My code for this newton's cradle isn't working. How do I fix this?

PVector start1;
PVector end1;
PVector start2;
PVector end2;
float e = 0; //angle
float l = 350; //length
float add = 0.05;//add(to angle)
float e2 = 0;//other angle
float add2 = 0; //add to second angle

void setup() { //setup the canvas

    size(1600, 1000);
    smooth();
    strokeWeight(10);
    start1=new PVector(950,300);
    end1=new PVector();
    start2=new PVector(650,300);
    end2=new PVector();
}

void draw() {
    background(0);

    stroke(57,255,20);
    fill(57,255,20);
    ellipse(850,650,100,100);
    ellipse(750,650,100,100);
    line(750,300,750,600);
    line(850,300,850,600);

    end1.x=start1.x+l*sin(e);
    end1.y=start1.y+l*cos(e);
    end2.x=start2.x+l*sin(e2);
    end2.y=start2.y+l*cos(e2);

    ellipse(end1.x,end1.y,100,100);
    ellipse(end2.x,end2.y,100,100);
    line(start1.x,start1.y,end1.x,end1.y);
    line(start2.x,start2.y,end2.x,end2.y);

    e+=add;
    e2-=add2;
    if(e<0){
        add=0;
        add2=0.05;
    }

    if(e>1){
        add*=-1;
    }
    if(e2<-1){
    }
}

I know that the problem is within the last few lines but I don't know how to get around the problem. The problem is that each time e2 gets to negative, specifically less than -1, the code says that now add2 must multiply by -1 to go the other way. But, as soon as it is more than -1, the code is also telling it that when e is less than 0(which it is), add2=0.05. So what's happening is that it is fluctuating between >-1 and <-1. How do I get around this problem? P.S. This explanation is only what I think the problem is but it could be completely different.