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MicroBot

Brandon King| Summer, 2022

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Thesis

The goal with Microbot was to design a small 6DOF robot arm, while retaining the ability to pickup >200g payload. I was a broke college student at the time, so the smaller joint lengths meant less money spent on motors.

I started the napkin sketch phase as I always do:

1. Patent Research
2. Open source docs
3. Technical Papers

After some quick calculations arm length and torque calcs, I landed on this design footprint which was 300mm x 300mm:

Early CAD model

Design Process

I believe design and hardware iteration should be intertwined. Often these two are seperated which leads to a delayed feedback loops

For about a month I spent my nights testing and iterating on each joint. This process includes tolerances, ease of assembly, wiring configurations, etc.

Full Assembly

Initial testing

Once each joint had been redesigned a few times, I landed on a aesthetic/function that I was happy with. Initial testing of the assembled arm included: testing motors/electronics, stopless homing, etc.

Axis Homing

Homing Code

delay(10000);
digitalWrite(EN321_PIN, LOW);
digitalWrite(EN4_PIN, LOW);
digitalWrite(EN5_PIN, LOW);
digitalWrite(EN6_PIN, LOW);
delay(1000);
// go to the home position (all joints equal to 0)
// joint #2
digitalWrite(DIR2_PIN, HIGH);
int delValue=4000;
int incValue = 7;
int accRate=530;
int totSteps=2791*2;
for (int i=0; i < totSteps; i++)
{
 if (totSteps > (2*accRate + 1)){
    if (i < accRate){
      //acceleration
      delValue = delValue - incValue;
    } else if (i > (totSteps - accRate)){
      //decceleration
      delValue = delValue + incValue;
    }
  } else {
    //no space for proper acceleration/decceleration
    if (i < ((totSteps - (totSteps % 2))/2)){
      //acceleration
      delValue = delValue - incValue;
    } else if (i > ((totSteps + (totSteps % 2))/2)){
      //decceleration
      delValue = delValue + incValue;
    }
  }
  digitalWrite(PUL2_PIN, HIGH);
  delayMicroseconds(delValue);
  digitalWrite(PUL2_PIN, LOW);
  delayMicroseconds(delValue);
}
// joint #3
digitalWrite(DIR3_PIN, HIGH);
delValue=4000;
incValue=7;
accRate=530;
totSteps=6569;
for (int i=0; i < totSteps; i++)
{
 if (totSteps > (2*accRate + 1)){
    if (i < accRate){
      //acceleration
      delValue = delValue - incValue;
    } else if (i > (totSteps - accRate)){
      //decceleration
      delValue = delValue + incValue;
    }
  } else {
    //no space for proper acceleration/decceleration
    if (i < ((totSteps - (totSteps % 2))/2)){
      //acceleration
      delValue = delValue - incValue;
    } else if (i > ((totSteps + (totSteps % 2))/2)){
      //decceleration
      delValue = delValue + incValue;
    }
  }
  digitalWrite(PUL3_PIN, HIGH);
  delayMicroseconds(delValue);
  digitalWrite(PUL3_PIN, LOW);
  delayMicroseconds(delValue);
}
// joint #5
digitalWrite(DIR5_PIN, HIGH);
delValue=4000;
incValue=7;
accRate=530;
totSteps=90/dl5;
for (int i=0; i < totSteps; i++)
{
 if (totSteps > (2*accRate + 1)){
    if (i < accRate){
      //acceleration
      delValue = delValue - incValue;
    } else if (i > (totSteps - accRate)){
      //decceleration
      delValue = delValue + incValue;
    }
  } else {
    //no space for proper acceleration/decceleration
    if (i < ((totSteps - (totSteps % 2))/2)){
      //acceleration
      delValue = delValue - incValue;
    } else if (i > ((totSteps + (totSteps % 2))/2)){
      //decceleration
      delValue = delValue + incValue;
    }
  }
  digitalWrite(PUL5_PIN, HIGH);
  delayMicroseconds(delValue);
  digitalWrite(PUL5_PIN, LOW);
  delayMicroseconds(delValue);
}

//--------------------------------------------------------GoGoGo-------------------
curPos1=0.0;
curPos2=0.0;
curPos3=0.0;
curPos4=0.0;
curPos5=90.0;
curPos6=0.0;
float Xhome[6]={164.5, 0.0, 241.0, 90.0, 180.0, -90.0}; //{x, y, z, ZYZ Euler angles}

float X1[6]={164.5, 0.0, 141.0, 90.0, 180.0, -90.0};
float X11[6]={164.5+14.7, 35.4, 141.0, 90.0, 180.0, -90.0};
float X12[6]={164.5+50.0, 50.0, 141.0, 90.0, 180.0, -90.0};
float X13[6]={164.5+85.3, 35.4, 141.0, 90.0, 180.0, -90.0};
float X14[6]={164.5+100.0, 0.0, 141.0, 90.0, 180.0, -90.0};
float X15[6]={164.5+85.3, -35.4, 141.0, 90.0, 180.0, -90.0};
float X16[6]={164.5+50.0, -50.0, 141.0, 90.0, 180.0, -90.0};
float X17[6]={164.5+14.7, -35.4, 141.0, 90.0, 180.0, -90.0};

float X18[6]={164.5+50.0, 0.0, 141.0, 90.0, 180.0, -90.0};

float X2[6]={264.5, 0.0, 141.0, 0.0, 90.0, 0.0};
float X3[6]={164.5, 100.0, 141.0, 90.0, 90.0, 0.0};
float X4[6]={164.5, -100.0, 141.0, 90.0, -90.0, 0.0};

float Jhome[6], J1[6], J11[6], J12[6], J13[6], J14[6], J15[6], J16[6], J17[6], J18[6], J2[6], J3[6], J4[6];
InverseK(Xhome, Jhome);
InverseK(X1, J1);
InverseK(X11, J11);
InverseK(X12, J12);
InverseK(X13, J13);
InverseK(X14, J14);
InverseK(X15, J15);
InverseK(X16, J16);
InverseK(X17, J17);
InverseK(X18, J18);
InverseK(X2, J2);
InverseK(X3, J3);
InverseK(X4, J4);

Future Plans

I am now working on neural network pick and place using a low res camera on Joint 6.

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