RC Servo-13837.PNG

Good Morning,

I am wanting to try to control a hobby servo with the KFlop. Anyone ever tried this? They are run by a 50 Hz signal, and varying the pulse width between 1 to 2 ms.

I have been thinking of making a dedicated thread to do something like the code below. I am wondering if this would make a consistent 20 Hz square wave, with an accurate pulse time set by the variable "Position". Is there a better way of doing this?

main()

{

double Position;

SetBitDirection(1,1);

for (;;) // loop forever

{

SetBit(0); //Start Pulse

Delay_sec(Position/1000); //Time Pulse length 

ClearBit(0); //End pulse

Delay_sec((20-Position)/1000); //Keep 20 Hz frequency

}

Thanks,

Scott

Hi Scott,

The timing for Hobby Servos is difficult because of microsecond timing over long periods of time (20ms).  Hardware is basically too fast (KFLOP PWMS only slow down to 250HZ), and software doesn't have the precision (Time Slices basically only occur every 180us).

We came up with a method that enables and disables hardware PWMs in Software to create relatively accurate pulses at low rates.  The Example shows how to control 3 Hobby Servos but can be expanded for up to 7.  The Cyan and Purple plots below show two outputs.  See the article in the wiki here:

http://www.dynomotion.com/wiki/index.php?title=Driving_Hobby_Servos

 

Good Morning,

I am wanting to try to control a hobby servo with the KFlop. Anyone ever tried this? They are run by a 50 Hz signal, and varying the pulse width between 1 to 2 ms.

I have been thinking of making a dedicated thread to do something like the code below. I am wondering if this would make a consistent 20 Hz square wave, with an accurate pulse time set by the variable "Position". Is there a better way of doing this?

main()

{

double Position;

SetBitDirection(1,1);

for (;;) // loop forever

{

SetBit(0); //Start Pulse

Delay_sec(Position/1000); //Time Pulse length 

ClearBit(0); //End pulse

Delay_sec((20-Position)/1000); //Keep 20 Hz frequency

}

Thanks,

Scott

 

Tom,

I have been spending some time trying to understand this code. I am trying to drive a total of 4 servo motors with an M code driving 4 global variables to move to different positions. I am trying to see just what to modify to add 2 more servos.

I am guessing I would be adding two more "FPGA(IO_PWMS" values equal to the new global variables. Unfortunately I dont understand the "+2,+3,+4,+5" numbers. How do I know what to add for the other two motors? I could just keep going up to +6,+7,+8,+9? 

Does the modified code below look right? Are there any areas other than this that would need to be modified (other than declaring the new variables v3 and v4)?

            if (++i == ncycles)  // count mostly high pulses, special cycle?

            {

                FPGA(IO_PWMS+2) = v1;   // Pulse size

                FPGA(IO_PWMS+3) = 1;    // Enable

                FPGA(IO_PWMS+4) = v2;   // Pulse size

                FPGA(IO_PWMS+5) = 1;    // Enable

FPGA(IO_PWMS+6)=v3; // Pulse Size Correct??

FPGA(IO_PWMS+7)=1; //Enable

FPGA(IO_PWMS+8)=v4; // Pulse size Correct??

FPGA(IO_PWMS+9)=1 //Enable

                i=0;

            }

            else

            {

                FPGA(IO_PWMS+3) = 0;   // Disable

                FPGA(IO_PWMS+5) = 0;   // Disable

                FPGA(IO_PWMS+7) = 0;   // Disable

                FPGA(IO_PWMS+9) = 0;   // Disable

            }