In Which Jarrett Builds

I’ve opened up two sacrificial motors, and they definitely seem to have some sort of on-board Hall effect sensors. I haven’t looked for the pinout yet, but chips were all labelled 1036 for one of the motors, and J588m for the other one. Google turns up nothing about these (that I can find).

The motor connector has eight pins, three of which are used up by the motor windings A, B, and C. That means two of the remaining pins are probably VCC and GND. The last three pins must be the Hall sensor outputs.

Currently, I’ve only got the motor running in open loop. That results in a working, but pretty crappy rotation. When I have some time, I’ll grab the feedback, and close the motor loop. Here’s the PIC code I have right now:

#include <htc.h>

//Int osc, wdt, mclr disabled, bor, fscm
__CONFIG(0x3BD4);

#ifndef _XTAL_FREQ
 #define _XTAL_FREQ 4000000
#endif

//Pres butan
#define PITCHFW    RA4
#define PITCHRV    RA3

#define YAWFW    RA2
#define YAWRV    RA5
//Outputs

//Motor variables (RC0, RC1, ETC)
#define PITCHA    0
#define PITCHB    1
#define PITCHC    2

#define FLOATA    3
#define FLOATB    4
#define FLOATC    5

//String constants
#define PITCHMOTOR    1
#define YAWMOTOR    0

//AC', AB', B'C, A'C, A'B, BC'
#define FORWARD        0
//BC', A'B, A'C, B'C, AB', AC'
#define REVERSE        1

unsigned char iPortCValue, iPitchStep, iYawStep;

void set_bit(unsigned char iAddress, unsigned char bBit) {
    iPortCValue |= (1<<bBit);
    PORTC = iPortCValue;
}    

void clear_bit(unsigned char iAddress, unsigned char bBit) {
    iPortCValue &= ~(1<<bBit);
    PORTC = iPortCValue;
}    

void delay_motor(void) {
    unsigned char i, e;
    for (e = 0; e < 6; e++) {
        for(i = 0; i < 170; i++) {
            asm (" nop ");
            //__delay_ms(1);
        }
            CLRWDT();
    }
}

void move(unsigned char iDirection) {

    delay_motor();

    //AC', AB', B'C, A'C, A'B, BC'
    switch (iPitchStep % 6) {
        case 0:        //AC'    AB'C'    
            PORTC = 0x29;
            break;
        case 1:        //AB'    AB'C    
            PORTC = 0x19;
            break;
        case 2:        //B'C    A'B'C    
            PORTC = 0x34;
            break;
        case 3:        //A'C    A'BC    
            PORTC = 0x2C;
            break;
        case 4:        //A'B    A'BC'    
            PORTC = 0x1A;
            break;
        case 5:        //BC'    ABC'    
            PORTC = 0x02;
            break;

    }
    if(iDirection == 1) {
        iPitchStep++;
    } else {
        iPitchStep--;
    }        
}    

void main(void){
    OSCCON = 0xF1;    //Internal osc
    TRISC = 0x00;    //Port C Tris output
    TRISA = 0xFF;    //Port A Tris input    
    iPortCValue = 0;
    iPitchStep = 0;
    iYawStep = 0;
    int i = 0;

    while(1){

        //if(RA2 == 1) {

            for (i = 0; i < 36; i++) {
                if(RA5 == 1) {
                    move(1);
                } else if (RA4 == 1) {
                    move(0);
                }
            }
            for (i = 0; i < 200; i++) {
                delay_motor();    
            }
        //}            

    }
}

At this stage in the game, this project is on a clear path to completion, with no major revisions in sight. What I’d like to do is identify some issues that have made themselves apparent during the build and tweaking processes. Some are things that I would fix in the version 2, if one were to exist. Some I need to fix right now.

This also marks the end of the “let’s build something cool!” phase and into the “ugh. WHY isn’t this working?” phase. It’s a lot harder to stay interested in finishing, but I’m going to power through.

Here’s where I’m at:

1. Limited rotation: any rotational movement that goes too far would tangle up cables that are driving the pitch gear motor. Everything in this system is designed to be battery-powered, so the obvious solution would be to mount the yaw motor on the rotating platform. That could mesh with an inside gear that’s been fixed to the base.
2. Non-prime gears: this is one of the topics that have come up while doing ongoing research for what constitutes a “good” mechanical design. Generally, teeth shouldn’t continually mesh with exactly the same tooth and the opposing gear. That’s a good way to cause excess wear through dirt or inconsistancies in the the teeth hitting the same spot every time. To make sure that doesn’t happen, you want the gears to be co-prime. Right now, my two gear sizes have 55 teeth, and 280 teeth. That’s no good. Fortunately, 281 is prime, so that neatly solves that problem. The pitch gear doesn’t ever rotate all the way through, so that doesn’t fix the issue for those mates, but there’s nothing I can do about it, so why worry?
3. Catching: the top gear(I’ve been calling it the pitch gear) catches up between the two gears providing support. When it gets caught, the gear likes to try and shove the rear support struts up and out of the base. This is the only problem(so far) that I haven’t foreseen. Fortunately, I was able to move that top support gear a little closer to the bottom portion using some holes that already existed. Anything less than 90 degrees seems to do the trick.
4. Squeezed bearings: I used some flat washers on either sides of the bearings, but that still caused too much friction for them to rotate properly. I need to find some smaller nylon washers, or maybe flanged bearings.
5. Wobbly base: the lower gear(I’ve been calling it the yaw gear) is mostly just sitting on a huge bolt that I had kicking around. I was hoping it would work, but no dice. It doesn’t quite. The gear wobbles around in relation to the base just enough to lose contact with the motor gear. When I can get some more laser cutting in, I’ll build another base with an additional cage around the bolt to provide more support.

Putting it all together.

The materials I used are a little more than the final product requires, some material was used up in mistakes or scrapped in newer revisions, but here is what I started with:

• 2′ x 3′ 3/8″ acrylic ($20)
• 6″ x 6″ 1/8″ acrylic ($10)
• 4x 3/8 bolts
• 4x 3/8 lock washers
• 8x 3/8 flat washers
• 4x 3/8 nuts
• 1x #6 machine screw
• 1x #6 lock washer
• 2x #6 nuts
• 1x 5/8 bolt
• 3x 5/8 nuts
• 1x 5/8 lock washer (about $4 for all)
• 1 cheap tripod for the head (can be replaced with 10mm bolts or threaded rod) ($3)
• 2x bearings (26mm OD, 10mm ID, 8mm width) ($6)
• 2x BLDC motors (I got these for free)