Robot Platform including h-bridges from $10 R/C Car

Step 4 Test the PCB and add on your controller

Note - There is a small chance the PCB in other Tumblers has different pinouts, so you will want to check yours to see.   These boards where made for the absolute cheapest they could be that day, and other days might have had something else be cheaper.  Then again, the pin configuration is based on the integrated circuit, which probably doesn't change on a day to day basis.  So this should be close. :)

After looking at the PCB and doing some testing, I found out the following pin info:

pin 2 - ground
pin 6,7 - controls the left motor h-bridge
pin 10,11 - controls the right motor h-bridge
pin 13 - Vcc output from the battery.

I'm assuming the other pins are housekeeping and getting the input from the receiver components.  While having a wireless input into the PCB might be handy for something in the future, right now I'm interested in the h-bridges and how you control them.


The h-bridge for each side is made of 4 power transistors and 2 regular transistors.  On my PCB, the power transistors where a pair of H8050 and H8550, controlled by a couple of regular transistors, C945s.  All are in the TO-92 physical package.  I suspect that other transistors might be used on other PCBs, it was a matter of who had what in stock at a cheap price that day.    I found some datasheets for the H8050 and H8550 and it looks like each h-bridge is rated to 1.5 Amps.    Again, there might be different components on other PCBs on other Tumblers, but the basic 1.5A rating should stay the same.

For each h-bridge, there is a pair of pins that controls it.  Pins #6 and #7 for the left side, and #10 and #11 for the right side.


Left Wheel:

Pin 6: OFF, Pin 7: OFF - nothing, no movement
PIN 6: ON, Pin 7: OFF - wheel rotates - forward direction
PIN 6: OFF, Pin 7: ON - wheel rotates - reverse direction
PIN 6: ON, Pin 7: ON - untested, suspect this might fry something in a puff of smoke. 

Right Wheel:

Pin 10: OFF, Pin 11: OFF - nothing, no movement
PIN 10: ON, Pin 11: OFF - wheel rotates - reverse direction
PIN 10: OFF, Pin 11: ON - wheel rotates - forward direction
PIN 10: ON, Pin 11: ON - untested, suspect this might fry something in a puff of smoke. 

For the pins on the "OFF" position, N/C or ground both seem to work.  On general principle I suggest sticking to ground and not N/C.


What does this all mean?

To drive a particular side of the robot, you need two digital outputs, hopefully PWM capable.  For both sides it takes four outputs.  For instance, if I wanted to go forward at 40% max speed I would set my pins like this:

pin 6:   PWM signal at 40%
pin 7:   ground (PWM 0%)
pin 10:  ground (PWM 0%)
pin 11:  PWM signal at 40%

I've been using the standard Arduino PWM frequency of around 500Hz and that works for switching the h-bridges off and on just fine.  I would not be surprised if the components handled up to the 20KHz range.

When hooking up your microcontroller and using a different battery for the data signals (like the 9V I used), don't forget to "share a ground" wire between the two.  If you look at my pictures, that is why I have a wire from the #2 pin on the IC Socket into the ground plane of my breadboard.

So for my test setup, I used the Arduino PWM signals:

Arduino : Tumbler
pin 9 ---- pin 6
pin 10 --- pin 7

pin 3 ---- pin 11
pin 11 --- pin 10

Here is some hardwired, ugly test code.  However, it does work and proves the general idea.  It is a loop that goes like this:

start loop
drive forward at 50% power for 2 seconds
wait 2 seconds
drive in reverse at 50% power for 2 seconds
wait 2 seconds
loop to top

It's showing me that this is not the most precise motor/wheel alignment I've seen, but it does work.  I'll work on better wheel control code over time - need to get the laser rangefinder working first!


// Tumbler1
// by Ray Alderman
//
//  Connections to the Tumber PCB
//
//  Arduino : Tumbler
//  pin 9 ---- pin 6
//  pin 10 --- pin 7
//  pin 3 ---- pin 11
//  pin 11 --- pin 10
//  ground --- pin 2 (ground)
//
//

                         
int RightFwd = 3;       // PWM Output to go Foward on Right Wheel
int RightRev = 11;    // PWM Output to go Reverse on Right Wheel
int LeftFwd = 9;    // PWM Output to go Forward on Left Wheel
int LeftRev = 10;    // PWM Output to go Reverse on Left Wheel

int delaytime = 2000;    // delay between steps
int speedval = 127;    // speed forward and reverse, at 50% (of 255 max)



void setup()
{

 pinMode(RightFwd, OUTPUT);
 digitalWrite(RightFwd, LOW);    // Make sure Output is initally at LOW
 pinMode(RightRev, OUTPUT);
 digitalWrite(RightRev, LOW);    // Make sure Output is initally at LOW
 pinMode(LeftFwd, OUTPUT);
 digitalWrite(LeftFwd, LOW);    // Make sure Output is initally at LOW
 pinMode(LeftRev, OUTPUT);
 digitalWrite(LeftRev, LOW);    // Make sure Output is initally at LOW

 delay(delaytime);

}

void loop()
{

   

    analogWrite(LeftRev, 0);
    analogWrite(LeftFwd, speedval);        // turns on the left wheel in forward direction at the speed value
    analogWrite(RightRev, 0);
    analogWrite(RightFwd, speedval);    // turns on the right wheel in forward direction at the speed value
   
    delay(delaytime);
    
    analogWrite(LeftFwd, 0);        // turns off the left wheel
    analogWrite(RightFwd, 0);        // turns off the right wheel

    delay(delaytime);
    
    analogWrite(LeftRev, speedval);        // turns on the left wheel in reverse direction at the speed value
    analogWrite(RightRev, speedval);    // turns on the right wheel in reverse direction at the speed value

    delay(delaytime);

}

Comments

[needlenoodles]

Cool!  Very detailed Instructable.  :)