Category: Motors

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);
}