. While waiting on shipping I found an ESC for a boat and a few for quads in one robot junk bins. Quads are single directions but the boat one was good enough for testing. It had no torque in the low end but that’s not a surprise based on the application with the motor type. I needed a way to program this ESC without a controller and receiver. Programming is typically performed w/ the receiver/controller by pushing the speed to min-max in a certain order. Well that can be done with the arduino of course. Here is a super simple piece of code for you if you don’t want to reinvent the wheel. This will also allow you to control your ESC once it’s programmed and you can uncomment my basic acceleration code if desired.

Hook up the ESC control signals (servo input). On the ESC the white (signal in, sometimes I think the alternate color is orange?) to digital output 9 on the Arduino Uno or Mega. Tie the black (or brown) wire to one of the grounds. DO NOT HOOK UP RED. We don’t need the power from the ESC.. it’s usually not something we want anyways (like 6V… ).

You’ll need this library. Download it and place the uncompressed directory in your Arduino libraries directory.

https://github.com/maxpowel/ESC

/*
 * Charles Ihler, iradan.com
 * 2020-04-27 build from example of library. 
 * 
 * Open the serial monitor... enter 0 (and enter) for reverse
 * 1 for foward and 2 for idle/stop.. 
 * Most ESCs want a motor hooked up or warn of damage.. make sure the motor is safe and can't spin off and hurt something. 
 * 
 */

#include <Servo.h>
#include "ESC.h"



ESC esc(ESC::MODE_FORWARD_BACKWARD);


int sel = 0;
String ssel;

void setup() 
{
  Serial.begin(115200);  
  pinMode(LED_BUILTIN, OUTPUT);
  esc.attach(9); //change to some other PWM pin if required

} 

void output_high() {
   digitalWrite(LED_BUILTIN, HIGH);
   esc.setDirection(ESC::FORWARD);
   esc.setSpeed(500);   //comment this out and uncomment below for acceleration. When test running motor.
   //for (int i = 0; i <= 150; i++) {
   //   esc.setSpeed(i);
   //delay(25);
   //}
}
void output_low() {
  digitalWrite(LED_BUILTIN, LOW);
  esc.setDirection(ESC::BACKWARD);
  esc.setSpeed(500);   //comment this out and uncomment below for acceleration. When test running motor.
  //  for (int i = 0; i <= 150; i++) {
  //    esc.setSpeed(i);
  //  delay(25);
  //}
}
void output_n() {
  digitalWrite(LED_BUILTIN, LOW);
  esc.setDirection(ESC::BACKWARD);
  esc.setSpeed(0);
}
void loop() 
{
    Serial.print("Forward (1), Reverse (0), Stop/N(2)?(1/0/2): "); 
    while (Serial.available() == 0) {}  
    ssel = Serial.readString();  
    Serial.print(" --> ");
    Serial.println(ssel);
    sel = ssel.toInt();
    if (sel == 1) {
      output_high();
      Serial.println("ON!");
    }
    if (sel == 0) {
      output_low();
      Serial.println("OFF.");
    }
    if (sel == 2) {
      output_n();
      Serial.println("Neutral");
    }
  delay(100);

} 
The setup project with motor removed.

Enjoy…

Project: MOSFET Driver v1 (Product?)

Today I received the first of a couple batches of PCBs from OSH Park. This set is a simple MOSFET w/ driver. The MOSFET can be logic level driven and all my testing was done at 5VDC however the driver had a wide voltage range so running this at 9V or 12V should present no issues (16V max! VGS). I do have a few minor adjustments I want to add (silk screen additions and adjustments). I built this board as an electric scooter motor drive and I tested it with the motor I was interested in using and thankfully all testing worked out well including loading my power supply at max load for over an hour straight 🙂 This board can be used for an assortment of load control applications.

MOSFET Driver v1

The build was easy enough, next board I think I’ll just skip the chipquik and stick to straight soldering iron… and I think I also “figured out” the trick to solder the heat sink without making too much of a mess.

MOSFET Driver v1

I tested the load for 60 minutes at 66% duty cycle and 1.5KHz PWM with total load at 140watts (45Volts 3.1 Amps)..  the heat sink temperature on the MOSFET raised from ambient (78 deg F) to 90.7 deg F (32.3 deg C) steady for an hour.  The MOSFET is rated for 55V (max) at 30 amps but the board isn’t designed to handle that load. I used 50mil power traces which is roughly 3 amp handling according to the google machine; 5A if you don’t mind a 40 deg C rise (though there is a fan) so I’ll call this a 140W MOSFET board (47×3). I personally feel I could squeeze more current out of this in short bursts but I would need to do more testing.. and I can’t promise anything along those lines. The PWM signal was generated and directly fed from a PIC 18F16K22 microcontroller running @ 5V. You’re NOT going to be able to drive this at 3.3V.

 

Fresh off the soldering iron!
Fresh off the soldering iron!

Driving an electric scooter motor. Note the diode for flyback near the bottom of the photo just hanging out. The flyback is a must in this application.
Driving an electric scooter motor. Note the diode for flyback near the bottom of the photo just hanging out. The flyback diode is a must in this application.

MOSFET PWM signal vs VDSS
MOSFET PWM signal vs VDSS

 

I will likely stick a 75VDSS MOSFET in the next revision…

.. I’m considering selling these on Tindie. If you’re interested in getting on of these “BETA” boards at cost let me know before they’re gone.

PIC 18F26K22 PWM+A/D with MOSFET, the start of an eScooter?

I’m considering building an electric scooter; considering it probably putting it lightly.. I have almost everything I need for it.  Interested? Why type so much when you can just watch my proof of concept!

If you’re following along and want to use the same hardware (warning totally untested… ):
Controller found on the TAUTC Tindie Store
Search on eBay for “24VDC scooter motor” ..
..and pick up a MOSFET that’ll pull off a couple 20 amps and saturates at or below 5VDC.
…what am I talking about? Try google or read this.

To the important stuff, the code:


/* 
 * File:   main.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com
 *
 * Created on March 27, 2014, 4:12 PM
 *
 * Target Device:
 * 18F26K22 on TAUTIC Dev Board
 *
 * Project:
 * Electric Scooter
 *.. a real hack job, comment, delete garbage, etc.
 *
 * Version:
 * 0.1
 *
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include 
#include 
#include 
#include 

//config bits
#pragma config FOSC=INTIO67, WDTEN=OFF, PWRTEN=OFF, CP0=OFF, CP1=OFF, BOREN=ON
#pragma config STVREN=ON, LVP=OFF, HFOFST=OFF, IESO=OFF, FCMEN=OFF

//WRT=OFF, FOSC=INTOSC, MCLRE=ON

#define _XTAL_FREQ 4000000 //defined for delay

//clean up on isle 2.. 

    int     an9_value;          //value for a/d
    char    buf[10];            //buff for iota
    long int    fvar;           //long for format math
    long int    tens;           //left of decm
    long int    decm;           //decimal places
    int     tempi;              //to add leadign zeros..
    int     vtxdata;             //volts int for TX
    int     itxdata;

    volatile unsigned int uart_data;    // use 'volatile' qualifer as this is changed in ISR
/*
 * 
 */
void interrupt ISR() {

    if (PIR1bits.RCIF)          // see if interrupt caused by incoming data
    {
        uart_data = RCREG;     // read the incoming data
        PIR1bits.RCIF = 0;      // clear interrupt flag
    }

}

void init_io(void) {
    TRISAbits.TRISA0 = 0; // output
    TRISAbits.TRISA1 = 0; // output
    TRISAbits.TRISA2 = 0; // output
    TRISAbits.TRISA3 = 0; // output
    TRISAbits.TRISA4 = 0; // output
    TRISAbits.TRISA5 = 0; // output
    TRISAbits.TRISA6 = 0; // output
    TRISAbits.TRISA7 = 0; // output

    ANSELA = 0x00; // all port A pins are digital I/O

    TRISBbits.TRISB3 = 1; // AN9
    TRISBbits.TRISB4 = 0; // RB4 = nc
    TRISBbits.TRISB5 = 1; // RB5 = nc
    TRISBbits.TRISB6 = 0; // RB6 = nc
    TRISBbits.TRISB7 = 0; // RB7 = nc

    ANSELB = 0b00001000;     //RB3, AN9

    TRISCbits.TRISC0 = 0; // output
    TRISCbits.TRISC1 = 0; // output
    TRISCbits.TRISC2 = 0; // output
    TRISCbits.TRISC3 = 0; // output
    TRISCbits.TRISC4 = 0; // output
    TRISCbits.TRISC5 = 0; // output
    TRISCbits.TRISC6 = 1; // input
    TRISCbits.TRISC7 = 1; // input
    ANSELC = 0x00; // all port C pins are digital I/O
}

void pwm_init(){

//         PSTR1CONbits.STR1A
//hackhackhackhack... TODO

//    CCPR1L = 0x120;
    CCPR1Lbits.CCPR1L = 0xFE;
    PR2 = 0xFE;
    CCPTMRS0bits.C1TSEL = 0;     //CCP TMR2 Selection
    CCP1CONbits.P1M = 0x00;
    CCP1CONbits.DC1B = 0x00;
    PWM1CONbits.P1RSEN = 0;
    T2CONbits.T2CKPS = 1;  //1:2 Prescale
    T2CONbits.TMR2ON = 1;  //timer 2 go

    CCP1CON = 0x0C;       //PWM (CCP)1 ON

}

void uart_xmit(unsigned int mydata_byte) {

    while(!TXSTA1bits.TRMT);    // make sure buffer full bit is high before transmitting
    TXREG = mydata_byte;       // transmit data
}

void serial_init(void)
{
    //9600 8N1
    // calculate values of SPBRGL and SPBRGH based on the desired baud rate
    //
    // For 8 bit Async mode with BRGH=0: Desired Baud rate = Fosc/64([SPBRGH:SPBRGL]+1)
    // For 8 bit Async mode with BRGH=1: Desired Baud rate = Fosc/16([SPBRGH:SPBRGL]+1)

    TXSTA1bits.BRGH=1;       // select low speed Baud Rate (see baud rate calcs below)
    TXSTA1bits.TX9=0;        // select 8 data bits
    TXSTA1bits.TXEN = 1;     // enable transmit

    RCSTA1bits.SPEN=1;       // serial port is enabled
    RCSTA1bits.RX9=0;        // select 8 data bits
    RCSTA1bits.CREN=1;       // receive enabled

    SPBRG1=25;  // here is calculated value of SPBRGH and SPBRGL
    SPBRGH1=0;

    PIR1bits.RCIF=0;        // make sure receive interrupt flag is clear
    PIE1bits.RCIE=1;        // enable UART Receive interrupt
    INTCONbits.PEIE = 1;    // Enable peripheral interrupt
    INTCONbits.GIE = 1;     // enable global interrupt

         __delay_ms(50);        // give time for voltage levels on board to settle

    uart_xmit('R');         // transmit some data "restart" notification
}

int main(void) {

    init_io();
    serial_init();
    LATCbits.LATC2 = 0;
    pwm_init();

    // set up oscillator control register, using internal OSC at 4MHz.
    OSCCONbits.IRCF = 0x05; //set OSCCON IRCF bits to select OSC frequency 4MHz
    OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block

    ADCON0 = 0b00100101;                            //select AN9 and enable
    ADCON1 = 0b00000000;                  //speed Vref=AVdd, VssRef=AVss
    ADCON2 = 0b00111011;                //ledft justified, 20RAD, FRC
    __delay_us(5);

//loop

    while (1) {

        PORTAbits.RA0 = 1; //blinky i'm alive.
        __delay_ms(140);
        PORTAbits.RA0 = 0;
        __delay_ms(140);

            GO = 1;
    while (GO) continue;              //wait for conversion
    an9_value = ADRESH;               //AN9 value

        fvar = an9_value; //this is hacked off another project but works
        fvar = fvar * 10749;        //calibration
        fvar = fvar / 256;
        tens = fvar / 100;
        //tens = tens % 10;
        decm = fvar % 100;
        vtxdata = fvar / 43; //because I'm lazy... I'll change this later.
        uart_xmit(vtxdata);
        CCPR1Lbits.CCPR1L = vtxdata;

    }
    return (EXIT_SUCCESS);
}

%d bloggers like this: