Need help with VERILOG and a Parallax Servo!

Tobben

Hi!
I have bought a Parallax Servo, http://www.parallax.com/tabid/768/txtSearch/900-00005/List/0/SortField/4/Default.aspx
I'm working on a project, where I need the servo to go to 0 degrees and to 180 degrees.
I use a Altera DE2 card and Quatus II.

Anyone that knows how to make·a block in verilog to do this?

Thanks from a Norwegian student!

Tobben

I forgot to say that there is to clock inputs on the card, one on 50 MHz, and on on 27 MHz.

Franklin

I guess I could ask, how do you get the card to output a 1ms to 2ms pulse? That is key to controlling the servo.

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- Stephen

Tobben

With verilog i can create a block to create a 1 ms and a 2 ms pulse, but I'm not sure how to write the code.. Is 1 ms 0 degrees and 2 ms 180 degrees?

W9GFO

Tobben said...
Is 1 ms 0 degrees and 2 ms 180 degrees?

No.

Center is 1.520 milliseconds for Futaba Servos, 1.500 milliseconds for others. A crude approximation is .010 milliseconds per degree. You will have to experiment to find the correct pulse widths for your servo. Your servo will also respond to pulse widths outside the 1 mS to 2 mS range. Each servo is different so be sure to approach the endpoints in small steps so as not to bind the servo and strip the gears.

The servo will expect to receive a pulse fifty times every second. A little slower or faster is okay. If the pulses get too far apart it will move in a jerky fashion.

Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

Post Edited (W9GFO) : 5/14/2010 9:35:32 AM GMT

Tobben

Okay, thanks. I've already managed to make a 1 mS puls, and with .010 mS per degree I would expect the servo to somewere between -90 degrees and 0, but the servo dosen't stop at all, and I have to cut the power.

This is the verilog file (if anyone understands it :P )



module impuls1ms (in,clock,s1ms,GND);

input in,clock;
output reg s1ms, GND;

integer status,teller,t2000;

initial
begin
status=0;
teller=0;
t2000=0;
GND=0;
end






always @ (posedge clock)
begin




if (in==0)
begin
GND=0;
teller=0;
t2000=0;
status=0;
s1ms=0;
end
else
begin

t2000=t2000+1;
if(t2000==5000)
begin
t2000=0;
teller=teller+1;


if (teller==195)
s1ms=1;
else if (teller==200)
begin
teller=0;
s1ms=0;
end
end
end
end




endmodule

W9GFO

Are you sure that you don't have this (continuous rotation) servo?

www.parallax.com/StoreSearchResults/tabid/768/txtSearch/servo/List/0/SortField/4/ProductID/102/Default.aspx

A standard servo will go to a position and stay there.

A continuous rotation servo keeps turning. The speed and direction it turns depends on the pulse width.

Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

Tobben

Yes I'm sure. It can only rotate 180 deg.

W9GFO

So when you say "but the servo dosen't stop at all" do you mean that it hits the stop but tries to keep going? If so, it sounds like the pulse width is not actually 1.000 mS.

Rich H

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Simple Servo Tester, a kit from Gadget Gangster.